Scheduling real-time traffic in wireless networks

This dissertation concerns the problem of scheduling real-time traffic in wireless TDMA channels. The most important characteristic of real-time traffic is that it has straight end-to-end delay constraint. We begin the investigation by studying a scheduling principle which naturally achieves the best delay performance in stationary channel conditions. Since the resulting scheduling algorithm maintains equal flow delays across the whole system, it is termed the equal-delay policy. There are a number of advantages associated with this scheduling method. First, it is very simple and practical to implement in real system. Secondly, it can be easily modelled mathematically and admits an analytical solution, which is very important for the construction of an admission control algorithm, we present a mathematical model describing the dynamics of the scheduling system, as well as devising a tractable analytical solution to the problem.A third advantage of the equal-delay policy is that it can be easily extended to support flows with multiple delay constraints. We propose a multiple-class scheduling scheme based on similar allocation concepts as the equal-delay technique. The extended scheme can similarly be mathematically modelled and analytically characterized.A natural objection to the above proposed techniques is that wireless transmission resources can be under-utilized, since the scheduling algorithm pays no attention to the changing individual channel conditions. The reduction in channel utilization can also adversely affect the delay performance, We explain this phenomenon and study the impacts for a variety of different channel characteristics, Specifically, we propose an alternative channel-aware scheduling policy, which aims to maximize channel utilization while keeping a minimum probability of delay violation, The proposed channel-aware policy achieves near-optimal delay performance. However, unlike in the equal-delay case, the channel-aware policy is not practical to implement in a real system. The complicated system dynamics associated with the channel-aware scheme also hamper the development of a mathematical model and analytical solution for admission control.On the other hand, we observe from simulation results that under most circumstances, the equal-delay scheme achieves close to the pertonnance obtained by the channel-aware technique, With the additional benefits of simplicity and admitting analytical analysis. the equal-delay policy appears to be a more practical and suitable choice for scheduling real-time traffic in wireless networks