Reliable Spectrum Sensing and Opportunistic Access in Network-Coded Communications

We consider the problem of reliable spectrum sensing and opportunistic access on channels with stochastic traffic in batch processing systems such as network coding (NC). We show how a secondary user (SU) can leverage the structure induced by block-based NC on primary users´ (PUs) channels to mitigate the effects of channel sensing errors and improve the detection of idle PU spectrum and the throughput. NC is known to improve the transmission efficiency and therefore when applied on a PU channel, it can extend the spectrum availability for the SUs. We refer to the additional gain of spectrum predictability from NC and show that under possible sensing errors the SU can more reliably detect the idle spectrum if the PUs´ channels carry network-coded transmissions even when the channel utilization is fixed. We consider two different objectives at the SU. For quickest detection, the SU applies the Cumulative Summation (CUSUM) algorithm to detect idle slots on a PU channel and further improves the detection capability with the Viterbi algorithm, if the PU spectrum dynamics are known. For throughput maximization, the SU tracks the PU spectrum with the Partially Observable Markov Decision Process (POMDP) approach. Our results show that NC renders the spectrum more predictable, which can be used by the SUs to mitigate the effects of sensing errors and improve the throughput. We validate these results with real radio measurements taken in software-defined radio based wireless network tests.