coverage in heterogeneous networks · femtocells • femtocells are low-power wireless access...
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Coverage in Heterogeneous Coverage in Heterogeneous Networks
Xiaoli ChuKing’s College London
UC4G Beijing Workshop August 2010
Outline• Introduction
▫ Heterogeneous networksHeterogeneous networks▫ Challenges
• Coverage in heterogeneous networks▫ System model▫ Outage probability analysis▫ Maximum density of co-channel femtocell transmissionsy▫ Femtocell transmit power
• Simulation resultsA l ti l lt ifi d b i l ti▫ Analytical results verified by simulations
▫ Low attenuation vs. high attenuation environments• Conclusions• Future work
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Introduction
UC4G Beijing Workshop August 2010
Why Heterogeneous?Why Heterogeneous?• Needs for substantial improvements in cellular capacity
and coverageand coverage▫ Radio link improvement alone cannot meet increasing demands▫ Traffic demand and channel condition vary with time and location
• Improve spectral efficiency/area/cost▫ Need to increase cell density cost-effectively▫ Network topology provides gains beyond radio technologyp gy p g y gy
• Heterogeneous networks▫ Deploy macro-, pico-, femto-cells, and relays in the same spectrum
I d it th h b tt ti l▫ Improve coverage and capacity through better spatial reuse▫ Address hot-spot needs and coverage holes▫ Lower traffic load on macrocells
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DeploymentDeployment• Initial coverage with macro base stations (MBS)• Add pico, femto and relay stations for capacity increase, hot spots,
indoor coverage, etc.• Pico, femto and relay stations require lower power, offer flexible
site acquisition, and add little or no backhaul expense.
Source: Intel Labs
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Heterogeneous NetworksHeterogeneous Networks• Macrocells
▫ Operator-deployed BSs use dedicated backhaulp p y▫ Open to public access▫ PTx ~ 43 dBm, G ~ 12-15 dBi
• PicocellsPicocells ▫ Operator-deployed BSs use dedicated backhaul▫ Open to public access▫ PT ~ 23-30 dBm G ~ 0-5 dBiPTx 23 30 dBm, G 0 5 dBi
• Femtocells▫ User-deployed BSs use user’s broadband connection as backhaul▫ Open access closed access or a hybrid access policy▫ Open access, closed access, or a hybrid access policy▫ PTx ≤ 23 dBm, G ~ 0-2 dBi
• RelaysO t d l d BS th i li k t MBS b kh l▫ Operator-deployed BSs use over-the-air link to MBS as backhaul
▫ PTx ~ 23-30 dBm, G ~ 0-5 dBi
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HN CharacteristicsHN Characteristics• Coexistence of potentially different access technologies• Different cell scales: macro > micro > pico > femto• BSs owned by operators, enterprises and consumers
Wi d i l b kh l ith t d b t ff t Q S• Wired or wireless backhaul with guaranteed or best-effort QoS• Femtocells potentially offer coverage only to subscribed UEs
Source: Qualcomm
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ChallengesChallenges• Maintain uniform user experience▫ More cell-edges created▫ Near-far effect▫ Closed-access femtocells in co-channel deployments▫ Relay stations may have different duplexing schedulesH d ff d i i h t id b kh l it• Handoff decisions have to consider backhaul capacity, especially for relays and femtocells
• Optimized use of radio resourcesOptimized use of radio resources• Inter-cell interference management▫ Lack of coordination between cells▫ Scalability, security and limited backhaul bandwidth
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FemtocellsFemtocells• Femtocells are low-power wireless access points that operate in
li d t t t t d d bil d i tlicensed spectrum to connect standard mobile devices to a mobile operator’s network using residential DSL or cable broadband connections [Source: Femto Forum].
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CoverageCoverage• Inter-cell interference creates dead spots where UE QoS
t b t dcannot be guaranteed. ▫ Location w.r.t. MBS
Path loss shadowing fading▫ Path loss, shadowing, fading• Minimum distance of an FAP from the MBS s.t. a femto
outage probability (OP) constraintoutage probability (OP) constraint• Maximum density of simultaneously transmitting co-
channel femtocells meeting a macro/femto OP constraint• Maximum allowed transmit power of FAPs s.t. a macro
OP constraintMi i i d t it f FAP t f t OP• Minimum required transmit power of FAPs s.t. a femto OP constraint
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Coverage Analysisg y
UC4G Beijing Workshop August 2010
System ModelSystem Model• OFDMA downlink of collocated spectrum-sharing
macrocell and closed-access femtocells▫ A central MBS covers a disc area with radius rM
Femtocells of radi s are randoml distrib ted on R2 as a▫ Femtocells of radius rF are randomly distributed on R2 as a spatial Poisson point process (SPPP) with a density of λF.
▫ NF femtocells per cell site on averageF p g▫ UF indoor UEs per femtocell, each located on cell edge▫ MBS transmit power is PM,Tx per RB▫ FAP transmit power is PF,Tx per RB▫ Each FAP transmits with a probability ρ within each RB.
S ti l i t it f i lt l t itti h l▫ Spatial intensity of simultaneously transmitting co-channel FAPs is uF = λFρ.
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Channel ModelChannel Model• Each subchannel sees Rayleigh flat fading and lognormal
shadowingg• Path loss follows the IMT-2000 channel model ▫ MBS to outdoor UE
MMM
3-7.1MMM 10PL ααφ DfD ==
▫ MBS to indoor UE McMMM 10PL φ DfD
FMFMFMFM
3c
-7.1FMMFMFMFM 10PL ααα ξξφφ DfDD ===
▫ Home FAP to indoor UE
▫ FAP to outdoor UEFF
F7.3
FFF 10PL ααφ DD ==
FAP to outdoor UE
▫ Interfering FAP to indoor UE
MFMFMFFMFMFMFPL αα ξφφ DD ==
2
▫ ξ denotes wall-penetration lossFFFF
FF2
FFFFFFFPL αα ξφφ DD ==
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Femtocell DL SIRFemtocell DL SIR• For a given RB, the received SIR at an FUE is
1
∑Φ∈
−−−−
−−
+=
iiii DQHPDQHP
rQHPFFFM
F
FFFFFF1
FFFFMFMFM1
FMM
FFF1
FFFSIR αα
α
φφφ
▫ PF = PF,TxGFAPGUE, PM = PM,TxGMBSGUE;▫ DFM is the distance from the MBS to the FUE, DFFi is the distance
f i t f i FAP t th FUE
i
from interfering FAP i to the FUE; ▫ αF, αFM and αFF are path loss exponents from the home FAP, the
MBS and an interfering FAP to the FUE, respectively;g p y▫ HF, HFM and HFFi are unit-mean exponential channel power gains;▫ QF ~ LN(ζμF, ζ2σF
2), QFM ~ LN(ζμFM, ζ2σFM2) and QFFi ~ LN(ζμFF, ζ2σFF
2)denote lognormal shadowing ζ 0 1l 10denote lognormal shadowing, ζ = 0.1ln10;
▫ Φ is the set of FAPs transmitting in the given RB, with intensity uF.
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Macrocell DL SIRMacrocell DL SIR• Co-channel interference from neighboring macrocells is ignored.
S• For a given RB, the received SIR at an MUE is
∑ −−
−−
=DQHP
DQHPMF
M
1MMM
1MM
MSIR α
α
φφ
▫ DM is the distance from the MBS to the MUE, DMFi is the distance from FAP i to the MUE;
∑Φ∈i
iii DQHP MFMFMFMFMFFφ
i to the MUE;▫ αM and αMF are path loss exponents from the MBS and an FAP to the MUE;▫ HM and HMFi denote unit-mean exponential channel power gains;▫ QM ~ LN(ζμM, ζ2σM
2) and QMFi ~ LN(ζμMF, ζ2σMF2) denote lognormal
shadowing.
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Femto Outage ProbabilityFemto Outage Probability• Outage probability of an FUE w.r.t. the target SIR γF
⎞⎛( )
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛<
+=<
∑Φ
−− FFFFFFF
1FFFFM
FFF PSIRP
FFγ
φγ αDQHPI
S
iiii
⎟⎟⎠
⎞⎜⎜⎝
⎛≥<+⎟⎟
⎠
⎞⎜⎜⎝
⎛<=
⎠⎝ Φ∈
FFM
FFFF
FM
F ,SIRPP γγγIS
IS
i
• Based on the stochastic geometry theory and for an FUE at a distance dFM from the MBS,
⎠⎝⎠⎝ FMFM II
⎞⎛( )
⎫⎧
+⎟⎟⎠
⎞⎜⎜⎝
⎛+−≈=<
dPrPFdD 2
FM2FFMF
FMFMF
FFFMFMFMFF
~~,~~;SIRP FM
F
α
α
ϑ σσμμφ
γφγ
( )( )( ) ( )∑∑
−+++
⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎥⎥⎦
⎤
⎢⎢⎣
⎡−−−
N M
b
bbamn
mmn eeuvw
~
2~2
F~~22
FFexp1
FFFMFMFF αμσμσχ γκ((
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( ) ( )∑∑= = +n m
bmn
meba1 1~2 χχπ
Macro Outage ProbabilityMacro Outage Probability• Outage probability of an MUE w.r.t. the target SIR γM
⎞⎛( )
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛<=<
∑ −− MMFMFMF
1MFF
MMM MF
PSIRP γφ
γ αiii DQHP
S
• Based on the stochastic geometry theory and for an MUE at a distance dM from the MBS
⎟⎠
⎜⎝∑Φ∈i
distance dM from the MBS,
( ) ∑⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−−−−≈=<
Mmm buvdD
1 MF
M
MF
MFMMMMM
2~22expexp1SIRPαμ
ασκ
πγ
(
= ⎥⎦⎢⎣ ⎠⎝m 1 MFMF ααπ
⎟⎟⎞
⎜⎜⎛
+⎟⎟⎞
⎜⎜⎛ 2
MFMF
2
MF~2~2exp
MF σμγπκαP
⎟⎟⎠
⎜⎜⎝
+⎟⎟⎠
⎜⎜⎝
= 2MF
MF
MF
MF
MF
MFM exp
ααφπκ
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Minimum MBS-to-FAP DistanceMinimum MBS to FAP Distance• For an FUE at a distance dFM from the MBS,
⎟⎟⎠
⎞⎜⎜⎝
⎛<=⎟⎟
⎠
⎞⎜⎜⎝
⎛=<
FMFMF
FFFM
FMFM
FFFMFMF
FM
F PPFM
F
φγφγ α
α
dPrP
QHQHdD
IS
ϑ H Q /(H Q ) lognormal distribution
⎟⎟⎠
⎞⎜⎜⎝
⎛+−≈ 2
FM2FFMF
FMFMF
FFFM ~~,~~; FM
F
σσμμφ
γφα
α
ϑ dPrPF
▫ ϑ = HFQF/(HFMQFM) ~ lognormal distribution• Minimum dFM for P(SF/IFM < γF|DFM = dFM) ≤ εF,
FM
1221 ~~~~ αφ
−⎤⎡ ⎟⎞⎜⎛ FM
FFFFM
2FM
2FFMFF
1FMF
minFM,
~~,~~; α
α
ϑ
γφ
σσμμεφ −
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡ ⎟⎠⎞⎜
⎝⎛ +−
≈rP
FPd
• Any UE less than dFM,min from the MBS should be associated with the macrocell.
⎦⎣
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Maximum Femto DensityMaximum Femto Density• Maximum intensity of simultaneous co-channel femtocell
t i i t di t d ( ) f th MBS f P(SIRtransmissions at a distance dM (≤ rM) from the MBS for P(SIRM < γM|DM = dM) ≤ εM
( ) ( )MFM1
SIRMF ,, dPFdu ε−Δ=( ( ) ( )MFMSIRMF ,,
M
( ) ( ) MMMMMMFFSIR SIRP,,M
εγ ==<= dDdPuF
• Maximum effective femtocell density at a distance dFM (≥ dFM,min) from the MBS for P(SIRF < γF|DFM = dFM) ≤ εF
( ) ( )1~ dPFd −Δ
( ) ( )FMFF1
SIRFMF ,,F
dPFdu ε=
( ) ( ) FFMFMFFFMFFSIR SIRP,,F
εγ ==<= dDdPuF
• For dFM,min ≤ d ≤ rM, ( ) ( ) ( ){ }dududu FFF~,min (≤
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FAP Transmit PowerFAP Transmit Power• Maximum allowed PF at a distance dM (≤ rM) from the MBS s.t.
P(SIR |D d )P(SIRM < γM|DM = dM) ≤ εM
( ) ( )MFM1
SIRMF ,,M
duFdP ε−Δ=
(
• Minimum required PF at a distance dFM (≥ dFM,min) from the MBS s.t. P(SIRF < γF|DFM = dFM) ≤ εF
At a distance d (d ≤ d ≤ ) from the MBS
( ) ( )FMFF1
SIRFMF ,,~F
duFdP ε−Δ=
• At a distance d (dFM,min ≤ d ≤ rM) from the MBS, ▫ if , then ; ▫ otherwise, no femtocell coverage and have to reduce uF = λFρ.
( ) ( )dPdP FF~ (
≤ ( ) ( ) ( )dPdPdP FFF~ (
≤≤otherwise, no femtocell coverage and have to reduce uF λFρ.
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Simulations and Results
UC4G Beijing Workshop August 2010
Simulation SetupSimulation Setup• One MBS in the center
FAP d MUE d l d d ithi th ll• FAPs and MUEs are randomly dropped within the macrocell coverage following independent SPPPs.
• ξ = 5 dB 10 dB • PM T = 43 dBmξ 5 dB, 10 dB• αM = 4• αF = 3• α = α
PM,Tx 43 dBm• PF,Tx ≤ 23 dBm• GMBS = 15 dBi • G = 2 dBi• αFM = αM
• αFF = 3.5• αMF = αFF
8 dB
• GFAP = 2 dBi• GUE = 0 dBi• rM = 1000 m
30• σM = 8 dB • σF = 4 dB • σFF = 12 dB
10 dB
• rF = 30 m• UF = 2• γM = 3 dB
5 dB• σMF = 10 dB• σFM = 10 dB• fc = 2000 MHz
• γF = 5 dB• εM = εF = 0.1• M = N = 12
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Outage ProbabilityOutage Probability1
PM,Tx
= 43dBm, PF,Tx
= 23dBm, ξ = 10dB
OP
M, 300m, simulation
0.8
0.9
OPM
, 300m, simulation
OPM
, 300m, formula
OPF, 300m, simulation
OPF, 300m, formula
OPM
, 600m, simulation
0.6
0.7
babi
lity
M
OPM
, 600m, formula
OPF, 600m, simulation
OPF, 600m, formula
0.4
0.5
Out
age
Pro
ba
0.2
0.3
0 10 20 30 40 50 60 70 80 90 1000
0.1
Number of Co−Channel Femto Transmissions per Cell Site
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Number of Co−Channel Femto Transmissions per Cell Site
Minimum MBS-to-FAP DistanceMinimum MBS to FAP Distance500
PM,Tx
= 43dBm, OPF ≤ 0.1
ξ = 5 dB, simulation
450m
toce
ll (m
)
ξ = 5 dB, simulationξ = 5 dB, formulaξ = 10 dB, simulationξ = 10 dB, formula
350
400
acro
BS
and
Fem
to
300
ance
bet
wee
n M
ac
200
250
Min
imum
Dis
tanc
13 14 15 16 17 18 19 20 21 22 23150
200
FAP Transmit Power (dBm)
M
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FAP Transmit Power (dBm)
Maximum Femto Density Maximum Femto Density 10
3
PM,Tx
= 43dBm, PF,Tx
= 23dBm, OPM
≤ 0.1
ξ = 5dB, simulation
er C
ell S
ite
ξ = 5dB, simulationξ = 5dB, formulaξ = 10dB, simulationξ = 10dB, formula
102
Tra
nsm
issi
ons
per
101
Cha
nnel
Fem
to T
r
101
Max
imum
Co−
Ch
200 300 400 500 600 700 800 900 100010
0
Distance from Macro BS (m)
M
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Distance from Macro BS (m)
Maximum Allowed PF TMaximum Allowed PF,Tx50
PM,Tx
= 43dBm, NF = 100, OP
M ≤ 0.1
ξ = 5dB, ρ = 1, simulation
40
)
ξ = 5dB, ρ = 1, simulationξ = 5dB, ρ = 1, formulaξ = 5dB, ρ = 0.1, simulationξ = 5dB, ρ = 0.1, formulaξ = 10dB,ρ = 1, simulationξ = 10dB, ρ = 1, formula
30
mit
Pow
er (
dBm
) ξ = 10dB,ρ = 0.1, simulationξ = 10dB, ρ = 0.1, formula
23 dBm
10
20
imum
FA
P T
rans
m
0
10
Max
im
200 300 400 500 600 700 800 900 1000−10
Distance from Macro BS (m)
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Distance from Macro BS (m)
Minimum Required PF TMinimum Required PF,Tx35
PM,Tx
= 43dBm, NF = 100, OP
F ≤ 0.1
ξ = 5dB, ρ = 1, simulation
25
30)
ξ = 5dB, ρ = 1, simulationξ = 5dB, ρ = 1, formulaξ = 5dB, ρ = 0.1, simulationξ = 5dB, ρ = 0.1, formulaξ = 10dB, ρ=1, simulationξ = 10dB, ρ=1, formula23 dBm
15
20
mit
Pow
er (
dBm
) ξ = 10dB, ρ=0.1, simulationξ = 10dB, ρ=0.1, formula
23 dBm
5
10
15
mum
FA
P T
rans
m
0
5
Min
imu
200 300 400 500 600 700 800 900 1000−10
−5
Distance between Macro BS and Femtocell (m)
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Distance between Macro BS and Femtocell (m)
PF T under Low AttenuationPF,Tx under Low Attenuation40
PM,Tx
= 43dBm, NF = 100, ξ = 5dB
max P
F st OP
M ≤ 0.1, ρ = 1
30
35 (
dBm
)
max PF st OP
M 0.1, ρ = 1
min PF st OP
F ≤ 0.1, ρ = 1
max PF st OP
M ≤ 0.1, ρ = 0.1
min PF st OP
F ≤ 0.1, ρ = 0.1
max PF st OP
M ≤ 0.1, ρ = 0.5
20
25
Tra
nsm
it P
ower
(d max P
F st OP
M 0.1, ρ = 0.5
10
15
/Min
imum
FA
P T
ra
0
5
Max
imum
/M
200 300 400 500 600 700 800 900 1000−10
−5
Distance from Macro BS (m)
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Distance from Macro BS (m)
PF T under High AttenuationPF,Tx under High Attenuation50
PM,Tx
= 43dBm, NF = 100, ξ = 10dB
max P st OP ≤ 0.1, ρ = 1
40dB
m)
max PF st OP
M ≤ 0.1, ρ = 1
min PF st OP
F ≤ 0.1, ρ = 1
max PF st OP
M ≤ 0.1, ρ = 0.1
min PF st OP
F ≤ 0.1, ρ = 0.1
max PF st OP
M ≤ 0.1, ρ = 0.5
30
rans
mit
Pow
er (
dB max PF st OP
M ≤ 0.1, ρ = 0.5
10
20
/Min
imum
FA
P T
ra
0
10
Max
imum
/M
200 300 400 500 600 700 800 900 1000−10
Distance from Macro BS (m)
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Distance from Macro BS (m)
ConclusionsConclusions• OFDMA downlink of collocated spectrum-sharing
ll d l d f t llmacrocell and closed-access femtocells▫ Analytical expressions for outage probabilities
• It is possible to improve coverage by• It is possible to improve coverage by ▫ regulating femtocell transmit powers, which depend on the
distance from the MBS;▫ restricting the probability of each femtocell transmitting in
each RB, which can be controlled in both frequency and time domains.
UC4G Beijing Workshop August 2010 - 30 -
Future WorkFuture Work• Mechanism for an FAP to infer its distance from the
l t MBS th t th FAP d t it t itclosest MBS, so that the FAP can adapt its transmit power accordingly to ensure satisfactory coverage.
• Associate UEs to cells intelligentlyAssociate UEs to cells intelligently▫ UEs associated to a cell with least path loss▫ Allow more UEs to benefit from low-power BSs
• Distributed adaptive resource partitioning▫ BSs negotiate resource reservation with each other▫ Resource request/grant messages sent over backhaul ▫ Based on load status and feedback from active UEs
C di t d lti i t t i i i th h t• Coordinated multi-point transmission in the heterogeneous network
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Thank You !Thank You !Thank You !Thank You !Xiaoli Chu
E-mail: [email protected]
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