Power allocation and spectral efficiency in multirate DS-CDMA systems without channel state information at transmitters

Power allocation and spectral efficiency of multirate and single code (SC) direct-sequence code division multiple access (DS-CDMA) systems without channel state information at transmitters in frequency flat fading channels are discussed. An explicit expression is found for the optimal power allocation under some mild assumption. An interference cancelling and minimum-mean-square-error detection scheme is shown to achieve the optimal power consumption. Spectral efficiencies of both SC and multiple code (MC) schemes are obtained, and numerical results show that MC outperforms SC due to the former's utilization of user diversity.