A novel minimal set decode-amplify-forward (MS-DAF) relaying scheme for MIMO-NOMA

In non-orthogonal multiple access (NOMA) scheme, the strong users, located near to base station, demodulate their data by considering the information of other users as interference. One of the crucial challenges in NOMA is the design of sophisticated interference cancellation techniques to improve performance. An alternate approach is to exploit cooperative communication with more straightforward interference cancellation techniques to enhance performance without increasing computational complexity. In this paper, we propose a novel hybrid minimal set decode-amplify-forward (MS-DAF) relaying scheme with maximal ratio combining and space–time block coding for MIMO-NOMA to enhance the performance of weak users located away from the base station and/or having poor channel conditions. The proposed MS-DAF approach reduces the number of relayed links through an intelligent selection of relaying users. The aim is to minimize the re-transmission overhead without compromising the performance. Furthermore, the proposed MS-DAF approach switches between amplify-and-forward and decode-and-forward based on the channel conditions. Simulation results for both SISO- and MIMO- NOMA are presented to show the superiority of the proposed hybrid scheme over existing individual schemes. The proposed technique can be used to improve the performance of edge users in a cellular network with minimal relayed links.