Physical Layer Network Coding with Signal Alignment

Ruiting Zhou+, Zongpeng Li+, Chuan Wu*, Carey Williamson+

+University of Calgary*University of Hong Kong

Ruiting Zhou Univerisity of Calgary

Outline• 1. Introduction• 2. PNC-SA Scheme• 3. Precoding Design and BER Analysis• 4. General Applications of PNC-SA and

Throughput• 5. Conclusion

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1. Introduction• MIMO: Multi-input multi-output• Throughput is limited by the number of

antennas per AP

Figure 1: MIMO LANs

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1. Introduction• Second client-AP pair, transmit >2

packets? No!• Interference Alignment and Cancellation

(IAC) breaks through this bottleneck• IAC allows 3 concurrent packets Transmitters can control the alignment of their

signals at a receiver APs are typically connected to a backend Ethernet

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1. Introduction• IAC treats the second and third packets as

one unknown• AP1 sends on the Ethernet to AP21p

Figure 2: IAC example

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2. PNC-SA Scheme• Introduction to Digital Network Coding• Physical-Layer Network Coding• Physical layer Network Coding with

Signal Alignment Scheme

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2. PNC-SA Scheme• Traditional Transmission Scheduling: 4

time slots.

• Digital Network Coding: 3 time slots It is applied on digital bits that have been

correctly received:

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2. PNC-SA Scheme• Physical-Layer Network Coding (PNC): 2 time slots Additions of the EM signals are mapped to

additions of digital bit streams

BPSK maps from{-1, 1} to {0, 1} PNC demodulation maps from {+2, 0, -2} to {0,

1}

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2. PNC-SA Scheme• Physical layer Network Coding with

Signal Alignment (PNC-SA)• Align simultaneous transmissions from

multiple MIMO senders.

Figure 3: PNC-SA

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3. Precoding and BER Analysis

• Precoding — Alignment constraint:

• Solution:

Figure 3: PNC-SA

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3. Precoding and BER Analysis

• Comparison of the BER performance of

PNC-SA and IAC

Figure 4: BER performance

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4. Applications and Throughput• General applications of PNC-SA and

their throughput: PNC-SA for Info Exchange PNC-SA for Multi-Sender Multicast

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4. Applications and Throughput• PNC-SA for Info Exchange: Alice-and-

Bob communication

Figure 5: PNC-SA with three antennas per node

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4. Applications and Throughput• PNC-SA for Info Exchange PNC-SA: 6 packets in 2 time slots Digital network coding: 3 time slots, No coding:

4 time slots

Figure 6: Packet-level throughput for information exchange

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4. Applications and Throughput• PNC-SA for Multi-Sender Multicast PNC-SA: 6 packets in 4 time slots

Figure 7: Multicast from top layer to bottom layer

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4. Applications and Throughput• Digital network coding: 5 time slots• Straightforward multicast scheme without

coding: 7 time slots

Figure 8: Packet-level throughput for multicast

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5. Conclusion

• PNC-SA, SA coupled with PNC, can open new design spaces for routing in MIMO wireless networks

• Study the optimal precoding and BER performance

• Demonstrate the general applications

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• Thanks!

• Questions?

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