Performance Analysis of Cooperative Non-Orthogonal Multiple Access Based on Spectrum Sensing

This paper proposes and investigates a cooperative non-orthogonal multiple access scheme that is based on spectrum sensing (CNOMA-SS), where the primary user intends to communicate with the base station by the assistance of the secondary user. On the other hand, the secondary user can obtain an additional opportunity to access the spectrum band originally belonging to the primary user. Therefore, a win–win situation is achieved by our collaboration scheme. When employing the proposed scheme, the secondary user, i.e., the user relay, adopts the spectrum sensing technique to perceive the surrounding wireless environment by identifying the spectrum holes. According to the sensing results, the secondary user will intelligently determine its transmission signal form, eventually improving the overall system capacity. In this paper, we take the practical assumption of imperfect spectrum sensing into consideration. To characterize the performance of the proposed CNOMA-SS scheme, closed-form expressions for outage probability, system throughput in delay-limited transmission mode, ergodic rate, and system throughput in delay-tolerant transmission mode are derived, with or without the direct link between the base station and the primary user. Simulation results further validate these closed-form derivation expressions, verify the effectiveness of employing the spectrum sensing technique, and illustrate the superior performance of CNOMA-SS compared with two cooperative benchmarks, in terms of system throughput in delay-limited and delay-tolerant transmission modes with or without the direct link, respectively.