The Influence of Adaptive Multicoding on Mutual Information and Channel Capacity for Uncertain Wideband CDMA Rayleigh Fading Channels

TL;DR

This paper investigates how adaptive multicoding influences mutual information and channel capacity in uncertain wideband CDMA Rayleigh fading channels with imperfect CSI, providing bounds and approximations for system performance analysis.

Contribution

It introduces new bounds and approximations for mutual information considering multicoding and channel uncertainty in wideband CDMA Rayleigh fading channels.

Findings

Mutual information depends on signal subspace dimension and symbol distribution.

Bounds are explicitly expressed in terms of channel and system parameters.

Analysis quantifies the impact of signal dimension and estimation error on performance.

Abstract

We consider the problem of adaptive modulation for wideband DS-CDMA Rayleigh fading channels with imperfect channel state information (CSI). We assume a multidimensional signal subspace spanned by a collection of random spreading codes (multicoding) and study the effects of both the subspace dimension and the probability distribution of the transmitted symbols on the mutual information between the channel input and output in the presence of uncertainty regarding the true state of the channel. We develop approximations for the mutual information as well as both upper and lower bounds on the mutual information that are stated explicitly in terms of the dimension of the signal constellation, the number of resolvable fading paths on the channel, the current estimate of channel state, and the mean-squared-error of the channel estimate. We analyze these approximations and bounds in order to quantify the impact of signal dimension and symbol distribution on system performance.