Resource Allocation for Multiple-Sources Single-Relay Cooperative Communication OFDMA Systems

Abstract

Joint allocation of resources, namely subcarrier assignment and power profiles at the source and relay nodes, is considered for both relaying schemes amplify and forward (AF) and decode and forward (DF) with multiple users using orthogonal frequency division multiple access (OFDMA). The objective is to allocate the resources to maximize the weighted sum rate subject to individual power constraint on each node. We formulate such a problem as subcarrier based resource allocation that seeks joint optimization of subcarrier assignment and power profiles at the source and relay nodes. Using high signal to noise ratio (SNR) approximation, two algorithms are proposed based on channel gains' ordering. In the first algorithm, the ordered subcarriers are split into two partitions; the first partition of the ordered subcarriers are assigned to one of the users, whereas, the second partition is assigned to the remaining users. The algorithm is applied repeatedly in a nested fashion by splitting each second partition into two partitions until the last partition is split between the last two users. The partitions that maximize the weighted sum rate are then sought. The proposed algorithm is of a reduced computational complexity compared to the exhaustive search and the dual approaches. A heuristic algorithm is also proposed to reduce the computational complexity further; it is a two-stage algorithm; a basic stage, and a transfer stage. In the basic stage, each user is assigned a subset of the subcarriers based on an ordering function. In the transfer stage, subcarriers can be transferred between the users to maximize the weighted sum rate. The merits of the proposed algorithms are demonstrated by numerical simulations.