Rate Selection for Wireless Networks with Intra-and Inter-session Network Coding

A recent study shows that the throughput of wireless networks can be further improved via combining intra-and inter-session network coding (I-2 NC). The main idea of I-2 NC is to protect against packet loss by introducing additional redundancy via intra-session coding. However, the amount of redundancy depends on the quality of overhearing links. The poorer an overhearing link is, the less fraction of information is overheard, which results in a potential increase of redundancy needed. While lower transmission rate promises better link quality, it also means lower throughput. Motivated by this, we study the impact of transmission rates on network throughput and formulate the rate selection into an optimization problem. Also, we investigate the flow partition for the inter-session coding. In other words, we consider which sessions would be grouped together through network coding to improve the throughput. We aim to design a joint rate and partition selection in a wireless star network, so as to maximize the network throughput. We prove that finding the optimal joint rate selection and flow partition is NP-hard. An efficient heuristic algorithm is proposed for the networks with heterogenous rates and sessions that can be grouped together for the inter-session network coding. Simulation results show that the proposed scheme achieves throughput gains of up to 185% as compared to what is gained with a rate-unaware I-2 NC scheme.