Performance of a Tree-Based Collision Resolution Algorithm in Cellular Systems with Smart Antennas

A smart antenna´s ability to simultaneously resolve more than one user on the same channel is exploited to help expedite the process of random access, especially for the reverse channel. However, use of a smart antenna requires frequent array adaptation, a difficult task in a random access environment. In papers H. Jin and Acampora (2005), we proposed and studied the SINR performance of a media access protocol intended for use with smart antennas. In this paper, we study the random access performance of the proposed protocol when a fast collision resolution algorithm is used. Found are the maximum achievable throughput and an upper bound on the expected delay. The impact of the number of antennas on the performance with both flat fading and frequency selective fading is studied. Topical results show significant improvement in throughput for systems with smart antennas. For example, when the fading is flat, the gain in maximum achievable throughput can be as large as 232% and 550% with four and eight antenna elements respectively. Even when severe frequency selective fading is present, there is a gain of 40% and 145% with four and eight antenna elements, respectively. We also show that dynamically adjusting the retransmission probability in the collision resolution process is not worthwhile since this extra complexity produces a gain of only about 6.2% in the best case