Optimal Allocation of Bandwidth and Power Resources to OFDMA VoIP Channels

The fourth generation of wireless networks will all use OFDMA (orthogonal frequency domain multiple access) technology. In the forward link of an OFDMA network, each traffic and control channel within a frame must be allocated power, bandwidth (number of subcarriers) and time (number of OFDMA symbols) resources. This flexibility is one of the advantages of OFDMA but requires more sophisticated resource management than third generation networks. In this paper we focus on the power and bandwidth allocation problems for the downlink. The power allocated to a channel can be varied continuously however the bandwidth allocation must be provided in discrete units (number of subcarriers). For some applications, such as voice over IP (VoIP), the bandwidth allocation is fixed and closed loop power control is used to maintain the required frame error rate (FER). In this paper we demonstrate that by varying resources in the bandwidth dimension in addition to the power dimension one can increase the efficiency of the system. We demonstrate the gains through illustrative examples and propose a practical algorithm for achieving these gains