On bridging theory and practice of inter-session network coding for CSMA/CA based wireless multi-hop networks

Inter-session network coding is well known for its ability to spectral efficiency and end-to-end throughput in wireless multi-hop networks by up to four fold on some scenarios compared to standard routing. However, a variety of inter-session network coding implementations have consistently shown a decrease in throughput when operating at high traffic loads and significantly below the values expected theoretically. While still being superior to forwarding, this discrepancy between past analytical studies and real measurement results requires further understanding to realize inter-session network coding’s full potential in practice. This paper presents mathematical analysis for two of the key sources for this discrepancy, namely, long- and short-term channel asymmetries. We use this knowledge to develop, yet effective algorithm to cope with these asymmetries and bolster network coding’s performance in real systems. Our algorithm and other alternative algorithms have been implemented in a hardware platform that uses a CSMA/CA based medium access control (MAC) protocol. Performance evaluation is carried out via an extensive measurement campaign with node deployments in different testing environments, channel conditions, and active devices in the network with the equivalent to more than a month of continuous testing. Based on the measurement results, we demonstrate that our algorithm is capable of closing the gap to theoretically expected results despite being influenced by real world channel conditions while maintaining fairness to other network devices at the MAC level.