Joint Decoding of Primary and Secondary Users in Cognitive Radio Systems with Opportunistic Interference Cancellation

In underlay cognitive radio (CR) systems, besides decoding secondary users (SUs) in sequence with interference cancellation (IC), the cognitive base station (CBS) can also decode and cancel the signal of a primary user (PU) before processing some SUs´ signals. As the decodability of the PU depends on the opportunity created by the PU, this scheme is called the opportunistic interference cancellation (OIC). In CR systems with OIC, the joint decoding of PU and SUs needs to be studied, which involves the decoding order adjustment of all users and power allocation of SUs. Because the number of possible decoding orders is the factorial of the number of all users, the issue of joint decoding is an NP problem and the computationally efficient optimal algorithm cannot be found, thus the sub optimal algorithm should be developed. This paper proposes an efficient joint decoding algorithm of PU and SUs for addressing this NP problem. In the proposed algorithm, the feasible decoding order of PU and SUs will be efficiently adjusted as well as the powers of SUs are efficiently allocated. The extensive simulation experiments are conducted and the effectiveness of our algorithm is demonstrated by the numerical results.