Interference Management in Co-Channel Femtocell Deployment

Interference Management in Co-Channel Femtocell Deployment

Massinissa Lalam08-02-2012

BeFEMTO Winter School

6-10 February 2012

This document and the information contained are Sagemcom property and shall not be copied or disclosed to any third party without Sagemcom prior written authorization

BeFEMTO Winter School | SCET/URD1/Femtocell | Interference Management in Co-Channel Femtocell Deployment | © Sagemcom 2

Outline

• Femtocell Deployment Overview

• 3GPP status on Interference Management

• System-Level Simulation Framework

• Evaluation of Power Control

• Evaluation of Frequency Partitioning Schemes

• Conclusions



Femtocell Deployment Overview



• Femtocells are small base stations usually deployed within the macrocell network

• Mobile operator has “no control” over the deployment location

• Femtocells have 3 access policies• Closed (only femto users can connect)• Open (all users)• Hybrid (all users + priority to femto users)

Coexistence Scenario

macro base station

MUE1 femtocell

FUE

MUE2



Worst-case

• Co-channel deployment

• Same carrier

• Downlink + Closed access• Non authorised user in the vicinity of the femtocell may experience severe

interference coming from the femtocell

• Thus, the need of Interference Management solutions

macro base stationMUE1

FUE2

femtocell1

FUE1

MUE3

MUE2



3GPP status on Interference Management



X2

X2 S

1 S1

S1

S1

Architecture (Rel.10)

3GPP Rel.10



Rel.8/9 - Inter-Cell Interference Coordination (ICIC) (1/2)

• Frequency domain solution• Data channel protection

• Indicators exchange through X2• macro / pico

• Uplink interference management• Overload Indicator (OI)

• eNB reports the level of interference received

− Low, Medium, High

• Reactive process

• High Interference Indicator (HII)• eNB sends 1 bit per resource block

(RB) − Indicate Cell-edge user on this resource− Informed neighbours will avoid these RB at cell-edge

• Proactive process



Rel.8/9 - Inter-Cell Interference Coordination (ICIC) (2/2)

• Downlink interference management

• Relative Narrowband Transmit Power(RNTP) Indicator

• eNB advertises Tx power per RB• Proactive process

• Enables (dynamic) frequency partitioning

Soft-Frequency Reuse (SFR)Fractional Frequency Reuse (FFR)Hard Frequency Reuse



Rel.10 - enhanced ICIC (eICIC) (1/4)

• Specifically targets Heterogeneous Networks (HetNet)• Small Cells

• Time domain solution• Control channel protection

• Information exchange through X2• macro/pico

or OAM configuration (TR-069)• macro/pico/femto

• Focus only on Non-Carrier Aggregation (CA) scenarios




• Downlink power control• Targets femtocell• Power is adjusted based on surrounding

• Measurements performed by the femtocell− DL & UL

• Need of one Network Listen Module (NLM)− Not specified

− But always required by Operators




• Almost Blank Subframe (ABS)

• During defined subframes, the Aggressor cell does not transmit its (control + data) channels to protect a Victim cell

• ABS pattern transmitted via X2 (dynamic) for macro/pico• Macro/Pico → Aggressor/Victim

or via OAM (semi-static) for macro/femto• Macro/Femto → Victim/Aggressor

F e m t o

M a c r o

F e m t o

M a c r o

normal ABS




• Cell Range Extension (CRE)

• Through broadcasted information (handover/camp bias) UEs stay connected to picocells (hotspot)

• Bias leads to low SINR

• Requires advanced UE receiver to cope with low SINR• Interference cancellation



Rel.11 - ICIC still in discussion (1/2)

• further enhanced ICIC (feICIC) for non-CA based deployment

• Some proposals under discussion:• At the transmitter side in DL

− Combination of ABS + power reduction

• At the receiver side in DL− Use of advanced UE receiver (cancellation/discard of known signals such as CRS …)

• ICIC for CA based deployment• In CA deployment, several cells/ component carriers (CCs) are aggregated

• Up to 5 CCs (100MHz maximum bandwidth)

• Cross scheduling among the CCs is possible



• ICIC for CA based deployment

• For each Rel.10+ UE, • One Primary Cell (PCell) is assigned among the pool of cells

− Carrying control/data information

• The rest of the cells are seen as Secondary Cells (SCells)− Carrying data

• PCell/SCell selection is under discussion

Rel.11 - ICIC still in discussion (2/2)

Macro Pico

f 1

f 2

f 1

f 2

f 1

f 2

f 1

f 2

Macro UE B• Control signaling on f 1 • Data on f1 and/or f2

Pico UE • Control signaling on f 2 • Data on f1 and/or f 2

Macro UE A • Control signaling on f 1 and/or f2 • Data on f1 and/or f2



System-Level Simulation Framework



System-Level Simulation (SLS)

• SLS allows large scale network representation• Several (macrocell) base stations• Up to a hundred of users attached per base station

• SLS aims at evaluating the system performance in this large-scale configuration• Radio resource management algorithms• Interference mitigations techniques• Coverage estimation …

• Various statistics are gathered for this purpose• Throughput• Fairness• Outage• Cell activity• Realistic traffic statistics

• Frame/Packet error rates• Frame/Packet acknowledgement time …



Evaluation Methodology (3GPP/3GPP2/IEEE802.16m)

• Monte-Carlo ApproachLink System

Throughput, Coverage, …

Look-Up Table

(BLER vs SINR)SINR

Network construction

Mobile deployment

Computation of long-term parameters(pathloss, antenna gains, shadowing)

Computation of short-term parameters(fast-fading)

Scheduling, HARQ, …

Physical Layer Abstraction

Static

Dynamic



Macrocell Layout

• 2D hexagonal layout, each site has 3 sectors (cells)

• 1 Central site

• 1st tier: 6 Sites• 2nd tier: 12 Sites

Wrap-Around

�Copy of the main cluster to

combat the edge effect



Long Term Parameters (1/3)

• Let P be a point in the 2D plan

• Pathloss from a macrocell base station• @ 2GHz, R distance from a site in meters

• Antenna gain• Cell

• Point

[ ] dBin nattenuatio Wall)PL( 10log637315 ++= R. .R

( ) dBin ,12 min f2b

2

dB30

−= GGGBS θ

θθ

•-150 •-100 •-50 •0 •50 •100 •150•-10

•-5

•0

•5

•10

•15

•Direction (deg)•A

nten

naga

in (

dB)

dB01 ==GGUE

θR P




• Shadowing

• Random variable representing the obstacles between one cell and one point in the 2D plan

• Correlation• 1 between intra-site cells

• 0.5 between inter-site cells

• Power received by the point P from a base station (BS) in dB

• Signal to Interference-plus-Noise Ratio (Geometrical Factor)

( ) dBin ,0~SF 2SFσN

thermsinterfererRx

Rx

)(

)(factor-G

PP

P

BSitrf

BSserv

+=

∑

SF)PL()()()( TxRx -R-GGPP UEBSBSBS ++= θ




• G-factor can be evaluated every where in the 2D plan

without shadowing, without wrap-around with shadowing, with wrap-around



Users’ Drop

• Users are uniformly dropped over the 2D plan

• Attachment to the best macrocell

-3000 -2000 -1000 0 1000 2000 3000-3000

-2000

-1000

0

1000

2000

3000

01

2

34

5

67

8910

11

1213

14 1516

17

1819

20

2122

23

2425

26

2728

29

3031

32

3334

35

3637

38

3940

41

4243

44

4546

47

4849

50

5152

53

5455

56

meters

met

ers

Run 0 - Mobile drop: v=indoor, o=outdoor



Femtocell Urban Model (1/2)

• Dual-Stripes [3GPP TR.36.814]

• 2 stripes of 20 blocks, up to 6 floors

• Pathloss (dB, distance d in meter)

• Within the same stripe

• Otherwise

• Shadowing• 4dB of standard deviation

• No shadowing if d < 1m

46.012

,2 3.187.0(dB)B)Pathloss(d−

++

++++= n

n

extintindoorD nqApAdPL

RPL 10log2046.38(dB) +=

{ } log6.373.15 ,log2046.38 max(dB) 1010 RRPL ++=



Femtocell Urban Model (2/2)

• 5x5 Grid [3GPP TR.36.814]

• 25 blocks

• Pathloss (dB, distance d in meter)• No wall modelling

• Shadowing (dB)• 10dB of standard deviation

• No shadowing if d < 1m

• Aggressive femto-to-femto interference scenario

)(log3037B)Pathloss(d 10 d+=



Femtocell & Users’ Drop

• Femtocell deployment

• Deployment probability inside a block• Random position inside one block

• Users are dropped per deployed femtocell• Random position inside the same block

• Minimum femto-user distance = 20cm



Link to System

• With fast fading, SINR is computed on each subcarriers

• One SINR is derived using compression (MIESM, EESM)

• From this SINR• Look-Up Tables (BLER vs SINR)

• Enables realistic traffic modelling

• HARQ …

• Truncated Shannon Bound• Gives spectral efficiency

≤>+

=min

min2max

0

)1(log,min(

SINRSINR

SINRSINRSINR

t

tt

αηη

4.4max =η 6.0=α10)(min −=dBSINR



Evaluation of Power Control



System simulation assumptions

35%Inside 5x5 grid ratio

1 if same siteShadowing correlation between sectors 0.5 otherwise

500mInter-site distance

50mShadowing autocorrelation

46dBmMBS power

50Number of UEs per sector

7Number of sites

3Number of sectors per site

-174dBm/HzThermal noise density

2GHzCarrier frequency

10MHzTotal bandwidth

8dBShadowing std deviation

Parameter Value

15%Deployment ratio

20dBExternal wall attenuation

0Shadowing correlation


-10dBmMin FBS power


4Number of UEs per femto

21Number of 5x5 grids

10dBmMax FBS power

Parameter Value



-50 -40 -30 -20 -10 0 10 20 30 40 500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

GFactor (dB)

Cum

ulat

ive

Dis

trib

utio

n F

unct

ion

(cdf

)No PC - Macro - Avg=-0.29952, 5-perc=-22.1293No PC - Femto - Avg=9.0862, 5-perc=-11.4683PC(α=1,L

f=60) - Macro - Avg=2.0814, 5-perc=-9.7065

PC(α=1,Lf=60) - Femto - Avg=7.8147, 5-perc=-5.1789

Static Evaluation - 5x5 Grid (1/2)

• Independent CSG per femtocell



Static Evaluation - 5x5 Grid (2/2)

• Outage

• One user is in outage if its G-factor is below -6dB

• Independent CSG

• Common CSG

PCNo PCUE in outage (-6dB)

8.99%20.66%MUE

4.18%10.80%FUE

-1.188510FBS

PCNo PCAverage Tx power dBm


7.57%19.76%MUE

0.06%0.001%FUE

-1.188510FBS




System simulation assumptions (2)

35%Inside dual-stripes ratio




46dBmMBS power


7Number of sites






Parameter Value

5dBInternal wall attenuation

15%Deployment ratio




-10dBmMin FBS power



21Number of dual-stripes

10dBmMax FBS power

Parameter Value



Static Evaluation - Dual-Stripes

• Independent CSG

• Common CSG


3.05%10.72%MUE

0.58%1.32%FUE

-1.323310FBS



2.12%10.36%MUE

0.02%0.002%FUE

-1.323310FBS




Evaluation of Frequency Partitioning Schemes



Fractional Frequency Reuse (FFR)

• Cell space is divided in two:

• Inner Region• Outer Region (edge users)

• Edge users are given orthogonal subbands

• SINR significantly increased• Bandwidth not fully used within one cell

W2

Inner Region

Outer Region

W =

W0+W1+W2+W3

W1

W0

W0

W3W0

W0Tx power

Frequency

W1 W2 W3



Soft Frequency Reuse (SFR)

• Cell space is divided in two:

• Inner Region• Outer Region (edge users)

• Edge users are given more power

• SINR increased• Bandwidth fully used within one cell

W1

Inner Region

Outer Region

W =

W0+W1+W2

W0W0+W1

W2

W1+W2

W2+W0

W0Tx power

Frequency

W1 W2



Resource Allocation in LTE Rel.8/9

• In LTE, the total bandwidth (BW) is divided in many parts of increasing size

• Resource block (RB)• 1RB = 12 subcarriers

• Resource block group (RBG)• 1RBG = set of contiguous RBs

• Subband (SB)• 1SB = set of contiguous RBGs• Usually 1SB = 2 RBGs

• Bandwidth part (BP)• 1BP = set of contiguous SBs

• Example @10MHz in DL• BW = 3BPs = 9SBs = 17RBGs =

50RBs = 600 subcarriers• Allocation Type 0 allows one user to have

any set of RBGs

• However, user’s reporting has a subband granularity

Subband #0

Subband #1

Subband #2

Subband #0

Subband #1

Subband #2

Subband #0

Subband #1

Subband #2

Subband #0

Subband #1

Subband #2

Subband #0

Subband #1

Subband #2

Subband #0

Subband #1

Subband #2

Bandwidth part 2

Subband#0

#1

#0

#1

#2

#3

#2

#3

#16#16

#4

#5

#4

#5

RBG

#48 #49#48 #49

#36 #37 #38

#39 #40 #41

#36 #37 #38

#39 #40 #41

Bandwidth part 1

Bandwidth part 0

RB

#6

#7

#6

#7

#8

#9

#8

#9

#10

#11

#10

#11

#12

#13

#12

#13

#14

#15

#14

#15

#42 #43 #44

#45 #46 #47

#42 #43 #44

#45 #46 #47

#30 #31 #32

#33 #34 #35

#30 #31 #32

#33 #34 #35

#24 #25 #26

#27 #28 #29

#24 #25 #26

#27 #28 #29

#18 #19 #20

#21 #22 #23

#18 #19 #20

#21 #22 #23

#12 #13 #24

#15 #16 #17

#12 #13 #24

#15 #16 #17

#6 #7 #8

#9 #10 #11

#6 #7 #8

#9 #10 #11

#0 #1 #2

#3 #4 #5

#0 #1 #2

#3 #4 #5



Example of FFR/SFR in LTE Rel.8/9

• FFR: 2 subbands per outer region

• SFR : 2 subbands per outer region



• Comparison between FFR, SFR and Reuse 1 (IFR)

• FFR scheme improves significantly the SINR

• May be a good candidate for macrocell partitioning

Macrocell Only



System simulation assumptions





1Number of subbands for the outer region

46dBmMBS power

7Number of sites






Parameter Value


5dBInternal wall attenuation

10%Deployment ratio




2Number of subbands used for data


5Number of dual-stripes

20dBmFBS power

Parameter Value



Dynamic Evaluation - MIMO

• Cell throughput

0 10 20 30 40 50 60 700

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Cell Throughput (Mbits/s)

Cum

ulat

ive

Dis

trib

utio

n F

unct

ion

(cdf

)

Macro 1x1 - Avg=14.2392, 5-perc=9.1579Femto 1x1 - Avg=8.7766, 5-perc=5.3088Macro 2x2 - Avg=22.2534, 5-perc=14.3447Femto 2x2 - Avg=16.2933, 5-perc=8.4446Macro 4x4 - Avg=39.1508, 5-perc=25.4384Femto 4x4 - Avg=30.5246, 5-perc=13.6049



Dynamic Evaluation - MIMO

• Mobile throughput

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Mobile Throughput (Mbits/s)

Cum

ulat

ive

Dis

trib

utio

n F

unct

ion

(cdf

)

Macro 1x1 - Avg=2.0342, 5-perc=0Femto 1x1 - Avg=8.7766, 5-perc=5.3088Macro 2x2 - Avg=3.1791, 5-perc=0Femto 2x2 - Avg=16.2933, 5-perc=8.4446Macro 4x4 - Avg=5.593, 5-perc=0Femto 4x4 - Avg=30.5246, 5-perc=13.6049



Conclusions



Conclusions

• Spectrum being a scarce resource, frequency reuse is of major interest

• Under such co-channel deployment, interference management is a crucial factor for Heterogeneous Network success

• For LTE / LTE-A, control and data channels need to be protected

• Due to their positioning within one subframe, different schemes have been developed (time/frequency domain)

• Use of system-level simulations allows a large scale performance evaluation ofinterference management (for data & control channels)

Technology

Interference Management in Co-Channel Femtocell Deployment