Online Frequency Reassignment for New and Drop Calls in Wireless Cellular Networks

Online frequency assignment for wireless cellular networks is one of the important research areas in recent time, where the geographical coverage area is divided into regular hexagonal regions called cells. Sequence of requests arrives over time to the cells that are headed by the base stations. Each of the requests is either a new call or a drop-call which is served by the base station by assigning the frequencies or releasing the frequencies respectively. In order to minimize the span of frequencies use to serve all the requests for new calls originating from same or neighboring cells, reassignment of the frequency of the dropped-call is done to an already existing call that uses the highest frequency. For χ-colorable networks, which are the generalization of the (3-colorable) cellular networks, we have suggested an efficient online algorithm for frequency reassignment, minimizing the span of frequency usages. The competitive ratio of the proposed online algorithm is (χ+1)/3, which is sharper than the competitive ratio (χ+1)/2 of existing similar problem without allowing reassignment of frequency. The optimality of the new algorithm is verified by finding the absolute lower and upper bounds of its competitive ratio for 3-colrable cellular network as a particular case when χ = 3.