The throughput of adaptive spread spectrum communication over multipath dispersive channels

Abstract

We use analysis and simulation to investigate the downlink data rate of a wideband CDMA system, wherein the rate is adaptively varied based on the condition of the multipath fading channel. We use a previously published set of formulas for estimating output signal-to-distortion ratio which, in turn, permits us to compute the instantaneous allowed data rate per user for any fading channel response for three adaptive receivers. In addition, we use a previously published statistical model for path gain and delay spread to simulate a random population of downlink user terminals, including an ensemble of instantaneous channel responses for each. The result for each kind of receiver is a probability distribution, taken over the environment, of the multipath-averaged downlink data rate. We call the average of each such distribution the cell-averaged data rate (CADR), which we quantify for a variety of conditions (channel parameters, receiver type, cellular architecture). Our results demonstrate the superiority of the adaptive minimum mean square error (MMSE) receiver over the matched filter (MF) receiver, in terms of both data rate and robustness to the multipath parameters (e.g., median delay spread, delay profile shape). They also demonstrate the benefits against multipath fading of cell site diversity and the reductions in throughput due to multicell interference.