Controllability for Self-Optimisation of Home eNodeBs 2100... · Controllability for...
Transcript of 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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Varying Downlink Power
Cov A: s2s 1732 mm2h 285 m
Cov B: s2s 1732 mm2h 705 m
Cap A: s2s 500 mm2h 64 m
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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)
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
Hysteresis = 12 dB TTT = 640 ms UE 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
Hysteresis = 0 dB TTT = 0 ms UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector
Low hysteresis and TTT
– Many handovers to HeNBs
High hysteresis and TTT
– UE stays on macro eNB most of the time
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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)
UE speed = 3 km/h Separation distance = 165 m Load = 5 UEs/sector
TTT (ms)
Thro
ughput
(Mbps)
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6 3
0
0
100
320
640
1280
0
5
10
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Hysteresis (dB)
UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector
TTT (ms)
Thro
ughput
(Mbps)
3 km/h 30 km/h 100 km/h
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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)
UE speed = 3 km/h Separation distance = 165 m Load = 5 UEs/sector
TTT (ms)
Pin
g-p
ong h
andover
ratio
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6 3
0
0
100
320
640
1280
0
0.1
0.2
0.3
0.4
Hysteresis (dB)
UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector
TTT (ms)
Pin
g-p
ong h
andover
ratio
3 km/h 30 km/h
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Improving Throughput by Avoiding Handover
129
6 3
0
0
100
320
640
1280
0
2
4
6
Hysteresis (dB)
UE speed = 100 km/h Separation distance = 165 m Load = 0 UEs/sector
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)
UE speed = 100 km/h Separation distance = 165 m Load = 0 UEs/sector
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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
WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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