Channel adaptive scheduling for a wideband TDD/TCDMA wireless system under heterogeneous traffic conditions
In this paper we propose and investigate some channel adaptive scheduling algorithms for wideband time division duplexing/time and code division multiple access (TDD/TCDMA) air interfaces under heterogeneous traffic conditions. The particular case of the universal mobile telecommunication system (UMTS) standard is kept as a reference, but the concepts provided in this paper aim at being more general.The characteristics of the TDD/TCDMA transmission system (modulation, coding, spreading and despreading), the power control algorithm and a frequency selective fading channel are considered in our approach. These aspects make the paper more oriented to the assessment of the interactions between physical aspects (such as the power control mechanism, the fading rate, etc.) and the scheduling strategies than focused on the optimality of the scheduling algorithms themselves.We assess the advantage of scheduling the different services that can be offered to the system, characterized by different quality and delay requirements, taking both the service priority and the channel state into account. The methodology we apply is semi-analytical and allows the evaluation of the statistics of the error rate of data blocks and the average transmitted power per data unit, which is a measure of efficiency from the energy management point of view.The performance of the proposed scheduling algorithms is compared to a more traditional scheduling approach which takes only the priority of services into account, and it is shown that for the typical fading rates of the pedestrian (and indoor) environments our algorithms perform much better than those not based on channel adaptivity.