cooperative comm ppt

8/3/2019 Cooperative Comm Ppt

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Indian Institute of Science (IISc), Bangalore, India

Cooperative Communications

Neelesh B. Mehta

ECE Department

IISc, Bangalore

Collaborators:

Andreas Molisch (MERL), Ritesh Madan (Flarion), Raymond Yim (Olin College),

Hongyuan Zhang (Marvell), Natasha Devroye (Harvard), Jin Zhang (MERL),

Jonathan Yedidia (MERL), Vinod Sharma (IISc), Gaurav Bansal (IISc)


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Indian Institute of Science, Bangalore

Motivation Behind Cooperative Communications

Multiple antenna spatial diversity

using only single antenna nodes

Exploit two fundamental aspects

of wireless channels:

Broadcast

Multiple access

s

r1

dr2

r3

r4

Cooperative relays

d

s2

Two cooperative sources

s1h1d

h2d

h12

h1d

h4d

h2d

h3dhsd


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Outline

Various cooperation schemes

Cooperation in ad hoc networks

Cooperation in infrastructure-based networks

Cross-layer issues

Other interesting topics


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Cooperative Communication Schemes

Amplify and forward

Decode and forward

Estimate and forward

Possibilities: Orthogonal / Non-orthogonal cooperation

Coded / Uncoded cooperation


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Analysis of Basic 3 Node Scenario

Performance metrics

Outage

Power consumption

Diversity

BER (Coded/Uncoded)

d

s2

Two sources

s1h1d

h2d

h12

S1 transmits S2 transmits

d receives d receivesConventional

model

Tx

Rx

S1 tx S2 repeats S2 tx S1 repeats

d, S2 rx d rx d,S1 rx d rxCooperativesource model

Tx

Rx

[Laneman & Wornell, IEEE Trans. on Inf. Theory, 2004][Stefanov, Erkip, IEEE Trans. on Communications, 2004]


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Outage Analysis: Amplify and Forward

[1][1]

[2] [2]

sd dd

d rd sr rd r d

h wyx

y h h h w w

2

0

r

sr s

P

h P N

2 2

2

2 2

SNR SNRlog 1 SNR

SNR SNR

sr rd sr rd

AF sd sd

sr sr rd sr

h hI h

h h

d

r

s hsd

hrd

hsrx

yd

yr = hsr x + wr

222 2

2 2 2 2

2 11( , ) Pr

2 SNR

sr

sd sr

R

rd

out AF

rd

P SNR R I R

Relay power

constraint:

Tx. rate

Outage prob.

Diversity order = 2


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Outage Analysis: Decode and Forward

Case 1: Destination can decode only if relay decodes

rx x d rd d y h x w

2 2 21 min log 1 , log 1

2DF sr sd rdI SNR h SNR h SNR h

2

2

1 2 1( , ) Pr

R

out DF

sr

P SNR R I R

SNR

(Assume codeword level decoding)

Diversity order = 1


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Outage Analysis: Adaptive Decode and Forward

Case 2: Source forwards to destination instead of relay if SR channel is

poor

r

x x d rd d y h x w

22 2

2 2

1 2 1log 1 2 ,2

1log 1 , else

2

R

sd sr

DF

sd rd

SNR h hSNRI

SNR h SNR h

222 2

2 2 2 2

2 11( , ) Pr

2

R

sr rd out DF

sd sr rd

P SNR R I RSNR

(Similar results apply for non-orthogonal scheme in which source transmits

to destination in both time slots, and relay repeats in second time slot)


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DF Coded Cooperation: An Explicit Example

Codeword of N bits divided into two parts: N1 and N2

In next frame:

S2 relays N2 bits of S1 if it can decode it correctly Else, S2 sends its own N2 bits

[Hunter & Nosratinia, IEEE Trans. on Wireless Commn., 2006]

S1 bits S2 bits relay Inactive

Inactive S2 bits S1bits relay

S1

S2 Rx S1 bits

Rx S2 bits

N1 bits N2 bits N1 bits N2 bits


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Analysis: Pairwise Codeword Error Probability

Slow fading

1 1 2 2

1 1 1

( ) 2 1 1d dP d d SNR d SNR

1 1 2 2( ) 2 2d dP d Q d d

Fast fading

1 2

1 2( ) 2 ( ) 2 ( )

d dn n

P d Q n n

1 2

1 1

1 1 1( )

2 1 1

d d

d d

P dSNR SNR

Diversity order = 2

Diversity order = Hamming distance

(Same for non-cooperation case)

SNR in first frame

SNR in second frame


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Other Cooperation Schemes

Estimate and forward

[Cover & El Gamal, IEEE Trans. Inf. Theory, 1979]

Non-orthogonal transmission schemes

Perform better at the expense of a more complicated destination

receiver [Nabar, Bolczkei, Kneubuhler, IEEE JSAC 2004]


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Cooperation in Ad Hoc Networks

Basic 3 node scenario

Multiple sources/relays case


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Indian Institute of Science, BangaloreExtension to Multiple Node Scenarios

Non-orthogonal schemesOpen-loop scenario

Each relay that decodes

chooses its column of a pre-

specified ST code matrix

(e.g., Orthogonal ST design)[Chakrabarti, Erkip, Sabharwal,

Aazhang, IEEE Sig. Proc. Mag.,

2007]

Relay subset selection

Closed-loop scenario Relays that decode beamform

together to destination

2 Repeats 11 Tx 3 Repeats 1 ... N Repeats 11 Repeats 22 Tx 3 Repeats 2 ... N Repeats 21 Repeats 33 Tx 2 Repeats 3 ... N Repeats 3

1 Repeats NN Tx 3 Repeats N ... N-1 repeats Ntime

frequency

Orthogonal scheme

[Laneman & Wornell, IEEE Trans. on Inf. Theory, 2003]

1 Tx D(1) subset repeats

2 Tx D(2) subset repeats

N Tx D(N) subset repeats

time

freque

ncy

Non-orthogonal scheme


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C

2

2

2

2

22

Cooperative Beamforming and its Feasibility

Relays phase align and power control transmit signal

Equivalent to a multi-antenna array at transmitter

Two important practical issues

CSI needs to be acquired

Beamforming nodes need to be synchronized

1

1

1

1

1

1

C

Inter-cluster

communications

[Ochiai, Mitran, Poor & Tarokh, IEEE Trans. Sig. Proc. 2005]


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Acquiring CSI in Cooperative Beamforming

s

r1

tr2

r3

r4

r5

xx

1. Broadcast data 2. Acquire CSI

3. Select relays

[Madan, Mehta, Molisch, Zhang, To appear in IEEE Trans. Wireless Commn., 2008]

Acquiring CSI requires extra energy and time

s

r1

tr2

r3

r4

r5

Relay subsetselection by

destination

g1

g3

g2

h1

h2

h3

h5

s

r1

tr2

r3

r4

r5

4. Beamform data

|g1|/(|g1|+|g3|)

|g3|/(|g1|+|g3|)

x


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Trade-offs and Design Goals

Broadcast power: Less power: Signal reaches fewer relays, lose out on diversity

More power: Signal reaches more relays, but increases relay

training overhead

Relay selection by destination:

Select few relays: Lose out on diversity when transmitting data

Select many/all relays: More feed back energy spent to reach less

and less useful relays

Questions:

Optimum relay subset selection rule (subject to outage constraint)?

Energy savings achieved by cooperative beamforming?


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Average Energy Consumption: Including Cost of CSI

As a function of number of relayswho decode message

Total energy consumed: Effect ofrelay selection rule

Rule of thumb: Broadcast to reach 3-4 (best) relays, some of then

beamform upon selection


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Synchronization for Cooperative Beamforming

Performance robust to imperfect synchronization

Example: Two equal amplitude signals from two

transmitters. Signals are offset by a phase w

Resulting amplitude: |1+ ej| = 2 cos(/2)

Even if = 300, amplitude = 1.93 (instead of 2) Off by only 4% !

[Mudumbai, Barriac & Madhow, IEEE Trans. Wireless Commn. 2007]

General case:

2

2

1

2

1.

12. 2 ( 1) cos

i

N

jR i

i

R i

P g e

E P N EN


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Receive Power Distribution

Phase uniformly distributedbetween [-/10, /10]

[Mudumbai, Barriac & Madhow, IEEE Trans. Wireless Commn. 2007]


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Relay Selection: Relays Help Even When Not Used

Full diversity achieved by just selecting single best relay

Well understood classical result

[Win & Winters, IEEE Trans. Commn. 1999]

E.g., Antenna selection, Partial Rake CDMA receivers

Simple to implement


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Relay Selection: Selection Criteria and Mechanisms

s

r1

dr2

r3

r4

h1

h2

h3

h4

g1

g2

g3

g4

Selection criteria: Depends on SR and RD channels

Criteria: 2 22 2

2 2

1. min ,

2.

i i i

i ii

i i

h g

h gh g

[Blestsas, Khisthi, Reed & Lippman, IEEE JSAC, 2006; Luo et al, VTC 2005;

Lin, Erkip & Stefanov, IEEE Trans. on Commn., 2006]

Multiple access relay selection mechanism:

Relays overhear a RTS (request to send) from source, and

CTS (clear to send) from destination to estimate channels

Each relay sets a timer with expiry 1/i it


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Indian Institute of Science, BangaloreOpportunistic Relay Selection and Cooperation UsingRateless Codes

Rateless codes (e.g., digital fountain codes)

Convert a finite-length source word into an infinitely long

bitstream

Receiver decodes successfully when received mutual information

exceeds the entropy of the source word

Receiver only needs to send a 1-bit ACK

Ideal binning properties of rateless codes

1. Order in which bits received doesnt matter2. If destination receives data streams from N nodes, it accumulates

mutual informationfrom all N nodes

[Shokrollahi, ISIT 2004; Mitzenmacher, ITW 2004; Luby, FOCS 2002;

Palanki & Yedidia, ISIT 2004; Erez, Trott & Wornell, CoRR 2007]


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Asynchronous Cooperation With Rateless Codes

s

r1

dr2

r3

r4

s

r1

dr2

r3

r4

s

r1

dr2

r3

r4

Broadcast Best relay receives packetand starts transmitting to

destination

Second best relay alsoreceives packet and starts

transmitting to destination

[Molisch, Mehta, Yedidia, Zhang, IEEE Trans. Wireless Commn, 2007]

Time taken for best relay to decode packet:

2log 1 maxi iB

th

h1

h4

h2

h3


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Performance: Transmission Energy & Time

Mean transmission time and energy usage Energy usage statistics

Performance primarily depends on inter-relay link strength

Meantx.energy M

eantx.time

Number of relays

CDF(tx.time)

Tx. time (normalized)


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Cooperation in Infrastructure-Based Networks


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Cooperation in Infrastructure-Based Networks

Downlink

Base station cooperation

Relay cooperation

Uplink Similar to schemes we have seen thus far

[Lee & Leung, IEEE Trans. Vehicular Technology, 2008]


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Base Station (BS) Cooperation

Much more capable base stations (source nodes) Each base station possesses multiple transmit antennas

CSI shared between base stations

Extreme case: Full CSI at all BSs

Benefit: Significantly better co-channel interference

management BS1 BS2

MS1 MS2


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Giant MIMO Array: Transmission Techniques

Linear precoding

Generalized Zero Forcing (GZF)

SLNR criterion based designs

Sum rate criterion based designs

Non-linear techniques

Dirty paper coding


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Indian Institute of Science, BangaloreBase Station Cooperation: Is It Giant MIMO?

No!

BS1 BS2

MS1 MS2

1H

2H

Super BS

MS1 MS2

1 2, H H

I di I i f S i B l


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Interference is fundamentally asynchronous

Even with perfect timing-advance!

(1)

2H

(1)1H

( 2)1H

( 2)

2H

(1)

1

(2)

2

(1)

2

(2)

1

BS1 BS2

MS2

MS10 0

(1) (1)

2 1 (2) ( 2)2 1

[Zhang, Mehta, Molisch & Zhang, IEEE Trans. Wireless Commn. 2008]

I di I i f S i B l


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Implications on Fundamental System Model

( ) ( ) ( ) ( ) ( )

1 1 1( ) ( ) ( )

B K Bb b b b b

k k k k k k jk k b j bm m m

y H T s H T i n

( ) ( ) ( ) ( )

1 1 1

( ) ( ) ( ) ( )B K Bb b b b

k k k k k j j k

b j b

m m m m

y H T s H T s n

Changes the basic model!

Should be:

Was:

Generalized zero forcing constraint is no longer sufficient

Channel from BS b to MS k

Precoding at BS b for MS k

I di I tit t f S i B l


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Asynchronous Interference-Aware Precoding

Linear precoding design methods

1. Sum rate maximization (CISVD)

Non-trivial, non-convex

Game theoretic approach in DSL: [Yu, Ginis, Cioffi 02]

2. Mean square error minimization (JWF)

[Zhang, Wu, Zhou, Wang 05]

3. Signal to leakage plus noise ratio criterion (JLS)

[Tarighat, Sadek, Sayed 05][Dai, Mailaender, Poor 04]



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Modeling Asynchronicity Helps

-5 0 5 10 15 200

2

4

6

8

10

12

Transmit SNR per User(dB)

AverageSpectrumE

ffic

iencyPerUser(bps/HZ)

JWF

JWF: Ignoring async. intf.

JLS

JLS: Ignoring async. intf.

CISVD

CISVD: Ignoring async. intf.

Rate penalty for ignoring asynchronicity is significant

JWF

JLS

CISVD

Transmit SNR per user [dB]

A

ve.spectralefficiency(bits/s/Hz)

2 cell, 2 UE set up



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Relay Cooperation System Model

1 11 21 11 21 1 1

2 12 22 12 22 2 2

Y h h b b U N

Y h h b b U N

Receivedsignals

BS-MSchannel

Linearprecoding

Informationsymbols

AWGN

Linear precoding at relays



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Asymmetric Relaying Arises Naturally

Optimal asymmetric linear precoder is unknown!

Can reduce the dimensionality of the optimization problem

considerably

Indian Institute of Science Bangalore


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Cross Layer Aspects of Cooperation



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Cross-Layer Aspects of Cooperation

Cooperative MAC

[Liu, Lin, Erkip, Panwar, IEEE Wireless Commn., 2006]

Cooperative Hybrid ARQ

[Zhao & Valenti, IEEE JSAC 2005]

Cooperative routing

General routing problem

Progressive accumulative routing

Queued cooperation

[Mehta, Sharma, Bansal, Submitted, 2008]

Impact of physical layer non-idealities



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Cooperative Multi-Hop Routing

Which relay subset should cooperate in which step? Number of possibilities/step: 2N instead of N

Channel fading: Drives how local the cooperation can be

s

r1

tr2

r3

r4

r5

r6

r7

r9

[Khandani, Abounadi, Modiano & Zheng, Allerton 2003]



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Reducing Problem to Conventional Routing Problem

Only allow nodes k edges/hops apart to cooperate

Construct hyper graph of neighbour nodes

Determine optimal cooperation/non-cooperation scheme to transmit between

neighbours

Assign energy cost to each edge in hyper graph

Distributed conventional routing algorithms now applicable to determine best

multihop route from source to destination, e.g., Belman-Ford routing

[Madan, Mehta, Molisch, Zhang, Allerton 2007]



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Indian Institute of Science, BangaloreProgressive (Energy) Accumulative Routing

s

r1

tr2

r3

r4r6

Nodes do not discard previous transmissions in a route

Energy-efficient unicast, multicast and broadcast

Unicast: [Yim, Mehta, Molisch & Zhang, IEEE Trans. Wireless Commn., 2008]

Broadcast/Multicast routing: [Maric & Yates, IEEE JSAC 2002, 2005]



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1st Relay Addition: Necessary & Sufficient Conditions

A node rhelps if and only if

(Any eligible node can

overhear source to

destination transmission)

Source (s) and relay (r) transmit powers for maximal power savings

s thrt > hst(Relaydoesnt help)

hsr > hst(Relaydoesnt help)

hst < min{hsr,hrt} (Relay saves power)



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Indian Institute of Science, BangaloreProgressive Accumulative Routing: Protocol Design

s

r

t

s

r

t

q

s

r

t

q

s t

u v

l

w

Update routes without tearingthem down

Sufficient conditions to add a

relay turn out to be nice!

Packet header fields can be

designed so that only local

CSI is needed

How to select optimal relays?

Optimal relay transmission

power?



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s t

u v

l

w

s t u v whwt hwv

MSrc MDest RSrc RDest RelayIDGainD GainR

Ready to cooperate packet

Data Packet and Cooperation Packet Structures

PAR Protocol q

s t u v hst/hsq + hqt/hqu hut huv

MSrc MDest RSrc RDest FracDelivered GainD GainR

Data

Local CSI info

u to v

w to u

1 1 1

wt ut

uw uw uv

h h

h h h

Sufficient conditionsto be a useful relay

Energy accumulatedthus far



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Simulations: Gains from PAR

100 nodes distributed uniformly

in a grid of size 20 x 20 grid

Source at (5,10) and destination

at (15,10)

Total power consumption

decreases from 100% to 13.6%

to 2.84% to 1.47% and 1.35% in

5 iterations.

Box plot

Number of iterations

Totalpowerco

nsumed



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Other Aspects

Network lifetime maximization and cooperation

[Himsoon, Siriwongpairat, Han & Liu, IEEE JSAC 2007]

Distributed detection and estimation using cooperation in

sensor networks [Nayagam, Shea & Wong, IEEE JSAC 2007]

Cognitive radios and cooperation

[Ganesan & Li, IEEE Trans. Wireless Commn 2007]



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Summary and Conclusions

Cooperation effectively exploits three essential wireless

characteristics:

Physical layer spatial diversity

Broadcast advantage

Multiple access characteristics of wireless

Affects physical layer and higher layer design

Some key problems:

General multihop scenarios Cross-layer design with cooperation

Robust synchronization schemes

Infrastructure-based cooperation in next generation wireless

cooperative comm ppt

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