Frequency-Shift Zero-Forcing Time-Varying Equalization for Doubly Selective SIMO Channels
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Frequency-Shift Zero-Forcing Time-Varying Equalization for Doubly Selective SIMO Channels Francesco Verde Dipartimento di Ingegneria Elettronica e delle Telecomunicazioni, Universit`a degli Studi di Napoli Federico II, via Claudio 21, 80125 Napoli, Italy Received 1 June 2005; Revised 26 February 2006; Accepted 30 April 2006 This paper deals with the problem of designing linear time-varying (LTV) finite-impulse response zero-forcing (ZF) equalizers for time- and frequency-selective (so-called doubly selective) single-input multiple-output (SIMO) channels. Specifically, relying on a basis expansion model (BEM) of the rapidly time-varying channel impulse response, we derive the canonical frequency-domain representation of the minimal norm LTV-ZF equalizer, which allows one to implement it as a parallel bank of linear time-invariant filters having, as input signals, different frequency-shift (FRESH) versions of the received data. Moreover, on the basis of this FRESH representation, we propose a simple and effective low-complexity version of the minimal norm LTV-ZF equalizer and we discuss the relationships between the devised FRESH equalizers and a LTV-ZF equalizer recently proposed in the literature. The performance analysis, carried out by means of computer simulations, shows that the proposed FRESH-LTV-ZF equalizers significantly outperform their competitive alternative. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
1.
INTRODUCTION
In many wireless applications, such as high-speed Internet access, networking, digital audio, and video broadcasting, the increasing need to provide either high data-rate services for low-mobility users or low data-rate services for highmobility users has made Doppler spreading and intersymbol interference the main performance limiting factors. The design of low-complexity reliable detection strategies for wireless communication systems operating over timeand frequency-selective, so-called doubly selective, channels requires an accurate description of the time-varying behaviour of the transmission media. Several approaches for modeling finite-impulse response (FIR) linear time-varying (LTV) channels have been developed in the last decade (see [1] for a comprehensive review). Among all the others, deterministic basis expansion models (BEMs) [2–6] seem to be favoured for representing rapidly time-varying channels, since they offer well-structured parsimonious modeling of channel time variations. Specifically, BEMs allow one to express the channel impulse response as a superposition of time-varying complex exponentials with time-invariant coefficients. As pointed out in [1, 7], BEMs with complex exponentials approximate well the Jakes statistical model [8], which is widely adopted for simulating wireless communication channels.
Recently, relying on a BEM to represent doubly selective channels, serial and block FIR-LTV equalizers have been developed in [9], which are synthesized by resorting to both zero-forcing (ZF) and minimum mean-square error (MMSE) criteria. In parti
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