Encode When Necessary: Correlated Network Coding Under Unreliable Wireless Links

Recent research has shown that network coding has great potential to improve network performance in wireless communication. The performance of network coding in real-world scenarios, however, varies dramatically. It is reported that network coding brings negligible improvements but extra coding overhead in some scenarios. In this article, for the first time, we analyze the impact of link correlation on network coding and quantify the coding benefits. We propose correlated coding, which encodes packets only when performance improvement is achieved. Correlated coding uses only one-hop information, which makes it work in a fully distributed manner and introduces minimal communication overhead. The highlight of the design is its broad applicability and effectiveness. We implement the design with four broadcast protocols and three unicast protocols, and we evaluate them extensively on one 802.11 testbed and three 802.15.4 testbeds. The experimental results show that (i) more coding operations do not lead to fewer transmissions, and (ii) compared to existing network coding protocols, the number of transmissions is reduced with lower coding overhead.