Permutation trellis coded multi-level FSK signaling to mitigate primary user interference in cognitive radio networks

In this paper, we propose a novel spectrum underlay approach for secondary users where a permutation trellis code (PTC) is employed in conjunction with multi-level frequency shift keying signaling in the presence of multiple narrowband primary users (PUs). The PUs are assumed to be dynamic in that they appear intermittently and stay active for an unknown duration. Our proposed approach derives its resilience to the interference caused by PUs and noise disturbances via dispersal of the information in SU's messages over multiple frequencies and time intervals. Our proposed underlay-design improves the SU data rate by accumulating a large amount of spectrum from several PUs, while simultaneously operating at low power to minimize the interference caused at PUs' receivers. We evaluate our system performance in terms of bit error rate (BER) and throughput by approximating the actual BER using properties of the Viterbi decoder. We corroborate our analytical results with simulation results and show that our proposed coded system is robust to heavy interference caused by multiple narrowband PUs.