An Efficient Relay Selection and Power Allocation Schemes for Cognitive MIMO DF Relay Networks with Buffers

In this paper, decode-and-forward buffer-aided opportunistic relay selection and antenna transmission power allocation for underlay cognitive radio are considered. All the transmitting and receiving nodes are assumed to be equipped with multiple antennas resulting in a multiple-input multiple-output (MIMO) system. First, a low-complexity MIMO-based relay selection scheme that maximizes the single-hop normalized sum rate of the primary network (PN) and secondary network (SN) is proposed. Second, a sub-optimal antenna transmission power allocation scheme that maximizes the normalized sum rate of the PN and SN is proposed. For power optimization, first, optimal expressions for antenna transmission power of both the PN and SN nodes are derived separately. The derived expressions are then used in an iterative algorithm to produce a near-optimum solution that maximizes the normalized sum rate 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. The findings show that the proposed relay selection and antenna transmission power allocation schemes introduce a satisfactory performance with much lower complexity compared to the optimal schemes. Additionally, results show that using a buffer-aided relaying significantly enhances the SN performance while slightly deteriorates the performance of the PN.