401-387-047R2 4 0 Alcatel-Lucent Small Cell Mobility Management SDS (Issue 1 April 2011)

Title page

Alcatel-Lucent 9360

Small Cell | Release 2.4.0

Mobility Management System Definition Specification

401-387-047

Issue 1

April 2011

Alcatel-Lucent – Proprietary

Use pursuant to applicable agreements


Legal notice

Legal notice

Alcatel, Lucent, Alcatel-Lucent and the Alcatel-Lucent logo are trademarks of Alcatel-Lucent. All other trademarks are the property of their respective

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The information presented is subject to change without notice. Alcatel-Lucent assumes no responsibility for inaccuracies contained herein.

Copyright © 2011 Alcatel-Lucent. All rights reserved.

Contains proprietary/trade secret information which is the property of Alcatel-Lucent and must not be made available to, or copied or used by anyone outside

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Not to be used or disclosed except in accordance with applicable agreements.




Contents

About this document

Purpose ............................................................................................................................................................................................. xixi

Reason for revision ...................................................................................................................................................................... xixi

New in this release ....................................................................................................................................................................... xixi

Intended audience ....................................................................................................................................................................... xiixii

How to use this document ........................................................................................................................................................ xiixii

Vocabulary conventions ............................................................................................................................................................ xiixii

Typographical conventions ..................................................................................................................................................... xiixii

Document support .................................................................................................................................................................... xiiixiii

Technical support ...................................................................................................................................................................... xiiixiii

How to order ................................................................................................................................................................................ xiiixiii

How to comment ........................................................................................................................................................................ xiiixiii

1 Cell reselection to/from macro layer (2G or 3G, intra/inter frequency)

Overview ...................................................................................................................................................................................... 1-11-1

Cell reselection to/from macro layer (2G or 3G, intra/inter frequency) ............................................................... 1-21-2

Small Cell/Macro cell reselection ....................................................................................................................................... 1-51-5

Reselection recommendations .............................................................................................................................................. 1-71-7

Cell reselection requirements ............................................................................................................................................. 1-131-13

Cell selection and reselection parameters ...................................................................................................................... 1-181-18

2 Handover from Small Cell to macro 3G

Overview ...................................................................................................................................................................................... 2-12-1

Handover from Small Cell to macro 3G ........................................................................................................................... 2-22-2

Handover methods .................................................................................................................................................................... 2-52-5

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Handover to 3G macrocell ..................................................................................................................................................... 2-92-9

Handover parameters ............................................................................................................................................................ 2-112-11

Attempted Small Cell to W-CDMA measurement ..................................................................................................... 2-152-15

Successful Small Cell to UMTS measurement ............................................................................................................ 2-172-17

3 Handover from Small Cell to macro 2G

Overview ...................................................................................................................................................................................... 3-13-1

Handover Small Cell to macro 2G ..................................................................................................................................... 3-23-2

Handover methods .................................................................................................................................................................... 3-53-5

Handover to 2G macrocell ..................................................................................................................................................... 3-63-6

Handover parameters ............................................................................................................................................................... 3-83-8

Attempted Small Cell to GSM measurement ................................................................................................................. 3-93-9

Successful Small Cell to GSM measurement ............................................................................................................... 3-103-10

4 Hierarchical Cell Structure

Overview ...................................................................................................................................................................................... 4-14-1

Hierarchical Cell Structure .................................................................................................................................................... 4-24-2

Cell reselection control ........................................................................................................................................................... 4-44-4

Network layers ........................................................................................................................................................................... 4-54-5

Hierarchical Cell Structure parameters ............................................................................................................................. 4-64-6

5 Small Cell to Small Cell Handover

Overview ...................................................................................................................................................................................... 5-15-1

Small Cell to Small Cell handover ..................................................................................................................................... 5-25-2

Autoconfiguration and Self Optimization ........................................................................................................................ 5-45-4

Handover trigger and procedure .......................................................................................................................................... 5-65-6

Inter-Small Cell signaling interface ................................................................................................................................... 5-75-7

Use cases ...................................................................................................................................................................................... 5-95-9

Small Cell to Small Cell handover parameters ............................................................................................................ 5-115-11

Contents

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6 Small Cell to Small Cell Handover Improvements

Overview ...................................................................................................................................................................................... 6-16-1

Small Cell to Small Cell Handover Improvements ...................................................................................................... 6-26-2

Enhanced Handover ................................................................................................................................................................. 6-46-4

7 3G Macro to Small Cell CS Handover & 2G Macro to Small Cell Handover

Overview ...................................................................................................................................................................................... 7-17-1

3G Macro to Small Cell CS Handover & 2G Macro to Small Cell Handover ................................................... 7-27-2

Handover from macro network to Small Cells cluster ................................................................................................ 7-57-5

Single Small Cell Target ....................................................................................................................................................... 7-77-7

Multiple Target Small Cells .................................................................................................................................................. 7-87-8

Small Cell Preparation .......................................................................................................................................................... 7-107-10

Macro Network Considerations ........................................................................................................................................ 7-127-12

Macro to Small Cell Handover Parameters .................................................................................................................. 7-137-13

8 Service Based Redirection and Handover to Targeted Macro Layer

Overview ...................................................................................................................................................................................... 8-18-1

Service based redirection and handover to targeted macro layer ............................................................................ 8-28-2

Service based redirection and handover to targeted macro layer description ..................................................... 8-48-4

OAM Model Description ....................................................................................................................................................... 8-68-6

Glossary

Index

Contents

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List of tables

7-1 Attributes of class BSR ......................................................................................................................................... 7-137-13

7-2 Attributes of class LCell ....................................................................................................................................... 7-167-16

8-1 RRC Connection Mapping Table – rrcMappingTable ................................................................................. 8-88-8

8-2 RAB Establishment Mapping Table – sBCsRabMappingTable ............................................................... 8-98-9

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List of tables

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List of figures

7-1 Small Cell PSC to Cell ID mapping ................................................................................................................... 7-87-8

7-2 Wrong Small Cell identified and prepared .................................................................................................... 7-107-10

7-3 Decreasing quality with proximity to Small Cell ........................................................................................ 7-127-12

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List of figures

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About this documentAbout this document

Purpose

The purpose of this information product is to provide details of the following features:

• Cell Reselection to/from macro layer (2G or 3G, intra/inter frequency) (34529)

• Handover Small Cell to Macro 3G (34530)

• Handover Small Cell to Macro 2G (34531)

• Hierarchical Cell Structure (75392)

• Small Cell to Small Cell Handover (75494)

• Small Cell to Small Cell Handover Improvements (84331)

• 3G Macro to Small Cell CS Handover & 2G Macro to Small Cell Handover (75389 &

75390)

• Service Based Redirection and Handover to Targeted Macro Layer (10889)

Reason for revision

The reissue reasons are:

Issue number Issue date Reason for reissue

1 April 22, 2011 Standard

0.1 September 30, 2010 Preliminary

New in this release

This section details what is new in the Alcatel-Lucent 9360 Small Cell Solution Mobility

Management System Definition Specification, 401-387-047 for Release 2.4.0.

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Features

The following features have been implemented in release 2.4.0:

• Handover Small Cell to Macro 2G (34531), see Chapter 3, “Handover from Small

Cell to macro 2G”

• Handover Small Cell to Macro 3G (34530), see Chapter 2, “Handover from Small

Cell to macro 3G”

• Small Cell to Small Cell Handover Improvements (84331), see Chapter 6, “Small Cell

to Small Cell Handover Improvements”

• 3G Macro to Small Cell CS Handover & 2G Macro to Small Cell Handover (75389 &

75390), see Chapter 7, “3G Macro to Small Cell CS Handover & 2G Macro to Small

Cell Handover”

• Service Based Redirection and Handover to Targeted Macro Layer (10889), see

Chapter 8, “Service Based Redirection and Handover to Targeted Macro Layer”

Other changes

• BSR Femto has been changed to Small Cell

• Femto Management System (FMS) has been changed to Small Cell Management

System (SCMS)

• BSR Cluster had been changed to Small Cells Cluster

• BSR Femto Gateway has been changed to BSR Signaling Gateway

• Brick has been changed to Security Gateway.

• Minor editorial changes.

Intended audience

The primary audience for this IP is personnel who work with the Small Cell in one of the

following capacities:

• Network Operation and Maintenance Specialists

• System Administrators

• Engineers with responsibility for network planning, design, configuration, or

optimization

How to use this document

Refer to this document for information on the Mobility Management features.

Vocabulary conventions

None.

Typographical conventions

No special conventions are used in this information product.

About this document

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Document support

For support in using this or any other Alcatel-Lucent document, contact Alcatel-Lucent at

one of the following telephone numbers:

• 1-888-582-3688 (for the United States)

• 1-317-377-8618 (for all other countries)

Technical support

For technical support on the product, contact your local Alcatel-Lucent customer support

team. See the Alcatel-Lucent Support web site (http://www.alcatel-lucent.com/support/)

for contact information.

How to order

To order Alcatel-Lucent documents, contact your local sales representative or use Online

Customer Support (OLCS) (http://support.alcatel-lucent.com).

How to comment

To comment on this document, go to the Online Comment Form (http://infodoc.alcatel-

lucent.com/comments/enus/) or e-mail your comments to the Comments Hotline

([email protected]).

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mailto:[email protected]

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1 1Cell reselection to/from

macro layer (2G or 3G,

intra/inter frequency)

Overview

Purpose

This chapter describes the cell reselection (34529) feature.

Contents

Cell reselection to/from macro layer (2G or 3G, intra/inter frequency) 1-2

Small Cell/Macro cell reselection 1-5

Reselection recommendations 1-7

Cell reselection requirements 1-13

Cell selection and reselection parameters 1-18

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Cell reselection to/from macro layer (2G or 3G, intra/inter

frequency)

Feature number

Feature number 34529.

Feature description

The Small Cell supports Small Cell co-deployment in UMTS and/or GSM macro

networks. Cell reselection is supported to and from UMTS macro cells on the same or

different UMTS frequencies, and to and from GSM macro cells.

For cell reselection from the Small Cell, the Small Cell broadcasts the following with

their associated cell selection and reselection parameters in SIB11:

• intra-frequency neighbour cells

• inter-frequency neighbour cells

• GSM neighbour cells

Auto-configuration, self-configuration and self-optimisation procedures determine the

neighbour cells.

For cell reselection to the Small Cell, the macro cells must broadcast the frequency and

primary scrambling code of the Small Cells with associated cell selection and reselection

parameters.

Two main rules determine cell reselection to and from the Small Cell:

• The UE camps on a Small Cell as soon as Small Cell coverage is provided.

• The UE camps on the Small Cell, even when macro cell quality is better than Small

Cell quality in a relevant range, such as when the Small Cell is near a macro base

station.

The mechanisms described below ensure that these rules are adhered to.

3G Macro to and from Small Cell

The Small Cell is capable of supporting cell reselection based on the minimum coverage

thresholds (Sintrasearch, Sintersearch, Treselection and offsets). A hysteresis mechanism

ensures that a mobile device in idle mode, moving from the indoor environment to the

immediate outdoor environment, or from the outdoor environment to an indoor

environment, stays attached to the Small Cell as long as the quality of the signal from the

Small Cell is sufficient in the immediate outdoor environment.

To favour cell reselection from the macro cell to the Small Cell as soon as the Small Cell

is considered to be of suitable quality, the UMTS macro cells broadcast scrambling codes

reserved for Small Cell in the neighbour cell list of SIB11/12. To prioritise the Small Cell


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for cell reselection, the Qoffset parameters of the Small Cell neighbour cells should be set

to a very low value for all Small Cell neighbour cells. As soon as a UE considers a Small

Cell to be suitable, it will reselect to the Small Cell due to the low Qoffset value.

The strategy for outgoing inter/intra-frequency cell reselection from a Small Cell to a

macro cell is that the UE remains as long as possible on the Small Cell.

The main Small Cell parameters to control cell reselection toward the macro cell are:

• Qqualmin/Qrxlevmin, SintraSearch, Sintersearch, Qhyst1/Qhyst2 and Treselection for

the serving cell (Small Cell). These parameters are broadcast by the Small Cell in

SIB3 messages.

• Qqualmin/Qrxlevmin and Qoffset1/Qoffset2 for the macro neighbour cells. These are

broadcast by the Small Cell in SIB11 messages.

Based on the cell re-selection parameters, the UE performs cell reselection from the Small

Cell to a macro cell. To ensure the UE stays on the Small Cell as long as possible, the

main parameters to use are the search parameters. Alcatel-Lucent recommends that you

use low Qqualmin/Qrxlevmin and SintraSearch/SinterSearch values. If cell reselection

between Small Cells is enabled, Qoffset1/Qoffset2 can be used to penalize macro cells and

prioritize Small Cells. Then the Treselection timer is used to ensure that temporary RF

fluctuations do not cause cell reselection to the macro cell network.

2G Macro to and from Small Cell

The GSM macro cell broadcasts UMTS frequency and scrambling codes reserved for

Small Cells in the UMTS neighbour cell list. To prioritise the Small Cell for cell

reselection, the GSM macro network favours the Small Cell UMTS neighbour cells by a

very low offset value (FDD_Offset). When a UE camps on a GSM macro cell, it

considers a Small Cell UMTS neighbour cell to be suitable, if the FDD_Qmin and

RSCP_min values are fulfilled. That is, the UE must be close enough to the Small Cell.

The FDD_Qmin and RSCP_min parameters are expected to be the main tuning parameters

on the GSM system. If the GSM system supports RSCP_min, then Alcatel-Lucent

recommends that FDD_Qmin and RSCP_min are broadcast per UMTS Small Cell on the

GSM system.

Small Cell-Small Cell reselection

The Alcatel-Lucent Small Cell Solution supports Small Cell-Small Cell reselection.

However, this capability is not used for closed access Small Cells.

Feature benefits

As an enhancement to basic idle mode mobility support to end users, this feature provides

a relative stickiness to the Small Cell. This feature prevents ping-pong affects between the

Small Cell and the macro layers.


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Impacted systems

Small Cell

Dependencies

Hardware None

Software None

Feature Auto-configuration, self-optimisation

Interworking CN must support cell selection/reselection

procedure.

Devices None

Standards TS25.331

Reference documents None

Restrictions and limitations

A number of interactions exist with the access restriction capability of the Small Cell. In

closed access mode, only UEs with access rights are allowed to camp on the Small Cell.

Engineering impacts

To achieve the required behaviour, tuning is required for the cell reselection parameters

associated with both the Small Cells (broadcast by the macro cells) and the macro cells

(broadcast by the Small Cells).

Operational requirements

Small Cell provides configuration management for:

• Macro cell broadcast parameters (used in SIB11).

• Small Cell broadcast parameters (used in SIB3).

Feature type

Basic


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Small Cell/Macro cell reselection

Cell reselection goal

The goal of the cell reselection procedure is always to camp on a suitable cell. When

camped normally, the UE monitors relevant system information (SIB3 and SIB11) and

performs the measurements required for the cell reselection procedure, that is, the

procedure to find the most appropriate cell.

The UE performs the cell reselection procedure as defined by the 3GPP standards. Small

Cell broadcasts the cell reselection parameters for the serving cell and the neighbour cells

in the system information.

Cell reselection starts with UE measurements, followed by cell ranking followed by the

cell reselection procedure.

Parameters for 3G macro cell resection

The Small Cell broadcasts the neighbour cell list and parameters for measurements in the

system information. If the serving cell quality is below certain thresholds, the UE

measures the neighbour cells. The thresholds are specific for measuring intra-frequency

neighbour cells and inter-frequency neighbour cells.

Parameter Description

Qqualmin Minimum quality Ec/No of CPICH in the

serving cell in dB.

Qrxlevmin Minimum Rx level of CPICH in the serving

cell in dBm.

Sintrasearch Threshold for serving cell quality to start/stop

intra-frequency measurements. This threshold

is relative to Qqualmin.

Sintersearch Threshold for serving cell quality to start/stop

inter-frequency measurements. This threshold

is relative to Qqualmin.

Cell ranking for 3G macro cells

All cells fulfilling the selection criterion S and the evaluation criteria to start measuring

other suitable cells defined by the thresholds in “Parameters for 3G macro cell resection”

(p. 1-5) are ranked. The UE uses the cell-ranking criterion R:

• Equation 1: Rs= Q

meas,s+ Qhyst

s(for serving cell)

• Equation 2: Rn

= Qmeas,n

- Qoffsets,n

(for neighbour cells)


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• Qmeas,s

: Measured quality of serving cell (CPICH RSCP or CPICH Ec/N0)

• Qmeas,n

: Measured quality of neighbour cell (CPICH RSCP or CPICH Ec/N0)

The hysteresis value Qhystsis used to favor the serving cell. The offset value Qoffset

s,n

may favor (negative value) or penalize (positive value) a neighbour cell.

Small Cell broadcasts the hysteresis value Qhystsfor the serving cell and the offset values

Qoffsets,n

for the neighbour cells. The UE calculates the R values using the formulas

above and performs cell reselection to the best-ranked cell.

GSM to UMTS cell reselection

The UE selects a suitable UMTS cell, if the UMTS cell fulfils the following criteria for a

period of 5 seconds:

• Measured RSCP value > RLA_C – FDD_Qoffset for all GSM cells

• Measured Ec/No >= FDD_Qmin –FDD_Qmin_Offset

• Measured RSCP value >= FDD_RSCP_threshold

Parameters for 2G macro cell reselection

Parameter Description

FDD_Qmin Minimum threshold for Ec/No for UMTS

FDD cell reselection.

FDD_RSCPmin Minimum threshold of RSCP for UMTS FDD

cell reselection.

Qsearch_I Search for UMTS cells if signal level is below

or above threshold.

FDD_Qoffset Applies an offset to RLA_C for cell

reselection to UMTS FDD cells.

FDD_Qmin_Offset Applies an offset to FDD_Qmin value

(optional).


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Reselection recommendations

Overview

This topic analyses the Macro and Small Cell coverage comparison in a building. Cell

selection and reselection results and recommended parameter settings are presented.

Macro and Small Cell indoor coverage

The scenario investigated here corresponds to one Small Cell per apartment. There are

four apartments on each floor, as shown in the following diagram, within a multi-storey

apartment building. The red stars represent the Small Cell location in the apartments.

Apartment layout in apartment building

It is assumed that macro and Small Cells are operating at different frequencies and that

the other related parameters used in the simulations are:

Power settings:

• Macro Cell Tx Power = 20 W, Pilot Power = 2 W

• Small Cell Tx Power = 1 mW, Pilot Power = 0.1 mW

Indoor shadow fading parameters:

• Shadow fading space correlation length = 0.5 meters

• Shadow fading standard deviation = 4 dB

• Site to site shadow fading correlation = 0.5


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Wall and penetration losses

Small Cell location in the apartment is indicated by the red stars in “Apartment layout in

apartment building” (p. 1-7). Different floor and wall penetration losses are as assumed in

the following table.

Wall Type Penetration Loss (dB)

External wall 15

Window 1

Indoor 3

Outdoor 30

Internal wall 10

Flat floor loss 20

Indoor floor 7

The apartment building can be located anywhere within the underlying macro cell

network coverage area, as shown in the following diagram, where the coordinates are in

meters. The red square indicates the location of the apartment building in the underlying

macro cell network.

Macro Cell Pilot

“Macro Cell Pilot RSCP in dBm” (p. 1-9) shows the macro cell pilot RSCP coverage in

the area around the building (in dBm). There is a strong macro cell pilot signal strength in

the building close to the windows. In the centre of the building, the signal strength is

reduced significantly due to wall penetration losses.


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“Macro Cell Pilot Ec/Io in dB” (p. 1-10) shows the macro cell pilot Ec/Io in the area

around the building (in dB). The macro cell maintains acceptable coverage within the

building on a separate frequency.

Macro Cell Pilot RSCP in dBm


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Macro Cell Pilot Ec/Io in dB

Small Cell Pilot

“Small Cell Pilot RSCP in dBm” (p. 1-11) and “Small Cell Pilot Ec/Io (dB) coverage

plot” (p. 1-11) show the Small Cell pilot RSCP and Ec/Io coverage. There is still some

Small Cell coverage outside the apartments with pilot power of -10dBm. Due to mutual

interferences among Small Cells, some areas in the building may not have good pilot

Ec/Io coverage.


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Small Cell Pilot RSCP in dBm

Small Cell Pilot Ec/Io (dB) coverage plot


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Cell reselection requirements

Strategy for cell reselection

The strategy for inter-frequency cell reselection is that a UE changes to the Small Cell as

soon as the Small Cell coverage reaches a certain quality. The Small Cell is then

considered to be suitable.

As described previously, the UMTS macro cells broadcast scrambling codes reserved for

Small Cell in the inter-frequency neighbor cell list of SIB11. To prioritize the Small Cell

for cell reselection, the Qoffset parameters of the Small Cell inter-frequency neighbor

cells must be set to a very low value (negative value) for all Small Cell neighbor cells. As

soon as a UE considers a Small Cell to be suitable, it reselects the Small Cell due to the

low Qoffset value.

Cell selection criteria

The UE considers the Small Cell to be suitable only if the cell selection criteria are

fulfilled, that is, the UE must be close enough to the Small Cell. The conditions of the cell

selection criteria can be defined in either of two ways. Cell selection criteria are either

defined by SIB3 parameters Qqualmin and Qrxlevmin or they can be tuned specifically

for the inter-frequency Small Cell, if they are broadcast in SIB11. Normally a UE does

not select a Small Cell when it passes an indoor Small Cell on the street. The parameters

Qqualmin and Qrxlevmin of the Small Cell neighbor cells are the main tuning parameters.

Measuring UMTS frequencies

To reselect an inter-frequency Small Cell from the macro network, the UE must measure

other UMTS frequencies. The parameter Sintersearch determines when the UE starts

measuring the inter-frequency macro and Small Cell neighbor cells. Sintersearch must be

set such that the UE starts with inter-frequency measurements when the quality of the

macro cell is still good. Sintersearch value may be increased depending on the current

strategy of the existing macro network.

If a UE reselects to a Small Cell to which the UE does not have access permission, then

the access restriction mechanism ensures that the UE remains camped on the macro cell.

Requirements for the 3G macro network

• The macro network must support provisioning of neighbor cell specific cell

reselection parameters (Qoffset1/Qoffset2 and Qqualmin/Qrxlevmin).

• The macro network must support the broadcasting of inter-frequency neighbor cells in

SIB11.

• The macro network must support the broadcasting of cell reselection parameters in

SIB11 for inter-frequency cell reselection.


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The following parameters are recommended for macro cell to Small Cell reselection. The

cell selection and reselection quality measure is based on Ec/No.

• Femto Qrxlevmin = -101 dBm

• Femto Qqualmin = -15 dB

• Femto Qoffset1 = -40 dB

• Femto Qoffset2 = -40 dB

• Sintersearch = 14 dB

“UE serving areas” (p. 1-14) indicates the simulated UE serving area between macro and

Small Cell based on the macro network cell re-selection parameter setting. The brown

area means that the UE is registered on the macro cell and the purple area means that the

UE is registered on the Small Cell.

UE serving areas

Requirements for the 2G macro network

• The 2G macro network must support provisioning of neighbor cell specific cell

reselection parameters (FDD_Qmin, FDD_RSCPmin, Qsearch_I, FDD_Qoffset and

FDD_Qmin_Offset).

• The 2G macro network must support the broadcasting of GSM neighbor cells in

SIB11.

• The 2G macro network must support the broadcasting of cell reselection parameters in

SIB11 for GSM neighbor cell reselection.


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The following parameters are recommended for 2G macro cell to Small Cell reselection:

• FDD_Qmin = -14 dB

• FDD_RSCPmin = -100 dBm

• Qsearch_I = search always

• FDD_Qoffset = minus infinite (that is, always select a cell if acceptable)

• FDD_Qmin_Offset1

= 0 (0 indicates not needed)

1Optional parameter

Requirements for the Small Cell

A UE camping on a Small Cell must perform neighbor cell measurements on the macro

cell layer only when the quality of the serving Small Cell becomes weak. Therefore the

threshold parameters Sintersearch of the Small Cells must be set to a relatively low value.

The UE only considers a cell, if it fulfills cell selection criterion. The cell selection

threshold parameters Qqualmin and Qrxlevmin are set accordingly.

The cell selection threshold parameters Qqualmin and Qrxlevmin for the macro cells are

set to minimum service quality requirements. Alcatel-Lucent recommends setting the

threshold parameters Qqualmin and Qrxlevmin to higher values for the Small Cells, to

ensure that the Small Cell provides good service quality. The macro cell quality at the

Small Cell boundary is usually good, and the macro cell provides good service quality at

the Small Cell boundary.

The following parameters are recommended for Small Cell to Macro cell reselection.

These parameters are broadcast in the Small Cell SIB.

• Femto Qrxlevmin = -111 dBm

• Femto Qqualmin = -19 dB

• Macro Qrxlevmin = -111 dBm

• Macro Qqualmin = -19 dB

• Sintersearch = 2 dB

• Qhyst1 = 2

• Qoffset1 = 0

• Qhyst2 = 2

• Qoffset2 = 0

“Small Cell to macro cell reselection” (p. 1-16) shows the simulated UE serving area

between the macro cell and the Small Cell, based on the Small Cell reselection parameter

settings. The brown area indicates that the UE is registered on the Small Cell. The purple

area indicates that the UE is registered on a macro cell.


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Small Cell to macro cell reselection

Ping pong effect

In mobility management, the ping pong effect is one of the crucial issues that must be

handled carefully. If ping pong effects cannot be avoided, many network resources are

required , leading to network overload in extreme cases. “Ping pong effect”

(p. 1-17) shows the combination of “UE serving areas” (p. 1-14) and “Small Cell to

macro cell reselection” (p. 1-16). The green area indicates no ping pong effect between

macro cells and Small Cells, with the parameter values recommended here, when the UE

is not moving.


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Ping pong effect


frequency)


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Cell selection and reselection parameters

Overview

The Small Cell supports broadcast of the cell selection and reselection parameters in

system information messages. These parameters are specific to the serving cell and the

neighbouring cells.

A UE in idle mode reads the System Information Block (SIB) 3 and SIB 11 message for

cell selection and reselection.

Configuration

The cell selection/reselection parameters can be configured using the Small Cell

Management System (SCMS). The parameters are part of a Small Cell profile. The Small

Cells defined in the same profile share common configuration values.

Attributes of LCell class: Serving Small Cell

Parameter Description Syntax Values

sIntraSearch Specifies the intra-frequency specific

threshold (in dB) in the serving Small Cell

used in the intra frequency measurement

rules for cell reselection.

integer (-32..20),

step=2,

unit=dB

sInterSearch Specifies the inter-frequency specific


used in the inter frequency measurement

rules for cell reselection.

integer (-32..20),

step=2,

unit=dB

sSearchRAT Specifies the inter-RAT specific quality


used in the inter-RAT measurement rules

for cell re-selection.

integer (-32..20),

step=2,

unit=dB

qQualmin Specifies the minimum required quality

level in the serving cell (dB). Applicable for

intra-frequency and inter-frequency cell

reselection only if the quality measure for

cell selection and re-selection is set to

CPICH Ec/No. Used in the cell selection

criterion S.

integer (-24..0),

unit=dB

qRxLevMin Specifies the minimum required RX level

in the serving cell in dBm. Used in the cell

selection criterion S.

integer (-115..-25),

step=2,

unit=dB


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sib3qHyst1s Specifies the hysteresis value for the

serving cell. Used in cell ranking criterion

R.

integer (0..40), step=2,

unit=dB

sib3qHyst2s Specifies the hysteresis value for the

serving cell. Used as second cell Ranking

criterion R if the quality measure for cell

selection and re-selection is set to CPICH

Ec/No.

integer (0..40), step=2,

unit=dB

sIB3Inter- FreqScaling-

Factor

Specifies the scaling factor to be used by

the UE for scaling the parameter

Treselection for inter-frequency cell

reselection.

real [1.00.. 4.75],

step=0.25,

precision=2

maxAllowedULTXPower Specifies the maximum TX power level a

UE can use when accessing the serving

Small Cell on RACH.

integer (-50..33),

unit=dBm

sIB3CrQuality- Measure Selection of the use of Ec/N0 or RSCP as

the quality measure for cell reselection.

enum

Measure-

mentQuality

sib4qHyst1sPCH Specifies the hysteresis value for the

serving cell. Used by the UE in the

URA_PCH state if included in the SIB 4.

Used in cell Ranking criteria R.

integer (0..40),

unit=dB

sib4qHyst2sPCH Specifies the hysteresis value for the

serving cell. Used by the UE in URA_PCH

state if included in the SIB 4. Used as

second cell Ranking criteria R by the UE.

integer (0..40),

unit=dB

sIB3InterRATScalingFactor Specifies the scaling factor to be used by

the UE for scaling the parameter

Treselection for inter-RAT cell reselection.

real [1.00..4.75],

step=0.25,

precision=2

sHCSRAT Specifies the RSCP threshold in the serving

Small Cell used in the inter-RAT

measurement rules for cell reselection.

Provisioning of a negative value disables

the RCSP triggered GSM measurements.

integer (-1..91) step=2,

unit=dB

sSearchHCS Specifies the RSCP threshold in the serving

Small Cell used in the inter-frequency

measurement rules for cell re-selection.

Provisioning of a negative value disables

the RCSP triggered inter-frequency

measurements.

integer (-1..91) step=2,

unit=dB


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Global definitions: Small Cell neighbour cell

The following parameters exist for each Small Cell neighbour cell.

Type Parameter Description Syntax Permitted

values

InterBSRCellRs-

Info

qOffset1s Specifies the offset between

the serving and neighbour cell.

Used when the quality

measure for cell selection and

re-selection is set to CPICH

RSCP.

integer (-50..50),

unit=dB

InterBSRCellRs-

Info


the serving and neighbour

cells. Used when the quality

measure for cell selection and

reselection is set to CPICH

Ec/No. Used in second cell

ranking criterion R.

integer (-50..50),

unit=dB

InterBSRCellRs-

Info

maxAl-

lowedULTXPwr

Specifies the maximum TX

power level a UE can use

when accessing the neighbour

Small Cell on RACH.

integer (-50..33),

unit=dBm

InterBSRCellRs-

Info

qQualMin Specfies the minimum

required quality level in the

neighbour cell (dB).

integer (-24..0),

unit=dB

InterBSRCellRs-

Info

qRxLevMin Specifies the minimum

required RX level in the

neighbour cell (dBm).

integer (-115..-25),

step=2,

unit=dBm

InterBSRCellRs-

Info

enableBroadcast Enables or disables broadcast

of Small Cells for cell

reselection.

Boolean

InterBSRCellRs-

Info

individualOffset Specifies an offset, which is

added to the measurement

quantity before the UE

evaluates if an event has

occurred.

real (-10.0..10.0),

precision=1,

step= 0.5,

unit=dB

3G Global definitions: 3G Macro neighbour cell

The following parameters exist for all macro neighbour cells.


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values

UmtsMacroCell-

RsInfo


the serving Small Cell and

neighbour UMTS cell. Used

when the quality measure for

cell selection and re-selection

is set to CPICH RSCP.

integer (-50..50),

unit=dB

UmtsMacroCell-

RsInfo


the serving Small Cell and

neighbour UMTS cells. Used

when the quality measure for

cell selection and re-selection

is set to CPICH Ec/No. Used

in second cell ranking criteria

R.

integer (-50..50),

unit=dB

UmtsMacroCell-

RsInfo

maxAl-

lowedULTXPwr


power level a UE may use

when accessing the neighbour

UMTS cell on RACH.

integer (-50..33),

unit=dBm

UmtsMacroCell-

RsInfo

qQualMin Specifies the minimum

required quality level in the

neighbour UMTS cell (dB).

integer (-24..0),

unit=dB

UmtsMacroCell-

RsInfo

qRxLevMin Specifies the minimum

required RX level in the

neighbour UMTS cell (dBm).

integer (-115..-25),

step=2,

unit=dBm

UmtsMacroCell-

RsInfo

enableBroadcast Indicates whether the UMTS

macro neighbour cell should

be broadcast in the SIB of the

serving cell.

If true, the UMTS macro

neighbour cell is broadcast in

the SIB of the serving cell.

boolean

UmtsMacroCell-

RsInfo

individualOffset Specifies an offset, which is




occurred.

real (-10.0..10.0),

precision=1,

step= 0.5,

unit=dB


frequency)


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Global definitions: Inter-RAT neighbour cell

The following parameters exist for all inter-RAT neighbour cells.


values

GsmMacroCellRs-

Info

qOffset1s Specifies the offset between the

serving Small Cell and

neighbour GSM cell (CPICH

RSSI).

integer (-50..50),

unit=dB

GsmMacroCellRs-

Info

maxAl-

lowedULTXPwr


power level a UE can use when

accessing the neighbour GSM

cell on RACH.

integer (-50..33),

unit=dBm

GsmMacroCellRs-

Info

qRxLevMin Specifies the minimum required

RX level in the neighbour GSM

cell (dBm).

integer (-115..-25),

step=2,

unit=dBm

GsmMacroCellRs-

Info

enableBroadcast Indicates whether the inter-RAT

neighbour cell is broadcast in

the SIB of the serving cell.

If true, the inter-RAT neighbour

cell is broadcast in the SIB of

the serving cell.

Boolean

GsmMacroCellRs-

Info

cellIndividu-

alOffset

Specifies an offset, which is




occurred.

real (-50..50),

unit=dB


frequency)


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2 2Handover from Small Cell

to macro 3G

Overview

Purpose

This chapter describes the handover from Small Cell to macro 3G (34530) feature.

Contents

Handover from Small Cell to macro 3G 2-2

Handover methods 2-5

Handover to 3G macrocell 2-9

Handover parameters 2-11

Attempted Small Cell to W-CDMA measurement 2-15

Successful Small Cell to UMTS measurement 2-17

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Handover from Small Cell to macro 3G

Feature number


Feature description

The Small Cell supports blind hard handover from the Small Cell to a macro 3G cell

(intra-frequency and inter-frequency) for CS voice calls. The handover to the macro 3G

cell occurs when the Small Cell coverage or signal strength falls below an acceptable

level.

Blind handover is the preferred method for handover from Small Cell to macro cell,

because it allows the fast mobility procedure execution required for residential indoor

coverage due to round-the-corner effects.

Handover between the Small Cell and the macro network is performed using the RANAP

relocation procedure (also known as an “SRNS relocation UE involved”). This procedure

performs a handover of the call between two IuCS interfaces. That is, between two RNCs

(Small Cell and macro RNC). The Small Cell monitors the Small Cell quality and level

using UE event triggered intra-frequency measurements (event 2D) with measurement

quantities EcNo and RSCP.

This feature assumes that the auto-configuration and self-optimisation functions provide

the information required by the Small Cell Mobility Management function for HO to 3G

macro cells.

Handover scenario

A handover from the Small Cell to a 3G macro cell involves the following steps:

1. The source Small Cell initiates handover by sending the RANAP Relocation Required

message to the 3G-MSC.

2. An inter-MSC or intra-MSC SRNS relocation procedure is executed. The source

Small Cell is the source RNC in this procedure.

3. To switch the traffic, the 3G-MSC sets up a new IuCS connection to the Target RNC

(blue link) before releasing the previous IuCS connection to the source Small Cell

(brown link).

These steps are illustrated in the following diagram. The diagram does not show any

firewalls.

Handover from Small Cell to macro 3G Handover from Small Cell to macro 3G

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Feature benefits

Service continuity is a high value feature for the Small Cell. Dropped calls when the user

leaves the Small Cell coverage area are avoided by using intra-frequency and

inter-frequency handover from the Small Cell to 3G macro cell.

Impacted systems

Small Cell, BSG


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Dependencies

Hardware None

Software None

Feature Autoconfiguration

Interworking The UMTS network (UTRAN and CN) must

support interfrequency and intrafrequency

UMTS hard handover for CS.

Devices None

Standards 23.009 R6 Handover Procedures

25.331 R6 RRC Protocol Specification

25.413 R6 UTRAN Iu Interface RANAP

Signaling



This feature implements blind handover only. All target cells with a configurable

minimum level are considered for handover. If the handover fails, it retries to the next

best cell.

Engineering impacts

None


Counters Call handover success rate is operator

viewable.

Configuration management and parameters The Small Cell supports the full set of event

2D parameters separately for EcNo and RSCP

measurements. Therefore the following

parameters are required twice:

• threshold

• timeToTrigger

• hysteresis

Feature type

Optional


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Handover methods

Supported methods of handover

Small Cell Solution supports outgoing hard handover of CS voice calls to:

• Inter-frequency macro cells

• Intra-frequency macro cells

• Inter-RAT GSM cells

Note: This is a subsection of the 3G macro handover section but also includes aspects

of the inter-RAT HO.

Deployment scenarios

The following diagram shows the Small Cell deployment scenario within a macro

network. The macro network can be UMTS inter- or intra-frequency, inter-RAT to GSM,

or a combination of the layers.

Handover from Small Cell to macro 3G Handover methods

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Target layer determination

The Small Cell determines if, and to which target layer, handover is applicable. The Small

Cell reevaluates this after each:

• Iu connection establishment

• RAB set up or deletion (for example, triggered by RANAP RAB Assignment, Iu

Release, Reset)

Macro Cells

Femto-BSRs

Handover from Femto tomacro cellSmall CellsHandover from Small

Cells to Macro cell


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The following table shows the relevant MIM parameters for the handover decision

dependent on the established RABs and Iu connections:

Iu / RAB combination Configuration option Parameter

IuCS Options: disable, gsm, fdd,

gsmPreferred, fddPreferred

LCell::targetHOCS

IuCS + IuPS Options: disable, gsm, fdd,

gsmPreferred, fddPreferred

LCell::targetHOCSPS

In the current version of the Small Cell:

• Handover is only applicable if the UE has a CS voice RAB

• Handover of PS RABs is not supported

The Small Cell determines the target cell list, and the start and end measurements

depending on the applicability of the handover. And if applicable, the Small Cell

determines the target layer.

Handover target determination

The Small Cell determines the target based on the relevant parameter

LCell::targetHOCS/targetHOCSPS (as per established Iu connections) and the target cell

availability as shown in the following table:

Note: Handover is only applicable if the UE has a CS voice RAB. If the UE has no CS

voice RAB, then handover is disabled.

The settings in this table apply to Small Cell handover to 3G (34530) and Small Cell

handover to 2G (34531):

Setting of LCell::targetHO Target cell availability Handover decision

disabled any Handover is disabled

any none Handover is disabled

gsm 2G (plus optional 3G) Handover to 2G

gsm 3G Handover is disabled

fdd 3G (plus optional 2G) Handover to 3G

fdd 2G Handover is disabled

gsmPreferred 2G Handover to 2G

gsmPreferred 2G + 3G Handover to 2G. Fallback to

3G possible if 2G handover

fails.

gsmPreferred 3G Handover to 3G


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Setting of LCell::targetHO Target cell availability Handover decision

fddPreferred 2G Handover to 2G

fddPreferred 2G + 3G Handover to 3G. Fallback to

2G possible if 3G handover

fails.

fddPreferred 3G Handover to 3G

If at least one suitable 3G cell is found, then the Small Cell assumes 3G target cells to be

available.

The Small Cell builds an internal sorted list of all suitable 3G cells (blindHO3GList) with

decreasing level, based on EcNo if available, else based on RSCP.


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Handover to 3G macrocell

SRNS relocation

The Handover to 3G macro cell (intra- or inter-frequency hard handover) involves the

SRNS relocation procedure. Initially the Small Cell supports relocation of CS

connections.

Simultaneous PS connections are released before the relocation occurs.

The Small Cell performs the following main tasks for the SRNS relocation procedure:

• Send Relocation Required message to the CN

• Supervise the Relocation Preparation procedure

• Transfer the RRC Handover message (for example, Radio Bearer Reconfiguration)

received from the target RNC to the UE

• Supervise the handover to 3G procedure

• Release the Small Cell resources and remove the call context after successful

handover to 3G

• Cancel the Relocation procedure and continue the call in Small Cell after unsuccessful

relocation preparation or unsuccessful handover with UE returning to Small Cell

• Initiate the call release if the UE connection is lost during handover

• Coordinate the SRNS relocation with other interacting procedures

SRNS Relocation for CS Domain

This diagram shows an overview of the whole procedure at IuCS, including interworking

within the UTRAN and the CN. The example includes change of MSC and related

inter-MSC messages.

Handover from Small Cell to macro 3G Handover to 3G macrocell

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Handover parameters

Attributes of Class BSR: Handover


tHandoverGuard Specifies the length of time handover

attempts are disabled.

If handover fails and no alternative

target is available, then further

handover attempts are disabled for

this length of time.

integer (1..60), unit=secs

tRelocOverall Specifies the length of time the Small

Cell will wait for an Iu Release

command from the core network after

receiving an Iu RELOCATION

COMMAND message.


tRelocPrep Specifies the length of time the Small

Cell will wait for a response from the

core network after sending

RELOCATION REQUIRED message

to the CN.


Attributes of class LCell: Handover


BlindHO2d2fEcno

threshold2d

Specifies the threshold for sending a 2d

measurement report.

If the measured EcNo value of the used

frequency falls below the value

(threshold2d – hysteresis2d/2) for the time

timeToTrigger2d then blind HO is triggered.

integer (24..0), unit=dB,

step=1

BlindHO2d2fEcno

threshold2f

Specifies the threshold for sending a 2f

measurement report.

If the measured EcNo value of the used

frequency rises above the value (threshold2f

+ hysteresis2f/2) for the time

timeToTrigger2f then HO due to EcNo is no

longer necessary.

integer (24..0), unit=dB,

step=1

Handover from Small Cell to macro 3G Handover parameters

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BlindHO2d2fEcno

timeToTrigger2d

Specifies the period of time during which

the event condition must be satisfied, before

sending a 2d Measurement Report.

If the measured EcNo value of the

frequency used falls below the value



enum

TimetoTrigger

BlindHO2d2fEcno

timeToTrigger2f



sending a 2f Measurement Report.


frequency used rises above the value

(threshold2f + hysteresis2f/2) for the time


longer necessary.

enum

TimetoTrigger

BlindHO2d2fEcno

hysteresis2d

Specifies the hysteresis value for the 2d

measurement report.





real (0.0..14.5),

unit=dB,

step=0.5,

precision=1

BlindHO2d2fEcno

hysteresis2f

Specifies the hysteresis value for the 2f

measurement report.





longer necessary.

real (0.0..14.5),

unit=dB,

step=-++0.5,

precision=1

BlindHO2d2fRscp

threshold2d

Specifies the threshold for sending a 2d

measurement report.

If the measured RSCP value of the




integer (-115.. 25),

unit=dBm, step=1


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BlindHO2d2fRscp

threshold2f

Specifies the threshold for sending a 2f

measurement report.





longer necessary.

integer (115.. 25),

unit=dBm, step=1

BlindHO2d2fRscp

timeToTrigger2d



sending a 2d Measurement Report.

If the measured RSCP value of the used




enum

TimetoTrigger

BlindHO2d2fRscp

timeToTrigger2f



sending a 2f Measurement Report.





longer necessary.

enum

TimetoTrigger

BlindHO2d2fRscp

hysteresis2d

Specifies the hysteresis value for the 2d

measurement report.

If the measured RSCP value of the used




real (0.0..14.5),

unit=dB, step=

0.5, precision=1

BlindHO2d2fRscp

hysteresis2f

Specifies the hysteresis value for the 2f

measurement report.





longer necessary.

real (0.0..14.5),

unit=dB, step=

0.5, precision=1

minBlindHoUmts-

Macro EcNo

Specifies the minimum CPICH EcNo of a

macro cell for blind handover. Mapping

between the value and the real EcNo value

is given in TS25.133 Section 9.1.2.3.

integer (0..49)


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minBlindHoUmts-

Macro RSCP

Specifies the minimum CPICH RSCP of a

macro cell for blind handover. Mapping

between the value and the real RSCP value

is given in TS25.133 Section 9.1.1.3.

integer (0..91)

targetHOCS Specifies the allowed and preferred target

system for outgoing handover of UEs with

CS calls.

disable=0, gsm=1,

fdd=2,

gsmPreferred=3,

fddPreferred=4

targetHOCSPS Specifies the allowed and preferred target

system for outgoing handover of UEs with

simultaneous CS and PS calls.

disable=0, gsm=1,

fdd=2,

gsmPreferred=3,

fddPreferred=4

intrafrequencyFilter-

Coefficient

Depending on the measurement quantity,

filtering is performed by the UE before UE

event evaluation.

enum

FilterCoefficient

interFreqFilterCoef-

ficient

Specifies the inter-frequency filter

coefficient.

Depending on the measurement quantity,

filtering is performed by the UE before UE

event evaluation.

enum

FilterCoefficient

sIB3CrQuality

Measure

Indicates whether EcNo or RSCP is used as

the quality measure for cell reselection.

enum

Measure-

mentQuality

sIB3InterFreq

ScalingFactor

Specifies the scaling factor to be used by the

UE for scaling the parameter Treselection

for inter-frequency cell reselection.

real [1.00.. 4.75],

step=0.25,

precision=2


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Attempted Small Cell to W-CDMA measurement

Measurement name

Attempted Small Cells Cluster to W-CDMA Hard Handovers

Description

This measurement provides the number of attempted Small Cells Cluster to W-CDMA

macro cell hard handovers.

Collection method

CC

Trigger condition

When the Small Cell sends the last handover command to the UE in a series of handover

attempts (retries), this handover attempt is for hard handover to a W-CDMA macro cell

and no further handover attempt is made because, either:

• This last handover attempt was successful, or

• This last handover attempt was not successful and no further possible target cell is

available while handover would still be needed.

The handover command can be one of the RRC messages: Radio Bearer Setup, Radio

Bearer Reconfiguration, Radio Bearer Release, Transport Channel Reconfiguration, or

Physical Channel Reconfiguration.

The target W-CDMA system selects the message that is actually used.

Measurement result

1 integer value

Measurement type

HHO.AttBsrUmts

Measurement basis

Cell

Measurement interface

Itf-BSR

Handover from Small Cell to macro 3G Attempted Small Cell to W-CDMA measurement

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Switching technology

CS/PS

Handover from Small Cell to macro 3G Attempted Small Cell to W-CDMA measurement

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Successful Small Cell to UMTS measurement

Measurement name

Successful Small Cell cluster to UMTS Hard Handovers

Description

This measurement provides the number of successful Small Cell cluster to UMTS macro

cell hard handovers.

Collection method

CC

Trigger condition

Whenever the Small Cell receives Iu Release Command from the core network with

cause "Successful Relocation" or "Normal Release" during handover execution (timer

tRelocOverall is running) and the handover is a hard handover to a UMTS macro cell.

Measurement result

1 integer value

Measurement type

HHO.SuccBsrUmts

Measurement basis

Cell


Itf-BSR


CS/PS

Handover from Small Cell to macro 3G Successful Small Cell to UMTS measurement

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Handover from Small Cell to macro 3G Successful Small Cell to UMTS measurement

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3 3Handover from Small Cell

to macro 2G

Overview

Purpose

This chapter describes the handover from Small Cell to macro 2G (34531) feature.

Contents

Handover Small Cell to macro 2G 3-2

Handover methods 3-5

Handover to 2G macrocell 3-6

Handover parameters 3-8

Attempted Small Cell to GSM measurement 3-9

Successful Small Cell to GSM measurement 3-10

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Handover Small Cell to macro 2G

Feature number


Feature description

The Small Cell supports inter-RAT handover to 2G for CS voice calls when the Small cell

coverage or signal strength falls below an acceptable level. The handover is executed to a

pre-defined and optimised GSM target cell (blind handover).

As with 3G HO, blind handover is the preferred method for handover from Small cell to

macro cell, because it allows the fast mobility procedure execution required by residential

indoor coverage due to round-the-corner effects.

To facilitate this feature the Small Cell supports:

• Inter-RAT relocation preparation procedure including UE capability transfer.

• Handover execution procedure.

The Small Cell monitors the Small cell quality and level using measurements triggered by

UE event 2D, with measurement quantities EcNo and RSCP. Although the 2D event

measures an intra-frequency quantity, it is part of the 25.331 inter-frequency

measurements. The 2D measurement control parameters can be pre-configured.

This feature assumes that the auto-configuration and self-optimization functions provide

the information required by the GSM target cell and handoff to the Small Cell Mobility

Management function.

Feature benefits

As for 3G handover, CS call continuity to 2G network is a high value feature. Dropped

CS calls when the user leaves the Small cell coverage area are avoided with the help of

inter-RAT handover from the Small Cell to the 2G macro cell.

Impacted systems

Small Cell

Dependencies

Hardware None

Software None

Feature Autoconfiguration

Self-optimisation

Handover from Small Cell to macro 2G Handover Small Cell to macro 2G

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Interworking The MSC and the GSM network must support

UMTS to GSM handover for CS.

Devices Mobile supports UMTS and GSM.

Standards 23.009 R6 Handover Procedures

25.331 R6 RRC Protocol Specification

25.413 R6 UTRAN Iu Interface RANAP

Signalling



This feature implements blind inter-RAT handover only.

All GSM target cells with a configurable minimum level are considered for handover. If

the handover fails, it retries to the next best cell.

Small to macro 2G handover is supported for CS voice calls only.

The handover is only initiated for those UEs that support GSM handover.

Engineering impacts

None


Counters Call handover success rate must be operator

viewable.

Configuration management and parameters The Small Cell supports the full set of 2D

parameters separately for EcNo and RSCP

measurements. Therefore the following

parameters are required twice:

• threshold

• timeToTrigger

• hysteresis

The target GSM neighbour cell is delivered by

the auto-configuration or self-optimisation

function.

Fault management and alarms None


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Feature type

Optional


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Handover methods

Supported methods of handover

Small Cells supports outgoing hard handover of CS voice calls to inter-RAT GSM cells.

Deployment scenarios

See “Deployment scenarios” (p. 2-5) for more information.

Target layer determination

See “Target layer determination” (p. 2-6) for more information.

Handover target determination

If at least one suitable 2G cell is found then the Small Cell assumes 2G target cells are

available.

The Small Cell builds an internal sorted list of all suitable 2G cells (blindHO2GList) with

decreasing level, based on RSSI.

See the table in “Handover target determination” (p. 2-7) for additional information.


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Handover to 2G macrocell

CS inter-RAT Handover

The CS inter-RAT Handover involves the inter-system relocation procedure during which

the Small Cell performs the following main tasks:

• Send the Relocation Required message to the CN

• Supervise the Relocation Preparation procedure

• Transfer the GSM handover command received from target GSM BSS to the UE

• Supervise the handover to GSM procedure

• Release UMTS resources and remove the call context after successful handover to

GSM

• Cancel the Relocation procedure and continue the call in UMTS after unsuccessful

Relocation Preparation or unsuccessful handover with UE returning to UMTS

• Initiate call release if the UE connection is lost during handover

• Coordinate the inter-system relocation with other interacting procedures

Small Cell to GSM CS inter-RAT Handover

The following diagram shows the message sequence chart across the UMTS and GSM

network for performing UMTS to GSM handover. The UMTS messages related to

UTRAN are in bold text. UMTS CN and GSM internal interworking is included.


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Handover parameters

Attributes of class LCell: Blind handover


minBlindHoGsmMacro

RSSI

Specifies the minimum BCCH/GSM

carrier RSSI of the GSM cell for

blind handover. Mapping between the

value and the real RSSI value is

given in TS25.133 Section 9.1.4.

integer (0..63)

Reference

See “Handover parameters” (p. 2-11) for additional parameters.


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Attempted Small Cell to GSM measurement

Measurement name

Attempted Small Cell cluster to GSM Hard Handovers for CS Voice.

Description

This measurement provides the number of attempted Small Cell cluster to GSM macro

cell hard handovers for CS voice calls.

Collection method

CC

Trigger condition

When the Small Cell sends the last handover command to the UE (RRC message

HANDOVER FROM UTRAN COMMAND) in a series of handover attempts (retries),

this handover attempt is for CS voice handover to a GSM macro cell and no further

handover attempt is made because, either:

• This last handover attempt was successful, or

• This last handover attempt was not successful and no further possible target cell is

available while handover would still be needed.

Measurement result

1 integer value

Measurement type

HHO.AttBsrGSMCSVoice

Measurement basis

Cell


Itf-BSR


CS

Handover from Small Cell to macro 2G Attempted Small Cell to GSM measurement

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Successful Small Cell to GSM measurement

Measurement name

Successful to W-CDMA GSM Handovers for CS Voice

Description

This measurement provides the number of successful Small Cells cluster to GSM macro

cell hard handovers for CS voice calls.

Collection method

CC

Trigger condition

Whenever the Small Cell receives Iu Release Command from the MSC with cause

"Successful Relocation" or "Normal Release" during handover execution (timer

tRelocOverall is running) and the handover is a handover to a GSM macro cell for CS

voice.

Measurement result

1 integer value

Measurement type

HHO.SuccBsrGSMCSVoice

Measurement basis

Cell


Itf-BSR


CS

Handover from Small Cell to macro 2G Successful Small Cell to GSM measurement

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4 4Hierarchical Cell Structure

Overview

Purpose

This chapter describes the Hierarchical Cell Structure (HCS) (75392) feature.

Contents

Hierarchical Cell Structure 4-2

Cell reselection control 4-4

Network layers 4-5

Hierarchical Cell Structure parameters 4-6

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Hierarchical Cell Structure

Feature number


Feature description

This feature enables controlling the cell reselection of UEs from Small Cell to Macro

cells using the 3GPP HCS cell reselection parameters.

HCS allows an operator to prioritise cell layers for mobiles in idle mode, and in

connected mode when supported by the Small Cell. 3GPP defines a special cell

re-selection algorithm for Hierarchical Cell Structures. This algorithm is performed by the

UE, but HCS parameters must be broadcast by the Small Cell in the system information

message, enabling the UE to run the HCS algorithm.

This feature introduces all HCS parameters defined by 3GPP in Rel-6 and covers the

configuration of the new HCS parameters.

Feature benefits

Service provider benefits

The application of HCS in the Small Cell improves the cell reselection behavior of UEs

camping on the Small Cell:

• HCS allows UEs to stay in the Small Cell, even if the Small Cell quality diminishes

temporarily.

• Additional HCS parameters allow more flexibility in the configuration to keep

stationary UEs in the Small Cell.

• HCS provides enhanced management for the multi-layer scenario. The use of

priorities enables the preferred macro cell layer to be determined.

By better managing the reselection and minimising the cell re-selection ping-pong

between Small Cell and macro cells, NAS registration procedures and CN signalling load

can be minimised.

End user benefits

The user stays longer in their home zone and thus obtains more benefits from their home

zone tariff.

Impacted systems

Small Cell, SCMS.

Hierarchical Cell Structure Hierarchical Cell Structure

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Restriction/Limitation

This feature supports the configuration of the HCS priority for three hierarchical layers:

• Small Cell

• UMTS

• GSM

This feature does not allow the configuration of different HCS priorities for multiple

GSM and multiple Small Cell layers.

Different HCS priorities are only possible for multiple UMTS layers, if:

• The UMTS macro neigbour cells have been configured manually, or

• The UMTS macro cell is also using HCS, enabling the 3G network listening function

to provide the HCS priority of detected UMTS macro neighbour cells.

Feature type

Optional.

Hierarchical Cell Structure Hierarchical Cell Structure

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Cell reselection control

Cell reselection

Hierarchical Cell Structure (HCS) enables cell reselection control in a multi-layer

network. The HCS algorithm is based on the classical principles of the re-selection

algorithm performed by the UE but with additional capabilities to detect slow and fast

moving UEs and to act accordingly.

If HCS is supported in the serving cell, the UE supports two mobility states: the low

mobility state for slow moving UEs and the high mobility state for fast moving UEs. The

state change is based on the number of cell reselections within a certain time interval.

Cell layers

HCS allows you to prioritize cell layers by assigning an HCS priority. Larger cells should

have a lower priority than smaller cells. If moving fast, the UE selects cells with lower

priority.

HCS applied in the macro network prevents fast moving UEs from selecting a Small Cell,

but can also delay cell reselection to a Small Cell for slow moving subscribers.

Activating HCS

HCS can be activated in the Small Cell layer while not supported in the macro layer. The

use of HCS in the Small Cells does not imply that the macro network must also

implement HCS.

With HCS in the Small Cell layer, cell reselection to the macro layer can be delayed by a

penalty time for macro cells. Hence it is possible to prefer cell reselection between Small

Cells for a group deployment providing contiguous Small Cell coverage.

State and frequencies

The UE is usually in the low mobility state when camping on a Small Cell and speed

detection is switched off (for example, for residential Small Cells). However, this feature

also supports broadcast of the HCS parameters for UE speed detection, which may be

applicable for open access Small Cells enhancing the public network coverage.

This feature does not restrict the use of frequencies on Small Cell and UMTS macro

layers, for example, the Small Cell layer and the UMTS macro layer may operate on the

same or different frequencies. However Alcatel-Lucent recommends the use of different

frequencies for the Small Cell and the macro layers.

Hierarchical Cell Structure Cell reselection control

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Network layers

Network layers

Feature 75392 supports the following network layers:

• GSM layer

• UMTS layer

• Small Cell layer

Cell reselection parameters can be defined for each of these layers. This defining of

parameters allows the UE's cell reselection behaviour between the layers to be controlled

and for layers to be prioritised.

HCS example

If the UMTS macro network has multiple layers (micro/macro cells) and more than one

macro frequency has been configured in the Small Cell, then all UMTS layers are treated

equally. The UE will always reselect to the best UMTS macro cell. The UE may then be

moved to another layer according to the HCS parameters of the macro network.

If the 3G network listener has provided the HCS priority of UMTS neighbor cells, then

the Small Cell can apply different HCS cell reselection parameters for these layers.

Small Cells

UMTS Macro cells

GSM Macro cell

HCS priority level 3



Hierarchical Cell Structure Network layers

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Hierarchical Cell Structure parameters

Attributes of LCell class: Hierarchical Cell Structure


enableHCS Enables/disables the use of

hierarchical cell structure

(HCS) for cell reselection.

boolean

hcsPrioS Specifies the HCS priority

level (0-7) for the serving cell.

HCS priority level 0 = lowest

priority, HCS priority level 7 =

highest priority.

integer 0-7

qHCSs Specifies the quality threshold

levels for applying prioritized

hierarchical cell re-selection

for the serving cell.

integer 0-99

sLimitSearchRAT Determines, when the UE

starts/stops performing GSM

measurements in low mobility

state when HCS is used.

integer (-32..20), step=2,

unit=dB

tCRmax Measurement interval for

low/high mobility detection.

enum TCRmax

nCR Number of cell reselections

during TCRmax in order to

detect low/high mobility:

• Condition for high

mobility: Cell reselections

> NCR within TCRmax

• Condition for low

mobility: Cell reselections

<= NCR within

TCRmax+TCRmaxHyst

integer 1-16

tCRmaxHyst Additional time to TCRmax

before a UE can revert to low

mobility state.

enum TCRmaxHyst

Hierarchical Cell Structure Hierarchical Cell Structure parameters

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sIB3SpeedDependent

ScalingFactor

Specifies the scaling

(multiplication) factor to be

used by the UE in idle mode or

RRC connected mode states

for the parameter Treselections

in case high-mobility state has

been detected.

real (0.0..1.0), step=0.1,

precision=1

hcsCellRsInfo Defines the HCS cell

reselection parameters for

neighbor cells dependent on

their HCS priorities.

sequence [8..8] of struct

HcsCellRsInfo

Attributes of LCell class: Non-HCS cell reselection


nonHCStCRmax Specifies the duration for

evaluating allowed amount of

cell reselection(s) in case of

non-HCS usage.

enum TCRmax

nonHCSnCR Specifies the maximum

number of cell reselections in

case of non-HCS usage.

integer (1..16)

nonHCStCRmaxHyst Specifies the additional time

period before the UE can

revert to low-mobility

measurements in case of

non-HCS usage.

enum TCRmaxHyst

Attributes of FDDExtCell class: Hierarchical Cell Structure

Parameter Description Permitted Values Units

hcsPrioN Specifies the HCS priority

level for the provisioned

UMTS macro cells. HCS

priority level 0 = lowest


highest priority. hcsPrioN > 7

indicates that no HCS priority

is assigned to the neighbor cell.

integer (0..255)


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Global definitions: Hierarchical Cell Structure


values

InterBSRCellRs-

Info

hcsPrioN Specifies the HCS priority level

for the Small Cell neighbors.

HCS priority level 0 = lowest


highest priority.

integer (0..7)

UmtsMacroCellRs-

Info


common for the UMTS macro

cells. HCS priority level 0 =

lowest priority, HCS priority

level 7 = highest priority.

integer (0..7)

UmtsMacroCellRs-

Info

useOfDetectedHc-

sPrio

Enable/disable of the use of the

HCS priority provided by the

3G sniffer for the UMTS macro

neighbour cells

boolean

GsmMacroCellRs-

Info


for the GSM macro cells. HCS



highest priority.

integer (0..7)

UmtsMacroNCell hcsPrioN Contains the HCS priority level

for the detected or provisioned

UMTS macro cells. HCS



highest priority. HCS priority >

7 indicates that no HCS priority

is assigned.

In contrast to the other

parameters, this parameter is

read only, that is, it cannot be

configured by the operator.

integer (0..255)

HcsCellRsInfo qHCSn Specifies the quality threshold

levels for applying prioritised

hierarchical cell re-selection for

neighbour cells with a certain

HCS priority level.

integer (0..99)


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values

HcsCellRsInfo penaltyTime Specifies the duration for which

the TEMP_OFFSET is applied

for neighbour cells with a

certain HCS priority level.

enum

PenaltyTime

HcsCellRsInfo tempOffset1 Used to favor neighbor cells

with a certain HCS priority

level over another in case of Rx

level measurements for the

duration of the penalty time.

enum

TempOffset1

HcsCellRsInfo tempOffset2 Specifies the quality threshold

levels for applying prioritised

hierarchical cell re-selection for

neighbour cells with a certain

HCS priority level.

enum

TempOffset2

HcsCellRsInfo qOffset1 Specifies the offset between the

serving Small Cell and the

neighbour cells for a certain

HCS priority level. This is used

in case the quality measure for

cell selection and re-selection is

set to CPICH RSCP and for first

cell ranking.

integer (-50..50),

unit=dB

HcsCellRsInfo qOffset2 Specifies the offset between the

serving Small Cell and the

neighbour cells for a certain

HCS priority level. This is used

in case the quality measure for

cell selection and re-selection is

set to CPICH Ec/No.

integer (-50..50),

unit=dB


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5 5Small Cell to Small Cell

Handover

Overview

Purpose

This chapter describes the Small Cell to Small Cell Handover (75494) feature.

Contents

Small Cell to Small Cell handover 5-2

Autoconfiguration and Self Optimization 5-4

Handover trigger and procedure 5-6

Inter-Small Cell signaling interface 5-7

Use cases 5-9

Small Cell to Small Cell handover parameters 5-11

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Small Cell to Small Cell handover

Feature number


Feature description

The Small Cell supports intra-frequency hard handover between Small Cells belonging to

the same group. Small Cells are assigned to groups through the OAM. The support of

inter- Small Cell handover on a Small Cell is configurable through the OAM.

Small Cell to Small Cell handover (inter-Small Cell handover) is supported for both open

and closed access groups.

The inter-Small Cell handover algorithm is based on UE measurements of the serving and

neighboring Small Cells. The handover is triggered when the quality of a Small Cell

neighbor cell is better than the current serving Small Cell by a configurable hysteresis

value. The Small Cell neighbour list is generated automatically by using the Small Cells

network listening function (3G-sniffer). If the 3G-sniffer cannot detect the Small Cell

neighbour cells, Small Cell neighbours can be configured manually.

Inter-Small Cell handover is supported for CS voice calls. PS calls are dropped when the

coverage area of a Small Cell is left. If the user has both CS and PS calls established, then

the PS call is released and the CS call is handed over to the target Small Cell. In both

cases the PDP context of the UE is preserved in the SGSN and the UE and can be

reestablished when the UE camps on a new cell in IDLE mode or the CS handover has

been completed in connected mode.

Inter-Small Cell handover does not impact the CS core network. The handover procedure

is performed locally within the Small Cells Cluster. The source and target Small Cell must

belong to the same cluster and be connected to the same Security Gateway, which is

ensured by the SCMS through Small Cell Group Management.

Inter-Small Cell communication is performed securely through the existing IPsec tunnels

established between the Small Cells and the Security Gateway. The Security Gateway

routes the signaling IP packets between the Small Cells IPSec tunnels.

Feature benefits

Service provider benefits

The feature enables seamless services for CS voice calls in connected mode, when the

user moves between Small Cells belonging to the same group. The feature is applicable

for closed access groups and open access groups to enhance Small Cell coverage in

enterprises or public places.

Small Cell to Small Cell Handover Small Cell to Small Cell handover

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End user benefits

The feature enables Small Cell groups to be deployed providing contiguous coverage (for

example, in enterprise buildings). Without the feature, CS voice calls of subscribers are

dropped when the subscriber moves out of the coverage area of an individual Small Cell

and no coverage of a macro cell is present.

Impacted systems

Small Cell, BSG, SCMS.

Restriction/Limitation

This feature supports intra-cluster Small Cell to Small Cell handover.

Handover is not possible between Small Cells belonging to different clusters. Handover is

only supported for Small Cells belonging to the same group and between Small Cells

connected to the same Security Gateway. The SCMS ensures this for Small Cell groups.

Feature type

Optional.

Small Cell to Small Cell Handover Small Cell to Small Cell handover

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5-3

Autoconfiguration and Self Optimization

Overview

The requirements placed on autoconfiguration and self optimisation for support of Small

Cell to Small Cell handover are a subset of the autoconfiguration and self optimisation

requirements placed on Small Cell groups.

This topic identifies aspects of autoconfiguration and self optimisation that are developed

under feature 80569, which Small Cell to Small Cell handover is dependent on.

Small Cell neighbour list generation

The Small Cell creates the Small Cell neighbor list autonomously. The 3G sniffer of the

Small Cell detects its neighbours and reads the information needed for mobility

management from the system information of the detected Small Cell neighbors. Also

neighbour cell information of direct neighbours is exchanged through messages between

neighbouring Small Cells to increase the probability of a complete Small Cell neighbour

cell list.

The Small Cell neighbor cells can also be individually provisioned per Small Cell through

the SCMS. Manual provisioning can be applied when the automatic detection does not

provide the needed neighbours. The auto-configuration/self-optimisation function copies

all configured Small Cell neighbours into the Small Cell neighbour list.

The generated Small Cell neighbour cell list contains all neighbours independent of a

potential group assignment.

Small Cell to Small Cell Handover Autoconfiguration and Self Optimization

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The mobility management function uses the generated Small Cell neighbour list as input

to derive the neighbours sent to the UE in the measurement control message.

Small Cell to Small Cell Handover Autoconfiguration and Self Optimization

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Handover trigger and procedure

Handover trigger

The inter-Small Cell handover algorithm is based on UE measurements of the serving and

neighboring Small Cells, that is, UE assisted handover is applied. The handover is

triggered, when the quality of a Small Cell neighbor cell is better than the current serving

Small Cell by a certain hysteresis value. The handover parameters for Small Cell to Small

Cell handover are configurable through the SCMS.

The Small Cell instructs the UE to measure Small Cell neighbour cells after the CS voice

RAB has been setup between the UE and the CS domain. Only those Small Cells are

measured, which belong to the same group as the current Small Cell. Event triggered

handover is used. The handover procedure is performed to the best Small Cell reported by

the UE.

The Small Cell to Small Cell handover algorithm can run in parallel to the supported

Small Cell to macro handover algorithms. In this case the handover parameters are set

such that Small Cell to Small Cell handover is performed, if possible, before a call is

handed over to the macro network.

Handover procedure

The handover procedure between Small Cells is a hard handover procedure. The user

plane is interrupted during the switch over from the source to the target Small Cell. Small

Cell to Small Cell handover is seamless for CS voice calls.

Small Cell to Small Cell handover is supported for CS voice calls. CS data and PS only

calls are dropped when they leave the coverage area of a Small Cell. If the user has both

CS voice and PS calls established, then the PS call is released and the CS voice call is

handed over to the target Small Cell.

Small Cell to Small Cell handover does not impact the core network, that is, the handover

procedure is performed locally within the Small Cells cluster. The control plane is

switched from the source Small Cell to the target Small Cell in the BSG.

The CS user plane is switched in the BVG. Source and target Small Cells must belong to

the same Small Cells cluster. Source and target Small Cells must be connected to the

same Security Gateway.

Small Cell to Small Cell Handover Handover trigger and procedure

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Inter-Small Cell signaling interface

Small Cell to Small Cell signaling path

The Small Cell network provides an inter-Small Cell signaling interface enabling the

execution of the handover procedure between source and target Small Cell.

The interface is supported through the existing IPsec tunnels of the Small Cells, which

also carry the signaling with network entities in the central office, for example, Iu

signaling, BSGAP signaling.

The Security Gateway routes the signaling IP packets between the Small Cells, if the

source Small Cell addresses the target Small Cell through its IPsec tunnel end point

address.

A proprietary Small Cell application protocol (BSRAP) on top of a transport stack

enables the execution of inter-Small Cell procedures without involving the core network

or the BSG.

The following figure shows the stack in the Small Cells and Security Gateway.

Small Cell to Small Cell Handover Inter-Small Cell signaling interface

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The Security Gateway receives the encrypted signaling packet (over UDP) through the

IPsec tunnel of the source Small Cell. The Security Gateway decrypts the signaling

message, routes the message to the target Small Cells IPsec tunnel and encrypts the

message for transmission to the target Small Cell. The data of the BSRAP and SCTP

layers are transparent for the Security Gateway.

Small Cell to Small Cell Handover Inter-Small Cell signaling interface

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Use cases

Handover procedure

The following flow diagram outlines the handover procedure between two Small Cells for

a CS call.

1. The UE has established a CS call in the source Small Cell.

2. The UE sends a measurement report triggering the handover from source to target

Small Cell. If the UE also has a PS connection, then it is released towards the SGSN

and the UE.

3. The source Small Cell initiates the hard handover procedure.

4. The target Small Cell performs call admission control, allocated the resources for the

CS call and prepares the air interface for the incoming handover. The target Small

Cell includes the Radio Bearer Reconfiguration message in the Small Cell Handover

Request Acknowledge message.

5. The source Small Cell forwards the Radio Bearer Reconfiguration message received

from the target Small Cell to the UE.

6. After the source Small Cell has received an indication of the successful transmission

of the RRC message to the UE, it stops transmitting to the UE and triggers the

switching of the CS user plan.

12. BSRAP: BSR UE ConextRelease Acknowledge

11. BSRAP: BSR UEContext Release

3.

10.9.

8.

7.

6.5.

4.

STRMGR: Stream RedirectResponse

Control Plane has beenswitched to target BSR

Small Cell to Small Cell Handover Use cases

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7. The target Small Cell switches the user plan in the BVG from the source to the target

Small Cell.

8. The UE and target Small Cell have synchronized on the air interface. The user plane

is now established between the UE and the MSC.

9. The UE sends a Radio Bearer Reconfiguration Complete message. The UE has

completed the handover procedure and the RRC connection is now established with

the target Small Cell.

10. The target Small Cell switches the signaling plane in the BSG from the source to the

target Small Cell.

11. The UE context is deleted in the source Small Cell.

12. The source Small Cell acknowledges the UE context deletion and forwards messages

received during the handover phase from the MSC to the target Small Cell.

Small Cell to Small Cell Handover Use cases

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Small Cell to Small Cell handover parameters

Global definitions: Small Cell to Small Cell handover

Type Parameter Description Syntax Values

BSRToBSR-

ReportingCriteria-

1c

timetoTrigger Indicates the time

during which the event

condition has to be

satisfied, before sending

a measurement report.

enum TimetoTrigger

BSRToBSR-

ReportingCriteria-

1c

Hysteresis Defines a hysteresis

parameter for reporting

events.

A hysteresis parameter

may be connected with

each reporting event to

limit the amount of

event-triggered reports.

real (0.0..7.5),

precision=1,

step=0.5 ,

unit=dB

BSRToBSR-

ReportingCriteria-

1c

reportingInterval Indicates the interval of

periodical reporting

when such reporting is

triggered by an event.

The interval is defined

in milliseconds.

0 indicates no periodical

reporting.

enum

ReportingInterval

For definitions of type umtsFemtoNCell, see the Small Cell Group Support chapter in

Alcatel-Lucent 9365 Base Station Router Small Cell Specific Features System Definition

Specification, 401-387-048.

Attributes of LCell class: Small Cell to Small Cell handover


intrafrequencyFilterCo-

efficient

Depending on the

measurement quantity, filtering

is performed by the UE before

UE event evaluation.

enum FilterCoefficient

intraFreqNumCells-

MeasReport

Specifies the number of cells to

be included in the

measurement report.

integer (1..6)

Small Cell to Small Cell Handover Small Cell to Small Cell handover parameters

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bSRToBSR-

reportingCriteria1c

Defines Small Cell to Small

Cell reporting criteria 1c.

struct BSRToBSRRe-

porting Criteria1c

Attributes of BSR class: Small Cell to Small Cell handover


enableIncomingFemto-

Handover

Determines whether a Small

Cell supports incoming

handover from another Small

Cell.

Boolean

enableOutgoingFemto-

Handover

Determines whether a Small

Cell supports outgoing

handover to another Small

Cell.

Boolean

interBsrInterface Defines attributes for use in the

interface between Small Cells.

struct InterBSRInterface

tBsrRelocPrep Defines the time a source

Small Cell waits for a target

Small Cell to complete

relocation preparation for

Small Cell to Small Cell

handover.

integer [1..30], unit=secs

tBsrRelocOverall Defines the time a source

Small Cell and target Small

Cell waits for completion of a


handover.


tBsrUeContextRelAck Defines the time a target Small

Cell waits for the source Small

Cell to forward signaling

messages following successful


handover.


tInterFemtoHandover-

Guard

Specifies the minimum time

the source Small Cell prevents

the same UE from attempting

handover to the same Small

Cell when handover to a target

Small Cell fails for a UE.



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Attributes of BSRNeighbourCell class: Small Cell to Small Cell handover


bSRIdentity Specifies the BSR ID of the

neighbour Small Cell.

integer (0..65535)


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6 6Small Cell to Small Cell

Handover Improvements

Overview

Purpose

This chapter describes the Small Cell to Small Cell Handover Improvements (84331)

feature.

Contents

Small Cell to Small Cell Handover Improvements 6-2

Enhanced Handover 6-4

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Small Cell to Small Cell Handover Improvements

Feature number


Feature description

This feature provides a number of enhancements to the procedures used for the handover

of calls between neighboring Small Cells for seamless mobility and reliable to the

end-user.

Impacted systems

Small Cell, SCMS

Feature Benefits

The feature improves the reliability of handover between neighboring Small Cells and as

a result of improved handovers, fewer calls are dropped when users move between

neighboring Small cells configured as a Small Cell group. This results in an improved

end-user experience.

This feature improves the Auto Configuration aspects required for handover between

neighbor Small Cells. Small Cell groups are capable of self configuration and therefore

reduce ambiguity in the unique identification of neighbor cells which is important for the

correct selection of the target cell for handover. Therefore there is less restriction on high

density Small Cell deployments and less reliance on manual configuration of Small Cell

groups to ensure uniqueness among neighboring cells.

Dependencies

None

Restrictions and Limitations

Handover is only supported for Small Cells managed within the same Small Cell group,

handover is not supported between groups.

Engineering Impacts

None

Small Cell to Small Cell Handover Improvements Small Cell to Small Cell Handover Improvements

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Operational Requirements

To use the Small Cell to Small Cell handover improvements, all Small Cells within the

group must be upgraded to support the feature. It is not required to upgrade all Small

Cells in the cluster, but only Small Cells which are deployed in the area where handover

is applied and Small Cells belonging to the same group.

The Small Cell to Small Cell handover improvements feature is backwards compatible

with the existing Small Cell to Small Cell handover functionality to allow for the situation

that small cells within a group may not all upgrade to the same version of the software or

have the feature enabled at the same time.

Feature type

Basic

Small Cell to Small Cell Handover Improvements Small Cell to Small Cell Handover Improvements

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Enhanced Handover

Introduction

The Small Cell network supports functionality of call handovers between neighboring

Small Cells and this feature provides a more comprehensive and flexible Small Cell to

Small Cell handover solution and improves the Small Cell KPIs for handovers and calls

drops.

The Small Cell to Small Cell handover feature is enhanced in the following key areas:

• Enhanced Primary Scrambling Code selection to avoid clash with neighbors-

neighbors and improve handover decision

• Discovery and use of neighbor cell timing for improved handover decision

• Implementation of better call admission control on the target cell to improve the

success rate of handover for priority services

• Improvement in the handover retry mechanism

Enhanced Primary Scrambling Code allocation using Neighbors-Neighbors cell information

During auto configuration and self optimization, the Small Cell minimizes clashes of the

Primary Scrambling Code (PSC) with its immediate Small Cell neighbors. However

another problem exists for handover scenarios where the PSC reported by the UE in

measurements used for handover is used to select the target cell.

Consider the following scenario:

• There is a pool of six PSC (1, 2,...,6) allocated to the Small Cell network.

• Small Cell 1 has configured with PSC-2, Small Cell 2 has configured with PSC-1.

• Small Cell 3 cannot detect Small Cell 2.

• Small Cell 3 performs autoconfiguration and determines that it cannot allocate PSC-2

(which is used by Small Cell 1), it can then select a PSC from the set 1,3,4,5,6. There

is a 20% chance that it selects PSC-1 which is used by Small Cell 2.

• If Small Cell 3 did select PSC-1, there is then the problem that UEs attached to Small

Cell 1 sends measurement reports for PSC-1 and Small Cell 1 cannot determine if the

UE must be handed over to Small Cell 2 or Small Cell 3.

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• This feature enhances the ability of the Small Cell performing autoconfiguration to

exchange information with its neighbor Small Cells to determine the neighbor cells of

these neighboring Small Cells. The autoconfiguring Small Cell then has PSC

information about its neighbors and its neighbors-neighbors and uses that to minimize

PSC clashes.

• As an example, using this algorithm, Small Cell 3 contacts Small Cell 1 and find out

that Small Cell 1 has neighbor Small Cell 2 on PSC-1, therefore Small Cell 3 allocates

a PSC other than PSC-1 or PSC-2 (in this case it selects PSC-3) when allocating its

PSC

Improvements in the uniqueness of the PSC used by Small Cells in the Small Cell group

provides improvements in the target cell selection for handover by the source Small Cell.

Discovery of neighbor cell timing for improved handover decision

With dense reuse of PSC it is still possible to have PSC ambiguity even with

neighbor-neighbor information being used. The neighbor-neighbor information helps

reduce the probabilities of ambiguity but does not avoid it.

In the following example with six PSC, the problem is shown:

• When Small Cell 7 performs autoconfiguration it can determine, using

neighbors-neighbor cell information that all PSCs have been either used by its direct

neighbor cells, or its neighbors-neighbors, therefore it must select one that has already

been used within the group.

• If a UE was then connected on Small Cell 1, if the UE reported measurements for

PSC-1, Small Cell 1 would not be able to determine if the target cell for handover was

Small Cell 3 or Small Cell 7.


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In this feature the Small Cell uses timing information of neighbor cells to assist in the

determination of the handover target.

Each Small Cell, during autoconfiguration, shares the timing information (based upon

SFN-SFN differences) with neighboring Small Cells

For handover, the UE reports the SFN-CFN offset of measured cells along with the PSC

within measurement reports, the source Small Cell may then use this information to

compare with the information shared during autoconfiguration to determine the correct

handover target when there are multiple neighbors on the reported PSC

Improved handover for Higher Priority Services

The call admission control on the target Small Cell is improved by this feature to perform

the release of lower priority resources to allow the incoming handover of another UE to

proceed. Resources are freed up on the target Small Cell using:

• Preemption of existing calls

• Redirecting existing calls to Macro Cells

• Reducing the resources allocated to existing UE's by reducing the data rate of PS

sessions

This enhancement improves mobility of higher priority services such as emergency calls

when target Small Cells are fully loaded.


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Optimizations of Handover Retry Mechanism

Enhancements are implemented such that if a handover failure occurs to a target Small

Cell, if there were other neighboring Small Cells reported in the measurement report used

for handover that are better than the current Small Cell then it immediately attempts to

perform handover to the next best target Small Cell. This continues until either all

candidate cells have been attempted or the conditions have changed such that those cells

are no longer considered candidate cells.

This enhancement results in fewer call drops when handover failures occur as it reduces

the possibility of the UE leaving the coverage of the source cell before handover has been

attempted to other candidate target cells. The source Small Cell attempts handover to

other potential target cells rather than wait for another handover trigger to be received.

Configurable Parameters

Parameters used for the Small Cell to Small Cell Handover improvements feature are

defined as attributes of class Small Cell as follows:

• Enhanced PSC Allocation

Name Description Syntax Values

enableGrpNeigh-

NeighPSCevaluation

Enables a Small Cell

in a group to use

information of its

neighbours-

neighbours during

PSC evaluation to

reduce the

probability of two

neighbors having the

same PSC.

Boolean default = false

pscReallocMinRscp-

NeigbNeig

Used when the

Small Cell is in a

group. During

determination of a

PSC clash on

neighbors-neighbors,

this is the minimum

CPICH RSCP to be

considered in a clash

evaluation.

Integer Units: dBm -115..-25 default =

-110


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pscReallocDelta-

NeigbNeigb

Used when the

Small Cell is in a

group. During

determination of a

PSC clash on

neighbours-neighbours,

the RSCP difference

between the source

to neighbor and

neighbor to

neighbors-neighbor

on the same PSC

must be smaller than

this to determine a

PSC clash.

Integer Units: dB 0..50 default = 10

• Enhanced Handover using Neighbor Cell Timing information


enableTimingMea-

surements

When configured in

a Small Cell Group,

this enables the

source Small Cell to

incorporate timing

measurements for

HO assistance.

When set as TRUE,

the Small Cell

evaluates the time

from midnight UTC

that it takes for the

SFN mod 256 to

cross zero. This

parameter may be

shared between

Small Cells (SFN

Offset From

Reference )



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timingMargin Margin that the

Small Cell applies to

consider a match for

Small Cell-Small

Cell HO in timing

against that reported

by a UE and that

which the Small Cell

has determined

against the neighbor.

Integer Units:

millisecond

0..2560 default =

100

isUEmeasRepor-

tUsedToUpdateTim-

ing

If set as TRUE, the

Small Cell updates

any timing

measurement

derived from Small

Cell-Small Cell

signaling with the

UE timing

measurements

following a

successful handover.

If set as FALSE, the

Small Cell uses the

timing measurement

derived from Small

Cell-Small Cell

signaling in target

cell evaluation.


• Improved Handover for Higher Priority Services


enableNonEmergen-

cyFemtoHandover-

Preemption

Flag to determine

whether the

handover of a

normal call from

another Small Cell

can trigger

preemption of

existing calls

boolean default = true


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enableEmergency-

FemtoHandoverPre-

emption

Flag to determine

whether the

handover of an

emergency call from

another Small Cell

can trigger

preemption of

existing calls


enableEmergency-

FemtoHandover-

CallRedirection

Flag to determine

whether the

handover of an

emergency call from

another Small Cell

can trigger call

redirection of

existing calls


• Optimisations for Handover Retry


enableHandover-

ToNextBestCell

Enables the source

Small Cell to

handover to the next

best candidate Small

Cell whenever a UE

fails to handover

successfully to a

target Small Cell.



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7 73G Macro to Small Cell CS

Handover & 2G Macro to

Small Cell Handover

Overview

Purpose

This chapter describes the 3G Macro to Small Cell CS Handover & 2G Macro to Small

Cell Handover (75389 & 75390) features.

Contents

3G Macro to Small Cell CS Handover & 2G Macro to Small Cell Handover 7-2

Handover from macro network to Small Cells cluster 7-5

Single Small Cell Target 7-7

Multiple Target Small Cells 7-8

Small Cell Preparation 7-10

Macro Network Considerations 7-12

Macro to Small Cell Handover Parameters 7-13

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3G Macro to Small Cell CS Handover & 2G Macro to Small Cell

Handover

Feature number

Feature numbers 75389 and 75390.

Feature description

This feature enables the support of an incoming handover of CS voice from a UMTS or

GSM macro network to a Small Cell. In such a handover the target Small Cell is

identified by its primary scrambling code (PSC). Due to constraints on the size of

neighbor lists in UMTS, PSC are heavily reused by the Small Cells within the coverage

area of a single macro cell. This breaks the traditional straightforward mapping between

scrambling code and Cell-ID.

The Macro network has a mapping of Cell ID to Small Cell PSC, and with incoming

handover request, the BSG selects a target Small Cell based upon a matching PSC and

matches on the ACL.

Impacted systems

Small Cell, BSG, SCMS

Feature Benefits

This feature allows seamless mobility during voice calls from the macro network to the

Small Cell. The end-user can then benefit from the coverage and services offered by the

Small Cells. This supports call continuity in areas where otherwise a call may drop.

Handing calls over to the Small Cells may also improve voice call quality when the

macro cell quality is poor.

For the operator, it relieves the macro layer from calls which are best handled by the

Small Cells. In addition, Small Cells can be added or removed without the need for

re-configuration of neighbor cells in the macro network. When Macro RF resources are

stretched to the limits for a UE, users can be handed off to the Small Cells.

Dependencies

Feature 83083 - Incoming CS handover in Open access is dependent upon 75389,75390

3G Macro to Small Cell CS Handover & 2G Macro to Small

Cell Handover


Cell Handover

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Restrictions and Limitations

The macro to Small Cell handover has the following limitations:

• Incoming handover is restricted to Small Cells operating in Closed Access Mode with

75389,75390. Feature 83083 provides a solution for open access.

• The target Small Cell is identified by its primary scrambling code. As there are only

512 primary scrambling codes available in UMTS, they must be reused by the Small

Cells within the coverage area of a single macro cell. This breaks the traditional

straightforward mapping between scrambling code and Cell-ID. Without a direct

mapping between the scrambling code and the Cell-ID of the cell targeted for

handover, it is only possible to identify the target cell with a certain probability.

Furthermore, in this release only one target Small Cell can be prepared.

• The macro network might try to handover to a Small Cell where the user is not

registered. At the same time the user may have access to another Small Cell with the

same PSC in the same cluster. The Small Cell cluster accepts the handover, but the

target Small Cell measured by the UE is not prepared for handover. Nevertheless,

handover to the Small Cell is continued. The handover fails and the UE returns to the

old active set. The macro network might repeat the handover attempt and each time

the user plane is interrupted.

• If two different Small Cell clusters are partly covered by the current active set, the

RNC can only consider Small Cells of one cluster in the combined neighbor list.

Handover is not possible if the UE wants to handover to a Small Cell of the other

cluster not contained in the neighbor list.

• Collisions of parallel handover attempts can happen on the air interface.

• Handover attempts of emergency calls of UEs without SIM/USIM are rejected.

• Handover attempts of simultaneous CS/PS calls fail. It is not possible to handover the

CS call only, but not the PS call. The Macro network releases the PS call on a CS+PS

connection before relocation can be successful.

• Incoming handover failures affect the macro network KPIs. This affect is more

pronounced if the macro RNC keeps repeating the handover request.

• Incoming handover attempts may result in false preparations of Small Cells and a

capacity degradation of the Small Cell while these prepared resources are held up.

Engineering Impacts

Following are the engineering impacts of the feature:

• Provisioning of the macro network Cell ID.

• Proper engineering is required in the macro network as, for instance, setting specific

handover thresholds towards the Small Cell layer.

Operational Requirements

The macro network must be configured to attempt relocation only when the quality of the

macro network is poor.


Cell Handover


Cell Handover

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Feature type

Basic


Cell Handover


Cell Handover

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Handover from macro network to Small Cells cluster

Handover procedure

Upon a handover trigger, UTRAN initiates the Relocation Preparation Procedure at the Iu

interface towards the CN. The UE has reported the primary scrambling code of the cell

targeted for handover. RNC includes the parameters provisioned for the reported primary

scrambling code consisting of Cell ID, RNC-Id, PLMN-Id and LAC/RAC (of the Macro

cell) in the Relocation Required message and sends the message to the CN. This is a

normal action for the standard relocation procedure and does not require special measures

in the macro network for the Small Cell handover.

The CN selects the target RNC based on addressing information received in the

Relocation Required message and initiates the Relocation Resource allocation procedure

with the Small Cell cluster, which appears to be an RNC for the core network.

The BSG maps the Cell ID received with the Relocation Request message to a group of

Small Cells, which might be the target for the requested handover. The Cell ID points to a

primary scrambling code identifying a group of Small Cells. This group can still have a

huge number of potential handover targets.

Assuming the Small Cells are operating in closed access mode, it does not make sense to

handover the user to a Small Cell, where they are not allowed to get service. Therefore, in

a second step, the BSG identifies those Small Cells out of the Small Cell potential list

which have listed the user on their access control list. (The BSG receives the IMSI of the

user in the Relocation Request message). If the IMSI is not available, the BSG rejects the

relocation request.

Checking the access rights of the user can result in the following cases:

• User is not registered in any Small Cell - The BSG rejects the relocation request

with the cause Relocation Target not allowed.

• User is registered in a single small Cell - The BSG forwards the relocation request

to the Small Cell and the handover procedure is performed with the selected Small

Cell.

• User is registered in multiple Small Cells - The user is listed on multiple access

control lists resulting in multiple handover targets. In this case the BSG must select

one Small Cell to prepare. If the Relocation fails, the BSG starts a timer against the

combination of Cell ID and IMSI. When an incoming relocation request comes in

again with the same Cell ID and IMSI combination, the BSG tries a different target

Small Cell until the targets are all exhausted.

Note: In this release only one target is prepared (if any) and in future releases the

Small Cell network supports handover to multiple potential targets.


Cell Handover


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It depends on the macro network whether it hands over both CS calls and PS calls. The

Small Cell network only supports handover of CS calls, therefore the incoming handover

of a CS+PS call fails, as it is not possible to handover the CS call only but not the PS call.

If the macro network does not support relocation of simultaneous CS and PS calls, the PS

signaling connection is released by the macro network before the handover attempt and

the PDP contexts are preserved in the SGSN and UE. After the handover, the UE initiates

the Routing Area Update procedure, which triggers the transfer of the GMM and PDP

contexts to the target system and the re-establishment of the packet bearers without user

involvement in the Small Cell.

The relocation procedure between the macro network and the Small Cell cluster is fully

3GPP compliant. The handover attempt to multiple Small Cells is not recognized by the

macro network. Also the interface to the UE is not impacted by this approach, only one

radio bearer reconfiguration message is sent to the UE in order to reconfigure the radio

for the handover target cell.


Cell Handover


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Single Small Cell Target

Single target

Ideally the Small Cell and BSG must support the preparation of multiple target Small

Cells during relocation. However this functionality has a high impact on both, the Small

Cell and BSG, and is deferred until a later release.

This has the following impacts :

• When the user is registered with multiple Small Cells on the same PSC, the handover

performance may be poor.

• Feature 83083 - Incoming CS Handover in Open Access, requires that few open

access Small Cells may share the same PSC within the same Macro cell coverage.

RAB combinations

Macro to Small Cell handover is supported only for CS 12.2kbps speech. Any other

request from the macro network is rejected by the BSG/Small Cell and the UE moves to

the Small Cell through Cell Reselection procedures (idle or connected mode).

Feature Signaling Speech CSD PS CS+PS

3G to Small

Cell 75389

No Yes

(mono-rate

12.2)

No No No

2G to Small

Cell 75390

No Yes

(mono-rate

12.2)

No No No

Access modes

Within the scope of features 75389 and 75390, the BSG filters the Target Cell ID from the

Relocation Request message which is mapped directly to a Small Cell PSC. Feature

83083 extends this filtering to more elaborate mappings of Target Cell ID and is aimed at

narrowing down the selection of Small Cells for both closed and open access Small Cells.


Cell Handover

Single Small Cell Target

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Multiple Target Small Cells

Multiple targets

Typically the Small Cell network may be allocated a code, as low as 6 PSC, throughout

the network in order to relieve the burden on the Macro Network SIB capacity for cell

reselection information broadcast. Also with the Small Cell topology, there are many

Small Cells overlaid on top of a macro network. The macro network is typically

provisioned to map a PSC to a Cell ID in OAM for handover. With Macro to Small Cell

handover, each macro cell has a mapping of each Small Cell PSC to a Cell ID which is

passed in the relocation messages. An example is provided in the following figure, where

each color represents a Small Cell PSC.

Consider the case where the macro network receives a measurement report from a Small

Cell on PSC 102. The macro cell maps this to Cell ID 2, and trigger relocation to the

MSC which is then routed to Small Cell network through a relocation procedure. The

BSG receives the Relocation Request and then attempts to map the request to a specific

Small Cell.

The following issues occur :

• The BSG may serve around 60,000 Small Cells.

• The incoming Cell ID match, roughly narrows it down to one in 10,000 Small Cells.

And the list must be narrowed down further.

In closed access, the BSG narrows the list down further, based upon the IMSIs matching

the Access Class List (ACL) of each Small Cell.

When UEs are registered across multiple Small Cells, the BSG may still have more than

one match, but the list is considerably reduced. In open access, there is no ACL so the

problem, of filtering on all open access Small Cells in a cluster to find the correct one,

Figure 7-1 Small Cell PSC to Cell ID mapping


Cell Handover


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remains. This requires some additional PSCs to be set aside for open access as well as

some further encoding on Cell ID, and this is left to the scope of feature 83083.


Cell Handover


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7-9

Small Cell Preparation

Wrong Small Cell Prepared

Due to highly reused PSC, a handover request from the macro network points to multiple

Small Cells. In closed access, this is limited to cells with an IMSI in the access list, but

there is no guarantee that the UE is reporting to the cell it is registered with.

The following scenario may occur, for example, the UE may go into area of poor

coverage nowhere near its own Small Cell and report a PSC which matches one it is

registered with. This results in wasted resources in the Small Cells, the UE is interrupted

while trying to establish on the home Small Cell which is not available, and the Macro

network may retry the same procedure periodically.

To help mitigate for the periodic retry, the BSG rejects repeated handover requests within

a defined period.

From the diagram, consider the following scenarios:

• Scenario 1

The handover process progresses as follows:

1. PSC1-6 available to Small Cell.

2. UE is in a voice call on Macro Cell 1 and gets into poor coverage.

3. UE sees signal from Small Cell 1 (where it is not listed in the ACL) and sends a

measurement report indicating Small Cell PSC1 is strong.

4. The macro cell attempts to relocate the UE to the Small Cell network, indicating a

Cell ID that maps to Small Cell PSC1.

5. The BSG maps the incoming relocation request to one which matches the ACL of

the UE and the PSC mapped to the Cell ID, i.e. Small Cell 2.

6. The macro cell sends the RB Reconfig message to the UE to relocate, but Small

Cell 1 is not prepared for handover.

Figure 7-2 Wrong Small Cell identified and prepared


Cell Handover


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7. The UE searches for the physical channel configuration and does not find it, as the

prepared configuration is far away.

8. The UE has an interruption to the speech call (T312 for example, 1 second), and

leads to an unsuccessful handover.

• Scenario 2

Small Cell 1 already has an ongoing voice call on the same channelization code that

Small Cell 2 selected (The Small Cell normally tries to allocate the lowest codes in

the code tree). In this case, the UE stays on the wrong Small Cell with its own call

blocked until the radio links are torn down or RLC disrupts in the UE - The power

control of the UE takes a random walk which could interfere with the whole cell UL.

Feature 83083 attempts to improve this scenario, by narrowing down the search based

upon enhanced information in the Cell ID mapping. In addition, features 75389 and

75390 overcome the second scenario regarding the channelization code clash, by

allocating a different branch in the code tree to which voice calls are normally established

on.


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7-11

Macro Network Considerations

Macro network configuration considerations

In inter-frequency deployments the macro network will not be able to configure

measurements to the Small Cell network at all times, as the measurements will typically

require compressed mode to be activated. As the macro network has no knowledge of

which UEs require handover, permanent measurements of the Small Cell frequency

would apply to all UEs, and would result in an unacceptable degradation in the macro

network. In addition the macro network is not able to discriminate between UEs which

are in the ACL of the Small Cell network and those which are not. This would result in a

high volume of handover requests to the MSC and the BSG.

Therefore it is necessary for the Macro network to configure the UE to trigger Macro to

Small Cell HO measurement reports only when the quality of the macro network is

degraded. In the Intra-Frequency case degradation will occur naturally as the UE

approaches the Small Cell where the Small Cell network interferes on the same frequency

as the Macro network. In the inter-frequency case it will be less prone to handover, but

adjacent channel interference can still result in a degradation of signal quality when the

UE is connected to a Macro cell and moves close to the Small Cell.

The following diagram shows the deterioration in quality with a decreased proximity to

Small Cell.

Figure 7-3 Decreasing quality with proximity to Small Cell


Cell Handover

Macro Network Considerations

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Macro to Small Cell Handover Parameters

3G Macro to Small Cell CS handover & 2G Macro to Small Cell handover parameters

Table 7-1 Attributes of class BSR


hoFromUmtsMac-

roEnabled

Enables/disables

incoming handover

from a UMTS source

cell. If set to TRUE

the feature 3G Macro

to Small Cell CS

Handover is enabled.

Boolean [default = false]

hoFromGsmMacroE-

nabled

Enables/disables

incoming handover

from a GSM source

cell. If set as TRUE

the feature 2G Macro

to Small Cell CS

handover is enabled.

Boolean [default = false]

tRelocComplete Timer to guard the

relocation procedure

in case of incoming

handover from a

UMTS or GSM

macro cell.

integer (1000..600000),

unit=ms [default =

6000]

tHoFromMacroCom-

plete

Timer to guard the

post relocation

procedures until the

handover procedure is

complete.

integer (1000..600000),

unit=ms [default =

3000]


Cell Handover


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7-13

Table 7-1 Attributes of class BSR (continued)


rABCommitLatency-

DeltaReconfigStd-

Profile

Delta added to

rABCommitLatency-

Time during a Radio

Bearer

Reconfiguration

Procedure for

reconfiguring a UE

from a Default 3GPP

physical/transport

profile to a BSR

physical/transport

profile.

integer (-256..256),

unit=frames [default

= 0]

uERadioBear-

erReconfigResponse-

Timer

Timer to guard

reception of

RADIOBEARER

RECONFIGURA-

TION COMPLETE/

FAILURE message.

integer (0..2147483647),

unit=ms [default =

5000]

maxUmtsCellsRegis-

ter

The maximum

number of 3G cells

for a Small Cell to

register with the BSG

following network

listening. A setting of

0 means that no cells

are registered.

integer [0..3] [default = 0]

maxGsmCellsRegis-

ter

The maximum

number of 2G cells

for a Small Cell to

register with the BSG

following network

listening. A setting of

0 means that no cells

are registered.

integer [0..3] [default = 0]

thrRscpUmtsRegister RSCP threshold in dB

from the maximum

RSCP for registering

3G Macro Cell

information to the

BSG.

integer [0..90], unit=dB

[default = 0]


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Table 7-1 Attributes of class BSR (continued)


thrRssiGsmRegister RSSI threshold in dB

from the maximum

RSSI threshold for

registering 2G Macro

Cell information to

the BSG.

integer [0..60] , unit=dB

[default = 0]

femtoPSClistAdd Additional list of PSC

on top of

femtoPSClist to be

included for network

listening but not PSC

allocation.

sequence [0..16] of

struct FemtoPSC

shortScrambling-

CodePoolStart

Starting value of the

UL scrambling code

with short index used

within the default

configuration.

integer [0..8191] [default =

0]

shortScrambling-

CodePoolSize

Pool size of the UL

scrambling code with

short index used

within the default

configuration.

integer [1..8192] [default =

8192]


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7-15

Table 7-2 Attributes of class LCell


virtualCellIdUmts Used in 3G Macro to

Small Cell Relocation

as a signature on the

Target Cell ID. The

Target Cell ID is

typically encoded

with a PSC identifier

in some of the LSBs,

and Virtual Cell ID

use the remainder. Up

to three Virtual Cell

IDs may be

provisioned to a

Small Cell. A setting

of zero means that no

Virtual Cell ID is

allocated.

sequence [3..3] of

struct VirtualCellId

virtualCellIdGsm Used in 2G Macro to

Small Cell Relocation

as a signature on the

Target Cell ID. The

Target Cell ID is

typically encoded

with a PSC identifier

in some of the LSBs,

and the Virtual Cell

ID uses the

remainder. Up to

three Virtual Cell IDs

may be provisioned

to a Small Cell. A

setting of zero means

that no Virtual Cell

ID is allocated.

sequence [3..3] of

struct VirtualCellId


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8 8Service Based Redirection

and Handover to Targeted

Macro Layer

Overview

Purpose

This chapter describes the Service Based Redirection and handover to targeted Macro

Layer (10889) feature.

Contents

Service based redirection and handover to targeted macro layer 8-2

Service based redirection and handover to targeted macro layer description 8-4

OAM Model Description 8-6

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8-1

Service based redirection and handover to targeted macro

layer

Feature number


Feature description

This feature allows the Small Cell to redirect, at connection establishment or handover at

RAB establishment, selected services to the neighboring macro layer. The service types

and the macro layer (2G or 3G) to redirect or handover can be configured.

Feature benefits

The feature provides the following benefits:

• Increases the data capacity of a network in hot spots.

• Provides quick deployment and requires minimal reconfiguration of the existing

network.

• Provides the operator with the ability to redirect and handover PS streaming types

which are not currently supported on the Small Cell.

Note: The third benefit is of limited use for redirection, as the streaming cause is

rarely used to request streaming initially, more normally used is interactive or

background.

Dependencies

The feature depends on the following features:

• 1586- 3G Network Listening

• 75888 - 2G Network Listening

• 75888 - 2G Network Listening

• 10888 - PS and PS+CS handover from Small Cell to 3G macro (until this feature is

introduced only the handover of CS calls is possible).


Service based handover of PS calls are not supported.

Engineering impacts

None

Service Based Redirection and Handover to Targeted Macro

Layer


layer

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None

Impacted systems

Small Cell

Feature type

Basic


Layer


layer

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8-3


layer description

Deployment of Small Cell with feature

A typical deployment of a Small Cell with this feature enabled, increases the data

capacity of an existing macro network in hot spots, for example, coffee shops, shopping

malls, train stations, so on, to:

• Redirect or handover all voice calls leaving the Small Cell as a data only network

element to increase data capacity

• Redirect or handover all voice and non-HSPA PS traffic leaving the Small Cell as a

high speed data only network element to increase high speed data capacity

The service types and combinations allowed are configurable by the operator. And

include CS conversational, PS data for non-HSPA terminals, PS data for HSPA capable

terminals and PS streaming. Also the target macro layer (3G and 2G), and if 3G, the

frequency and band is also configurable.

Feature 100889 provides Small Cell, with the means to redirect or handover to the macro

layer certain types or combination configured service types, which includes CS voice,

non-HSPA PS data, HSPA PS Data and PS streaming to the macro layer.

This may occur at one of 2 stages in the call establishment procedure:

• At RRC connection where the connection request is rejected with redirection

information included before the connection can be established

• Following RAB establishment by handover to the targeted macro layer.

Enabling the feature

The feature can be enabled by the operator through the SCMS and the service types and

target macro layer and frequency are configurable. The target layer can be UMTS, GSM

or either with one preferred.

RRC connection

At RRC connection establishment, the establishment cause, and access stratum release

indicator elements in the RRC Connection Request message. This is used to determine if

the call is suitable for redirection. Once determined the connection can be redirected

using the RRC Connection Reject message, with the optional Redirection Info element

included. For the UMTS layer only inter-frequency cells are considered as a target for

redirection.


Layer


layer description

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RAB connection

At RAB establishment, the traffic class element in the RANAP RAB Assignment Request

is used to determine the service type. In addition, when PS service based handover is

supported, UE capability is also considered. In order not to hold up call establishment, the

RAB is allowed to establish. And once established, an SRNS relocation procedure is

triggered, for the RAB selected, for service-based handover. RAB establishment follows

the existing RAB establishment and admission control procedures prior to handover,

therefore this may result in existing calls being downgraded, actively redirected or

preempted. If the handover fails the call is allowed to continue on the Small Cell.

As long as PS handover to 2G or 3G macro is supported, only RABs from the CS domain

are considered.

Emergency calls are not subject to service based redirection or handover. Incoming

handover calls are not subject to service based handover.

The handing over the CS leg of a simultaneous bearer call, is configurable. This is when a

terminal has an existing Iu PS connection, whenever a new CS RAB is established, and in

this case handover depends on this parameter value. While a PS handover is not

supported, any existing PS RAB is dropped when a simultaneous bearer call is handed

over.

The target 3G macro cell for redirection or handover is from a configured frequency and

band, if configured (for handover the cell must also be in the detected list). Else the

strongest of the cells, detected by the 3G Network listening function run during

auto-configuration and self-optimization.


Layer


layer description

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8-5

OAM Model Description

Configuration management

Parameter Description Syntax Interface Provis ion

LCELL::sBEn-

able

Feature enabled

for service base

redirection and

targeted

handover

Boolean False =

disable (default),

True = enable

bulkcm preprovi sion

LCELL::sBSim-

BearerHO

Allows the

service based

handover of

simultaneous

bearer

Boolean False =

do not Handover

sim bearer, True

= Handover sim

bearer

bulkcm bsrprofi le

LCELL::s-

BReDirRe-

peatAl lowed

Allows repeat

attempts at

redirection for

service based

redirection

Boolean False =

do not allow,

True = allow

(default)

bulkcm bsrprofi le

LCELL::rrc-

MappingTable

RRC Mapping

table RRC

connection,

establishment

cause to action

to be taken per

service type

Sequence

[0…21] of struct

of

rrcMapping-

Table

bulkcm bsrprofi le

LCELL::sBCs-

RabMapping

Table

Service based

mapping table

CS RAB

establishment,

traffic class to

action to be

taken per service

type

Sequence

[0…21] of struct

of

rrcMapping-

Table

bulkcm bsrprofi le


Layer


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Parameter Description Syntax Interface Provis ion

LCELL::tar-

getHOFddFreq

CS

Defines the

service based

preferred

frequency and

band for

outgoing

handover of UEs

with CS calls.

[0..1] Structure

of frequency

bulkcm bsrprofi le

LCELL::tar-

getHOFddFreq

CSPS

Defines the

service based

preferred

frequency and

band for

outgoing

handover of UEs

with

simultaneous CS

and PS calls.

[0..1] Structure

of frequency

bulkcm bsrprofi le

SbRrcConnec-

tionAttemptT

imer (existing

parameter)

BRRM-OAM

internal

parameter Timer

to gate RRC

reject returning

with follow up

RRC Connection

Request

[0..65535],

unit=secs

Default = 60

static bsrprofi le

targetHOCS

(existing

parameter)

Defines the

allowed and

preferred target

system for

enum TargetHO

Default =

fddPreferred

bulkcm bsrprofi le

The existing parameters LCELL::hoFromGsmMacroEnabled and LCELL::hoFromUmts-

MacroEnabled are used to control incoming CS handovers.

Frequency is an existing structure.

Type Name Field Name Description Syntax

rrcMappingTable establishmentCause RRC connection

establishment cause

Enum:establishment-

Cause

rrcMappingTable sBReDirect Redirection allowed Enum sBAllowed

Default = No


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8-7

Type Name Field Name Description Syntax

rrcMappingTable sBMacroTarget Macro Target for

redirection

Enum TargetHO

Default =

fddPreferred

rrcMappingTable sBTargetFddULFreq Macro FDD UL

frequency for

redirection,

uARFCNUL

Integer [0 …16383]

Default = 0 indicates

frequency not

populated

rrcMappingTable sBTargetFddDLFreq Macro FDD DL

frequency for

redirection,

uARFCNDL

Integer [0 …16383]

Default = 0 indicates

frequency not

populated

sBCsRabMapping-

Table

trafficClassRab Traffic class for CS

RAB

Enum:trafficClass-

Rab

The following enum are used:

Name Description Permitted value

sBAllowed Determines if Service Based

redirection or Handover is

allowed taking into account

the terminal type

No = 1 AllUE = 2

AllNonHspaUE = 3

AllHspaUE = 4

Notes:

1. The following existing ENUMs is used: TargetHO, trafficClassRab, FDDRadioFrequenct-

Band

2. The following enum from the Cell FACH feature is used: establishment Cause

3. The following tuneable static is used RRCConnectAttempt_timer

The following is an example of the data population for service type - CS voice:

Table 8-1 RRC Connection Mapping Table – rrcMappingTable

establish-

mentCause

sBReDirect sBMacroTar

get

sBTargetF

ddULFreq

sBTargetF

ddDLFreq

sBTarget

FreqBand

originating-

Conversa-

tionalCall

AllUE gsmPreferred UL ARFCN DL ARFCN fdd2100

originating-

Streaming-

Call

No disable n/a n/a n/a


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Table 8-1 RRC Connection Mapping Table – rrcMappingTable (continued)

establish-

mentCause

sBReDirect sBMacroTar

get

sBTargetF

ddULFreq

sBTargetF

ddDLFreq

sBTarget

FreqBand

originating-

Interactive-

Call


originating-

Background


terminating-

Conversa-

tionalCall


terminating-

Streaming-

Call


terminating-

Interactive-

Call


terminating-

Background-

Call


Table 8-2 RAB Establishment Mapping Table – sBCsRabMappingTable

LCELL::sBCsRabMappingTable

trafficClassRab

conversational

Notes:

1. The action taken by the core network when redirecting terminating calls is unclear and

therefore to ensure a good and reliable experience for the customer, the call will be accepted

and later handed over at RAB establishment. The terminating establishment causes have

been left in the table in case terminating call redirection is required.


Layer


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8-9


Layer


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Glossary

...................................................................................................................................................................................................................................

Numerics

3G

Third-generation wireless

Used to describe technologies such as UMTS and CDMA-2000 that support both voice channels

and higher-capacity data channels.

Also used to describe products that support these technologies.

3G-MSC

Third Generation - Mobile Switching Center

3GPP

Third Generation Partnership Project

...................................................................................................................................................................................................................................

A Ack

Acknowledge

ACM

Address Complete Message

ALCAP

Access Link Control Application Protocol

...................................................................................................................................................................................................................................

B BCCH

Broadcast Control Channel

BSC

Base Station Controller

BSG

BSR Signaling Gateway

BSR

Base Station Router

BSS

Base Station Subsystem

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GL-1

BTS

Base Tranceiver Station

...................................................................................................................................................................................................................................

C CC

Cumulative Counter

CN

Core Network

CPICH

Common Pilot Channel

CS

Circuit Switched

...................................................................................................................................................................................................................................

D DAHO

Database Assisted Handover

dB

Decibel

dBM

A power level compared with 1 milliwatt

...................................................................................................................................................................................................................................

E Ec/Io

The received energy per chip divided by the total power density in the band.

Ec/No

The received energy per chip divided by the power density in the band.

...................................................................................................................................................................................................................................

F FACH

Forward Access Channel

FDD

Frequency Division Duplex

...................................................................................................................................................................................................................................

G G-MSC

Global - Mobile Services Switching Center

GSM

Global System for Mobile communications

Glossary

....................................................................................................................................................................................................................................

....................................................................................................................................................................................................................................

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...................................................................................................................................................................................................................................

H HCS

Hierarchical Cell Structure

HHO

Hard Handover

HO

Handover

...................................................................................................................................................................................................................................

I IAM

Initial Address Message

IPsec

Internet Protocol Security

Itf

Interface

Iu

Interface UTRAN

...................................................................................................................................................................................................................................

M MAP

Mobile Application Part

MSC

Mobile Services Switching Center

...................................................................................................................................................................................................................................

P PDU

Protocol Data Unit

PS

Packet Switched

PSTN

Public Switched Telephone Network

...................................................................................................................................................................................................................................

R RAB

Radio Access Bearer

RACH

Random Access Channel

Glossary

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GL-3

RANAP

Radio Access Network Application Part

RAT

Radio Access Technology

RL

Radio Link

RLA_C

Average power of the signal carrier wave.

RNC

Radio Network Controller

RRC

Radio Resource Control

RSCP

Received Signal Code Power

RSSI

Received Signal Strength Indicator

Rx

Receiver, Receive side

...................................................................................................................................................................................................................................

S SABM

Set Asynchronous Balanced Mode

SCMS

Small Cell Management System

SIB

System Information Broadcast

SMS

Short Message Service

SRNS

Serving Radio Network Subsystem

...................................................................................................................................................................................................................................

T TS

Technical Specification

Glossary

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TX

Transmitter, Transmit side

...................................................................................................................................................................................................................................

U UA

Unnumbered Acknowledgement

UE

User Equipment

UMTS

Universal Mobile Telecommunication System

UTRAN

UMTS Terrestrial Radio Access Network

...................................................................................................................................................................................................................................

V VLR

Visitor Location Register

Glossary

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GL-5

Glossary

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Index

Numerics

2G macro cell reselection

parameters, 1-6

3G macro cell reselection

parameters, 1-5

3G macro cells

cell ranking, 1-5

................................................................................................

A ACL, 7-8, 7-12, 7-13

................................................................................................

B Blind handover, 2-2, 3-2

................................................................................................

C Cell layers, 4-4

Cell ranking

3G macro cells, 1-5

Cell reselection, 4-4

GSM to UMTS, 1-6

on macro layer, 1-2

................................................................................................

F Feature number

10889, 8-2

34529, 1-2

34530, 2-2

34531, 3-2

75389 & 75390, 7-2

75392, 4-2

75494, 5-2

84331, 6-2

Frequencies

HCS, 4-4

................................................................................................

G Goals

cell reselection, 1-5

GSM, 7-2

GSM to UMTS

cell reselection, 1-6

................................................................................................

H Handover

cell reselection mechanisms, 1-2

inter-RAT, 3-2

to macro cell (2G), 3-2

to macro cell (3G), 2-2

HCS

activating, 4-4

Hierarchical Cell Structure feature, 4-2

How to

comment, xiii

................................................................................................

I Idle mode support, 1-2

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IN-1

Indoor coverage

Macro and Small Cell, 1-7

Inter-RAT handover, 3-2

................................................................................................

L Layers

cell, 4-4

................................................................................................

M Macro cell pilot, 1-8

Macro layer cell reselection, 1-2

................................................................................................

N Neighbour cell selection

on macro layer, 1-2

................................................................................................

P Parameters

2G macro cell reselection, 1-6

3G macro cell reselection, 1-5

Penetration losses, 1-8

Pilot

macro cell, 1-8

Small Cell, 1-10

Priorities

HCS, 4-4

PSC, 7-10

................................................................................................

R RAB, 7-7

RANAP relocation procedure, 2-2

Recommendations

reselection, 1-7

Reselection

cell, 4-4

................................................................................................

S Service Based Redirection, 8-2

Small Cell

Pilot, 1-10

Small Cell to Small Cell Handover feature, 5-2

Small Cell to Small Cell Handover Improvements, 6-2

States

HCS, 4-4

................................................................................................

U UMTS, 7-2

Index

....................................................................................................................................................................................................................................

....................................................................................................................................................................................................................................

IN-2 Alcatel-Lucent – Proprietary


Alcatel-Lucent SC

401-387-047 Release 2.4.0

Issue 1 April 2011

Documents

401-387-047R2 4 0 Alcatel-Lucent Small Cell Mobility Management SDS (Issue 1 April 2011)