DS-CDMA Receiver Based on a Five-Port Technology
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DS-CDMA Receiver Based on a Five-Port Technology Ivo Maljevi´c The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, Canada M5S 1A1 Email: [email protected]
Elvino S. Sousa The Edward S. Rogers Sr. Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON, Canada M5S 1A1 Email: [email protected] Received 29 February 2004; Revised 15 November 2004 High data rates, low-power consumption, and low complexity will be the most important parameters in the design of the nextgeneration 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. Keywords and phrases: five-port device, CDMA receiver, direct conversion, RAKE receiver.
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INTRODUCTION
When it comes to designing wireless receivers, issues of complexity and low-power consumption have become as important as achieving high performance. Besides the all-digital approach that addresses the performance issue, the old, yet improved, analog design approach is beginning to emerge. Hagenauer et al. [1] have demonstrated that it is possible to implement data detection, equalization, and decoding in analog VLSI circuits, resulting in a significant speed gain and lower power consumption. In an in-depth overview [2] of a low-power WCDMA system design, that also 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. Not surprisingly, a majority of work on lowpower consumption is focused on a correlator
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