Tradeoff between source coding and spreading in a multicarrier DS-CDMA system operating over multipath fading channels with narrow-band interference

Abstract

Abstruct-For a fixed total bandwidth expansion factor, and for a fixed channel code rate, we consider the probIem of optimal bandwidth allocation between the source coder and the spreadspectrum unit €or a multicarrier direct-sequence CDMA system operating over a frequency-selective fading channel with narrowband interference. Assuming a Gaussian source with the optimum smlar quantizer and a binary convolutional code with softdecision decoding, we obtain both a lower and an upper bound on the end-to-end average source distortion. The o p t i d bandwidth allocation is then numerically computed by minimixing upper and lower bounds on the average distortion. We show that the upper bound based cost function is a convex function of the source code rate, and the optimal allocation depends on the system and the channel conditions, such as the total number of active users, the number of carriers, and the average jammer-tosignal power ratio.