Equivalence of Linear MMSE Detection in DS-CDMA and MC-CDMA Systems over Time and Frequency Selective Channels

Tamer A Kadous,Akbar M Sayeed

doi:10.1155/s1110865702209099

Abstract

The goal of this paper is to compare the performance of the linear minimum mean square error (MMSE) detector for a class of code division multiple access (CDMA) systems in time and frequency selective channels. Specifically, we consider direct sequence (DS)-CDMA, multicarrier (MC)-CDMA, and the MC-DS-CDMA systems. Two key tools are used in our development. First, a general time-frequency framework that includes the different CDMA systems as special cases. Second, the duality between time and frequency domains that is used to derive equivalences between the different CDMA systems operating over purely frequency selective and purely time selective channels. We then combine the insights obtained from these special cases to assess the performance of CDMA systems over time and frequency selective channels. We provide sufficient conditions for the codes employed by the CDMA systems for the equivalences to hold. Numerical results are presented to illustrate the results.

Highlights

code division multiple access (CDMA) has emerged as a promising wireless technology for meeting the physical layer challenges of modern communication networks
We show the near identical performance of the different CDMA systems when using the sufficient conditions in Propositions 1, 2, and 3 even after relaxing the assumptions used in their proofs
We have studied linear minimum mean square error (MMSE) multiuser detection for a class of CDMA systems in frequency selective (FS), time selective (TS), and time and frequency selective (TFS) channels

Summary

Introduction

CDMA has emerged as a promising wireless technology for meeting the physical layer challenges of modern communication networks. The signature code is transmitted over a set of basis waveforms, each of which has a duration To and essential two-sided bandwidth Bo. The different signaling schemes differ in how To and Bo are chosen. In MC-CDMA [2, 3, 4], the basis waveforms are generated via frequency shifts of a narrowband pulse with duration To = T and bandwidth Bo = B/N. The transmitter and the distributions of signature code in time and frequency domains for this system are shown in Figures 1b and 2b, respectively. The basis functions are generated via the time-frequency shifts of a pulse of duration To = T/Nt and bandwidth Bo = B/N f. The MC-DS-CDMA transmitter and the distributions of signature code in time and frequency domains are shown in Figures 1c and 2c, respectively

Objectives

Results

Conclusion