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Coverage in Heterogeneous Coverage in Heterogeneous Networks Xiaoli Chu King s College London UC4G Beijing Workshop August 2010 Outline Introduction Heterogeneous networks Heterogeneous networks Challenges Coverage in

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SLIDE 1

Coverage in Heterogeneous Coverage in Heterogeneous Networks

Xiaoli Chu

King’s College London

UC4G Beijing Workshop August 2010

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SLIDE 2

Outline

  • Introduction

▫ Heterogeneous networks Heterogeneous networks ▫ Challenges

  • Coverage in heterogeneous networks

▫ System model ▫ Outage probability analysis ▫ Maximum density of co-channel femtocell transmissions y ▫ Femtocell transmit power

  • Simulation results

A l ti l lt ifi d b i l ti ▫ Analytical results verified by simulations ▫ Low attenuation vs. high attenuation environments

  • Conclusions
  • Future work

UC4G Beijing Workshop August 2010

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SLIDE 3

Introduction

UC4G Beijing Workshop August 2010

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SLIDE 4

Why Heterogeneous? Why Heterogeneous?

  • Needs for substantial improvements in cellular capacity

and coverage and 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 technology p 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

UC4G Beijing Workshop August 2010

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SLIDE 5

Deployment Deployment

  • 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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SLIDE 6

Heterogeneous Networks Heterogeneous Networks

  • Macrocells

▫ Operator-deployed BSs use dedicated backhaul p p y ▫ Open to public access ▫ PTx ~ 43 dBm, G ~ 12-15 dBi

  • Picocells

Picocells

▫ Operator-deployed BSs use dedicated backhaul ▫ Open to public access ▫ PT ~ 23-30 dBm G ~ 0-5 dBi PTx 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

  • Relays

O 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

UC4G Beijing Workshop August 2010

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SLIDE 7

HN Characteristics HN 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 UC4G Beijing Workshop August 2010

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SLIDE 8

Challenges Challenges

  • Maintain uniform user experience

▫ More cell-edges created ▫ Near-far effect ▫ Closed-access femtocells in co-channel deployments ▫ Relay stations may have different duplexing schedules

H 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 resources

Optimized use of radio resources

  • Inter-cell interference management

▫ Lack of coordination between cells ▫ Scalability, security and limited backhaul bandwidth

UC4G Beijing Workshop August 2010

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SLIDE 9

Femtocells Femtocells

  • Femtocells are low-power wireless access points that operate in

li d t t t t d d bil d i t licensed spectrum to connect standard mobile devices to a mobile operator’s network using residential DSL or cable broadband connections [Source: Femto Forum].

UC4G Beijing Workshop August 2010

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SLIDE 10

Coverage Coverage

  • Inter-cell interference creates dead spots where UE QoS

t b t d cannot 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
  • utage probability (OP) constraint
  • utage 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 constraint Mi 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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SLIDE 11

Coverage Analysis g y

UC4G Beijing Workshop August 2010

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SLIDE 12

S ystem Model S ystem 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 average

F

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.

UC4G Beijing Workshop August 2010

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SLIDE 13

Channel Model Channel Model

  • Each subchannel sees Rayleigh flat fading and lognormal

shadowing

  • Path loss follows the IMT-2000 channel model

▫ MBS to outdoor UE

M M

M 3

  • 7.1

M M M

10 PL

α α

φ D f D = =

▫ MBS to indoor UE

M c M M M

10 PL φ D f D

FM FM FM

FM 3 c

  • 7.1

FM M FM FM FM

10 PL

α α α

ξ ξ φ φ D f D D = = =

▫ Home FAP to indoor UE ▫ FAP to outdoor UE

F F

F 7 . 3 F F F

10 PL

α α

φ D D = =

FAP to outdoor UE ▫ Interfering FAP to indoor UE

MF MF

MF F MF MF MF

PL

α α

ξ φ φ D D = =

2

▫ ξ denotes wall-penetration loss

FF FF

FF 2 F FF FF FF

PL

α α

ξ φ φ D D = =

UC4G Beijing Workshop August 2010

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SLIDE 14

Femtocell DL S IR Femtocell DL S IR

  • For a given RB, the received SIR at an FUE is

1

∑

Φ ∈ − − − − − −

+ =

i i i i

D Q H P D Q H P r Q H P

FF FM F

FF FF FF 1 FF F FM FM FM 1 FM M F F F 1 F F F

SIR

α α α

φ φ φ

▫ 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, ζ2σFM 2) and QFFi ~ LN(ζμFF, ζ2σFF 2)

denote lognormal shadowing ζ 0 1l 10 denote lognormal shadowing, ζ = 0.1ln10;

▫ Φ is the set of FAPs transmitting in the given RB, with intensity uF.

UC4G Beijing Workshop August 2010

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SLIDE 15

Macrocell DL S IR Macrocell DL S IR

  • Co-channel interference from neighboring macrocells is ignored.

S

  • For a given RB, the received SIR at an MUE is

∑

− − − −

= D Q H P D Q H P

MF M

1 M M M 1 M M M

SIR

α α

φ φ

▫ DM is the distance from the MBS to the MUE, DMFi is the distance from FAP i to the MUE;

∑

Φ ∈ i i i i

D Q H P

MF

MF MF MF MF Fφ

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, ζ2σMF 2) denote lognormal

shadowing.

UC4G Beijing Workshop August 2010

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SLIDE 16

Femto Outage Probability Femto Outage Probability

  • Outage probability of an FUE w.r.t. the target SIR γF

⎞ ⎛

( )

⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎝ ⎛ < + = <

∑

Φ − − F FF FF FF 1 FF F FM F F F

P SIR P

FF

γ φ γ

α

D Q H P I S

i i i i

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ≥ < + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ < = ⎠ ⎝

Φ ∈ F FM F F F F FM F

, SIR P P γ γ γ I S I S

i

  • Based on the stochastic geometry theory and for an FUE at a

distance dFM from the MBS,

⎠ ⎝ ⎠ ⎝

FM FM

I I ⎞ ⎛

( )

⎫ ⎧ + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + − ≈ = < d P r P F d D

2 FM 2 F FM F FM FM F F F F M FM FM F F

~ ~ , ~ ~ ; SIR P

FM F

α α ϑ

σ σ μ μ φ γ φ γ

( )

( )

( )

( )

∑∑

− + + +

⎪ ⎭ ⎪ ⎬ ⎫ ⎪ ⎩ ⎪ ⎨ ⎧ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ − − −

N M b b b a m n

m m n

e e u v w

~ 2 ~ 2 F ~ ~ 2 2 F F

exp 1

FF FM FM F F

α μ σ μ σ χ

γ κ

( (

UC4G Beijing Workshop August 2010

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( )

( )

∑∑

= =

+

n m b m n

m

e b a

1 1

~ 2

χ

χ π

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SLIDE 17

Macro Outage Probability Macro Outage Probability

  • Outage probability of an MUE w.r.t. the target SIR γM

⎞ ⎛

( )

⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎝ ⎛ < = <

∑

− − M MF MF MF 1 MF F M M M

MF

P SIR P γ φ γ

α i i i

D Q H P 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,

( )

∑

⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − − − − ≈ = <

M m m

b u v d D

1 MF M MF M F M M M M M

2 ~ 2 2 exp exp 1 SIR P α μ α σ κ π γ (

=

⎥ ⎦ ⎢ ⎣ ⎠ ⎝

m 1 MF MF

α α π

⎟ ⎟ ⎞ ⎜ ⎜ ⎛ + ⎟ ⎟ ⎞ ⎜ ⎜ ⎛

2 MF MF 2 M F

~ 2 ~ 2 exp

MF

σ μ γ π κ

α

P ⎟ ⎟ ⎠ ⎜ ⎜ ⎝ + ⎟ ⎟ ⎠ ⎜ ⎜ ⎝ =

2 MF MF MF MF MF M F M

exp α α φ π κ

UC4G Beijing Workshop August 2010

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SLIDE 18

Minimum MBS-to-F AP Distance Minimum MBS to F AP Distance

  • For an FUE at a distance dFM from the MBS,

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ < = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = <

FM FM F F F F M FM FM F F FM FM F FM F

P P

FM F

φ γ φ γ

α α

d P r P Q H Q H d D I S ϑ H Q /(H Q ) lognormal distribution ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + − ≈

2 FM 2 F FM F FM FM F F F F M

~ ~ , ~ ~ ;

FM F

σ σ μ μ φ γ φ

α α ϑ

d P r P F ▫ ϑ = HFQF/(HFMQFM) ~ lognormal distribution

  • Minimum dFM for P(SF/IFM < γF|DFM = dFM) ≤ εF,

FM

1 2 2 1

~ ~ ~ ~

α

φ

−

⎤ ⎡ ⎟ ⎞ ⎜ ⎛

FM F

F F F M 2 FM 2 F FM F F 1 FM F min FM,

~ ~ , ~ ~ ;

α α ϑ

γ φ σ σ μ μ ε φ

−

⎥ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + − ≈ r P F P d

  • Any UE less than dFM,min from the MBS should be associated

with the macrocell.

⎦ ⎣

UC4G Beijing Workshop August 2010

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SLIDE 19

Maximum Femto Density Maximum Femto Density

  • Maximum intensity of simultaneous co-channel femtocell

t i i t di t d ( ) f th MBS f P(SIR transmissions at a distance dM (≤ rM) from the MBS for P(SIRM < γM|DM = dM) ≤ εM

( ) ( )

M F M 1 SIR M F

, , d P F d u ε

− Δ

= ( (

) ( )

M F M SIR M F

, ,

M

( )

( )

M M M M M M F F SIR

SIR P , ,

M

ε γ = = < = d D d P u F

  • Maximum effective femtocell density at a distance dFM (≥ dFM,min)

from the MBS for P(SIRF < γF|DFM = dFM) ≤ εF

( ) ( )

1

~ d P F d

− Δ

( ) ( )

FM F F 1 SIR FM F

, ,

F

d P F d u ε =

( )

( )

F FM FM F F FM F F SIR

SIR P , ,

F

ε γ = = < = d D d P u F

  • For dFM,min ≤ d ≤ rM,

( ) ( ) ( ) { }

d u d u d u

F F F

~ , min ( ≤

UC4G Beijing Workshop August 2010

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SLIDE 20

F AP Transmit Power F AP 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

( ) ( )

M F M 1 SIR M F

, ,

M

d u F d P 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

( ) ( )

FM F F 1 SIR FM F

, , ~

F

d u F d P 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.

( ) ( )

d P d P

F F

~ ( ≤

( ) ( ) ( )

d P d P d P

F F F

~ ( ≤ ≤

  • therwise, no femtocell coverage and have to reduce uF

λFρ.

UC4G Beijing Workshop August 2010

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SLIDE 21

S imulations and Results

UC4G Beijing Workshop August 2010

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SLIDE 22

S imulation S etup S imulation S etup

  • 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 dBm

ξ 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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SLIDE 23

Outage Probability Outage Probability

1 PM,Tx = 43dBm, PF,Tx = 23dBm, ξ = 10dB OPM, 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 bability

M

OPM, 600m, formula OPF, 600m, simulation OPF, 600m, formula 0.4 0.5 Outage Proba 0.2 0.3 10 20 30 40 50 60 70 80 90 100 0.1 Number of Co−Channel Femto Transmissions per Cell Site

UC4G Beijing Workshop August 2010

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Number of Co−Channel Femto Transmissions per Cell Site

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SLIDE 24

Minimum MBS-to-F AP Distance Minimum MBS to F AP Distance

500 PM,Tx = 43dBm, OPF ≤ 0.1 ξ = 5 dB, simulation 450 mtocell (m) ξ = 5 dB, simulation ξ = 5 dB, formula ξ = 10 dB, simulation ξ = 10 dB, formula 350 400 acro BS and Femto 300 ance between Mac 200 250 Minimum Distanc 13 14 15 16 17 18 19 20 21 22 23 150 200 FAP Transmit Power (dBm) M

UC4G Beijing Workshop August 2010

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FAP Transmit Power (dBm)

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SLIDE 25

Maximum Femto Density Maximum Femto Density

10

3

PM,Tx = 43dBm, PF,Tx = 23dBm, OPM ≤ 0.1 ξ = 5dB, simulation er Cell Site ξ = 5dB, simulation ξ = 5dB, formula ξ = 10dB, simulation ξ = 10dB, formula 10

2

Transmissions per 10

1

Channel Femto Tr 10

1

Maximum Co−Ch 200 300 400 500 600 700 800 900 1000 10 Distance from Macro BS (m) M

UC4G Beijing Workshop August 2010

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Distance from Macro BS (m)

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SLIDE 26

Maximum Allowed PF T Maximum Allowed PF,Tx

50 PM,Tx = 43dBm, NF = 100, OPM ≤ 0.1 ξ = 5dB, ρ = 1, simulation 40 ) ξ = 5dB, ρ = 1, simulation ξ = 5dB, ρ = 1, formula ξ = 5dB, ρ = 0.1, simulation ξ = 5dB, ρ = 0.1, formula ξ = 10dB,ρ = 1, simulation ξ = 10dB, ρ = 1, formula 30 mit Power (dBm) ξ = 10dB,ρ = 0.1, simulation ξ = 10dB, ρ = 0.1, formula 23 dBm 10 20 imum FAP Transm 10 Maxim 200 300 400 500 600 700 800 900 1000 −10 Distance from Macro BS (m)

UC4G Beijing Workshop August 2010

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Distance from Macro BS (m)

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SLIDE 27

Minimum Required PF T Minimum Required PF,Tx

35 PM,Tx = 43dBm, NF = 100, OPF ≤ 0.1 ξ = 5dB, ρ = 1, simulation 25 30 ) ξ = 5dB, ρ = 1, simulation ξ = 5dB, ρ = 1, formula ξ = 5dB, ρ = 0.1, simulation ξ = 5dB, ρ = 0.1, formula ξ = 10dB, ρ=1, simulation ξ = 10dB, ρ=1, formula 23 dBm 15 20 mit Power (dBm) ξ = 10dB, ρ=0.1, simulation ξ = 10dB, ρ=0.1, formula 23 dBm 5 10 15 mum FAP Transm 5 Minimu 200 300 400 500 600 700 800 900 1000 −10 −5 Distance between Macro BS and Femtocell (m)

UC4G Beijing Workshop August 2010

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Distance between Macro BS and Femtocell (m)

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SLIDE 28

PF T

under Low Attenuation

PF,Tx under Low Attenuation

40 PM,Tx = 43dBm, NF = 100, ξ = 5dB max PF st OPM ≤ 0.1, ρ = 1 30 35 (dBm) max PF st OPM 0.1, ρ = 1 min PF st OPF ≤ 0.1, ρ = 1 max PF st OPM ≤ 0.1, ρ = 0.1 min PF st OPF ≤ 0.1, ρ = 0.1 max PF st OPM ≤ 0.1, ρ = 0.5 20 25 Transmit Power (d max PF st OPM 0.1, ρ = 0.5 10 15 /Minimum FAP Tra 5 Maximum/M 200 300 400 500 600 700 800 900 1000 −10 −5 Distance from Macro BS (m)

UC4G Beijing Workshop August 2010

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Distance from Macro BS (m)

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SLIDE 29

PF T

under High Attenuation

PF,Tx under High Attenuation

50 PM,Tx = 43dBm, NF = 100, ξ = 10dB max P st OP ≤ 0.1, ρ = 1 40 dBm) max PF st OPM ≤ 0.1, ρ = 1 min PF st OPF ≤ 0.1, ρ = 1 max PF st OPM ≤ 0.1, ρ = 0.1 min PF st OPF ≤ 0.1, ρ = 0.1 max PF st OPM ≤ 0.1, ρ = 0.5 30 ransmit Power (dB max PF st OPM ≤ 0.1, ρ = 0.5 10 20 /Minimum FAP Tra 10 Maximum/M 200 300 400 500 600 700 800 900 1000 −10 Distance from Macro BS (m)

UC4G Beijing Workshop August 2010

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Distance from Macro BS (m)

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SLIDE 30

Conclusions Conclusions

  • OFDMA downlink of collocated spectrum-sharing

ll d l d f t ll macrocell 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.

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SLIDE 31

Future Work Future Work

  • Mechanism for an FAP to infer its distance from the

l t MBS th t th FAP d t it t it closest MBS, so that the FAP can adapt its transmit power accordingly to ensure satisfactory coverage.

  • Associate UEs to cells intelligently

Associate 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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SLIDE 32

Thank You ! Thank You ! Thank You ! Thank You !

Xiaoli Chu E-mail: xiaoli.chu@kcl.ac.uk

UC4G Beijing Workshop August 2010

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