Balanced allocation strategy in multi-user OFDM with channel state information at the transmitter

Multi-user systems based on OFDM are frequently used in powerline or quasi-static wideband wireless channels. Typical scenarios assume that precise channel state information can reasonably be obtained at the transmitter and at the receiver. In downlink, a spectral mask constraint is usually imposed too. In such previous context, we assume two multiple access schemes, MC-DS-CDMA and a simpler OFDMA, and we investigate their achievable-rate regions. In particular, we study the so-called "balanced rate criterion", in order to select a point of the achievable-rate region which guarantees fairness between all the active users. We propose a simplified algorithm to calculate an approximate balanced rate solution for the OFDMA case. The loss of the OFDMA solution with respect to the MC-DS-CDMA solution is shown to be acceptable. Comparisons with other OFDMA allocation algorithms have also been reported.