Network-Coded Multiple Access Presented by Soung Liew (Joint Work with Lu Lu, Lizhao You, Shenghao Yang) Institute of Network Coding The Chinese University of Hong Kong March 2014 Soung Liew, CUHK 1

March Background on PNC First proposed in Mobicom 06 [1] A subfield of Network Coding building up momentum in recent years: - Google scholar citations: (annual growth ~300) - A main topic in special journal issues and numerous conferences. - A main topic in an upcoming IEEE JSAC issue on wireless network coding - Half-day workshop in IEEE WNCN 2013: New Advances for PNC - Invited talks [1] S. Zhang, S. C. Liew, P. P. Lam, “Physical-Layer Network Coding,” ACM Mobicom Similar idea in [2] P. Popovski and H. Yomo, “The anti-packets can increase the achievable throughput of a wireless multi-hop network,” ICC Soung Liew, CUHK

March 2014 Simplest Set-up: Two-Hop Linear Network 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 R? A RB SASA SBSB Soung Liew, CUHK 3

PNC March 2014 A RB SASA SBSB Time slot 1 Time slot 2 Transmissions by nodes A and B are simultaneous! Soung Liew, CUHK 4

March 2014 PNC for Multiple Access (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? Relay Network Soung Liew, CUHK 5 Wireless LAN Access Point

PNC In Non-Relay Network: Network Coding Multiple Access (NCMA) Nodes A and B send C A and C B to AP simultaneously AP tries to decode packets C A, C B, and March 2014 Soung Liew, CUHK 6 A APB

PHY-Layer Decoders of NCMA March 2014 Soft Information (Log Likelihood Ratio:, k=1,2,… ) Soung Liew, CUHK 7

PHY-layer Bridging March 2014 Soung Liew, CUHK 8

Are Lone XOR Packets Useful? March 2014 Complementary XOR Lone XOR Soung Liew, CUHK 9 Do lone XOR packets have a role to play?

March 2014 MAC-Layer Erasure Code + PHY- Layer Channel Code Soung Liew, CUHK 10

MAC-Layer Bridging with L = 3 March 2014 Soung Liew, CUHK 11

Experiments: Layout of Indoor Environment for 9 USRP N210 Nodes Institute of Network Coding (INC) March 2014 Soung Liew, CUHK 12

PHY-Layer Packet Decoding Statistics (Balanced Power Case) 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 March 2014 Soung Liew, CUHK 13

PNC decoding works but MUD does not when phases are aligned March 2014 Soung Liew, CUHK 14 Received Signal Decode Outcomes

PNC does add value when phases are severely misaligned March 2014 Soung Liew, CUHK 15 Decode Outcomes Received Signal

Combination of PNC and MUD is effective when phases are moderately misaligned March 2014 Soung Liew, CUHK 16 Received Signal Decode Outcomes

March 2014 Soung Liew, CUHK 17 Overall Throughputs of Different Schemes for Different SNRs L A = 1.5×L B = 24.

Pairing Strategies March 2014 Soung Liew, CUHK 18 Scenario: Four users at locations 2, 3, 4, 5. How to form pairs? Pair “strong with weak” rather than “strong with strong and weak with weak” Strategy 1: pair 2 with 3; 4 with 5 Strategy 2: pair 3 with 4; 2 with dB 9dB 7dB 7.4dB

Linearly Coupled Codes at MAC Layer Single-equation System: March 2014 Soung Liew, CUHK 19

Linearly Coupled Raptor Codes Near optimal and availability of fast decoding March 2014 Soung Liew, CUHK 20

Dynamic Equation March 2014 Soung Liew, CUHK 21

Degree Optimization Problem March 2014 Soung Liew, CUHK 22 For some positive integer

Use SIC at low SNR Regime Suppose an (N,3) RS code March 2014 Soung Liew, CUHK 23 Slot Index PHY-layer SIC Cross-layer SIC Message decoding

Overall Throughputs of Different Schemes for Different SNRs L A = 1.5×L B = 24. March 2014 Soung Liew, CUHK 24

NCMA: Conclusion First venture into non-relay (multiple-access) setting for PNC PNC may have a role to play in the multiple access scenario: To simplify decoder design For delivering jumbo messages Ongoing NCMA Investigations: Better performance for high and low SNR regime Investigation of linearly-coupled code for MAC layer of NCMA March 2014 Soung Liew, CUHK 25

The End March 2014 Soung Liew, CUHK 26

Throughputs of Four User Pairs March 2014 Soung Liew, CUHK 27

Overall Throughputs of Different Schemes with RS code parameter L A = 4, 8, 16, 32, and fixed SNR = 9dB. March 2014 Soung Liew, CUHK 28

Throughputs of Nodes A and B, with SNR of Node A fixed at 9.5dB, and SNR of Node B Varied. March 2014 Soung Liew, CUHK 29

March Frequency-Domain PNC (FPNC) in GNU Radio testbed, PNC Implementation: Wireless Soung Liew, CUHK A B R