Interference Management with Limited Channel State Information in Wireless Networks

Motivation Channel Feedback in Communications Degrees of Freedom (DoF) notion ICR Scheme for Alternating CSIT ,

Interference Management with LimitedChannel State Information in Wireless

NetworksMohamed Seif, Amr El-keyi, and Mohammed Nafie, "Achievable Degrees of Freedom of the K-userMISO Broadcast Channel with Alternating CSIT via Interference Creation-Resurrection", IEEE 84th

Vehicular Technology Conference: VTC 2016-Fall, Montreal, Canada, Sept. 2016

Mohamed Seif

Wireless Intelligent Networks Center (WINC), Nile University, Egypt

July 27, 2016

Mohamed Seif Nile University

Interference Management with Limited Channel State Information in Wireless Networks 1


1 Motivation

2 Channel Feedback in Communications

3 Degrees of Freedom (DoF) notion

4 ICR Scheme for Alternating CSIT

5 ,




The Big Problem in Wireless Communications

Figure: An illustrative example for a heterogeneous network.

Interference is a fundamental bottleneck in many wirelesssystemsInterference management is getting convoluted

Homogeneous → Heterogeneous

How to manage interference in an efficient manner?






Interference is a fundamental bottleneck in many wirelesssystems

Interference management is getting convolutedHomogeneous → Heterogeneous





















Coding Against Interference

Interference shaping using CSIT 1 is a key enabler formitigating interference

1Channel state information at transmitter.




Coding Against Interference

Interference shaping using CSIT 1 is a key enabler formitigating interference

1Channel state information at transmitter.




1 Motivation




5 ,




Closed Loop Systems

Figure: Illustration of the CSIT feedback and sharing process.




Challenges in Obtaining Global and Accurate CSIT

Tx

Channel Feedback

User1

User2

User3

Possible error sources in the CSI feedback processChannel estimation errorQuantization error (e.g., Compressed channel feedback)Feedback delay (Maddah Ali et al.’12)

CSIT sharing via backhaul links (e.g., CoMP in LTE)





Tx

Channel Feedback

User1

User2

User3


CSIT sharing via backhaul links (e.g., CoMP in LTE)





Tx

Channel Feedback

User1

User2

User3


CSIT sharing via backhaul links (e.g., CoMP in LTE)Mohamed Seif Nile University



1 Motivation




5 ,




Degrees of Freedom (DoF)

DoF notion:

1 Lizhong and Tse in IEEE IT Trans. 20032 Rigorous approximation to the network capacity in the high

SNR regime.

Mathematically,

C∑(P) = DoF log(P) + o(log(P)) (1)

where limP→∞o(log(P))

log(P) = 0.

Alternatively,It represents the number of interference-free signallingdimensions in the network.





DoF notion:1 Lizhong and Tse in IEEE IT Trans. 2003

2 Rigorous approximation to the network capacity in the highSNR regime.

Mathematically,



log(P) = 0.






DoF notion:1 Lizhong and Tse in IEEE IT Trans. 20032 Rigorous approximation to the network capacity in the high

SNR regime.

Mathematically,



log(P) = 0.





1 Motivation




5 ,




System Model

The received signal at the i th receiveris given by

Yi(t) = Hi(t)X(t) +Ni(t), i = 1, . . . ,K(2)

The total DoF of the network is definedas

DΣ(K ) = max(d1,d2,...,dK )∈D

d1 + d2 + ⋅ ⋅ ⋅ + dK

(3)

UE3

UE1 UE2

UE4

UEi

)(tHi

K-antenna Tx

UEK

Figure: Network Model




CSI Model

Perfect and global CSIR.

Three states of the availability of CSITabout each receiver:

Perfect CSIT (P): instantaneousand without error.Delayed CSIT (D): delay greaterthan or equal one time slotduration (coherence time) andwithout error.No CSIT (N): not available totransmitter at all.

UE3

UE1 UE2

UE4

UEi

)(tHi

K-antenna Tx

UEK

Introduced by Tandon and Shamai in IEEE IT Trans. 2012 for the 2-user BC




Alternating CSIT Model

The fraction of time associated withCSIT state S,

λS = ∑nt=1∑K

i=1 I(Si(t) = S)nK

(4)

where n is the number of channeluses,

∑S∈{P,D,N}

λS = 1. (5)

UE3

UE1 UE2

UE4

UEi

)(tHi

K-antenna Tx

UEK




ICR SchemePhase I: Interference Creation

UE2

UE1

Tx

UE3

1u

2u

3u

),,( 321

1

1 uuuL

),,( 321

1

2 uuuI

),,( 321

1

3 uuuI

N

D

D

Figure: ICR scheme t = 1.





UE2

UE1

Tx

UE3

1v

2v

3v

),,( 321

1

1 vvvI

),,( 321

1

2 vvvL

),,( 321

1

3 vvvI

N

D

D






UE2

UE1

Tx

UE3

1p

2p

3p

),,( 321

1

1 pppI

),,( 321

1

2 pppI

),,( 321

1

3 pppL

D

D

N





ICR SchemePhase II: Interference Resurrection (Based on orthogonal projection pre-coding and PNC)

UE2

UE1

Tx

UE3

),,( 321

2

1 uuuL

),,( 321

2

2 vvvL

),,( 321

2

3 pppL

Old interference terms from UE3

P

N

P


Based on orthogonal projection pre-coding and PNCMohamed Seif Nile University



ICR SchemePhase II: Interference Resurrection (Based on orthogonal projection pre-coding and PNC)

UE2

UE1

Tx

UE3

),,( 321

3

1 uuuL

),,( 321

3

2 vvvL

),,( 321

3

3 pppL

Old interference terms from UE2

N

P

P


Based on orthogonal projection pre-coding and PNCMohamed Seif Nile University



ICR Scheme

UE2

UE1

Tx

UE3

1u2u 3u

1v2v 3v

1p2p 3p

Figure: D∑ = 95 , S5

123 = {NDD,DND,DDN,PPN,PNP}.




Synergistic Alternating CSIT

Phase I: Creation Phase II: Resurrection

(NDD,DND,DDN) (PPN,PNP)(NDD,DDN,DND) (PNP,PPN)(DND,DDN,DDN) (PPN,NPP)(DND,DDN,NDD) (NPP,PPN)(DDN,DND,NDD) (NPP,PNP)(DDN,NDD,DND) (PNP,NPP)

Table: All synergistic CSIT patterns for the 3-user BC.

Synergy Definition

Synergy is the interaction of multiple elements in a system toproduce an effect greater than the sum of their individualeffects.




Upper Bound on the DoF for the K-user BC

Bounds were introduced by Tandon et al.’13

DΣ(K ) = d1 + d2 + ⋅ ⋅ ⋅ + dK ≤ K 2 + (K − 1)∑Ki=1 γi

2K − 1(6)

where,

γi =∑n

t=1 I(Si(t) = P)n

≤ γ,∀i = 1, . . . ,K (7)




DoF Region Characterization for the 3-user BC

Given perfect CSIT distribution (γ1,γ2,γ3),

P1: maxd1,d2,d3

d1 + d2 + d3

s.t. 3d1 + d2 + d3 ≤ 3 + 2γ1 (8)d1 + 3d2 + d3 ≤ 3 + 2γ2 (9)d1 + d2 + 3d3 ≤ 3 + 2γ3 (10)0 ≤ di ≤ 1, ∀i = 1,2,3 (11)

Closed form solution,

d∗i =3 + 4γi −∑3

j=1,j≠i γj

5, ∀i = 1,2,3 (12)






P1: maxd1,d2,d3

d1 + d2 + d3


Closed form solution,

d∗i =3 + 4γi −∑3

j=1,j≠i γj

5, ∀i = 1,2,3 (12)






P1: maxd1,d2,d3

d1 + d2 + d3


Solution,Given: (γ1, γ2, γ3) = (2

5 ,15 ,

15)

Optimal DoF tuple: d∗ = (0.84,0.64,0.64)

Achievable DoF tuple: d = (0.6,0.6,0.6).Conjecture: The outer bound can be achieved by addingmulti-cast messaging in the network.






P1: maxd1,d2,d3

d1 + d2 + d3



5 ,15 ,

15)

Optimal DoF tuple: d∗ = (0.84,0.64,0.64)Achievable DoF tuple: d = (0.6,0.6,0.6).

Conjecture: The outer bound can be achieved by addingmulti-cast messaging in the network.






P1: maxd1,d2,d3

d1 + d2 + d3



5 ,15 ,

15)

Optimal DoF tuple: d∗ = (0.84,0.64,0.64)Achievable DoF tuple: d = (0.6,0.6,0.6).

Conjecture: The outer bound can be achieved by addingmulti-cast messaging in the network.




ICR Scheme vs MAT Scheme

Achievable DoF for this network is given by

DΣ(K ) =K 2

2K − 1> K

1 + 12 + ⋅ ⋅ ⋅ +

1K

´¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¶Delayed CSIT - MAT scheme

(17)

and the distribution of fraction of time of the different states{P,D,N} required for our proposed scheme is

λP = (K − 1)22K 2 −K

, λD = K − 12K − 1

, λN = 1K. (18)




Results

1 2 3 4 5 6 7 8 9 101

1.5

2

2.5

3

3.5

4

4.5

5

5.5

K (users)

DoF

sum

(K)

CSIT with alternationCSIT with all delayed

Figure: DoF comparison for broadcast channel between all delayedand alternating CSIT models.




Results

1 2 3 4 5 6 7 8 9 101

2

3

4

5

6

7

8

9

10

K (users)

DΣ(K

)

Upper bound on the K−user BC, γ=1Upper bound on alternating CSIT for the K−user BCAchievable DoF based on ICR scheme

Figure: DoF comparison for the K-user BC.




Questions ?




Thank You !



Engineering

Interference Management with Limited Channel State Information in Wireless Networks