EFFECTS OF USER MOBILITY ON THE CAPACITY OF A CDMA CELLULAR NETWORK

In the recent technical literature on cellular networks Code Division Multiple Access (CDMA) has received a large attention as a promising r adio interface access technique. Many studies are devoted to the capac ity evaluation of the radio interface adopting CDMA, but seemingly non e of them accounts for the variability of the user spatial density due to user mobility. This should be a concern especially in a microcellu lar environment, where it cannot be relied upon a significant spatial average over the radio coverage area of a Base Station. The major aim of this work is a preliminary assessment of the effects of ''bursty'' user mobility on the capacity of the CDMA radio interface. To this end , we introduce a user mobility model apt to describe large fluctuation s of the number of users in a radio cell area. A reference model of a CDMA network is used to evaluate the effects of user mobility on the c apacity for a wide range of the model parameters, by means of simulati ons accounting for shadowing, call attempt process, voice activity and antenna directivity and assuming perfect power control. We show that user mobility can remarkably affect the CDMA capacity, mainly because of the resulting highly bursty behaviour of self-noise. A simple traff ic control scheme is devised to increase the capacity of the CDMA netw ork, under a joint constraint on link availability, call blocking and call dropping probabilities. It is pointed out that the concepts intro duced in this paper are independent of the specific CDMA implementatio n, i.e. they hold for any asynchronous CDMA based cellular network.