Opportunistic network coding for secondary users in cognitive radio networks

In cognitive radio networks (CRNs), secondary users (SUs) may employ network coding to pursue higher throughput. However, as SUs must vacate the spectrum when it is accessed by primary users (PUs), the available transmission time of SUs is usually uncertain, i.e., SUs do not know how long the idle state can last. Meanwhile, existing network coding strategies generally adopt a block-based transmission scheme, which means that all packets in the same block can be decoded simultaneously only when enough coded packets are collected. Therefore, the gain brought by network coding may be dramatically decreased as the packet collection process may be interrupted due to the unexpected arrivals of PUs. In this paper, for the first time, we develop an efficient network coding strategy for SUs while considering the uncertain idle durations in CRNs. At its heart is that systematic network coding (SNC) is employed to opportunistically utilize the idle duration left by PUs. To handle the uncertainty of idle durations, we utilize confidential interval estimation to estimate the expected duration for stochastic idle durations, and multi-armed bandits to determine the duration sequentially for non-stochastic idle durations, respectively. Then, we propose a coding parameter selection algorithm for SNC by considering the complicated correlation among the receptions at different receivers. Simulation results show that, our proposed schemes outperform both traditional optimal block-based network coding and non-network coding schemes, and achieve competitive performance compared with the scheme with perfect idle duration information.