TABLE OF CONTENTS The isolated CDMA cell capacity derived in Chapter 1 assumes only a single cell and ignores the interference from users in neighboring cells. The capacity of an isolated cell in a narrowband system would also be very high since a reuse factor of one can be employed and all channels can be assigned in the 1.25-MHz bandwidth. In fact, CDMA makes a big difference when the impact of neighboring cells is taken into account. Let us rewrite the isolated cell pole capacity given by
in which the interference was averaged only over the users in the same cell. To quantify the potential improvements of smart antennas in CDMA systems the characteristics of the interference must be understood. On the downlink, several base stations are radiating and a mobile unit suffers from interference from other cells as well as from its home cell. On the uplink of a direct sequence CDMA system, the capacity is related to the E b /N t, as was shown in Chapter 1. If E b /N t is too low, the frame error rate (FER) or BLER will be high and the system performance will degrade. If E b /N t is too high, the interference level will increase and this will decrease the reverse link capacity. In TDMA and GSM systems, for every time slot there is one desired signal and a very small number of cochannel interferers, which makes the application of...
