Physical-layer Network Coding: Prototyping and Application

1. Network Coding Innovation Technology Workshop Physical-layer Network Coding: Prototyping and Application Lu Lu 30th August 2013

2. Outlines • 1. Background of Physical-layer Network Coding (PNC) • 2. Real-time PNC Prototype • Demo Video • PNC Realization Challenges • 3. PNC in Non-relay Setting • Experimental Setup • Performance Evaluation • 4. Conclusion PNC Prototyping & Application

3. What is PNC? • Traditional view in wireless networking: interference is bad. • PNC turns things around by exploiting network coding (NC) performed by nature. • When electromagnetic waves superimpose, they add, a form of NC. • Benefits of PNC: • boost throughput PNC Prototyping & Application

4. Simplest Set-up: Two-Hop Relay Network R • System Model: Two-way Relay Channel (TWRC) • No direct channel between nodes A and B. • Half duplex: nodes cannot transmit and receive at the same time. • What is the minimum number of time slots needed for nodes A and B to exchange one packet via relay node R? B A PNC Prototyping & Application

5. Time slot 1 Traditional Scheduling (TS) • Transmissions non-overlapping in time PA PA A R B PB PB Time slot 2 Time slot 4 Time slot 3 PNC Prototyping & Application

6. Straightforward Network Coding (SNC) • Transmissions by nodes A and B still non-overlapping • Relay R uses one time slot to broadcast PA PB A R B Time slot 2 Time slot 1 Time slot 3 PNC Prototyping & Application

7. Physical-layer Network Coding (PNC) • Transmissions by nodes A and B are simultaneous! PA PB A R B Time slot 2 Time slot 1 PNC Prototyping & Application

8. Outlines • 1. Background of Physical-layer Network Coding (PNC) • 2. Real-time PNC Prototype • Demo Video • PNC Realization Challenges • 3. PNC in Non-relay Setting • Experimental Setup • Performance Evaluation • 4. Conclusion and Future Works PNC Prototyping & Application

9. Specifics • Frequency-domain PNC (FPNC) for TWRC • Build on OFDM technology as used in Wi-Fi • First PNC implementation in 2012 • First real-time PNC implementation in 2013 • Support “real” application in real-time through API PNC Prototyping & Application

10. PNC Implementation: Wireless • Frequency-Domain PNC (FPNC) in GNU Radio testbed A R B PNC Prototyping & Application

11. Demo Video: Real-Time File Exchange with PNC • A short video followed by a demo See demo video in http://www.youtube.com/watch?v=HmRBm_IIBQQ PNC Prototyping & Application

12. PNC Realization Challenges • Asynchrony • Signals from nodes A and B may arrive at the relay R with symbol and carrier-phase misalignments • Solution: PNC with OFDM (FPNC) • Channel Estimation • Relay needs to estimate two channels based on simultaneous signals • Solution: FPNC Frame Format Design PNC Prototyping & Application

13. Frame format for RPNC Data Totally Overlap User Detection Channel Estimation PNC Prototyping & Application

14. PNC Realization Challenges • Channel-decoding and Network Coding (CNC) • Tradeoff between optimality and simplicity • Solution: Opt for simplicity; adopt 802.11 convolutional code and XOR-CD CNC. Reduced constellation approach • ARQ for Retransmission • End-to-end ARQ or Relay-assisted ARQ • Solution: Opt for simplicity; adopt end-to-end ARQ PNC Prototyping & Application

15. Single-user Channel Decoder and PNC Channel Decoder in Overall RPNC System PNC Decoder Soft Information (Log Likelihood Ratio: , k = 1, 2,… ) PNC Prototyping & Application

16. Reduced Constellation Approach to Computing Soft Information on XOR bit Received sample with noise Mapping four constellation points to two Constellation points for log likelihood computation • BPSK for both nodes A and B • Between two points of the same XOR, choose the one with the shorter Euclidean distance PNC Prototyping & Application

17. PNC Realization Challenges • Long Latency between USRP-PC • The turn-around time for USRP-PC may be long and unpredictable • Solution: Burst Transmission Mode PNC Prototyping & Application

18. Burst Transmission Mode in RPNC Uplink Downlink PNC Prototyping & Application

19. Normalized throughput of PNC and TS PNC can double the throughput PNC Prototyping & Application

20. Outlines • 1. Background of Physical-layer Network Coding (PNC) • 2. Real-time PNC Prototype • Demo Video • PNC Realization Challenges • 3. PNC in Non-relay Setting • Network Coding Multiple Access (NCMA) • Performance Evaluation • 4. Conclusion and Future Works PNC Prototyping & Application

21. PNC in Non-Relay Setting? • Access point wants to get both Message A and Message B, not just their XOR. • Does PNC have a role to play? Access Point Wireless LAN PNC Prototyping & Application

22. PNC In Non-Relay Network: Network Coding Multiple Access (NCMA) A AP B • Nodes A and B send to AP simultaneously • AP uses three decoders to separately decode packet A, packet B, and packet A B • Eight possible events: • Packets A, B, and A B decoded • Packets A and B decoded • … • Packet A B decoded • None decoded PNC Prototyping & Application

23. PHY-Layer Decoders of NCMA Soft Information (Log Likelihood Ratio: , k = 1, 2,… ) PNC Prototyping & Application

24. Alternatives for MUD Decoding MUD Decoder PNC Prototyping & Application

25. NCMA: PHY-layer Bridging PNC Prototyping & Application

26. Are Lone XOR Packets Useful? Complementary XOR Lone XOR • Do lone XOR packets have a role to play? PNC Prototyping & Application

27. MAC-Layer Erasure Code + PHY-Layer Channel Code PNC Prototyping & Application

28. NCMA: MAC-Layer Bridging with L = 3 PNC Prototyping & Application

29. Experiments: Layout of Indoor Environment for 9 USRP N210 Nodes Institute of Network Coding (INC) PNC Prototyping & Application

30. PHY-Layer Packet Decoding Statistics(Balanced Power Case) Solo XOR packets AB: Both A and B decoded AX|BX: A and XOR decoded or B and XOR decoded A|B: Either only A or only B decoded X: Only XOR decoded PNC Prototyping & Application

31. Overall Throughputs of Different Schemes with RS code parameter LA = 4, 8, 16, 32, and fixed SNR = 9dB. PNC Prototyping & Application

32. Overall Throughputs of Different Schemes for Different SNRs LA = 1.5×LB= 24. PNC Prototyping & Application

33. Throughputs of Four User Pairs PNC Prototyping & Application

34. Pairing Strategies Scenario: Four users at locations 2, 3, 4, 5. How to form pairs? Strategy 1: P2 and P4 Strategy 2: P3 and P5 Pair “strong with weak” rather than “strong with strong and weak with weak” PNC Prototyping & Application

35. NCMA: Overall Summary A AP B • First venture into non-relay setting for PNC • PNC may have a role to play in the multiple access scenario • for simplification of decoder design • for jumbo messages PNC Prototyping & Application

36. Outlines • 1. Background of Physical-layer Network Coding (PNC) • 2. Real-time PNC Prototype • Demo Video • PNC Realization Challenges • 3. PNC in Non-relay Setting • Experimental Setup • Performance Evaluation • 4. Conclusion PNC Prototyping & Application

37. Conclusions • There has been a lot of theoretical work on PNC • Relatively few experimental investigations • RPNC: The first real-time PNC prototype • NCMA: PNC can be applied in a non-relay setting to boost system throughput • Future: apply PNC and NCMA to commercial wireless networks: cellular (e.g., LTE-A) and WLAN PNC Prototyping & Application

38. PNC Prototyping & Application

39. To Probe Further • “Implementation of Physical-layer Network Coding,” in ICC ’12 and Phycom, Mar. 2013. • “Real-time Implementation of Physical-layer Network Coding,” in SRIF ’13, an ACM SIGCOMM Workshop. • “Network-coded Multiple Access,” Technical Report, http://arxiv.org/abs/1307.1514. PNC Prototyping & Application