The asynchronous technique for carrier acquisition coordination

In third-generation mobile systems cell dimensions will become lower and lower. So, on the one hand, an higher variance of the offered traffic per cell is expected and, on the other hand, the issue of reducing the signaling exchanges among base stations (BS´s) becomes very important. A solution to the above-mentioned problems is the implementation of a dynamic channel allocation (DCA) strategy with distributed control. The DCA strategy foresees that the assignment of the carriers to the various cells is dynamically rearranged on a real time basis, in order to track the traffic evolution in the various cells. The distributed control entails that carrier acquisitions (and releases) are made by the BS´s with minimal signaling exchanges. A fundamental problem of DCA strategies with distributed control concerns the coordination among BS´s in order to avoid conflicting acquisitions of a same carrier from two BS´s located at a distance lower than the reuse distance. This paper considers two techniques for performing the above-mentioned coordination: the synchronous technique and the asynchronous technique. Both 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 acquisition stimulus time and the actual acquisition time; such acquisition 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 delays than the synchronous one and thus attains better performance