Wireless Network Coding Martin Xu

Outline Introduction New Solutions – COPE – ANC Conclusions

Introduction Wireless: mobility Problem: severe throughput limitation Solutions – COPE – ANC – … Let’s take a look at traditional wireless…

Traditional Wireless Router

4 transmission required Traditional Wireless

Router 4 time slots required Traditional Wireless

COPE Katti, S., Rahul, H., Hu, W., Katabi, D., Médard, M., and Crowcroft, J XORs in the air: practical wireless network coding. In Proceedings of the 2006 Conference on Applications, Technologies, Architectures, and Protocols For Computer Communications (Pisa, Italy, September , 2006). SIGCOMM '06. ACM Press, New York, NY, Forward multiple packets in a single transmission Let’s take a look at how COPE deals with the aforementioned example

XOR = Router COPE

Router COPE

XOR = = Router Higher throughput (3 transmissions required) COPE

Transparent coding layer between IP and MAC Forward multiple packets in a single transmission Never delay packets HOW? – Opportunistic Listening – Opportunistic Coding – Learning neighbor state

COPE - Listening “Broadcast” in a small neighbor Each node stores overheard packets for a limited time Pseudo broadcast – Broadcast results in poor reliability and lack of backoff – Pseudo broadcast unicast packets that are meant for broadcast

COPE - Coding To transmit n packets, p 1,..., p n, to n nexthops, r 1,..., r n, a node can XOR the n packets together only if each next-hop r i has all n − 1 packets p j for j = i.

COPE - data structure Reception report – Reports are piggybacked on packets – If no packets to send, periodically send reports Output queue (FIFO) Two per-neighbor virtual queue – packet-size distribution in the Internet is bimodal with peaks at 40 and 1500 bytes Packet info

COPE - Performance With no hidden terminals, TCP’s throughput can increase by 38% flows, COPE increases UDP throughput by 3-4x

ANC Katti, S., Gollakota, S., and Katabi, D Embracing wireless interference: analog network coding. In Proceedings of the 2007 Conference on Applications, Technologies, Architectures, and Protocols For Computer Communications (Kyoto, Japan, August , 2007). SIGCOMM '07. ACM Press, New York, NY, Strategically exploit interference instead of avoiding it – Interfered signal is not exactly the sum – Channel distorts signals – Two signals are never synchronized

ANC - Algorithm Decode small part of uninterfered signal (MSK) Decode interfered signal – Decomposition using amplitudes of the original ones and the interfered – Four possible angles – Choose the 90 degree one Decode the rest of the uninterfered signal

ANC - Performance For the example used at the beginning, median throughput gain of ANC over routing 70%, COPE 30% For X-topology, median throughput gain over routing is 65%, over COPE 28% For chain topology, median throughput gain over routing is 37%

Conclusion Both implementation that yields large throughput gains COPE – Simple and practical ANC – Embrace Broadcast and Interference