Symbol-level network coding for wireless mesh networks

This paper describes MIXIT, a system that improves the throughput of wireless mesh networks. MIXIT exploits a basic property of mesh networks: even when no node receives a packet correctly, any given bit is likely to be received by some node correctly. Instead of insisting on forwarding only correct packets, MIXIT routers use physical layer hints to make their best guess about which bits in a corrupted packet are likely correct and forward them to the destination. Even though this approach inevitably lets erroneous bits through, we show that it achieves high throughput without compromising end-to-end reliability. The core component of MIXIT is a novel network code that operates on small groups of bits, called symbols. It allows the nodes to opportunistically route correctly-received bits to their destination with low overhead. MIXIT's network code also incorporates an end-to-end error correction component that the destination uses to correct any errors that might seep through. We have implemented MIXIT on a software radio platform running the Zigbee radio protocol. Our experiments on a 25-node indoor testbed show that MIXIT has a throughput gain of 2.8 x over MORE, a state-of-the-art opportunistic routing scheme, and about 3.9 x over traditional routing using the ETX metric.