Analysis and minimization of loss of process gain with A/D conversion in DS-CDMA

This paper presents an analytical equation to estimate the process gain actually derived in the despreading process in DS-CDMA systems. The A/D converter (ADC) generates quantization and saturation noise, which reduces the process gain. The probability density function (PDF) of the ADC output is analytically expressed so that the PDF of the quantized and despread signal is shown. Then the SNR of the despread signal is obtained as the ratio of the expectation and the variance given by the PDF. Further by using the analytical equation, the optimum reference value of the AGC can be obtained without numerous computer simulations. In the wideband-CDMA system, the optimum reference value of the AGC is accurately estimated, which is confirmed in the computer simulation.