Power allocation and spectral efficiency of DS-CDMA systems in fading channels with fixed QoS-part II: multiple-rate case

Power allocation results for equal-rate systems developed in Part I are extended to multiple-rate systems. For both systems with and without channel state information at the transmitter (CSIT), conditions for the optimality of successive interference cancellation combined with minimum mean square error multiuser detection (SIC+MMSE) are obtained. When CSIT is available, the optimal decoding order is discussed for optimal SIC+MMSE and two sub-optimal decoding schemes. Explicit expressions for the spectral efficiency parameters in the low or high energy regions are also obtained.