Effects of cell distance on capacity of two-tier cellular networks

Two well known methods to increase the capacity in a cellular network, TDMA and CDMA, are evaluated on a two-tier cellular structure. In order to use the network resources preciously, we consider sharing the available spectrum effectively between these tiers. We investigate two models, called System I and System II. In System I, CDMA access methods are employed in both layers. In System II, TDMA is deployed for users in the microcell tier and CDMA for macrocell users. The results of numerical calculations are presented. The impact of interference caused by different distances among the related cells is assessed. It is shown that the capacity of the above systems is decreased as the distance of related cells becomes closer. The characteristics showing that System I is better than System II in terms of user capacity, can be recognized for various values of cell distances