Optimal transmission scheduling with base station antenna array in cellular networks

We study the downlink scheduling problem in a cellular wireless network. The base stations are equipped with antenna arrays and can transmit to more than one mobile user at any time instant, provided the users are spatially separable. In previous work, an infinite traffic demand model is used to study the physical layer beamforming and power control algorithms that maximize the system throughput. In this paper we consider finite user traffic demands. A scheduling policy makes a decision based on both the queue lengths and the spatial separability of the users. The objective of the scheduling algorithm is to maintain the stability of the system. We derive an optimal scheduling policy that maintains the stability of the system if it is stable under any scheduling policy. However, this optimal scheduling policy is exponentially complex in the number of users which renders it impractical. We propose four heuristic scheduling algorithms that have polynomial complexity. The first two algorithms are for the special case of single cell systems, while the other two algorithms deal with multiple cell systems. Using a realistic multipath wireless channel model, we evaluate the performance of the proposed algorithms through computer simulations. The results demonstrate the benefits of joint consideration of queue length and dynamic base station assignment