Polling based media access protocols for use with smart adaptive array antennas

The use of an adaptive antenna array at each base station of a wireless network can provide substantial immunity to the effects of multipath fading and co-channel interference. Among the expected benefits are higher data rates, greater frequency re-use factor, and, overall, higher capacity systems as needed to enable wireless multimedia services. Media access control (MAC) protocols which facilitate the deployment of such an array have been previously proposed and studied. These MAC protocols invoke the delivery of a pilot tone from each packet access unit in the network as needed, so that the array antenna at the associated base station may rapidly adjust its weighting coefficients, thereby ensuring subsequent reliable communication between the access unit and the base station. This paper considers two modifications to these earlier protocols with the intent of improving the utilization efficiency and mean delay performance. A more general traffic model is considered and reasonable approximations are invoked to study the performance of the modified protocol. It is shown that with the proposed modifications, a maximum link utilization efficiency of about 97% is readily achieved. Further, it is shown that this maximum utilization efficiency is independent of the number of remote users in the network. The modifications also help in achieving a considerable reduction in the average delay in low load regimes. For typical system parameters, results show that at very low loads, the average delay is only about 10% of the average delay experienced when the old protocol is used