EFFECTS OF DIVERSITY, POWER-CONTROL, AND BANDWIDTH ON THE CAPACITY OFMICROCELLULAR CDMA SYSTEMS

We evaluate the capacity and bandwidth efficiency of microcellular CDM A systems. Power control, multipath diversity, system bandwidth, and p ath loss exponent are seen to have major impact on the capacity. The C DMA system considered uses convolutional codes, orthogonal signaling, multipath/antenna diversity with noncoherent combining, and fast close d-loop power control on the uplink (portable-to-base) direction. On th e downlink (base-to-portable), convolutional codes, BPSK modulation wi th pilot-signal-assisted coherent reception, and multipath diversity a re employed. Both fast and slow power control are considered for the d ownlink. The capacity of the CDMA system is evaluated in a multicell e nvironment taking into account shadow fading, path loss, fast fading, and closed-loop power control. Fast power control on the downlink incr eases the capacity significantly. Capacity is also significantly impac ted by the path loss exponent. Narrowband CDMA (system bandwidth of 1. 25 MHz) requires artificial multipath generation on the downlink to ac hieve adequate capacity. For smaller path loss exponents, which are mo re likely in microcellular environments, artificial multipath diversit y of an order of as high as 4 may be needed. Wideband CDMA systems (10 MHz bandwidth) achieve greater efficiencies in terms of capacity per MHz.