Wcdma Rno Handover Algorithm Analysis And Parameter Configurtaion Guidance 20050316 A 1.0

Huawei Technologies Co. Ltd.

Product Version Confidentiality level

V100R001 For Internal UseProduct Name: WCDMA RNP Total pages: 53

WCDMA RNO Handover

Algorithm Analysis and

Parameter Configuration

Guidance

For internal use only

Prepared by: URNP-SANA Date: 2003-12-15Reviewed by: Date: Reviewed by: Date: Approved by: Date:

Huawei Technologies Co., Ltd.

All rights reserved

WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance For Intanal Use

Revision Record

Date Rev. Version

Description Author

2003/12/15 Initial transmittal Znag Liang

2005/03/16 1.0 Change the date, no content updated. Qinyan

23-4-10 Confidential Page 2 of 52


Table of Contents

1Introduction................................................................................................................................................72Handover Algorithm Analysis....................................................................................................................72.1Handover Measurement.........................................................................................................................7

2.1.1 Intra-Frequency Measurement...................................................................................................82.1.2 Inter-Frequency Measurement.................................................................................................132.1.3 Inter-System Measurement.......................................................................................................142.1.4 UE Internal Measurement.........................................................................................................15

2.2Handover Algorithms..........................................................................................................................162.2.1 Softer Handover and Soft Handover Algorithms....................................................................162.2.2 Intra-Frequency Hard Handover Algorithm.............................................................................172.2.3 Inter-Frequency Hard Handover Algorithm.............................................................................172.2.4 Inter-System Handover Algorithm............................................................................................192.2.5 Handover Caused by Load Balancing.....................................................................................192.2.6 Cell Penalty.................................................................................................................................202.2.7 Active Set Synchronization Maintenance................................................................................212.2.8 Direct Retry Algorithm................................................................................................................222.2.9 Principle for Generating Adjacent Cell List.............................................................................23

3Handover Parameter Setting.....................................................................................................................243.1Description...........................................................................................................................................243.2Handover Common Parameters...........................................................................................................25

3.2.1 Maximum Number of Cells in Active Set.................................................................................263.2.2 Penalty Time...............................................................................................................................263.2.3 Event 6F Trigger Threshold......................................................................................................273.2.4 Event 6G Trigger Threshold......................................................................................................273.2.5 Time-to-Trigger Parameters for Events 6F and 6G...............................................................283.2.6 BE Service Handover Rate Decision Threshold....................................................................283.2.7 Soft Handover Method Select Switch......................................................................................293.2.8 Handover Algorithm Switches...................................................................................................30

3.3Intra-Frequency Handover Measurement Algorithm Parameters........................................................313.3.1 Soft Handover Relative Thresholds.........................................................................................313.3.2 Soft Handover Absolute Thresholds........................................................................................323.3.3 Intra-Frequency Measurement Filter Coefficient (FilterCoef)...............................................333.3.4 Hysteresis Related to Soft Handover......................................................................................353.3.5 Time-to-Trigger Parameters Related to Soft Handover........................................................363.3.6 WEIGHT.......................................................................................................................................373.3.7 Detected Set Statistics Switch..................................................................................................38

3.4Inter-Frequency Handover Algorithm Parameters...............................................................................383.4.1 Inter-Frequency Measurement Filter Coefficient (FilterCoef)...............................................383.4.2 Cell Location Property................................................................................................................393.4.3 Hysteresis Related to Inter-Frequency Handover..................................................................403.4.4 Time-to-Trigger Parameters Related to Inter-Frequency Hard Handover.........................413.4.5 Compressed Mode Enable/Disable Threshold Denoted by RSCP.....................................423.4.6 Compressed Mode Enable/Disable Threshold Denoted by Ec/No.....................................423.4.7 Inter-Frequency Hard Handover RSCP Threshold................................................................433.4.8 Inter-Frequency Hard Handover Ec/No Threshold................................................................44

3.5inter-system handover measurement algorithm parameter..................................................................443.5.1 inter-system measurement filter coefficient FilterCoef..........................................................443.5.2 Inter-System Hard Handover Decision Threshold.................................................................453.5.3 Inter-system Hard Handover Hysteresis.................................................................................453.5.4 Time-to-Trigger Parameter for Inter-System Hard Handover..............................................463.5.5 Inter-System Measurement Periodic Report Interval............................................................46

3.6Compressed Mode Algorithm Parameter.............................................................................................473.6.1 CFN Offset to Enable Compressed Mode..............................................................................47



3.6.2 Spreading Factor Threshold.....................................................................................................483.7Direct Retry Algorithm Parameter.......................................................................................................48

3.7.1 Maximum Direct Retry Times...................................................................................................483.7.2 Candidate Set Absolute Threshold..........................................................................................493.7.3 Minimum Ec/No Value...............................................................................................................503.7.4 Linear Factor of Relative Threshold and Time Interval.........................................................503.7.5 Maximum Relating Time for Direct Retry Decision................................................................51



List of Tables

table 1 Recommended Soft Handover Hysteresis Settings for Different Movement Speeds.............35table 2 Recommended Time-to-Trigger Settings for Different Movement Speeds.................36table 3 Recommended Inter-Frequency Hard Handover Hysteresis Settings for Different Movement Speeds.................................................................................................................................40

table 4 Recommended Inter-Frequency Hard Handover Time-to-Trigger Settings for Different Movement Speeds.................................................................................................................41

List of Figures

Figure 1 Measurement Model..............................................................................................................8Figure 2 Example of Event 1A and Trigger Delay.............................................................................9Figure 3 Periodic Reporting Triggered by Event 1A.......................................................................10Figure 4 Example of Event 1C...........................................................................................................11Figure 5 Example of Event 1D...........................................................................................................11Figure 6 Restriction of measurement reporting by means of hysteresis.....................................12Figure 7 Example of Event 1E...........................................................................................................12Figure 8 Example of Event 1D1F......................................................................................................13Figure 9 Power Control Timing..........................................................................................................21Figure 10 MML Client..................................................................................................................25



WCDMA RNO Handover Algorithm Analysis and Parameter Configuration Guidance

Key words: handover algorithm, soft handover, hard handover, inter-system handover, parameter

setting

Abstract: This document first describes the measurements involved in the handover algorithms,

and then analyzes the measurement control and decision rules in the implementation of

the algorithm of each type of handover. Finally, it provides a detailed guidance for the

setting of various types of handover parameters, so that correct and effective handover

parameter adjustments can be carried out based on the actual requirements during

network optimization.

List of abbreviations: (Omitted)



1 Introduction

Handover types include softer handover, soft handover, intra-frequency hard handover,

inter-frequency hard handover and inter-system hard handover. A typical handover process is:

measurement control measurement report handover decision handover execution new

measurement control. Based on the measurement value, handover control method and handover

type selection required for the handover decision, the handover algorithm determines how the

UE carry out handover measurements and report the measurement result, and then makes

handover decision and guides the handover execution according to the reported measurement

result. Handover algorithms largely present themselves in the configuration of measurement control

parameters.

In Chapter 2, this document discusses the measurement control, reporting rules and related

handover decision algorithms involved in various types of handover. In Chapter 3, based on the

knowledge of the handover algorithms, this document provides detailed descriptions of the

specific parameter setting methods value assignment recommendations and ranges of effect of

the related algorithms of various types of handover, so as to provide a clear and practical

guidance for parameter adjustments in network optimization.

2 Handover Algorithm Analysis

Mobility management is an important part of radio resource management, while handover

algorithms are the most important part of mobility management. A handover algorithm involves

such contents as measurement control and handover decision. Therefore, to analyze a handover

algorithm, we should first analyze handover measurement.

2.1 Handover Measurement

The radio resource management module (RRM) initiated measurements include dedicated

measurement and common measurement. All the measurements in the UE are dedicated

measurement. Handover measurement is specific to the physical layer, which provides

measurement of various items for the higher layers, so as to trigger various functions, including

handover.

The measurement result will go twice through smoothening processing. The first processing

is in the physical layer, and the purpose is to filter off the influence of fast fading before the

physical layer reports the measurement result to the higher layer. The second processing is

implemented by the higher layer on the measurement result reported by the physical layer before

event evaluation. This processing is to determine the filter coefficient according to the time

relation and implemented weighted averaging processing of the measurement result. The latest



measurement result after L3 filtering is used for evaluation of the reporting rule, and as the

reported result. The process is as follows:

Figure 1 Measurement Model

The reporting types include “on-demand reporting”, “periodic reporting” and “event triggered

reporting” (Event A to Event F). Generally, the last two types of measurement reporting are

involved in handover.

In the UE, measured cells are divided into the following three types:

Active set cells: Cells in an active set communicate with the UE simultaneously. Active set

cells refer to those that are demodulated and correlatively combined at the UE and

communicate with the UE in the FDD mode, namely in soft handover and softer handover.

Cells in an active set are surely intra-frequency cells.

Monitored set cells: Among the cells included in the adjacent cell list delivered by the RNC,

some adjacent cells may have already entered the active set at the time of soft handover,

and the remaining cells are in monitored sets. Monitored sets include intra-frequency

monitored sets, inter-frequency monitored sets and inter-system monitored sets.

Detected set cell: Detected set cells refer to those cells detected by the UE itself, rather than

the cells in the active sets and monitored set.

The types of measurement involved in handover include intra-frequency measurement,

inter-frequency measurement and inter-system measurement, which will be discussed in the

following paragraphs.

2.1.1 Intra-Frequency Measurement

UTRAN uses the measurement control message to inform the UE what events need to

trigger measurement reporting. All intra-frequency measurement report events are identified with

1X.

Event 1A: A primary pilot channel enters the reporting range

If the network, in the measurement report mechanism field, requires the UE to report event

1A while the UE has entered the Cell_DCH state, then when a primary pilot channel enters the



reporting range, the UE will send a measurement report.

When the measurement values satisfy the following formulas, the UE deems that a primary

pilot channel has entered the reporting range:

1. Path loss:

2. Other measurement values:

Where,

MNew is the measurement result of the cell that has entered the reporting range

Mi is the measurement result of the cells in the active set

NA is the number of cells in the current active set

MBest is the measurement result of the best cell in the current active set

W is the weight factor

R is the reporting range. With the signal strength as an example, R equals to the signal strength

of the best cell in the current active set minus a value

H1a is the hysteresis value of event 1A

In order to reduce the signaling traffic flow of the measurement report, the TIME-TO-

TRIGGER parameter is used so that the UE will not trigger measurement reporting before the

primary pilot enters the reporting range and is maintained for a certain period of time. This

parameter is also used in other events. An example of measurement reporting triggered by event

1A is given below:

Figure 2 Example of Event 1A and Trigger Delay



Generally, if event 1A is triggered, the UE will send a measurement report to UTRAN, and

UTRAN will deliver an ACTIVE SET UPDATE signaling message to update the active set.

However, UTRAN may give no response after the UE sends the measurement report (for

example, due to insufficient capacity). In this case, the UE will shift from event reporting to

periodic reporting mechanism, and the content of the measurement report includes the

information of the cells in the active set and the cells in the monitored set that has entered the

reporting range. The UE will not stop sending periodically the measurement report until this cell is

successfully added into the active set or leaves the reporting range, as shown below:

Figure 3 Periodic Reporting Triggered by Event 1A

Event 1B: A primary pilot channel leaves the reporting range

When the following formulas are satisfied, the UE deems that a primary pilot channel has left

the reporting range

1, Path loss:

2, Other measurement values:

Where,

MOld is the measurement result of the cell that has left the reporting range

Mi is the measurement result of the cell in the active set

NA is the number of cells in the current active set

MBest is the measurement result of the best cell in the current active set

W is the weighted factor



R is the reporting range

H1a is the hysteresis value of event 1A

If several cells satisfy the reporting condition simultaneously after the trigger delay, the UE

will sort the cells according to the measurement values and report all the measurement results.

Event 1C: The primary pilot channel in a non active set is better than the primary pilot

channel in an active set

This event can be described through the following example:

Figure 4 Example of Event 1C

In this example, the cells where P CPICH 1, P CPICH 2 and P CPICH 3 are belong to an

active set, while that of P CPICH 4 does not. This event is used to replace the poor cells in the

active set, if the number of cells in the active set reaches or exceeds active set replacement

threshold.

Event 1D: The best cell changes

Figure 5 Example of Event 1D



In order to prevent frequent triggering of event 1D due to signal fluctuations when the

channel difference is small, which results in unnecessary increase of the air interface signaling

traffic flow, we can use the hysteresis parameter, as shown below:

Figure 6 Restriction of measurement reporting by means of hysteresis

As we can see, as the hysteresis condition is not met at the second time, event 1D reporting

is not triggered. This parameter can also be used in other events.

Event 1E: The measurement value of a primary pilot channel exceeds the absolute

threshold

Figure 7 Example of Event 1E

Event 1E can be used to trigger the measurement reports of cells including those detected

by the UE before it receives the adjacent cell list.



Event 1F: The measurement value of a primary pilot channel is lower than the absolute

threshold

Figure 8 Example of Event 1D1F

2.1.2 Inter-Frequency Measurement

Inter-frequency measurement events are identified with 2X. The frequency quality

estimation involved in events 2A, 2B, 2C, 2D and 2E is defined as follows:

Where,

Qcarrierj is the logarithmic form of the estimated quality value of frequency j

Mcarrier j is the estimated quality value of frequency j

Mi j is the measurement result of cell i with the frequency of j in the virtual active set

NA j is the number of cells with the frequency of j in the virtual active set

MBest j is the measurement result of the best cell with the frequency of j in the virtual active set

Wj is the weight factor

H is the hysteresis value

Before we describe events 2x, we should make the following two concepts understood:

“non-used frequency” refer to the frequency that the UE needs to measure but that is not in the

active set, and “used frequency” refers to the frequency that the UE needs to measure and that is

in the active set.



Event 2A: The best frequency changes

If the estimated quality value of the non-used frequency is better than that of the best cell in

the used frequency, and the hysteresis value and the “time to trigger” conditions are satisfied,

event 2A will be triggered.

Event 2B: The estimated quality value of the used frequency is lower than a certain

threshold, and that of the non-used frequency is higher than a certain threshold

If the estimated quality value of the used frequency is lower than the threshold defined by IE

“Threshold used frequency” delivered in the measurement control message, while that of the

non-used frequency is higher than the threshold defined by IE “Threshold non-used frequency”

delivered in the measurement control message, and the hysteresis value and the “time to trigger”

condition are satisfied, event 2B will be triggered.

Event 2C: The estimated quality value of the non-used frequency is higher than a

certain threshold

This threshold is specified by IE “Threshold non-used frequency” in the measurement control

message delivered by UTRAN.

Event 2D: The estimated quality value of the used frequency is lower than a certain

threshold

Event 2D can be used to enable the compressed mode to perform inter-frequency

measurement. This threshold is specified by IE “Threshold used frequency” in the measurement

control message delivered by UTRAN. This type of parameters can be modified through MML

commands.

Event 2E: The estimated quality value of the non-used frequency is lower than a

certain threshold

This threshold is specified by IE “Threshold non-used frequency” in the measurement control

message delivered by UTRAN.

Event 2F: The estimated quality value of the used frequency is higher than a certain

threshold

Event 2F can be used to disable the compressed mode to stop inter-frequency

measurement. This threshold is specified by IE “Threshold used frequency” in the measurement

control message delivered by UTRAN.

2.1.3 Inter-System Measurement



Inter-system measurement events are identified with 3X. The quality estimation of a UTRAN

active set involved in events 3A, 3B, 3C and 3D is defined as follows:

Where, QUTRAN is the logarithmic form of the estimated quality value of the UTRAN frequency currently in

use

MUTRAN is the estimated quality value of the UTRAN frequency currently in use

Mi is the measurement result of cell i in the active set

NA is the number of cells in the active set

MBest result is the measurement result of the best cell in the active set

W is the weight factor

Event 3A: The estimated quality value of the used UTRAN frequency is lower than a

certain threshold, and that of the other system is higher than a certain threshold

If the estimated quality value of the used UTRAN frequency is lower than the threshold

defined by IE “Threshold own system” delivered in the measurement control message, while that

of the other system is higher than the threshold defined by IE “Threshold other system” delivered

in the measurement control message, and the hysteresis value and the “time to trigger” condition

are satisfied, event 3A will be triggered.

Event 3B: The estimated quality value of the other system is lower than a certain

threshold

This threshold is specified by IE “Threshold other system” in the measurement control

message.

Event 3C: The estimated quality value of the other system is higher than a certain

threshold

This threshold is specified by IE “Threshold other system” in the measurement control

message.

Event 3D: The best cell in the other system changes

2.1.4 UE Internal Measurement

Two UE internal measurement events are involved in the handover algorithms: 6F and 6G.

Event 6F: The time difference between downlink receiving and uplink transmission of

the UE is bigger than an absolute threshold



This threshold is specified in IE “UE Rx-Tx time difference threshold” delivered by UTRAN.

Event 6G: The time difference between downlink receiving and uplink transmission of

the UE is smaller than an absolute threshold

This threshold is specified in IE “UE Rx-Tx time difference threshold” delivered by UTRAN.

2.2 Handover Algorithms

This section will describer the handover-related algorithms already supported by RNC V1.2,

so as to provide algorithm guidance for network optimization and parameter adjustments. The

contents of this section include softer handover and soft handover algorithms, intra-frequency

hard handover algorithm, inter-frequency hard handover algorithm, inter-system hard handover

algorithm, load balancing handover algorithm, cell penalty, direct retry algorithm and active set

synchronization maintenance and adjacent cell list maintenance method.

2.2.1 Softer Handover and Soft Handover Algorithms

Presently, RNC V1.2 uses two soft handover algorithms: loose-mode algorithm and relative

threshold algorithm. The user can make selection between these two algorithms through the

algorithm switch. By default, algorithm 2, namely, relative threshold algorithm is enabled.

1. Loose-mode algorithm

1) When either event 1A or event 1E (referred to as “1A or 1E”) is satisfied, it will be

deemed as the trigger condition for adding a soft handover branch;

2) After event 1A or 1E is received, if the number of cells in the active set is 3, no

processing will be implemented.

3) When neither the relative threshold nor the absolute threshold (event 1B and 1F) is

satisfied, it is deemed as the trigger condition for removing a soft handover branch.

4) If handover is triggered when either event 1B or event 1F is received, but the triggered

cell is the best cell, then no processing will be made.

5) When the UE active set is full, event 1A and event 1E reporting is stopped, and event 1C

reporting starts

6) Event 1C is the trigger condition for cell replacement in the active set.

7) Event 1D occurs in the active set cell, and measurement control changes, based on the

best cell operation algorithm.

8) Event 1D occurs in the monitored set cell, and this cell is added into the active set. If the

active set is full, remove any cell among non-best cells and then add the reported best cell, and



mark it as the best cell. After successful operation, the measurement control change process is

started.

2. Relative threshold algorithm

1) When event 1A report is received, if the active set is not full, then links are sequenced

and added in the order of good quality to poor quality (CPICH Ec/No) (in case that multiple cells

report event 1A), until the active set is full; if the active set is already full, no processing will be

made.

2) When event 1B is received, if there are more than one links in the active set, then the

braches are sequenced and removed in the order of poor quality to good quality (CPICH Ec/No)

(in case that multiple cells report event 1B), until only one link is left; if there is only one in the

active set, no processing will be made.

3) In case of event 1C, the UE will report the replacing and replaced cells in the event

trigger list. If the active set is not full, then the triggered cell link will be added; if the active set is

already full at this moment and the replaced cell is not the best cell in the active set, then this cell

link will be removed.

4) In case of event 1D, if the triggered cell is an active set cell, then it will be marked as the

best cell and measurement control is updated; if the triggered cell doe not belong to the active

set, then this cell link will be added (if the active set is full, one of the non-best cell will be

removed before this link is added) and marked as the best cell, with measurement control

updated.

2.2.2 Intra-Frequency Hard Handover Algorithm

Intra-frequency hard handover will occur in two cases: 1, handover between intra-frequency

adjacent cells that belong to different RNCs, between which no Iur interface is available; 2,

handover of high-rate PS Best Effort services that exceeds the rate threshold, because too much

forward capacity will be occupied if soft handover is adopted in this case.

Event 1D is used as the judgment criterion for event intra-frequency hard handover.

Namely, the event 1D triggered cell acts as the target cell of the handover.

2.2.3 Inter-Frequency Hard Handover Algorithm

1. Basic concepts



Carrier coverage verge cell: a cell located at the outmost verge of a carrier coverage area.

The characteristic is that the cell does have an intra-frequency adjacent cell in a certain direction.

Carrier coverage center cell: a cell other than carrier coverage verge cells. The

characteristic is that the cell has intra-frequency adjacent cells in all directions.

In a carrier coverage verge cell, when the UE moves towards the direction in which the cell

has no intra-frequency adjacent cell, the CPICH Ec/No changes slowly because CPICH RSCP

has the same speed with the fading of interference. Simulation shows that CPICH Ec/No can still

reach -12dB or so when CPICH RSCP is already lower than the demodulation threshold (about -

110dBm). At this moment, the inter-frequency handover algorithm based on CPICH Ec/No

measurement has actually failed. Therefore, for a carrier coverage verge cell, it is more suitable

and more efficient to use CPICH RSCP as the inter-frequency measurement quantity.

For a carrier coverage center cell, CPICH RSCP can also be used as the inter-frequency

measurement quantity, but CPICH Ec/No can better reflect the actual link communication quality

and the load situation of the cell.

2. Enabling/disabling inter-frequency measurement

Because inter-frequency measurement may use the compressed mode, which usually

affects the link quality and system capacity, we generally hope that inter-frequency measurement

is not enabled unless necessary. Currently, RNC V1.2 decides to enable or disable inter-

frequency measurement through the reporting of event 2D and event 2F.

When the UE enters the CELL_DCH state or when the best cell is updated, if the inter-

frequency handover algorithm is enabled and an inter-frequency adjacent cell list is available for

the best cell, then the measurement of event 2D and 2F is configured. The absolute thresholds of

events 2D and 2F are the enabling/disabling thresholds of inter-frequency measurement. CPICH

Ec/No or RSCP measurement quantity and thresholds will be adopted respectively according to

the location property of the best cell in the active set (carrier coverage center or carrier coverage

verge as previously described). If the measurement quantity is lower than the enabling

threshold , event 2D will be reported, and inter-frequency measurement will be enabled through

decision; if the active set quality rises and becomes higher than the disabling threshold, then

event 2F reporting will be triggered and inter-frequency measurement will be stopped.

3. Inter-frequency hard handover decision

Presently, the periodic measurement reporting mode is used for inter-frequency

measurement. In RNC V1.2, the absolute threshold decision method based on cell properties is

used for inter-frequency handover decision. According to different cell properties (carrier

coverage verge cell and carrier coverage center cell), different physical measurement quantities

(CPICH RSCP and CPICH Ec/No) and handover thresholds are used for handover decision.



Based on the inter-frequency measurement result periodically reported by the UE, if the

measurement values exceed the absolute threshold and the hysteresis values and the “time to

trigger” condition is met, then the RNC will implement inter-frequency hard handover with the

reported cell as the handover target cell.

Note: Due to lack of a special compressed mode control policy, it is recommended that

inter-frequency handover be used only for necessary handover caused by discontinuous carrier

coverage. In this case, we can consider to enable the compressed mode only at the carrier

coverage verge, while disable the compressed mode at the carrier coverage center by means of

parameter configuration (by setting the absolute threshold of event 2D to the minimum) to disable

inter-frequency hard handover.

2.2.4 Inter-System Handover Algorithm

RNC V1.2 supports 3G->GSM/GPRS handover. Presently, inter-system handover is used

only for inter-system handover caused by discontinuous coverage of 3G networks, and other

types of inter-system handover, such as load balancing, are not supported.

1) Inter-system handover is enabled only in cells located at the verge of WCDMA FDD

system coverage.

2) Inter-system handover algorithms and inter-frequency handover algorithms are mutually

exclusive. That is, when the compressed-mode measurement of inter-system handover is

enabled, the compressed-mode measurement of inter-frequency handover must be disabled.

3) Cells at the verge of WCDMA FDD system coverage are identified through the

configuration of GSM/GPRS adjacent cell list for them.

4) For inter-system handover, CPICH RSCP is used as the physical measurement quantity

and events 2D and 2F are used to decide enabling or disabling the compressed mode.

5) For inter-system handover, three compressed mode style sequences are used for

concurrent measurement of GSM RSSI, BASIC identification and BASIC reconfirm, and the

configuration of parameters is oriented to the cell type, namely, the parameters can be selected

and configured based on the cell characteristics and user mobility statistics characteristics.

6) Periodic measurement reports are used for inter-system handover, and the RNC decides

whether to implement hard handover according to the measurement reports.

2.2.5 Handover Caused by Load Balancing

When the loads of the adjacent cells become unbalanced, the load control algorithm will

balance the loads between the adjacent cells through handover. Generally, the algorithm



implements load balancing by changing the power of the common pilot channel between

adjacent cells. Since handover algorithms obtain the Ec/No of the common pilot channel of

adjacent cells through the measurement by the UE, while the handover thresholds of various

cells are also obtained through the RNC database, the load balancing control algorithm is

transparent to handover algorithms, without any direct interface in between.

When the loads become unbalanced among cells of different frequencies in the same Node

B, the performance of the entire system may deteriorate. In this case, the load control algorithm

will notify the handover algorithm to switch some UEs on heavy-load carries onto light-load

carriers thus to balance the loads. At this time, the load control entity selects the specific UEs.

Upon selecting the UEs, the load control entity sends the source cell information and the target

cell information to the selected UEs’ Handover Control entities , and what the handover entity

should to do is just to give out the handover command based on the message it has received.

Load balancing between different NodeBs is transparent to the handover algorithm.

Therefore, we mainly analyze handover requests caused by load balancing between different

carriers in the same coverage area. In this kind of handover, the handover entity actually does

not make any specific decision, but it only “forwards” the decision command made by the load

control entity. In this kind of handover, two principles are followed for UE selection:

(1) UEs in soft handover are not selected. Since the target cell’s synchronization

information may be unavailable, the timming re-initiation hard handover procedure is used here.

As RNC V1.2 does not support immediate macro diversity, if a UE in soft handover state is

selected at this moment for load transfer, it will necessarily result in damage to the soft handover

state of this UE, and increase call drop risk.

(2) UEs with inconsistent SRNC and CRNC are not selected, because this kind of transfer

involves signaling interworking on the Iur interface, while the Iur is an open interface, without this

type of signaling.

Upon receiving the load transfer signaling, the handover entity first implements handover

decision to judge whether the two conditions previously mentioned are satisfied. If so, it will

proceed with the next step of processing; otherwise, it will reject the request and indicate the

reason.

2.2.6 Cell Penalty

The purpose of cell penalty caused by handover failure is to prevent the handover algorithm

from deciding again on the handover of this UE to a cell that already has no more capacity. In

order to avoid making redundant judgments, in case of a handover failure (including soft

handover and hard handover), the involved UE will be restricted from initiating any further



handover request to the same cell within the penalty time, and the event periodic reporting

interval is required to be equal to the penalty time. Thus, after a handover failure, on one hand

penalty is exerted on the target cell involved in the handover failure, and on the other the periodic

reporting interval is made equal to the penalty time, so that large waste of processing capability

is avoided.

The Connection-oriented cell penalty algorithm is as follows:

(1) The cell penalty algorithm is to deny any handover access to the cell in penalty within

the specified period of time, namely, the involved UE is not allowed to initiate any further

handover request to this cell. The penalty flag is set to 1;

(2) After the penalty time expires, the penalty is released, and the penalty flag is set to 0.

2.2.7 Active Set Synchronization Maintenance

According to the 25.214 protocol, from the downlink receiving moment of the UE to the

corresponding uplink transmission moment, there should be a 1024-chip delay, so as to ensure

the normal 1-slot uplink and downlink power control, as shown below:

Figure 9 Power Control Timing



As illustrated in the diagram, when the UE complete receiving the downlink PILOT bit, it has

the time of 512 chips to generate the TPC bit for downlink power control according to the PILOT

bit. When the UE is in the soft handover state, the generation of the TPC bit should be based on

the PILOT calculation of all links. However, in the actual system, because the selection of the

downlink transmission time is obtained by the NodeB based on the RNC-configured frame offset

and code offset after roundup by 256 chips (the minimum time resolution of the NodeB is 256

chips), there is an error of ±128 chips between the actual transmission time and the RNC-

configured time. Plus errors in the UE movement speed and clock drift, there will be an error of

±(128+20) chips at the UE side. That is, when the Rx-Tx time difference is within the range of

1024±148 chips, the design of UE and NodeB should be able to satisfy the 1-slot power control

requirement; when it is out of this range, the system will be unable to guarantee the 1-slot power

control requirement, resulting in power control performance deterioration.

The UE Rx-Tx time difference is measured once every 10 frames. When the Rx-Tx time

difference is smaller than 876 (1024–148) chips, the UE-end processing time will be reduced,

and, as result, it will be likely that the downlink 1-slot power control cannot be guaranteed; when

the Rx-Tx time difference is greater than 1172 (1024+148) chips, the NodeB-end processing will

be reduced, and it will be likely that the uplink 1-slot power control cannot be guaranteed.

There are two UE internal measurement events for the measurement of the protocol-

provided synchronization maintenance information: event 6F and event 6G, as described

previously.

Algorithm description:

a) After the UE enters the CELL_DCH state, the algorithm enables the UE to report event

6F and event 6G through measurement control.

b) The thresholds, delays and hysteresis values of events 6F and 6G are used as algorithm

parameters, which can be adjusted through background configuration.

c) Once event 6F or event 6G occurs on a radio link, the network side will release this radio

link.

D) The cell with its link released may retrigger other events and then new RL could be

added to the active set.

2.2.8 Direct Retry Algorithm

When the UE requests to leave the IDLE mode and enter the CONNECTION mode, if the

admission fails, another best cell will be selected for an access attempt based on the RACH

measurement report previously reported by the UE. Such an access attempt is called direct retry.

The direct retry algorithm needs the following parameters:



1) DRMaxNumber: the maximum direct retry times for each direct retry candidate cell

2) DRDCSThreshold: a basic threshold for entering the candidate set

3) MaxRelatingTime: the maximum time that the RACH measurement report can continue

to be used

4) LinearFactor: the linear factor for the relative threshold and time interval during candidate

set screening

5) MinSignalRequired: basic access threshold.

Algorithm description:

(1) The direct retry algorithm is effective only when the UE initiates RRC setup request.

(2) The direct retry algorithm buffers the cell measurement value in the RACH measurement

report of the UE, deletes the originally saved cell measurement information after the RNC

receives a new RACH measurement report, buffers the cells of which the measurement signal

CPICH Ec/No is greater than MinSignalRequierd (basic access threshold), and records the

reporting time.

(3) When the UE initiates an RRC setup requests, if the connection setup fails, the RNC will

choose a new cell with the best quality for a further access attempt based on the cell

measurement information in the RACH measurement report carried in the RRC CONNECTION

REQUEST message, until all the available cells (candidate cells) fail and the number of attempts

reaches the maximum retry times.

(4) Candidate cells are picked up as follows:

1) Read the current system time, calculate the buffering time of the cell measurement value,

and discards the cells of which the buffering time is bigger than MaxRelatingTime

2) Based on the measurement value in the buffered RACH report and the LinearFactor,

convert the estimated value of the current cell signal quality: cell measurement value (CPICH

Ec/No) – buffer time (s) × LinearFactor (dB/s)

3) Put the cells of which the estimated quality value is greater than DRDCSThreshold into

the candidate set of the direct retry algorithm.

(5) Retry with the cell having the best estimated quality from the candidate set cells. If retry

fails, continue to retry, until the number of attempts reaches the maximum retry times

(DRMaxNumber).

2.2.9 Principle for Generating Adjacent Cell List

There are two adjacent cell list control methods:



1. Adjacent cell list control method based on the best cell

When the adjacent cell list is controlled based on the best cell, the basic policy is as follows:

(1) If there only one cell, the adjacent cell list will be controlled based on this cell;

(2) If a cell is added by event 1D, after it is successfully added, the adjacent cell list will be

controlled based on this cell;

(3) If a cell is added by an event other than event 1D, the adjacent cell list will not be

changed;

(4) If the best cell has not been removed, the adjacent cell list will not be changed;

(5) If the best cell has been removed, a new best cell will be selected based on the

information obtained during the removal action, and the adjacent cell list will be modified after

successful removal of the best cell;

(6) If event 1D occurs on a cell in the active set, the adjacent cell list will be modified.

(7) This method is relative simple, but is may bring the problem of inaccurate control for

UEs under the macro diversity.

2. Control method based on all the cells in the active set

A control method that can take the adjacent cells of all the cells in the active set is a good

policy. The adjacent cell list is generated by means of the following method:

Step 1: Add active set cells;

Step 2: Add the common adjacent cells of the cells of all the active sets (3 active sets) into

the adjacent cell list. If there are more than 32 adjacent cells after this action, remove randomly

cells added in this step;

Step 3: Add the common adjacent cells of every two active set cells into the adjacent cell

list. If there are more than 32 adjacent cells after this action, remove randomly cells added in this

step;

Step 4: Consider adding the common adjacent cells of each active set cell into the adjacent

cell list, starting from the adjacent cells of the best cell. If there are more than 32 adjacent cells

after this action, remove cells by starting from the worst cell.

Note: The RNC V1.2 version supports the adjacent cell list control method based on the

best cell.

3 Handover Parameter Setting



3.1 Description

The MML client utility can be used for handover parameter setting. This utility provide

convenient command navigation and function description, detailed usage and parameter

descriptions of various commands.

Figure 10 MML Client

According to the functioning scope, handover algorithm parameter configuration commands

are divided into categories: RNC-oriented global parameter configuration and cell-oriented

parameter configuration.

Handover common parameter configuration is RNC-oriented global parameter setting.

Both RNC-oriented setting commands and cell-oriented setting commands are available for

the configuration of intra-frequency handover measurement algorithm parameters, inter-

frequency handover measurement algorithm parameters and inter-system handover

measurement algorithm parameters. Generally, the adjustments of these parameters during

network optimization are all cell-oriented settings, while RNC-oriented global parameter

configuration commands facilitate modification of whole-network handover parameters. For one

same parameter, the cell-oriented command has higher priority.



3.2 Handover Common Parameters

3.2.1 Maximum Number of Cells in Active Set

Definition

MaxCellInActiveSet, maximum number of cells in the active set

Scope

Per RNC

Range and unit

Integer(1..3)

Working range

Integer(1..3)

Recommended value

3

Balance in setting

Modification of value is not recommended.

Modification/query

To configure this RNC-oriented global handover parameter, use the command set

hocomm; to view the current configuration of the parameter, use the command lst

hocomm.

3.2.2 Penalty Time

Definition

PenaltyTime, cell penalty time parameter, as described in Section 2.2.6.

Scope

Per RNC

Range and unit

Integer(1..255), s.

Working range

Integer(1..60)

Recommended value

30, namely the penalty time is 30 seconds

Balance in setting

The setting of this parameter is related to traffic statistics. According to the general traffic

statistics result, the average duration of a call is 60s, so the actual value range of this

parameter is 1 to 60 seconds. If this value is too small, the resources will not be timely

released, and therefore the penalty is meaningless; if this value is too big, radio links will

fail to be timely added, and this is bad for link QoS improvement.

Modification/query





hocomm.

3.2.3 Event 6F Trigger Threshold

Definition

RxTxtoTrig6F, the trigger threshold of event 6F. Namely, if the time interval between the

UE’s downlink receiving and the corresponding uplink transmission is greater than this

absolute threshold, event 6F will be triggered.

Scope

Per RNC

Range and unit

Integer(768..1280), chip.

Working range

Integer(1024..1280)chip

Recommended value

1172

Balance in setting

The value of this parameter should not be too close to 1024; otherwise radio links will be

removed too early. It is recommended that this parameter be adjusted within the range of

1172±3 chips. To guarantee the 1-slot power control, decrease the value of this

parameter; otherwise, it could be increased.

Modification/query



hocomm.

3.2.4 Event 6G Trigger Threshold

Definition

RxTxtoTrig6G, absolute threshold for triggering event 6G.

Scope

Per RNC

Range and unit

Integer(768..1280), chip.

Working range

Integer(768..1024)chip

Recommended value

876

Balance in setting



The value of this parameter should not be too close to 1024; otherwise radio links will be

removed too early. It is recommended that this parameter be adjusted within the range of

876±3 chips. To guarantee the 1-slot power control, increase the value of this parameter;

otherwise, it could be increased.

Modification/query



hocomm.

3.2.5 Time-to-Trigger Parameters for Events 6F and 6G

Definition

Time-to-trigger parameters for event 6F and event 6G, including TrigTime6F and

TrigTime6G.

Scope

Per RNC

Range and unit

Enum(D0, D10, D20, D40, D60, D80, D100, D120, D160, D200, D240, D320, D640,

D1280, D2560, D5000), ms.

Working range

Enum(0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240, 320, 640, 1280, 2560, 5000)ms

Recommended value

D240.

Balance in setting

UE Rx-Tx time difference type1 is measured once per 100ms, with measurement accuracy

being 1.5 chips. To avoid wrong judgment caused by measurement errors of the UE, a

delay can be set in the event trigger time, so that the UE can perform measurement at

least twice for judgment. The time delay on internal processing shall also be taken into

consideration. We recommend that this parameter be set at 240ms.

Modification/query



hocomm.

3.2.6 BE Service Handover Rate Decision Threshold

Definition

BEBitRateThd. When the PS BE service rate exceeds this threshold, intra-frequency hard

handover will be implemented; when it is lower than this threshold, soft handover will be

implemented.

Scope



Per RNC

Range and unit

Enum (D8, D32, D64, D128, D144, D256, D384), corresponding to (8k, 32k, 64k, 128k,

144k, 256k, 384k) bps.

Working range

Enum(D8,D32,D64,D128,D144,D256,D384)

Recommended value

D64.

Balance in setting

It is the rate decision threshold deciding whether soft handover is to be implemented for

the BE service. When the maximum rate of the BE service transmission channel is smaller

than this threshold, the system will perform soft handover for the service user so as to

ensure the QoS for the user; when the maximum rate of the BE service transmission

channel exceeds this threshold, the system will implement intra-frequency hard handover

for the service user so as to prevent excessive influence on the system capacity caused

by soft handover.

Modification/query



hocomm.

3.2.7 Soft Handover Method Select Switch

Definition

SHOMechod, used to select the loose-mode algorithm or the relative threshold algorithm

for soft handover decision.

Scope

Per RNC

Range and unit

Enum(SHO_METHOD1, SHO_METHOD2), soft handover algorithm 1, soft handover

algorithm 2

Working range

Enum(SHO_METHOD1, SHOMETHOD2)

Recommended value

Soft handover algorithm 2.

Balance in setting

Algorithm 1 is the loose-mode algorithm that adds a cell into the active set no matter the

cell triggers event 1A or event 1E, and removes a cell only after it triggers both event 1B

and event 1F simultaneously. Algorithm 2 is the relative threshold algorithm, which does



not involve events 1E and 1F. It adds a cell into the active set as soon as it triggers event

1A, and removes a cell from the active set as soon as it triggers event 1B.

Modification/query



hocomm.

3.2.8 Handover Algorithm Switches

Definition

This parameter defines the switches of various algorithms related to connection-oriented

handover. The specific algorithm parameters can function only after the corresponding

algorithm switches being enabled.

Scope

Per RNC

Range and unit

32 bits, 0~4294967295; each bit can be set at 0 or 1 to control a handover algorithm.

Currently there are the 17 handover algorithm switches, arranged as follows from the

lowest bit to the highest:

Soft handover

Compressed mode maintenance algorithm at soft handover synchronization

Intra-frequency hard handover

Inter-frequency hard handover

3G-2G inter-system hard handover

2G-3G inter-system hard handover

Compressed mode

Uplink compressed mode

6G & 6F measurement

Cell penalty

Location

RTT enhanced location

Relocation

Relocation based on time delay optimization

Relocation based on Iur transmission resource optimization

CS UE relocation based on Iur transmission resource optimization

Direct retry

Working range

Integer(0~32767)

Recommended value

1159, namely 00000010010000111:



Soft handover — On (1)

Compressed mode maintenance algorithm at soft handover synchronization — On (1)

Intra-frequency hard handover — On (1)

Inter-frequency hard handover — Off (0)

3G-2G inter-system hard handover — Off (0)

2G-3G inter-system hard handover— Off (0)

Compressed mode — Off (0)

Uplink compressed mode — On (1)

6G & 6Fmeasurement — Off (0)

Cell penalty — Off (0)

Location — On (1)

RTT enhanced location — Off (0)

Relocation — Off (0)

Relocation based on time delay optimization — Off (0)

Relocation based on Iur transmission resource optimization — Off (0)

CS UE relocation based on Iur transmission resource optimization — Off (0)

Direct retry — Off (0)

Balance in setting

Corresponding configuration should be carried out based on the implementation of each

version of algorithm.

1) Test compressed mode: compressed mode switch should be enabled.

2) Test inter-frequency hard handover: inter-frequency hard handover + compressed mode

switch should be enabled.

3) Test inter-system hard handover : inter-system handover enabled + compressed mode

switch should be enabled.

4) Test relocation: relocation enable switch — a main switch. When the main switch is off,

the following three will not function

Relocation based on time delay optimization enable switch

Relocation based on Iur transmission resource optimization enable switch

CS UE relocation based on Iur transmission resource optimization enable switch

Modification/query

For RNC-oriented settings, use the command set/lst corrmalgoswitch.

3.3 Intra-Frequency Handover Measurement Algorithm Parameters

3.3.1 Soft Handover Relative Thresholds

Definition



These parameters define the difference between the quality of a cell (currently it is

evaluated with PCPICH Ec/No) and the overall quality of the active set (if w=0, then it is

the quality of the best cell). The relative threshold parameters for soft handover include

IntraRelThdFor1A (relative threshold for event 1A) and IntraRelThdFor1B (relative

threshold for event 1B).

Scope

Per RNC/CELL

Range and unit

Integer(0~29), corresponding to 0 to 14.5dB; configuration step: 1 (0.5dB).

Working range

Integer(0~16)

Recommended value

10, namely, 5dB.

Balance in setting

Settings of these parameters determine the size of the soft handover area and the soft

handover subscriber proportion. In a CDMA system, it is required that the UE proportion in

soft handover should be 30% to 40% so as to ensure smooth handover. Based on the

simulation result, when the relative thresholds are set at 5dB, the proportion of UEs in the

soft handover state (number of active set cells ≥ 2) is around 35%. It is recommended that

this value be slightly bigger in the early stage of deployment (5 to 7dB). To save system

resources, this figure can be gradually decreased with the growth of the number of

subscribers, but it must be bigger than 3dB. The default configuration is 5dB. In addition,

in special applications, different relative threshold values can be set for event 1A and

event 1B to reduce the ping-pong effect and change the soft handover proportion in some

special applications. For example, if the adjustment of the hysteresis values for events 1A

and 1B is insufficient for good control of the ping-pong effect, the relative threshold for

event 1B can be set larger than that for event A to reduce the ping-pong effect. However,

the relative thresholds for events 1A and 1B should generally be kept consistent; instead,

the time-to-trigger setting, L3 filter coefficient and hysteresis value should used to reduce

the ping-pong effect.

Modification/query

To implement cell-oriented settings, use the commands add/mod/rmv/lst

cellintrafreqho. Otherwise, use the RNC-oriented global settings configured with the

command set intrafreqho as the configuration for the concerned cell.

3.3.2 Soft Handover Absolute Thresholds

Definition



These parameters correspond to the signal strength that satisfies the basic QoS

assurance. The soft handover absolute threshold parameters include IntraAblThdFor1E

(absolute threshold for event 1E) and IntraAblThdFor1F (absolute threshold for event 1F).

Scope

Per RNC/CELL

Range and unit

Integer(-20..-10), dB.

Working range

Integer(-20..-10)dB

Recommended value

-18.

Balance in setting

This value is the absolute threshold value used in the measurement reports of events 1E

and 1F in the soft handover algorithm, corresponding to the signal strength that satisfies

the basic QoS assurance. This value affects the trigger of events 1E and 1F. Because an

absolute threshold is only a necessary condition, but not a sufficient one, for access

judgment, this value should be relative loose. With value settings in IS-95 and the lower

threshold of -20dB, -18dB is deemed to be a reasonable value.

Modification/query

To implement cell-oriented settings, use the commands add/mod/rmv/lst cellintrafreqho.

Otherwise, use the RNC-oriented global settings configured with the command set

intrafreqho as the configuration for the concerned cell.

3.3.3 Intra-Frequency Measurement Filter Coefficient (FilterCoef)

Definition

The measurement filtering coefficient used in L3 filtering of intra-frequency measurement

report

Scope

Per RNC/CELL

Range and unit

Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D11, D13, D15, D17, D19), corresponding

to (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 17, 19)

Working range

Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8)

Recommended value

D5, namely 5

Balance in setting

The following formula is used for the calculation of measurement value filtering:



nnn MaFaF 1)1(

Where,

Fn: the updated measurement result after filtering processing.

Fn-1: the old measurement result of the previous moment after filtering processing.

Mn: The latest measurement value received from the physical layer.

a = (1/2)(k/2), where, k is from IE "Filter coefficient", namely “FilterCoef” here. When k=0

and a=1, L3 filtering is not implemented.

According to R2-000809, we recommend that the commonly used value of the filter

coefficient be in the range of {0,1,2,3,4,5,6}. The bigger the filter coefficient is, the stronger

the burr filtering capability will be, but the weaker the signal tracking capability will be.

Therefore, a balance must be made. Calculated based on the typical handover area size

[3], the distance between two NodeBs is 1000m, while calculated based on the 40%soft

handover ratio of the entire system, the typical handover distance between two cells is

about 150m. A mobile station that is moving at the speed of 20km/h goes across the

handover area in averagely 20 to 30 seconds, while it takes only 5 to 6 seconds for a

mobile station that is moving at the speed of 100km/h to go across the handover area.

When such factors as hysteresis and trigger delay in event judgment are taken into

account, the tacking time needs to be further reduced. Based on the analysis above,

FilterCoef should be configured as follows: 5 as the default setting for intra-frequency filter

coefficient, and this parameter can be adjusted according to the actual situation. In

addition, for different cell coverage types, typical values are recommended as follows:

a, if the cell covers urban area, the intra-frequency filter coefficient can be 7;

b, if the cell covers suburbs, the intra-frequency filter coefficient can be 6;

c, if the cell covers rural area, the intra-frequency filter coefficient can be 3.

Table 1 Filter Coefficient vs. Intra-Frequency Tracking Time

Filter

coefficient

0 1 2 3 4 5 6 7 8 9 11

Iteration times

1 2 3 5 7 10 15 21 30 42 85

The table above lists the iteration times required when different filter coefficients

are used to obtain 85% of the final output value. According to 25.133, in the

CELL_DCH state, L1 reports the intra-frequency measurement result to L3 at a

cycle of 200ms. When the iteration times are substituted with Intra-frequency

tracking time, the table above will become:

Filter

coefficient

0 1 2 3 4 5 6 7 8 9 11

Intra-frequency tracking time (s)

0.2 0.4 0.6 1 1.4 2 3 4.2 6 8.4 17



Modification/query


Otherwise, use the RNC-oriented global settings configured with the command set/lst


3.3.4 Hysteresis Related to Soft Handover

Definition

Hysteresis for event triggering, including Hystfor1A, Hystfor1B, Hystfor1C, Hystfor1D,

Hystfor1E and Hystfor1F

Scope

Per RNC/CELL

Range and unit

Integer(0..15) , corresponding to 0..7.5dB; configuration step 1(0.5dB)

Working range

table 1 Recommended Soft Handover Hysteresis Settings for Different Movement

Speeds

Speed (km/h) Range Recommended Value

5 6~10(3~5dB) 10(5dB)

50 4~10(2~5dB) 6(3dB)

120 2~6(1~3dB) 2(1dB)

Typical configuration 4~10(2~5dB) 6(3dB)

Recommended value

6(3dB) for events 1A and 1E, and 8(4dB) for events

Balance in setting

For UEs entering the soft handover area, increase of the hysteresis value means decrease

of the soft handover range, while for UEs leaving the soft handover area, it means

increase of the soft handover range. If the number of UEs entering the handover area is

the same as the number of UEs leaving the handover area, there will be no influence on

the actual soft handover proportion. The bigger the hysteresis value is, the stronger the

signal fluctuation resistance capability will be, and thus the better the ping-pong effect will

be suppressed, but the slower the handover algorithm can react on signal changes.

Therefore, in the setting of this parameter, not only the radio environment (slow fading

characteristic) but also the actual handover distance and the UE movement speed should

be taken into due consideration. The setting of this parameter can be adjusted within the

range of 2 to 5dB. As events that add cells to the active set, 1A and 1E are critical events.

In order to ensure timely handover, the hysteresis value for event 1A can be smaller, but



not be too smaller, than those for 1B, 1F, 1C and 1D; otherwise, the soft handover

proportion will be affected.

In addition, In addition, hysteresis adjustment should generally be considered together

with the filter coefficient and time-to-trigger settings.

Modification/query




3.3.5 Time-to-Trigger Parameters Related to Soft Handover

Definition

Time-to-trigger parameters, including TrigTime1A, TrigTime1B, TrigTime1C, TrigTime1D,

TrigTime1E and TrigTime1F, corresponding to the six events for intra-frequency

measurement respectively.

Scope

Per RNC/CELL

Range and unit


D1280, D2560, D5000), corresponding to (0, 10, 20, 40, 60, 80, 100, 120, 160, 200, 240,

320, 640, 1280, 2560, 5000)ms

Working range

Enum(D0, D200, D240, D640, D1280, D2560, D5000)

Recommended value

table 2 Recommended Time-to-Trigger Settings for Different Movement Speeds

Speed (km/h) Range (ms) Recommended value (ms)

5 640, 1280 1280

50 240, 640 640

120 240, 640 640

Typical configuration 640, 1280 640

Balance in setting

Simulation shows that the setting of the hysteresis value can effectively reduce the

average handover times and mis-handover times, and thus can prevent the occurrence of

unwanted handover. The bigger the hysteresis value is, the less the average handover

timers will be. However, the increase of the hysteresis value will bring more risks of call

drop. It is stipulated in TS 25.133V3.6.0 that the physical layer of intra-frequency

measurement updates the measurement result every 200ms. Therefore, a time-to-trigger

value below 200ms does not make any practical sense, and it should be as close as



possible to an integral multiple of 200ms. In addition, simulation also shows that mobile

stations moving at different speeds respond differently to the time-to-trigger value. The call

drop rate is more sensitive to the time-to-trigger value when the mobile station is in high-

speed movement, while it is less sensitive when the mobile station is in low-speed

movement, and ping-pong handover and mis-handover are suppressed to a certain extent.

Therefore, for cells where there are more high-speed moving mobile stations, this value

can be relatively small, while for cells where there are more low-speed moving mobile

stations, this value can be relatively big. Different types of events have different

requirements on the time-to-trigger setting: events that add cells to the active set (event

1A and event 1E) generally require a small time-to-trigger setting, while events that

replace cells in the active set (event 1C and event 1D) generally require low ping-pong

handover and mis-handover and do have produce remarkable influence on the call drop

rate. For the latter type of events, the time-to-trigger setting can be properly big. For

events that remove cells from the active set (event 1Band event 1F), the time-to-trigger

value is set mainly to reduce ping-pong handover; the initial setting can be the same as

that for event 1A and event 1E, and can be properly adjusted based on the actual network

statistics result.

Modification/query




3.3.6 WEIGHT

Definition

Weighted factor (see formulas on Section 2.1.1)

Scope

Per RNC/CELL

Range and unit

Integer(0..20), corresponding to 0..2; step: 0.1

Working range

Integer(0..10)

Recommended value

10, namely 1

Balance in setting

This parameter is used to determine the soft handover relative threshold based on the

measurement value of each cell in the active set. The bigger this parameter is, the higher

the relative threshold obtained under the same condition will be. When W=0, the



determination of soft handover relative threshold is related to only the best cell in the

active set.

Modification/query




3.3.7 Detected Set Statistics Switch

Definition

DetectStatSwitch, used to control whether the UE measurement report contains the

information of cells in the detected set, so as to provide statistics data for future network

optimization.

Scope

Per RNC/CELL

Range and unit

Enum(ON, OFF)

Working range

Enum(ON,OFF)

Recommended value

OFF

Balance in setting

In the beginning of network operation, when you are not absolutely sure about the adjacent

cell configuration, this switch can be set to ON so that missed adjacent cells can be

detected and thus handover can be smoothly implemented. After network optimization, this

switch can be set to OFF.

Modification/query




3.4 Inter-Frequency Handover Algorithm Parameters

3.4.1 Inter-Frequency Measurement Filter Coefficient (FilterCoef)

Definition

The measurement smoothening coefficient used in L3 filtering of inter-frequency

measurement report

Scope



Per RNC/CELL

Range and unit


to (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 17, 19)

Working range

Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8)

Recommended value

D5, namely 5

Balance in setting

The following formula is used for the calculation of measurement value filtering:

Where,

Fn: the updated measurement result after filtering processing.

Fn-1: the old measurement result of the previous moment after filtering processing.

Mn: The latest measurement value received from the physical layer.

a = (1/2)(k/2), where, k is from IE "Filter coefficient", namely “FilterCoef” here. When k=0

and a=1, L3 filtering is not implemented. According to R2-000809, we recommend that the

commonly used value of the filter coefficient be in the range of {0,1,2,3,4,5,6}. The bigger

the filter coefficient is, the stronger the burr filtering capability will be, but the weaker the

signal tracking capability will be. Therefore, a balance must be made. For different cell

coverage types, typical values are recommended as follows:

a, if the cell covers urban area, the inter-frequency filter coefficient can be 7;

b, if the cell covers suburbs, the inter-frequency filter coefficient can be 6;

c, if the cell covers rural area, the inter-frequency filter coefficient can be 3.

Modification/query

To implement cell-oriented settings, use the commands add/mod/rmv/lst cellinterfreqho.


interfreqho as the configuration for the concerned cell.

3.4.2 Cell Location Property

Definition

CellProperty (cell location property), indicating whether the cell is located at the verge or

center of the carrier coverage.

Scope

Per CELL

Range and unit


nnn MaFaF 1)1(


Enum(CARRIER_FREQUENCY_VERGE_CELL,

CARRIER_FREQUENCY_CENTER_CELL), (cell located at carrier coverage verge / cell

located at carrier coverage center)

Working range

Enum(CARRIER_FREQUENCY_VERGE_CELL,

CARRIER_FREQUENCY_CENTER_CELL)

Recommended value

None

Balance in setting

If a cell has intra-frequency adjacent cells around it in all directions, this cell is located at

the center of carrier coverage; otherwise, it is located at the verge of carrier coverage. The

location property of a cell determines whether RSCP or Ec/No should be used as the

measurement object for event 2D and event 2F.

Modification/query

For cell-oriented settings, use the command add/mod/rmv/lst cellinterfreqho.

3.4.3 Hysteresis Related to Inter-Frequency Handover

Definition

Hysteresis for event triggering, including Hystfor2D (hysteresis for event 2D), Hystfor2F

(hysteresis for event 2F) and HystforHHO (hysteresis for hard handover)

Scope

Per RNC/CELL

Range and unit

Integer(0..15) , corresponding to 0..7.5dB; configuration step 1(0.5dB)

Working range

table 3 Recommended Inter-Frequency Hard Handover Hysteresis Settings for Different

Movement Speeds

Speed (km/h) Range Recommended Value

5 6~10(3~5dB) 10(5dB)

50 4~10(2~5dB) 6(3dB)

120 2~6(1~3dB) 2(1dB)

Typical configuration 4~10(2~5dB) 6(3dB)

Recommended value

6(3dB)

Balance in setting

The bigger the hysteresis value is, the stronger the signal fluctuation resistance capability

will be, and thus the better the ping-pong effect will be suppressed, but the slower the

handover algorithm can react on signal changes. Therefore, in the setting of this

parameter, not only the radio environment (slow fading characteristic) but also the actual



handover distance and the UE movement speed should be taken into due consideration.

The setting of this parameter can be adjusted within the range of 2 to 5dB. In addition,

hysteresis adjustment should generally be considered together with the filter coefficient

and time-to-trigger settings.

Modification/query




3.4.4 Time-to-Trigger Parameters Related to Inter-Frequency Hard Handover

Definition

Time-to-trigger parameters, including TrigTime2D (time-to-trigger for event 2D),

TrigTime2F (time-to-trigger for event 2F) and TrigTimeHHO (time-to-trigger for hard

handover)

Scope

Per RNC/CELL

Range and unit



320, 640, 1280, 2560, 5000)ms

The value range of TrigTimeHHO is 0 to 64000ms

Working range

Enum(D0, D200, D240, D640, D1280, D2560, D5000)

Recommended value

table 4 Recommended Inter-Frequency Hard Handover Time-to-Trigger Settings for

Different Movement Speeds

Speed (km/h) Range (ms) Recommended value (ms)

5 640, 1280 1280

50 240, 640 640

120 240, 640 640

Typical configuration 640, 1280 640

Balance in setting

Simulation shows that the setting of the hysteresis value can effectively reduce the

average handover times and mis-handover times, and thus can prevent the occurrence of

unwanted handover. The bigger the hysteresis value is, the less the average handover

timers will be. However, the increase of the hysteresis value will bring more risks of call

drop. It is stipulated in TS 25.133V3.6.0 that the physical layer of intra-frequency

measurement updates the measurement result every 200ms. Therefore, a time-to-trigger

value below 200ms does not make any practical sense, and it should be as close as



possible to an integral multiple of 200ms. In addition, simulation also shows that mobile

stations moving at different speeds respond differently to the time-to-trigger value. The call

drop rate is more sensitive to the time-to-trigger value when the mobile station is in high-

speed movement, while it is less sensitive when the mobile station is in low-speed

movement, and ping-pong handover and mis-handover are suppressed to a certain extent.

Therefore, for cells where there are more high-speed moving mobile stations, this value

can be relatively small, while for cells where there are more low-speed moving mobile

stations, this value can be relatively big. The setting can be properly adjusted based on

the actual network statistics result.

Modification/query




3.4.5 Compressed Mode Enable/Disable Threshold Denoted by RSCP

Definition

This parameter corresponds to the absolute thresholds for inter-frequency measurement

events when RSCP is used as the measurement object, including

InterThdUsedFreqFor2DRSCP (absolute threshold for event 2D) and

InterThdUsedFreqFor2FRSCP (absolute threshold for event 2F)

Scope

Per RNC/CELL

Range and unit

Integer(-115..-25), dBm.

Working range

Integer(-115..-25)dBm

Recommended value

-95dBm

Balance in setting

Events 2D and 2F are the switches to enable/disable the compressed mode. When the cell

is located the verge of carrier coverage, the RSCP measurement value will be used as the

decision criterion for event 2D and event 2F. Therefore, if you hope to enable the

compressed mod as early as possible, set a big value; otherwise, set a small value.

Modification/query




3.4.6 Compressed Mode Enable/Disable Threshold Denoted by Ec/No



Definition

This parameter corresponds to the absolute thresholds for inter-frequency measurement

events when Ec/No is used as the measurement object, including

InterThdUsedFreqFor2DEcNo (absolute threshold for event 2D) and

InterThdUsedFreqFor2FEcNo (absolute threshold for event 2F)

Scope

Per RNC/CELL

Range and unit

Integer(-24..0), dB.

Working range

Integer(-24..0)dB

Recommended value

-24dB

Balance in setting

Events 2D and 2F are the switches to enable/disable the compressed mode. When the cell

is located the center of carrier coverage, the Ec/No measurement value will be used as the

decision criterion for event 2D and event 2F. Therefore, if you hope to enable the

compressed mod as early as possible, set a big value; otherwise, set a small value.

Modification/query




3.4.7 Inter-Frequency Hard Handover RSCP Threshold

Definition

This parameter corresponds to the absolute threshold for inter-frequency hard handover

when RSCP is used for measurement, HHOThdRSCP.

Scope

Per RNC/CELL

Range and unit

Integer(-115..-25), dBm.

Working range

Integer(-115..-25)dBm

Recommended value

-85dBm

Balance in setting

When RSCP is used as the physical measurement quantity and the quality of the measure

cell is higher than this threshold, this cell can be used as the target cell for inter-frequency

hard handover. If this cell is located at the verge of carrier coverage, the periodic reported



RSCP measurement value will be used as the decision criterion for inter-frequency hard

handover. If this value is too big, call drop is likely to occur due to failure of timely initiation

of inter-frequency hard handover; if it is too small, it may result in excessively frequent

verge hard handover.

Modification/query




3.4.8 Inter-Frequency Hard Handover Ec/No Threshold

Definition

This parameter corresponds to the absolute threshold for inter-frequency hard handover

when Ec/No is used for measurement, HHOThdEcNo.

Scope

Per RNC/CELL

Range and unit

Integer(-24..0), dB.

Working range

Integer(-24..0)dB

Recommended value

-16dB

Balance in setting

When Ec/No is used as the physical measurement quantity and the quality of the measure

cell is higher than this threshold, this cell can be used as the target cell for inter-frequency

hard handover. If this cell is located at the center of carrier coverage, the Ec/No

measurement value will be used as the decision criterion for inter-frequency hard

handover. If this value is too big, call drop is likely to occur due to failure of timely initiation

of inter-frequency hard handover; if it is too small, it may result in excessively frequent

verge hard handover or call drop after handover due to weak signals of the target cell.

Modification/query




3.5 inter-system handover measurement algorithm parameter

3.5.1 inter-system measurement filter coefficient FilterCoef

Definition



The measurement smoothening coefficient used in L3 filtering of inter-system

measurement report

Scope

Per RNC/CELL

Range and unit


to (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 13, 15, 17, 19)

Working range

Enum(D0, D1, D2, D3, D4, D5, D6, D7, D8)

Recommended value

D4, namely 4

Balance in setting

See Section 3.4.1. The bigger this parameter value is, the better the signal filtering effect

will be, and the stronger the anti-fading capability will be, but the weaker the signal tracking

capability will be.

Modification/query

To implement cell-oriented settings, use the commands add/mod/rmv/lst cellinterratho.


interratho as the configuration for the concerned cell.

3.5.2 Inter-System Hard Handover Decision Threshold

Definition

GSMRssiThd, namely the RSSI threshold required for handover to the GSM system.

Scope

Per RNC/CELL

Range and unit

Integer(0..63), corresponding relation: (1:-110; 2:-109; ...; 63:-48 ) dBm.

Working range

Integer(0..63)

Recommended value

26, namely -85dBm

Balance in setting

The quality requirement for inter-system cells during inter-system handover. Note: ”0” in

the parameter value range means the value is smaller than -110dBm. This value should

be adjusted according to the actual network situation.

Modification/query



interratho as the configuration for the concerned cell



3.5.3 Inter-system Hard Handover Hysteresis

Definition

HystThd, inter-system hard handover hysteresis.

Scope

Per RNC/CELL

Range and unit

Integer(0..15), corresponding to 0..7.5dB; configuration step: 1(0.5dB)

Working range

Integer(0..15)

Recommended value

4(2dB)

Balance in setting

This parameter and the inter-system quality threshold jointly decide whether to trigger a

inter-system handover decision. This value can be properly decreased in areas with small

shadow fading and properly increased in areas with big shadow fading.

Modification/query




3.5.4 Time-to-Trigger Parameter for Inter-System Hard Handover

Definition

TimeToTrigForSysHo, time to trigger

Scope

Per RNC/CELL

Range and unit



320, 640, 1280, 2560, 5000)ms

The value range of TimeToTrigForSysHo is 0 to 64000ms

Working range

Enum(D0, D200, D240, D640, D1280, D2560, D5000)

Recommended value

5000

Balance in setting

If the inter-system quality satisfies the decision condition for inter-system handover within

the time specified by this parameter, the network will start the inter-system handover

process. For cells where there are more high-speed moving mobile stations, this value can

be relatively small, while for cells where there are more low-speed moving mobile stations,



this value can be relatively big. The setting can be properly adjusted based on the actual

network statistics result.

Modification/query




3.5.5 Inter-System Measurement Periodic Report Interval

Definition

RptInterval, the time interval at which the UE reports the inter-system measurement result

to the RNC.

Scope

Per RNC/CELL

Range and unit

Enum(D250, D500, D1000, D2000, D3000, D4000, D6000, D8000, D12000, D16000,

D20000, D24000, D28000, D32000, D64000) ,corresponding to the physical range of (250,

500, 1000, 2000, 3000, 4000, 6000, 8000, 12000, 16000, 20000, 24000, 28000, 32000,

64000) ms

Working range

Enum(D250, D500, D1000, D2000, D3000, D4000, D6000, D8000, D12000, D16000,

D20000, D24000, D28000, D32000, D64000)

Recommended value

D1000

Balance in setting

If the value this parameter is too big, the measurement result may fail to be timely

reported, and thus the best handover chance may be missed, resulting in handover failure.

If the value of this parameter is too small, the measurement result will be frequently

reported, resulting in increase of the signaling burden of the system.

Modification/query




3.6 Compressed Mode Algorithm Parameter

3.6.1 CFN Offset to Enable Compressed Mode

Definition



DeltaCFN. In order to ensure that the UE and the NodeB enable the compressed mode

simultaneously, the delay of the compressed mode enabling moment in relation to the

current processing moment should be preset.

Scope

Per RNC

Range and unit

Integer(0..255) , frame

Working range

Integer(0..255)frame

Recommended value

80

Balance in setting

The value of this parameter depends on the sum of the maximum delay in the

transmission of signaling from the RNC to the UE and NodeB and hardware preparation

time required to start the compressed mode, and it is generally between 500 and 1500ms.

In WCDMA, the duration of one frame is 10ms, so the recommended value of this

parameter is between 50 and 150.

Modification/query

To configure this RNC-oriented global handover parameter, use the command set cmcf;

to view the current configuration of the parameter, use the command lst cmcf.

3.6.2 Spreading Factor Threshold

Definition

SFTurnPoint, a parameter used to select the compressed mode implementation method.

When the spreading factor used in the downlink is greater than or equal to this parameter,

the compressed mode will be implemented in priority by means of the spreading factor

minus half; otherwise the compressed mode will be implemented by means of the

punching method in priority.

Scope

Per RNC/CELL

Range and unit

Enum(D4,D8,D16,D32,D64,D128,D256), corresponding to 4,8,16,32,64,128,256

Working range

Enum(D4,D8,D16,D32,D64,D128,D256)

Recommended value

D64

Balance in setting

None

Modification/query



To configure this RNC-oriented global handover parameter, use the command set cmcf;

to view the current configuration of the parameter, use the command lst cmcf.

Alternatively, use the command add/mod/lst/rmv cellcmcf to add/modify/remove cell-

oriented parameter settings, which has a higher priority.

3.7 Direct Retry Algorithm Parameter

3.7.1 Maximum Direct Retry Times

Definition

DRMaxNumber, the maximum allowed retry times for the direct retry module after the

initial failure, as described in Section 2.2.8.

Scope

Per RNC

Range and unit

Integer(1..5)

Working range

Integer(1..5)

Recommended value

2

Balance in setting

None

Modification/query

To configure this RNC-oriented global handover parameter, use the command set drd; to

view the current configuration of the parameter, use the command lst drd.

3.7.2 Candidate Set Absolute Threshold

Definition

CsThreshold. When the signal quality of a cell is higher than this threshold, this cell will be

included in the direct retry candidate set.

Scope

Per RNC/CELL

Range and unit

Integer(-19..0)

Working range

Integer(-19..0)

Recommended value

-16

Balance in setting

After the UE fails to initiate an access process, the direct retry algorithm will automatically



initiate direct retry request to the cells in the candidate set. If this threshold is too high, it

will be difficult for the adjacent cells to enter the candidate set, and thus the UE will not be

able to access timely the adjacent cells, which makes direct retry meaningless; if this

threshold is too low, many cells can enter the candidate set but they may be all of low

quality, and a large amount of time will be used on retry attempts, which will all turn out to

be failures.

Modification/query

To configure this RNC-oriented global handover parameter, use the command set drd; to

view the current configuration of the parameter, use the command lst drd. Alternatively,

use the command add/mod/lst/rmv celldrd to add/modify/remove cell-oriented parameter

settings, which has a higher priority.

3.7.3 Minimum Ec/No Value

Definition

MinSignalRequired. The basic access threshold described in Section 2.2.8, namely the

minimum requirement of the UE form the receiving CPICH Ec/No density during normal

demodulation.

Scope

Per RNC/CELL

Range and unit

Integer(-19..0)

Working range

Integer(-19..0)

Recommended value

-18

Balance in setting

In the direct retry algorithm, the cell signal measurement value in the RACH report must be

higher than this threshold before the direct retry algorithm can consider this cell; otherwise

the cells with poor signal quality will be neglected. This parameter and the candidate set

absolute threshold can jointly prevent the occurrence of latter case mentioned above.

Modification/query

To configure this RNC-oriented global handover parameter, Use the command set drd; to

view the current configuration of the parameter, use the command lst drd. Alternatively,

use the command add/mod/lst/rmv celldrd to add/modify/remove cell-oriented parameter

settings, which has a higher priority.

3.7.4 Linear Factor of Relative Threshold and Time Interval

Definition



LinearFactor, the linear factor for the relative threshold and time interval during candidate

set selection, as described in Section 2.2.8.

Scope

Per RNC

Range and unit

Integer(0..100), which means 0 to 1.00; step: 0.01

Working range

Integer(0..100)

Recommended value

80

Balance in setting

This parameter reflects to what an extent the signal quality varies with the time. In areas

with big shadow fading (such as a town center full of tall buildings), this parameter can be

properly increased, while in areas with small shadow fading (such as open areas or the

suburbs), this parameter can be properly decreased.

Modification/query



3.7.5 Maximum Relating Time for Direct Retry Decision

Definition

MaxRelatingTime, the maximum time that the RACH measurement report can continue to

be used for the direct retry candidate set.

Scope

Per RNC

Range and unit

Integer(0..29), meaning 0 to 2900ms; step: 100

Working range

Integer(0..29)

Recommended value

20

Balance in setting

If the duration from the time the measurement report is received to the time the

measurement report is processed exceeds the value of this parameter, the measurement

report will become invalid. This parameter reflects the maximum effective time of the

measurement report used for direct retry. If the value of this parameter is too big, the

measurement result used for judgment may vary from the actual situation due too long a

duration and affect the judgment; if it is too small, then a lot of useful measurement

information is likely to be discarded.



Modification/query





List of references:

[1] 3GPP R99 25_series, 2002/09

[2] Xie Zhibin, 3Ghandover planning, 2001/08

[3] Li Zhen, WCDMA RNC V100R002 RAA Handover Algorithm Requirement Specification,

2003/6

[4] Li Zhen, WCDMA RNC V100R002 RAA Handover Parameter Configuration Specification,

2003/10

[5] Zhou Xinjie, WCDMA RNP System Parameter Setting Guidance, 2003/04


Technology

Wcdma Rno Handover Algorithm Analysis And Parameter Configurtaion Guidance 20050316 A 1.0