Capacity of DS/CDMA system under multipath fading with different adaptive rate adaptive power schemes

This paper investigates capacity of CDMA system employing adaptive transmission technique under multipath fading channel. Three power control schemes with rate adaptive capability are proposed to exploit the time variation of channel fading. In all the three schemes, adaptive transmission employing BPSK is realized through adapting the processing gain (PG) to the channel conditions. A minimum PG constraint is made to ensure multiple access capability. When PG is at this minimum value, the system can have an option to adjust the transmission rate through using higher constellation QAM. For scheme 1, system capacity rather than the lower bound reported in [Kim, S.W., 1999] is obtained. System capacities for scheme 2 and 3 are analyzed and computed using numerical calculations. Our numerical results show that the proposed power control schemes 2 and 3 can obtain higher system capacities than that of ideal constant received power at the base station, for a given constant average transmission power per user.