THE ASYNCHRONOUS TECHNIQUE FOR CARRIER ACQUISITION COORDINATION

In third-generation mobile systems cell dimensions will become lower a nd lower, So, on the one hand, an higher variance of the offered traff ic per cell is expected and, on the other hand, the issue of reducing the signaling exchanges among base stations (BS's) becomes very import ant, A solution to the above-mentioned problems is the implementation of a dynamic channel allocation (DCA) strategy with distributed contro l, The DCA strategy foresees that the assignment of the carriers to th e various cells is dynamically rearranged on a real time basis, in ord er to track the traffic evolution in the various cells, The distribute d control entails that carrier acquisitions (and releases) are made by the BS's with minimal signaling exchanges. A fundamental problem of D CA strategies with distributed control concerns the coordination among BS's in order to avoid conflicting acquisitions of a same carrier fro m two BS's located at a distance lower than the reuse distance. This p aper considers two techniques for performing the above-mentioned coord ination: the synchronous technique and the asynchronous technique, Bot h techniques are suitable for being applied in a possible evolution of the pan-European global system for mobile communications (GSM). These techniques base on the presence of an acquisition delay between the a cquisition stimulus time and the actual acquisition time; such an acqu isition delay permits coordination among BS's, but worsens performance in terms of blocking and dropping probabilities, It is shown that, in most cases, the asynchronous technique entails shorter acquisition de lays than the synchronous one and thus attains better performance.