Capacity Bounds of Finite Dimensional CDMA Systems with Fading/Near-Far Effects and Power Control

TL;DR

This paper analyzes the capacity of finite-dimensional CDMA systems under fading and near-far effects, showing that power knowledge improves capacity and traditional power control offers no asymptotic benefit, with bounds derived for imperfect power estimation.

Contribution

It introduces bounds on CDMA sum capacity considering fading and near-far effects, highlighting the limited impact of power control and providing methods for capacity estimation with imperfect power knowledge.

Findings

Knowledge of power variations improves sum capacity.

Traditional power control does not enhance asymptotic capacity.

Bounds are numerically evaluated for special cases.

Abstract

This paper deals with fading and/or near-far effects with or without power control on the evaluation of the sum capacity of finite dimensional Code Division Multiple Access (CDMA) systems for binary and finite nonbinary inputs and signature matrices. Important results of this paper are that the knowledge of the received power variations due to input power differences, fading and/or near-far effects can significantly improve the sum capacity. Also traditional power controls can not improve the sum capacity; for the asymptotic case, any type of power control on the near-far effects is equivalent to the case without any power control. Moreover, for the asymptotic case, we have developed a method that determines bounds for the fading/near-far sum capacity with imperfect power estimation from the actual sum capacity of a CDMA system with perfect power estimation. To show the power and utility of the results, a number of sum capacity bounds for special cases are numerically evaluated.