LTE Femtocells - · PDF fileActive in 3GPP RAN –co-authored TRs on HNB and HeNB ... (WCDMA not LTE) 53dB Local Area 45dB H(e) ... To determine algorithms and parameter values,

Slide 1 l 9 September 2010 l LTE Focus - Amsterdam l © picoChip 2010

LTE Femtocells

Dr Doug Pulley

CTO & co-Founder


Agenda

picoChip, femtocells and Self Organising Networks: An Overview

Why femtos for LTE? The physics

Principles of SON

Femtocell taxonomy

Handover

Interference mitigation


picoChip, femtocells and SON

An overview of the what and why of femtocells


„Innovator of the Year‟

Doug Pulley picoChip CTOApril 2010

picoChip

picoChip, Bath,UK

picoChip, Beijing, China

Fabless

Semiconductor

company

Femtocell market

leader

150+ employees

Major development

locations: UK, China


A what-o-cell? The traditional definition

femtocell - noun

a low-power domestic access point…

…using conventional mobile technology

…in licensed spectrum

…generating coverage

and capacity

…over internet-grade backhaul

…at prices comparable with Wi-Fi

access points

…with full operator management

Generic Femto Network Architecture


High hopes to High Street…

Additional Countries launching…

Launched January 2010

Connects to Vodafone network

Minimum download speed 1MB per second

Up to 4 users at once (up to 32 can be registered)

National launch March 2010

Connects to AT&T network

Supports up to 4 voice or data users at once

Seamless call hand-over

Vodafone AT & T


5 years of Industry Leadership

Demonstrated industry‟s first femtocell: 3GSM 2005

Coined the term „femtocell‟

First femtocell chip: PC202 in 2006

Founder members of Femto Forum

Elected to Board of Directors 2007 to date

Chair WG1 (Marketing)

Lead author for WG2 interference study (CDMA)

Co-lead author for WG2 interference study (OFDMA)

Active in 3GPP RAN – co-authored TRs on HNB and HeNB

First to demonstrate end-end IOT with 3rd party gateway

Commercial carrier launches:

Vodafone, AT&T, Softbank, SFR, etc

60+ in trials


but femtocells are not just for Christmas…

Rural

Residential Metro

Enterprise


Why does LTE need femtos?

QPSK

16QAM

signal

distance

wall

64QAM 60% of mobile

traffic

in-building

LTE is not magic!


“A game of two halves”: 3GPP Cell Specification

Base station class Minimum coupling loss

Wide Area 70dB

Medium Range (WCDMA not LTE) 53dB

Local Area 45dB

H(e)NB 45dB (assumed not specified)


Base Station Taxonomy

AKA Max Tx Power Range Typical

Simultaneous

Users/UEs

Mobility

Residential

Femtocell

Home BS ~13dBm

≤20dBm SISO

≤17dBm per ant

MIMO

<50m 4-8 <10km/h

Enterprise

Femtocell

Home BS or

Local Area BS

≤24dBm <300m 16-64

(LTE up to 80)

<30km/h

Rural

Femtocell

Local Area BS

or

Medium Range BS

≤24 or 38dBm >2m

<2000m

16-64

(LTE up to 80)

<120 km/h

Metro

Femtocell

Local Area BS ≤24dBm >2 m

<2000 m

16-64 <120 km/h


So how does a femtocell work…

plug-in and turn on

listens to network environment

adjusts: power levels; carrier; codes

self organizes into mobile network (SON)

connects through broadband

ipsec tunnel established to carrier

remote management

provides private mobile broadband cell

your coverage

your capacity

And what does this mean in LTE HeNB?


LTE Self Organising Networks: SON

eNB power on

(or cable connected)

(A) Basic Setup

(B) Initial Radio

Configuration

(C) Optimization /

Adaptation

a-1 : configuration of IP address

and detection of OAM

a-2 : authentication of eNB/NW

a-3 : association to aGW

a-4 : downloading of eNB software

(and operational parameters)

b-2 : coverage/capacity related

parameter configuration

b-1 : neighbour list configuration

c-1 : neighbour list optimisation

c-2 : coverage and capacity control

Self-Configuration

(pre-operational state)

Self-Optimisation

(operational state)

But what if you have millions of self-installed eNBs?


SON Functionality

SON covers a number of operations:

Self Configuration

This can be a periodic event determined by the network operator.

It uses OAM data and NMM measurements for the configuration

procedure

Self Optimisation

This is a continuous process where extra data us gathered from e.g.

UE Measurements, to optimise parameters used in the femtocell

Aimed at optimisations for local dynamic conditions

Stays within OAM parameters

Self Healing

To deal with unusual circumstances such as frequent switching of

UE between Macro and Home eNodeB.

Self Maintenance, Self Planning, Self Tuning etc..


Femtocell Access Point SON/RRM Technology:

Where it comes from and goes to..

Deployment Modelling

FAPIOT and

Carrier Integration

FF Recommendations

3GPP H(e)NB Recommendations

System Test

and

Verification


Provisioning and OA&M

Zero Touch Installation

Femtocell configuration via OA&M



Plug in and

turn on

Register

with HeNB-GW

over S1AP

Establish

secure network

connection

Synchronisation

via NMM, GPS

or NTP

Self-configuration

using NMM

OAM

Configuration

via TR-069

Start

transmitting



Zero Touch Installation combines the various aspects of

FAP application software in addition to other hardware

functions such as NMM to allow Home eNodeB to be self

configured after power up

Some aspects of Zero Touch Installation can be done on

a more frequent basis such as:

OAM data arriving from network

NMM updates

Synchronisation updates

Etc..


Femtocell Configuration via TR-069

TR-069 used for femtocell Configuration Management

TR-196 = femtocell data model (updated to support LTE)

3GPP have defined updates to:

E-UTRAN configurable parameters

Performance Management

Fault Management

HeNB(TR-069

agent)

HeNB GW

HeMS

TR-069 ACS

EPC

File Server

Sec GW

IPsec tunnel

TR-069

FTP

S1AP

Alternatives using

SSL/TLS


Femtocell Synchronisation

A howto


Why is it required?

Handover

Handsets do not follow same frequency requirements as Base stations

Handsets derive accurate frequency from Base stations

If femto and macro are not synchronised, HO may fail or call is disrupted

Network Interference

There can also be issues of interference between networks, typically reducing the call quality and network capacity

Frequency accuracy also allows the femtocell to “sniff out” adjacent cell sites, ensuring good behaviour to reduce interference

BS Class Frequency Accuracy

Wide Area 50 ppb

Local Area 100 ppb

Home 250 ppb


Available Timing References Timing over Packet

“Enhanced” NTP

(Network Time Protocol)

GPS signal

Indoor solutions available in the

market

Broadcast information

Adjacent macro cells

GSM

WCDMA

LTE

TV

INTERNET

NTP

Master

GPS

device

NTP

client

NTP

client

2G Macro

3G Macro

Radio

Scan

4G Macro


Femtocell Handovers

Outbound (femtocell to macrocell)

Inbound (macrocell to femtocell)

Femtocell to femtocell


Femtocell Handover

HeNBs have been built into LTE from the beginning

The UE understands the concepts of:

HeNB name (SIB 9)

CSG IDs (SIB 1)

Open/closed access (SIB 1)

CSG physical cell ID range (SIB 4)

In connect mode handover controlled by (H)eNB based on

measurements from UE and/or network loading

In idle mode, UEs have an autonomous search function to

find HeNBs

Handover to UMTS, GSM and CDMA2000 also defined


Femto-to-Macro Outbound Handover

Same principle as existing macro-to-macro handover. But

no X2 interface, so signalling is via S1

HeNB HeNB

HeNB-GW

EPC

eNB

S1

S1


Macro-to-Femto Inbound Handover

Same principle as existing macro-to-macro handover. But no X2 interface, so signalling is via S1 UE autonomously detects HeNBs.

HeNBs have an unique Physical Cell ID within the macrocell the UE is currently connected

Release 9 defines how macrocell identifies femtocells where UE is CSG member

PhysCell_Id1

PhysCell_Id4

PhysCell_Id2 PhysCell_Id3


Femto-to-Femto Handover

Same principle as existing macro-to-macro handover

Handled entirely within the HeNB-GW, via S1

If supported X2 could be used for handover

HeNB

HeNB-GW

HeNB

S1

HeNB

HeNB

S1

Part of the same

CSG – eg

enterprise or

campus


Interference Mitigation

Keep the noise down!


Deployment Considerations

Femto UE Femto AP

Shared or Dedicated carrier Neighbour

macrocell

Macro UE

Open, Closed or Hybrid Access

“Hybrid” access added in Rel-9 – allows all

UEs access the femto but gives priority

(higher QoS, etc) to those in the “Closed

Subscriber Group”

Femto can be on a dedicated

carrier frequency or co-channel

with macro layer.

Separation between Femto AP

and macrocell

Indoors or outdoors

Indoors or outdoors


Interference Scenarios – Detailed Case

1

UE Registered in HeNB is radiating at a power level that can be received by the Macro eNodeB

This is received as noise by Macro eNodeB and makes it more difficult to listen to the UEs camping on it

Depending on the interference level, Macro eNodeB would tell UEs to raise their power levels


Interference Scenarios

UE attached to Home eNode BHome eNode B6

Home eNode BUE attached to Home eNode B5

UE attached to Home eNode BMacro eNode B4

Home eNode BUE attached to Macro eNode B3

UE attached to Macro eNode BHome eNode B2

Macro eNode BUE attached to Home eNode B1

VictimAggressor

1

2

3

46

5

Attached

BS Victim

UE Victim


Deployment Modelling and Simulation

To determine algorithms and parameter values, extensive

simulation is necessary

picoChip has developed two in-house simulation systems

necessary for evaluating deployment issues:

macro/femto network co-existence

indoor femtocell performance

These have been used to provide results for activities in

Femtoforum and 3GPP on WCDMA, LTE and TDSCDMA

systems and benchmarked with other leaders


Macro/Femto Coexistence Simulator

Can test many scenarios:

co-channel/adjacent channel

open, closed and hybrid acccess

Can test:

interference mitigations

RF design parameters

Can determine:

femto network performance

any macro impairments

…


Indoor Wireless Modelling

Apartment block

Semi-detached


System Modelling

Femto Houses or apartments dropped within macro coverage area

house

Max UE area

Max femto BS area

10 m

10 m

10 m

10 m

10 m

2 apartment “stripes” with multiple floors

house


Enterprise Modelling

Three femtocell deployment in larger enterprise


Scenario 2: Femto to Macro Downlink: Macro Deadzone

Femto UE

Femto AP

Femto coverage area

Femto downlink SINR > threshold

Macro Deadzone

Macro DL SINR < threshold

Neighbour

macrocell


Protecting the Macrocell DL

Transmissions from nearby

uncontrolled HeNB results in

DL interference

Most severe for macro UEs

furthest from the macrocell

HeNB can mitigate by:

Enabling hybrid access, with HeNB power set to optimize total system (femtocell +

macrocell) performance eg. based on measurement reports from visiting UEs

smart usage of the sub-carriers in the case the macro eNB is using fractional frequency

re-use (avoid those SCs being used nearby)

smart power control where HeNB estimates pathloss from macro eNB to macro UE (by

means of “sniffing”) and sets its power appropriately. Enhancement is to only provide full

protection when nearby victim UEs are detected (e.g. based on Zadoff-Chu sequence

properties).


Network Monitor Mode (aka “sniffer”)

Measurement Type Purpose

Co-channel RSRP Setting femto Tx power for desired coverage and

protection of co-channel MUEs (incl. hybrid access)Co-channel RSRQ

Adjacent-channel carrier RSRPSetting femto Tx power for protection of adjacent-

channel MUEs, including adjacent channel operatorsAdjacent-channel ref signal Rx

power

Uplink Ref Signal Detection Detection of Victim UEs

Read system info Tx power (for pathloss calc), CSG status, Cell ID etc.

Transmitter

Receiver

DL

UL

Duplexer

DL Rx

UL Rx

DAC

ADC

Baseband

PHY &

NMM


Setting Femto Maximum Tx Power

Femto Pmaxfor different Co-Channel Target Deadzones

-20

-15

-10

-5

0

5

10

15

20

25

30

-90 -80 -70 -60 -50 -40

Macro RSSI (dBm)

Fem

to P

max (

dB

m)

70 dB

60 dB

50 dB

40 dB


Adjacent Operator Protection

Some signal power from the

femtocell leaks into the adjacent

channel, according to its ACLR

and the MUE ACS

3GPP Requirement:

If the adjacent channel belongs to a

different operator, the femto must limit

its transmit power to minimise

interference to that operator

Femto Tx

Channel

Adjacent

Channel

Femto

transmit

spectrum

ACLR

UE receive

filter

ACS


Protecting the Macrocell UL

Transmissions from femto UEs

results in a higher level of UL

interference at macro eNB

Impact most severe if HeNB

close to macro eNB.

Impact increases with femto

density.

◘ Femto can mitigate by:◘ Power control of its UEs based on pathloss estimates to limit “noise

rise” at macro eNB to acceptable value. Ideally make adaptive e.g.

acceptable noise rise per HeNB is a function of HeNB density.

Requires feedback from macro eNB (e.g. via X2 in future releases).

◘ For PUCCH control channel, femto could use different set of

subcarriers than the macro.


Use of X2

Macro

eNB

Macro

eNB

X2

Proxy

Home

eNB

Home

eNB

Home

eNB

Home

eNB

X2 Load Indications

X2 Load Indications

X2 Load Indications

One potential issue is that there could be a large number of femtos within the

macro coverage area which could lead to complexity issues at the macro eNB if

each femto had an X2 interface to the macro eNB

Two possible approaches to solving this

Have an X2 “concentration” function in an X2 proxy or gateway

Only send load indications in the direction from the macro to the femtos, rather than

being bidirectional


Use of X2 - benefits

System sim, average UL cell throughput for macro (lower curves) and femto (upper curves)

versus femto density. Femto provides “loose”, “tight” or “adaptive” (X2 based) protection to

macro. 3GPP/FF apartment block deployment model.


Protecting the Femtocell Uplink

Transmissions from nearby uncontrolled UEs results in a higher level of UL interference

Reflected in TS36.104 tests for Dynamic Range and ACS – upper limits increased for HeNB

Femto can mitigate with dynamic control of the receiver gain

Reduce gain to temporarily accommodate higher interference

Also known as adaptive noise figure

Attached femto UEs will power up to overcome interference

Small path loss to femto means UE have plenty of power headroom


Protecting the Femtocell Downlink (femto-femto)

Transmissions from nearby uncontrolled HeNB results in DL

interference

HeNB can mitigate by using a sub-set of sub-carriers not being used

by other nearby HeNB. Both centralized control (e.g. at HeNB GW) or

control at individual HeNBs has been considered by RAN4


Interference Mitigation Summary

DL interference to UEs attached to Macro eNodeB or neighboring HeNB

Adaptive transmit power control based on measurements of co-channel and

adjacent-channel macro signal strength and/or smart usage of subcarriers.

“Sniffer” (aka Network Monitor Mode) functionality in HeNB to measure Macro

DL transmissions

Enhancements based on nearby victim UE detection by HeNB

Balance required femto against macro performance, which may change with

hybrid access femtocells

UL interference to Macro Node B

Implement UE “power cap” based on estimate of path loss to macro eNode B

Ideally the power cap should be adaptive such that interference contribution

from individual HeNB is function of HeNB density

Support for X2 between macro eNodeB and HeNB desirable in future 3GPP

releases


Dr Doug PulleyCTO & co-Founder

picoChip LtdAddress: Riverside Buildings, 108 Walcot Street, Bath, BA1 5BG

Email: [email protected]

Website: www.picochip.com

mailto:[email protected]

http://www.picochip.com/


Documents

LTE Femtocells - · PDF fileActive in 3GPP RAN –co-authored TRs on HNB and HeNB ... (WCDMA not LTE) 53dB Local Area 45dB H(e) ... To determine algorithms and parameter values,