1. Cooperative Cross-Layer Communication
Month Year
doc.: IEEE /1767r0
November 2006
Cooperative Cross-Layer Communication
Date:
Authors:
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Monisha Ghosh, Philips
John Doe, Some Company

2. November 2006
Abstract
This presentation introduces various PHY layer cooperative communication concepts to the community.
Significant performance (throughput, range, reliability, etc.) enhancements are possible by the “cooperative” use of STAs in a network, as opposed to “combative” use.
Monisha Ghosh, Philips

3. Cooperative Communication Vs. Multihop
November 2006
Cooperative Communication Vs. Multihop
Direct Transmission
Multi-hop
Cooperative
Monisha Ghosh, Philips

4. Advantages Of Cooperative Communications
November 2006
Advantages Of Cooperative Communications
Space diversity is achieved without the use of additional antennae – each station acts as a diversity transmitter for its partner: all stations benefit.
Robustness against shadow fading.
Reduced interference /lower transmission power: increased battery life, better frequency reuse.
Greater range for the same transmitted power.
Increased reliability and QOS.
Higher throughput/lower delay: fewer retransmissions
For , minor modifications needed to implement cooperative communications between stations.
Monisha Ghosh, Philips

5. Some Cooperative Methods
November 2006
Some Cooperative Methods
Amplify and Forward
Cooperative Coding
Cooperative Symbol Rotation
Cooperative HARQ
Network Coding
Monisha Ghosh, Philips

6. Amplify And Forward November 2006
Relay simply amplifies received signal and retransmits to destination.
Destination processes signal from source AND relay.
Drawback: noise is amplified as well.
Nevertheless, has performance advantages.
Equivalent channel model:
Monisha Ghosh, Philips

7. Cooperative Coding Convolutional code, rate 1/4 November 2006
Source (S) transmits half the coded bits.
Relay (R) receives, and if it can decode correctly, transmits the remaining coded bits.
Destination receives all coded bits.
Source and Relay can use different modulations to maximize throughput.
Convolutional
code, rate 1/4
Bits transmitted by S
Bits transmitted by R
for S
Monisha Ghosh, Philips

8. Cooperative Coding: Performance
November 2006
Cooperative Coding: Performance
Ref.: Z. Lin, E, Erkip and M. Ghosh,
“Adaptive Modulation For Coded
Cooperative Systems,” SPAWC 2005
Monisha Ghosh, Philips

9. Cooperative Symbol Rotation
November 2006
Cooperative Symbol Rotation
Cooperation at the symbol level based on fully decode-and-forward at the bit level.
Rotation matrices for QAM signal constellations and lattice-based modulation scheme can be applied.
D-ReM-F: an application of linear modulation from integer rotation matrices to cooperative communications.
Equivalent channel model:
Monisha Ghosh, Philips

10. Cooperative Symbol Rotation: Performance
November 2006
Cooperative Symbol Rotation: Performance
Fast Rayleigh Fading channel.
Symmetric case: source and relay have equal distance to destination
Source-relay channel SNR = 20dB
Block inter-leaver after CC
BER performance
D-ReM-F can provide signal space diversity
Monisha Ghosh, Philips

11. Cooperative HARQ: concept
November 2006
Cooperative HARQ: concept
Cooperator selection
Select the best relay as potential cooperator
Cooperative HARQ
If direct link (DATA) fails, relay transmits ARQ packet (DATA2)
Receive combining
If DATA2 = DATA
Maximal-ratio combining of source and relay packets to get diversity gain
If DATA2 = function (DATA)
Optimal combining of source and relay packets to get coding and diversity gains
DATA
DATA2
Monisha Ghosh, Philips

12. Cooperative HARQ: performance
November 2006
Cooperative HARQ: performance
50% gain
over direct
Best application scenario
Diversity-limited channels and devices: low diversity available in space, time or frequency, e.g. single antenna devices in flat fading channels
Dense networks: can leverage user density as a resource, capacity scales linearly as in MIMO (Ozgur, Leveque and Tse, “How does the information capacity of ad-hoc networks scale,” Allerton 2006.)
Monisha Ghosh, Philips

13. Network coding: concept
November 2006
Network coding: concept
XOR in the air:
Takes 3 slots 1 2
Current approach:
Takes 4 slots 2 1
XOR the two packets, then broadcast 4 3 3
Decode, and then XOR with old packet
Simple idea, can be extended to more complex configurations
S. Katti, H. Rahul, W. Hu, D. Katabi, M. Medard, J. Crowcroft, “XORs in the air: practical wireless network coding,” ACM SIGCOMM’06
Monisha Ghosh, Philips

14. November 2006
Conclusions
Multiple cooperative modes, at both PHY and MAC levels, can provide improved performance.
In-home as well as enterprise deployments of are perfectly suited for cooperative modes.
Real-time applications, e.g. video would benefit from the higher throughput capabilities of cooperative methods.
Monisha Ghosh, Philips