A GSVD-Based Precoding Scheme for MIMO-NOMA Relay Transmission

Recently, the multiple-input-multiple-output (MIMO) nonorthogonal multiple-access (NOMA) transmission, denoted as MIMO- NOMA, has been widely applied for Internet of Things (IoT) systems due to its spectral efficiency. As a promising precoding method, the generalized singular value decomposition (GSVD)-based precoding scheme has been studied in MIMO- NOMA. In this study, we apply the GSVD-based precoding scheme to a downlink MIMO- NOMA communication system with an amplify-and-forward (AF) relay and two IoT users. A closed-form expression of the probability density function (PDF) of two channel matrices' generalized singular values (GSVs) is obtained in order to facilitate the performance analysis for cooperative MIMO- NOMA transmission. In particular, by this distribution characteristic result, the users' rates and outage probabilities achieved by MIMO- NOMA are studied for the insightful performance evaluation. In addition, the asymptotic approximations for outage probabilities at the high signal-to-noise-ratio (SNR) condition are presented. In addition to characterize the performance achieved by cooperative MIMO- NOMA, resource allocation for the addressed NOMA system is also investigated in this article, where a suboptimal power allocation algorithm to maximize the sum rate is given. The solution obtained by the proposed algorithm is studied, where the optimality condition of the solution is obtained. Finally, simulation results are presented to show the superiority of the scheme and verify these analytical results.