Throughput Maximization for Instantly Decodable Network Coded NOMA in Downlink Broadcast Communication Systems

Non-orthogonal multiple access (NOMA) employed at the physical layer and network coding employed at the network layer are two promising transmission technologies to improve the spectral efficiency. In this paper, we develop a cross-layer approach by employing power-domain NOMA at the physical layer and instantly decodable network coding (IDNC) at the network layer in downlink broadcast communication systems. Following this approach, two IDNC packets are broadcasted during each transmission by employing superposition coding, one for all receivers and the other only for the strong receivers which employ successive interference cancellation (SIC). IDNC packets selection, transmission rates adaption, and NOMA power allocation are jointly considered to improve the throughput. Given the intractability of the problem, we decouple it into two separate subproblems, i.e., IDNC schedule and NOMA power allocation. IDNC schedule can be formulated as the maximum weight clique (MWC) problem, and two heuristic algorithms named as maximum weight vertex (MWV) search and maximum weight path based maximum weight vertex (MWP-MWV) search are developed to solve the first subproblem. An iterative function evaluation (IFE) approach is proposed to solve the second subproblem. Simulation results demonstrate the throughput gains of the proposed approach over the existing schemes.