Orthogonal Frequency Division Multiple Access

Abstract: Adaptive resource allocation can drastically increase the throughput of an Orthogonal Frequency Division Multiple Access (OFDMA) system when the Channel State Information (CSI) is accurately known. Unfortunately, in practice, perfect CSI is rarely possible. In this paper, we study the efficiency of the OFDMA downlink for different vehicular user densities. In order to do so we assume that the transmitter knows the instantaneous CSI (ICSI) of the pedestrian users but only the statistical CSI (SCSI) of the users that exhibit high mobility (vehicular). We then address the problem of maximizing the sum-capacity of the system subject to user minimum Quality of Service (QoS) requirements. It is shown that when only the user SCSI is known loading channels with a rate equal to the Lambert W function of the average SNR leads to optimal channel utilization and important system throughput gains. Moreover, the impact of different channel models on the system throughput is investigated. The results show that the vehicular users can highly benefit from adaptive resource allocation under the assumption that their CSI is known by the transmitter