Time Sharing Policy in Wireless Networks for Variable Rate Transmission

For most of wireless services with variable rate transmission, both average rate and rate oscillation are important performance metrics. One often needs to decide how much rate oscillation the service can tolerate to obtain a higher average rate. Service satisfaction for each user is quantified by an increasing and concave utility function of instantaneous transmission rate. It is capable of facilitating the resource allocation with flexible combinations of average rate and rate oscillation. Particularly, we are interested in maximizing the time-average aggregate utility by scheduling user transmissions in a time-shared wireless network. A resource allocation policy is developed, namely, time sharing (TS), to exploit the concavity of utility function and the fluctuation of channel gain. This is formulated as a constrained convex optimization problem. Our analysis shows that in the TS policy the optimal scheduler allows multiple users with relatively better channel conditions to share a same time frame in an adaptive time-division manner. In addition, the more concave the utility function is, the higher the probability of time frame sharing is. An extension to quantized time sharing with limited channel feedback (QTSL) for practical systems is all studied. Simulation results show that, two to three bits of channel state information (CSI) are sufficient for the performance of QTSL scheme to approach that of the optimal TS policy when the number of time slots in a time frame is not less than the number of users, especially, in high SNR region.