Joint Network Coding and Subcarrier Assignment in OFDMA-Based WVireless Networks

Abstract

Orthogonal frequency division multiple access (OFDMA) has been integrated into emerging broadband wireless access technologies such as 802.16 wirelessMAN. Due to the diversity of channel gains among the downlink subscribers, it is known that dynamic allocation of subcarriers can significantly improve the overall performance of OFDMA systems, in terms of power efficiency and link throughput. A large body of work has focused on the joint subcarrier assignment and resource (bit and power) allocation for the OFDMA downlink. In this paper, we adopt a cross layer approach towards a network coding aware subcarrier assignment algorithm for the uplink and downlink of OFDMA based wireless networks. We formulate the maximal rate assignment problem as a mixed integer linear program and derive a polynomial time heuristic to approximate the solution. With network coding, it becomes possible to assign the same subcarrier to different downlinks without causing any interference. Consequently, our coding-aware assignment scheme improves the bandwidth efficiency and increases the network layer throughput by a substantial margin. We show that the total network throughput resulting from the heuristic is comparable to the optimal solution, with slight compromise of fairness. In addition, the coding aware subcarrier assignment mechanism can be applied to other multichannel wireless systems as well.