A low complexity relay selection & power allocation schemes for cognitive MIMO buffer-aided DF relay networks

In this paper, we consider decode-and-forward (DF) buffer-aided relay selection and transmission power allocation for underlay cognitive radio (CR) network that is equipped with multiple-input multiple-output (MIMO) antenna scheme. We propose a low complexity MIMO-based relay selection scheme that maximizes the single-hop normalized rate of the secondary network (SN). Also, we propose a sub-optimal antenna transmission power allocation scheme that maximizes the overall normalized sum rate of the primary network (PN) and the SN. We first derive optimal expressions for antenna transmission power of both the PN and the SN. The derived expressions are then used in an iterative algorithm to produce a near-optimum solution that maximizes the normalized sum rat per time slot. Simulation results are provided to evaluate the performance of the proposed MIMO-based relay selection and antenna transmission power allocation schemes and compare their performance with that of the optimal scenario. Impact of several system parameters including buffer maximum size, interference threshold and number of antennas on network performance are also investigated. Results reveal that the proposed sub-optimal relay selection and antenna transmission power allocation schemes introduce a satisfactory performance with much lower complexity compared to optimal relay selection and power allocation schemes. Findings also show that using buffer-aided relays significantly enhances the SN performance while slightly weakens the performance of the PN.