DS-CDMA Receiver Based on a Five-Port Technology

Ivo Maljević,Elvino S Sousa

doi:10.1155/asp.2005.1628

Abstract

High data rates, low-power consumption, and low complexity will be the most important parameters in the design of the next-generation mobile terminals. In this paper we are introducing a new paradigm in the design of direct sequence spread spectrum receiver by combining analog and digital signal processing. The main difference with respect to the conventional all-digital receiver design approach is that the proposed mixed analog/digital processing results in a symbol rate sampling rather than the high-rate subchip sampling. Analog signal despreading is the key part of the proposed receiver solution, which is based on a five-port device, a passive RF square-law-type device. It is used to perform two important tasks at the same time, namely, the direct conversion and analog despreading. To achieve lower complexity, the proposed receiver uses rectangular instead of pulse-matched despreading at the cost of only a small performance degradation. Also, we propose a new noncoherent pseudonoise (PN) code tracking scheme based on error signal generated through the L1 norm. This results in comparable or even better PN code tracking performance than L2 norm circuitry, using less complex hardware. Further, we explore how this technology can be applied in the design of DS-CDMA RAKE receiver for mobile terminals. Depending on how the pilot signal is multiplexed, we propose two types of RAKE receivers. It is shown that under Rayleigh fading channel such receiver structures offer robustness and high performance, while maintaining the low complexity achievable through the five-port device.

Highlights

When it comes to designing wireless receivers, issues of complexity and low-power consumption have become as important as achieving high performance
In an in-depth overview [2] of a low-power WCDMA system design, that relies on analog processing, it has been shown that direct sequence is well suited for a multiple access system in terms of power consumption
We will show that it is possible to improve the performance of the RAKE receiver with a small number of fingers, by converting each conventional RAKE finger into three fractionally spaced fingers without changing the hardware structure of the receiver

Summary

Introduction

When it comes to designing wireless receivers, issues of complexity and low-power consumption have become as important as achieving high performance. In an in-depth overview [2] of a low-power WCDMA system design, that relies on analog processing, it has been shown that direct sequence is well suited for a multiple access system in terms of power consumption. It has been estimated [3] that more than 50% of the total processing power in DS-CDMA receivers is spent on despreading. An alternative approach for power consumption reduction has been introduced in [5], where power savings are achieved by reducing precision from 16-bit to a 10-bit data path, and by reducing the sampling rate from two to one sample per chip at the cost of a small performance degradation

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Conclusion