Jointly optimized bit-rate/delay control policy for wireless packet networks with fading channels

In this paper, we consider the downlink rate control problem in a wireless channel. A dynamic programming optimization method is introduced to obtain the optimal bit-rate/delay control policy in the downlink for packet transmission in wireless networks with fading channels. We assume that the base station is capable of transmitting data packets in the downlink with different bit rates, R-0 < R-1 <... < RM-1. It is assumed that the symbol rate is fixed in the system, and different bit rates are achieved by choosing the transmitted symbols from the appropriate signal constellation (adaptive modulation). The derived optimal rate control policy, in each time slot, selects the highest possible bit rate which minimizes the delay and at the same time minimizes the number of rate switchings in the network. The optimal bit-rate control problem is an important issue, especially in packet data networks, where we need to guarantee a quality of service (QoS) in the network. Our analytical as well as simulation results confirm that there is an optimal threshold policy to switch between different rates.