MMSE Multiuser Receiver for Uniformly Quantized Synchronous CDMA Signals in AWGN Channels

We analyze and design the minimum mean-square error (MMSE) multiuser receiver for uniformly quantized synchronous code division multiple access (CDMA) signals in additive white Gaussian noise (AWGN) channels. The input-output relationship of the quantizer is represented by the gain-plus-additive-noise model. Based on this model, we derive the weight vector and the output signal-to-interference ratio (SIR) of the MMSE receiver. The effects of quantization on the MMSE receiver performance is characterized in a single parameter named "equivalent noise variance" which is a function of the sum of each active user's signal-to-noise ratio (SNR), processing gain, and the number of quantization levels. The optimal quantizer stepsize which maximizes the MMSE receiver output SNR is also determined. Simulation results validate the accuracy of our analysis.