Downlink flow control for wireless CDMA packet data networks

Abstract

We consider the control of downlink packet flow at the base stations of code-division multiple-access (CDMA) wireless networks in the presence of in-cell transmission power and out-of-cell interference limitations. The objective is to maximize data throughput while ensuring fairness among users and limiting queuing and transmission delays. The algorithm proposed assigns the packets to be transmitted to separate queues, one for each spatial zone within which packets require roughly equal resources from the target cell and impose equal interference on a neighbor cell. Packets are selected for transmission from the head of each queue until available resources for the slot interval are exhausted. Queues from which transmission would cause excessive out-of-cell interference are blocked. Fairness can be ensured by minimizing the delay variance for the remaining head-of-queue packets. We provide results for tradeoffs between throughput and fairness for constant and time-varying resource availability. Throughput drops significantly when fairness to distant mobiles is required.