Controllability for Self-Optimisation of Home eNodeBs 2100... · Controllability for...

FP7 ICT-SOCRATES

Controllability forSelf-Optimisation

of Home eNodeBs

Kristina Zetterberg, Ericsson AB

Neil Scully, John Turk, Vodafone

Ljupco Jorguseski, Adrian Pais, TNO

WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB

Outline

� Introduction to Home eNodeBs (HeNBs)

� Related Work and Scope

� Controllability for Self-Optimisation of HeNB Interference and Coverage

– Use Case Introduction

– Simulation Setup

– Control Parameters

– Results

– Conclusions and Further Work

� Controllability for Self-Optimisation of HeNB Handover

– Use Case Introduction

– Simulation Setup

– Control Parameters

– Results

– Conclusions and Further Work

� Summary and Questions


Introduction to Home eNodeBs

� LTE home base stations

� Create or extend coverage

� Improve capacity

� Typically within buildings, such as an office, a mall or a home

� Installed by customer

� Potentially large number

� Low transmit power

� Small coverage area

� Open or closed access


Related Work and Scope

� Feasability of HeNBs investigated in 3GPP and Femto Forum

� NGMN recognises the need of self-optimisation for HeNBs

� Self-optimisation discussed by H. Claussen et. al.

– Focus on open access HeNB power settings to optimise coverage to minimise mobility signalling increase

� SOCRATES projectDevelops self-organisation methods to enhance the operations of LTE networks

� Two HeNB use cases considered

– Self-Optimisation of HeNB Interference and Coverage

– Self-Optimisation of HeNB Handover

� Controllability analysis

– How and to which extent different parameter settings affect performance

– Evaluated using simulations of an LTE network with HeNBs deployed


Self-Optimisation of HeNB Interference and Coverage

� Optimise coverage area

� Minimise interference in the network

� Closed access HeNBs – open only for CSG users

� Same frequency as macro eNodeBs

� Main problem is dead zones

� Uplink and downlink HeNB power

varied to control trade-off

Only HeNB coverage (dead-zone)

Only macro coverage

Both macro and HeNB coverage


Simulation Setup

� Static Monte-Carlo simulator

� Hexagonal Layout, 7 sites with 21 cells– Coverage Driven Scenario – 1732 meters s2s distance

– Capacity Driven Scenario – 500 meters s2s distance

� Femto area with grid of houses

– 10 x 10 houses

– HeNB density 10%

– HeNB placement within house varies

� One CSG user per HeNB house

� On average one non-CSG user per HeNB house

� Requested bitrate 0.25 Mbps UL, 1 Mbps DL

� Results collected from users within the HeNB houses

Femto

area


Controllability Study

� Considered control parameters:

– Maximum DL Transmit Power

Varied from 0.2 mW to 20 mW in steps of 1 dB

Reference signal power follows DL transmit power

– Maximum UL Transmit Power

Varied from 20 mW to 316 mW in steps of 1 dB

� Considered macro – HeNB distances;

� A CSG user is connected to the HeNB only if

RSRPHeNB > RSRPmacro

64705285Macro-to-HeNB distance (m)

50017321732 Site-to-site distance (m)

Capacity Driven Scenario A

Coverage Driven Scenario B

Coverage Driven Scenario A


Result Plots

� X - axis show power difference in dB, compared to maximum setting

� Y - axis show ratio of users that can detect the reference signal, and have

non-zero uplink and downlink throughput, in the HeNB houses

� The three different plots show the ratio of

– CSG users with RS, UL & DL coverage (from macro or HeNB) in the HeNB

houses

– CSG users with RS, UL & DL coverage from HeNB in the HeNB houses

– Non-CSG users with RS, UL & DL coverage (from macro) in the HeNB houses


Varying Downlink Power

Cov A: s2s 1732 mm2h 285 m

Cov B: s2s 1732 mm2h 705 m

Cap A: s2s 500 mm2h 64 m


Varying Uplink Power

DL power 3.2 mW

Cov A: s2s 1732 mm2h 285 m

Cov B: s2s 1732 mm2h 705 m

Cap A: s2s 500 mm2h 64 m


Throughput

� For the given scenarios (with a maximum of one CSG user per home

eNodeB) throughput for HeNB connected UEs is equal to the requested

throughput both in uplink and downlink

� For the given scenarios, throughput for non-CSG users is not highly affected

� Seen effects are probably due to changed macro load

Cov A:

s2s 1732 m

m2h 285 m


Conclusions and Further Work

� Conclusions

– Dead-zones are the major problem when introducing closed access home

eNodeBs

– HeNB Maximum Transmit Power is a suitable parameter for controlling the

trade-off between HeNB coverage and the size of the dead-zone

� Possible Further Work

– Evaluate effects of adjusting the CSG user RSRP connect margin;

CSG user is connected to the HeNB only if

RSRPHeNB > RSRPmacro – margin

– Evaluate effects of using parts of the macro frequency band for the HeNB

– Evaluate effects of adjusting the transmit power on parts of the frequency band

– Algorithm development


Self-Optimisation of HeNB Handover

� Minimise dropped calls

� Maximise user throughput

� Open access HeNBs

� Indoor HeNBs, providing coverage also outdoor

� Macro – HeNB Handover

� HeNB – HeNB Handover


Simulation Setup

� Dynamic simulator

� Single 3-sector macro eNB– Wrap-around

– Site-to-site distance 500 meters

� Row of houses with HeNBs 165 meters from macro eNB

� 15 meters between each HeNB

� User experience of a UE moving downa street is modelled

� Full buffer traffic

� Study considers– Impact of UE speed

– Impact of relative signal strengthsbetween eNB and HeNB

– Impact of macro network load

165 m


Controllability Study

� Considered control parameters:

– Hysteresis (HYST)

Set to the values 0, 3, 6, 9 and 12 dB

– Time to trigger (TTT)

Set to the values 0, 100, 320, 640 and 1280 ms

� Considered scenarios;

510Macro cell load (UEs/sector)

28016550Macro-to-HeNB distance (m)

100303 UE speed (km/h)


SINR and Serving Cell

0 2 4 6 8 10 12 14-20

-15

-10

-5

0

5

10

15

20

25

30

Time (s)

Blu

e: D

ata

SIN

R (dB

) / R

ed: S

erv

ing c

ell

Hysteresis = 12 dB TTT = 640 ms UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector

30

40UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector


35

0 2 4 6 8 10 12 14-20

-10

0

10

20

30

40

Time (s)

Blu

e:

Data

SIN

R (

dB

) /

Red:

Serv

ing c

ell


Low hysteresis and TTT

– Many handovers to HeNBs

High hysteresis and TTT

– UE stays on macro eNB most of the time


Throughput

� Low TTT and small hysteresis gives higher throughput

� More pronounced at higher UE speed

� Same trends in throughput are seen for higher HeNB-to-macro eNB distance

� At a lower distance the impact is not as large, as the UE stays connected

to the macro eNB

129

6 3

0

0

100

320

640

1280

0

1

2

3

4

5

Hysteresis (dB)

UE speed = 100 km/h Separation distance = 165 m Load = 5 UEs/sector

TTT (ms)

Thro

ughput

(Mbps)

129

6 3

0

0

100

320

640

1280

0

5

10

15

Hysteresis (dB)


TTT (ms)

Thro

ughput

(Mbps)

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0

0

100

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1280

0

5

10

15

Hysteresis (dB)


TTT (ms)

Thro

ughput

(Mbps)

3 km/h 30 km/h 100 km/h


Ping-pong Handover Ratio

� Low hysteresis and TTT values gives high throughput, but could also

lead to ping-pong

129

6 3

0

0

100

320

640

1280

0

0.2

0.4

0.6

0.8

Hysteresis (dB)


TTT (ms)

Pin

g-p

ong h

andover

ratio

129

6 3

0

0

100

320

640

1280

0

0.1

0.2

0.3

0.4

Hysteresis (dB)


TTT (ms)

Pin

g-p

ong h

andover

ratio

3 km/h 30 km/h


Improving Throughput by Avoiding Handover

129

6 3

0

0

100

320

640

1280

0

2

4

6

Hysteresis (dB)


TTT (ms)

Thro

ughput

(Mbps)

129

6 3

0

0

100

320

640

1280

0

0.2

0.4

0.6

0.8

1

Hysteresis (dB)


TTT (ms)

Fem

to r

atio

� Throughput does not always decrease as handover parameter values

are increased

� Gain is only achieved for low macro cell load

Throughput Ratio of time connected to HeNB


Conclusions and Further Work

� Conclusions

– Handover settings have large impact on number of performed handovers and

on UE troughput

– Impact varies with distance, UE speed and macro load

– Set HO parameters low, but high enough to avoid ping-pong

– For rapidly moving UEs;

a) Set HO parameters low to handover promtly

b) Set HO parameters low to avoid handover to HeNB

� Possible Further Work

– Consider static UEs and ping-pong effects

– Consider lower HeNB density and subsequent macro-HeNB-macro handovers

– Study SINR and dropped calls together with throughput

– Algorithm development


Summary

Controllability studies performed for two use cases

� HeNB interference and coverage

– Closed access

– Uplink and downlink HeNB power evaluated

– Dead-zones is the major problem

– Downlink power is a suitable control parameter for the trade-off

� HeNB Handover

– Open access

– Time-to-trigger and hysteresis evaluated

– HO parameters should be low, but high enough to avoid ping-pong

– Rapidly moving UEs could gain from not handing over to HeNB


Controllability for Self-Optimisation of Home eNodeBs

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