Sub-channel assignment and power allocation in OFDMA-NOMA based heterogeneous cellular networks

In this paper, we study the downlink resource allocation and cross-tier interference management in a heterogeneous cellular network. To cross-tier interference control, we proposed an orthogonal frequency division multiple access (OFDMA)-non-orthogonal multiple access (NOMA)-based scheme which macro base station (MBS) only uses OFDMA-based sub-channels (OBSCs) and the total bandwidth (OBSCs and NOMA-based sub-channels (NBSCs)) is available for small BSs (SBSs). The resource allocation problem is formulated as a non-convex NP-hard optimization problem which jointly designs the sub-channel assignment and power allocation for maximizing the sum-rate performance. To reduce the computational complexity, we solve this problem with three steps. First, for sub-channel assignment, we solve a convex problem by using available on-line optimization solvers. Second, we approximate the nonconvex power allocation problem into a convex optimization problem and obtain the power allocation policy through the Lagrange dual approach. Third, we propose an iterative algorithm to obtain the joint sub-channel and power allocation strategies. Simulations results show that the proposed OFDMA-NOMA scheme performs better than the OFDMA-based scheme. (C) 2020 Elsevier GmbH. All rights reserved.