1. Interference Cancellation in Two-Path Successive Relay System with Network Coding Chunbo Luo, Dr. Yu Gong & Prof. Fuchun Zheng School of Systems Engineering University of Reading United Kingdom 28/09/2010

2. c.luo@reading.ac.uk Contents Introduction and System Model Physical-layer Network Coding Interference Cancellation Simulation Results Conclusion and Future Work

3. c.luo@reading.ac.uk Introduction Cooperative networks Demands in wireless communications: Higher data rate Higher spectrum efficiency Reliable connections Lower energy consumption Longer battery life … Dilemma: Limited resource Unlimited requirements Solutions? Cooperative networks

4. c.luo@reading.ac.uk Introduction Cooperative networks WHY and HOW? Please see one of the cooperative models: two- Path cooperative model Source: S Relays: R Destination: D RELAY

5. c.luo@reading.ac.uk Introduction Cooperative networks Large and better coverage Lower transmission energy More reliable connection …… There are loads of benefits. But …. The Limit of half-duplex transmission

6. c.luo@reading.ac.uk Introduction Cooperative networks At the relay: At the destination: R 1 and R 2 alternatively relay the data from S to D. Solution?

7. c.luo@reading.ac.uk Introduction Cooperative networks But … INTER RELAY INTERFERENCE (IRI)

8. c.luo@reading.ac.uk IRI Cancellation Inter relay interference (IRI) Interference cancellation schemes Our scheme: Physical Network Coding (PNC) What is PNC? Why can PNC solve the problem? How does it work? Solution

9. c.luo@reading.ac.uk IRI Cancellation To clearly show the basic mechanism: we use the following ideal model: Ideal environment: no noise, channels are stable (no fading) Why and how does PNC work to reduce IRI? R receives: At n+1 time slot, R transmits the PNC result. D receives: Then R performs PNC.

10. c.luo@reading.ac.uk IRI Cancellation Why and how does PNC work to reduce IRI? IRI is totally removed!!! At destination, we do another XOR:

11. c.luo@reading.ac.uk IRI Cancellation Why and how does PNC work to reduce IRI? Key: How does PNC work? The actual received signal at R is:

12. c.luo@reading.ac.uk 1-0.5*(Magnitude of received signal): 1: A and B are different 0: A and B are the same Physical-layer Network Coding PNC Example-BPSK A: -1, 1 B: -1, 1 So relay received patterns: -2 0 2, using the following equation: If BPSK used, we have: 1 Mapping to 1 0 Mapping to -1 XOR!

13. c.luo@reading.ac.uk Physical-layer Network Coding XOR in Physical layer: By using certain equations, we have: Y=A B XOR in Physical layer

14. c.luo@reading.ac.uk Physical-layer Network Coding XOR in Physical layer: But …. How about other modulation schemes? e.g. QPSK See the table below (It can be found in the paper)

15. c.luo@reading.ac.uk IRI Cancellation XOR in Physical layer: But …. The system model The transmissions suffer from channel fading and additive noises. How about in practical systems?

16. c.luo@reading.ac.uk IRI Cancellation In practical system 1) MAP Detection at relays: 2) Joint detection and PNC: 3) Relay transmission

17. c.luo@reading.ac.uk IRI Cancellation In practical situation: 4) MAP Detection at destination: 5) PNC decoding: where is the result we want!

18. c.luo@reading.ac.uk Simulation results Gaussian model:

19. c.luo@reading.ac.uk Simulation results Rayleigh model:

20. c.luo@reading.ac.uk Conclusion and future work The proposed PNC interference cancellation scheme can effectively reduce IRI Its performance depends on the accuracy of channel estimation (MAP detection) PNC can be used in signal processing areas to deal with interference problems

21. c.luo@reading.ac.uk Conclusion and future work The scenario with direct link available The joint coding and detection Multi-source multi relay scenario The complexity of MAP detection

22. c.luo@reading.ac.uk Thank you! Interference Cancellation in Two-Path Successive Relay System with Network Coding