International Technology AllianceIn Network & Information Sciences

International Technology AllianceIn Network & Information Sciences

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Cooperative Wireless Networks:From Radio to Network Protocol Designs

May 29, 2009

by Zhengguo ShengSupervisor: Prof. Kin K. Leung

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Outline

IntroductionIntroduction

Current Research

Conclusion

Introduction

• Cooperative diversity is a cooperative multiple antenna techniques which exploits user diversity by decoding the combined signal of the relayed signal and the direct signal in wireless multi-hop networks.

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motivation for cooperative diversity

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• Motivation for ad-hoc networks with cooperative transmission– Wireless links are unreliable due to multi-path propagation– Spatial diversity is bandwidth efficient to combat fading– Spatial diversity is difficult to achieve due to processing

complexity, power consumption, ...• Solution: Cooperative Transmission

– Allow users to share their antennas cooperatively to assist each other for successful reception

• Advantages of cooperative transmission: Virtual antenna array– Boosted reception reliability– Achieved higher data rates– Bandwidth efficient and increased coverage

A simple example of cooperative transmission

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Normalized TX power with or without cooperative transmission (CT). The data

rate is set as R = 0.1 bit/s/Hz, and the prefixed required outage probability is

P=10%. Two sources are located at (−5, 0) and (−5, 0).

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Outline

Introduction

Current ResearchCurrent Research Quality-of-Service Routing Algorithm for Wireless Quality-of-Service Routing Algorithm for Wireless

Cooperative NetworksCooperative Networks

Distributed and Power Efficient Routing in Wireless Cooperative Networks

Interference Subtraction with Supplementary Cooperation in Wireless Cooperative Networks

Conclusion

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QoS Routing Algorithm

• Algorithm description– Select the best relay and establish a one-hop cooperative route

from source to destination and compare its ETE (End-to-end) BER with the target BER

– If this BER is larger than target BER, identify the link with the highest BER along the route and improve its BER performance by selecting a new relay

– Repeat second stage, until the ETE BER is no larger than target BER, then the cooperative route is finalized

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Source

Destination

A Simple Network Scenario

[1] Z. Sheng, Z. Ding and K. K. Leung, "On the Design of a Quality-of-Service Driven Routing Protocol for Wireless Cooperative Networks", proc. of IEEE Vehicular Technology Conference (VTC), Singapore, MAY 2008.

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Routing Comparison between Proposed Algorithm and DV Algorithm

• Compared with 9 hops and 10% ETE BER of Distance-Vector (DV) algorithm, our proposed algorithm (5 hops and 3% end-to-end BER) shows better performance

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X (meters)

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met

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DV route Direct tranmissionRelay transmission

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BER Performance Comparison with DV Algorithm

• Under same number of hops, proposed routing algorithm can achieve much better error performance than DV algorithm as well as the scheme without relay transmission

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10-2

10-1

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Number of nodes in the network

End

-to-

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BE

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Proposed algorithm without relay linksDV algorithmProposed algorithm

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Number of hops in a route (considered by the algorithm)

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Proposed algorithm without relay linksDV algorithm with 9 hopsProposed algorithm

• As the number of hops increases in the route, the ETE BER of proposed algorithm is reduced correspondingly

ROUTING PERFORMANCE EVALUATION

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10-2

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Total number of hops

End

-to-

end

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Proposed routing algorithmDV algorithmUpper bound performance of proposed algorithm (Inf. nodes)Upper bound performance of optimal solution (Inf. nodes)

Theorem1: For infinitely dense network where node exists at any location, the upper bound BER for the proposed routing with N hops is proportional to , where A, being perfect power of 2, is the largest integer that smaller than the total number of hops N and k is the pass loss exponent.

The cooperative links of the optimal routing are uniformly distributed along the line between the source and the destination node

The performance of the proposed algorithm closes to optimal.

[2] Z. Sheng, Z. Ding, K. K. Leung, D. L. Goeckel and D. Towsley, "Error Performance Bound for Routing Algorithms in Wireless Cooperative Networks", proc. of The Second Annual Conference of The International Technology Alliance (ACITA 2008), UK.

(2k-1)1/ A

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Outline

Introduction

Current ResearchCurrent Research Quality-of-Service Routing Algorithm for Wireless

Cooperative Networks

Distributed and Power Efficient Routing in Wireless Distributed and Power Efficient Routing in Wireless Cooperative NetworksCooperative Networks

Interference Subtraction with Supplementary Cooperation in Wireless Cooperative Networks

Conclusion

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Transmission Power Optimization of Cooperative Link

• Observations– Both source and relay are assumed so far to transmit at the same

Tx power

– One can further reduce total Tx power to achieve a given target

BER

Source Destination

Relay

Cooperative Link

Question?Can we do better to minimize Ps+Pr ?

[3] Z. Sheng, Z. Ding and K.K. Leung, "Distributed and Power Efficient Routing in Wireless Cooperative Networks", Proc. of IEEE International Conference on Communications, ICC 2009.

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Transmission Power Optimization

• Tx Power Optimization with a target ETE BER

(Outage probability

• Using the Kuhn-Tucker condition, the minimum Tx power can be shown as

where

where R=data rate, =noise spectral density and B=bandwidth)

Simulation Result Power Reduction for CL

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source destination

50 Relay candidates

Network Topology

• Relay randomly placed in the 100m *100m square• Average power reduction for all relay nodes is 82.73% and 21.22%, compared with two-hop transmission and MPCR, respectively

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Tot

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nois

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(dB

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MPSDFMPCRDirect Transmission

Routing Performance Evaluation

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h (d

B)

CASNCP proposed algorithm DSDVCentralized algorithm

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Proposed algorithm Centralized algorithm

2 hops

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2 hops

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4 hops4 hops

3 hops 3 hops

The total power consumption of our proposed routing algorithm can reduce by a couple dB compared to the existing cooperative routing algorithms.

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Outline

Introduction

Current ResearchCurrent Research Quality-of-Service Routing Algorithm for Wireless

Cooperative Networks

Distributed and Power Efficient Routing in Wireless Cooperative Networks

Interference Subtraction with Supplementary Interference Subtraction with Supplementary Cooperation in Wireless Cooperative NetworksCooperation in Wireless Cooperative Networks

Conclusion

Motivation for Supplementary Cooperation

• Observations– Broadcast nature of wireless transmission can be

further explored – Cooperation can be extended across the CLs

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S1

S2 S3 S4

R1 R2R3

Cooperation? Yes

T2T1 T3 T4 T5 T6

[4] Z. Sheng, Z. Ding and K. Leung, “Interference Subtraction with Supplementary Cooperation in Wireless Cooperative Networks”, Proc. of IEEE International Conference on Communications, ICC 2009.

Outage Probability of Supplementary Cooperation

• Channel Capacity:

• Outage Probability:

• By computing the limit, we have

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BER Improvement with Supplementary Cooperation

• SC generates routes with a smaller number of hops and satisfactory BER when compared with CC

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Total number of hops

End

-to-

end

BE

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Conventional cooperationDirect transmissionSupplementary cooperation

34.87%

Motivation for Interference Subtraction

• Observations– No interference is considered so far

– Concurrent transmissions harm BER performance

– One can further reduce interference from prior information

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S1 S2 S3

R1 R2 R3

T1 T2 T3 T4 T5 T6

S1(1) R1(1) S2(1) R2(1) S3(1) R3(1)

S1(2)

S4

T1 T2 T3 T4 T5 T6 T7

S1(1) R1(1) S2(1) R2(1) S3(1) R3(1)

S1(2) R1(2) S2(2)

S4(1)

R2(2)

S1(3)

Linear Network Analysis

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A five-node linear network

Assumption:Transmission range=1; Interference range=2; Interference free, d>2

Each node successfully receives a messageon an average in every two time slots, the average throughput for direct transmission with interference subtraction is

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Linear Network Analysis

A five-node linear network

For conventional cooperative transmission:a message on an average requires three time slots to be received, the average throughput is

For supplementary cooperative transmission:The average throughput is

24%

42%

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Interference Effects on BER Performance

• Channel resource reuse factor: spatial frequency reuse for scheduling • Link throughput can be increased without bring in significant BER• Trade-off between throughput, reuse factor and end-to-end BER

• Link throughput

is the desired transmission rate

is the reuse factor

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Channel resource reuse factors

End

-to-

end

BE

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3-hop CC without IS6-hop CC without IS9-hop CC without IS3-hop SC with IS6-hop SC with IS9-hop SC with IS

Conclusion

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What we have done1) Optimal solution: QoS routing algorithm for cooperative

networks

2) Interference effects on BER performance

3) Transmission power optimization

4) Throughput analysis

• Future works1) Delay analysis

2) Multi-QoS solution; more insights on BER, delay and throughput

3) System performance for a general network scenario (stochastic geometry)

Thank you

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