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Interference Management in Co-Channel Femtocell Deployment
Massinissa Lalam08-02-2012
BeFEMTO Winter School
6-10 February 2012
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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
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Femtocell Deployment Overview
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• 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
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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
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3GPP status on Interference Management
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X2
X2 S
1 S1
S1
S1
Architecture (Rel.10)
3GPP Rel.10
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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
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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
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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
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Rel.10 - enhanced ICIC (eICIC) (2/4)
• 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
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Rel.10 - enhanced ICIC (eICIC) (3/4)
• 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
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Rel.10 - enhanced ICIC (eICIC) (4/4)
• 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
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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
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• 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
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System-Level Simulation Framework
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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 …
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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
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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
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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
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Long Term Parameters (2/3)
• 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
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Long Term Parameters (3/3)
• G-factor can be evaluated every where in the 2D plan
without shadowing, without wrap-around with shadowing, with wrap-around
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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
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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 ++=
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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+=
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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
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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
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Evaluation of Power Control
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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
10dBShadowing std deviation
-10dBmMin FBS power
3mShadowing autocorrelation
4Number of UEs per femto
21Number of 5x5 grids
10dBmMax FBS power
Parameter Value
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-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
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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
PCNo PCUE in outage (-6dB)
7.57%19.76%MUE
0.06%0.001%FUE
-1.188510FBS
PCNo PCAverage Tx power dBm
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System simulation assumptions (2)
35%Inside dual-stripes 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
5dBInternal wall attenuation
15%Deployment ratio
20dBExternal wall attenuation
0Shadowing correlation
4dBShadowing std deviation
-10dBmMin FBS power
3mShadowing autocorrelation
4Number of UEs per femto
21Number of dual-stripes
10dBmMax FBS power
Parameter Value
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Static Evaluation - Dual-Stripes
• Independent CSG
• Common CSG
PCNo PCUE in outage (-6dB)
3.05%10.72%MUE
0.58%1.32%FUE
-1.323310FBS
PCNo PCAverage Tx power dBm
PCNo PCUE in outage (-6dB)
2.12%10.36%MUE
0.02%0.002%FUE
-1.323310FBS
PCNo PCAverage Tx power dBm
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Evaluation of Frequency Partitioning Schemes
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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
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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
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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
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Example of FFR/SFR in LTE Rel.8/9
• FFR: 2 subbands per outer region
• SFR : 2 subbands per outer region
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• Comparison between FFR, SFR and Reuse 1 (IFR)
• FFR scheme improves significantly the SINR
• May be a good candidate for macrocell partitioning
Macrocell Only
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System simulation assumptions
7Number of UEs per sector
50mShadowing autocorrelation
1 if same siteShadowing correlation between sectors 0.5 otherwise
500mInter-site distance
1Number of subbands for the outer region
46dBmMBS power
7Number of sites
3Number of sectors per site
-174dBm/HzThermal noise density
2GHzCarrier frequency
10MHzTotal bandwidth
8dBShadowing std deviation
Parameter Value
3mShadowing autocorrelation
5dBInternal wall attenuation
10%Deployment ratio
20dBExternal wall attenuation
0Shadowing correlation
4dBShadowing std deviation
2Number of subbands used for data
1Number of UEs per femto
5Number of dual-stripes
20dBmFBS power
Parameter Value
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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
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BeFEMTO Winter School | SCET/URD1/Femtocell | Interference Management in Co-Channel Femtocell Deployment | © Sagemcom 42
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
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BeFEMTO Winter School | SCET/URD1/Femtocell | Interference Management in Co-Channel Femtocell Deployment | © Sagemcom 43
Conclusions
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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)