Efficient Sequence Detection of Multicarrier Transmissions over Doubly Dispersive Channels
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Efficient Sequence Detection of Multicarrier Transmissions over Doubly Dispersive Channels Sung-Jun Hwang and Philip Schniter Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH 43210, USA Received 2 June 2005; Revised 1 May 2006; Accepted 12 May 2006 We propose a high-spectral-efficiency multicarrier system for communication over the doubly dispersive (DD) channel which yields very low frame error rate (FER), with quadratic (in the frame length) receiver complexity. To accomplish this, we combine a non-(bi)orthogonal multicarrier modulation (MCM) scheme recently proposed by the authors with novel sequence detection (SD) and channel estimation (CE) algorithms. In particular, our MCM scheme allows us to accurately represent the DD channels otherwise complicated intercarrier interference (ICI) and intersymbol interference (ISI) response with a relatively small number of coefficients. The SD and CE algorithms then leverage this sparse ICI/ISI structure for low-complexity operation. Our SD algorithm combines a novel adaptive breadth-first search procedure with a new fast MMSE-GDFE preprocessor, while our CE algorithm uses a rank-reduced pilot-aided Wiener technique to estimate only the significant ICI/ISI coefficients. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
In wireless data communication, the information signal undergoes multipath propagation which, due to variations among path lengths, induces a time-domain spreading effect on the information signal. Furthermore, relative motion between the transmitter, receiver, and scattering objects imparts each path with a unique Doppler shift, so that multipath propagation also induces a frequency-domain spreading effect on the information signal. We refer to such channels as “doubly dispersive” (DD). Reliable high-spectral-efficiency communication over the DD channel is difficult. Consider that a sequence of N symbols transmitted over this channel will appear, to the receiver, as a complicated time-variant mixture corrupted by additive noise. The mixing may make it difficult to correctly infer the transmitted sequence, even when optimal maximum-likelihood (ML) sequence detection (SD) is used. Furthermore, the complexity of MLSD may be impractical. In general, communication over the DD channel is a compromise between spectral efficiency, frame error rate (FER), and implementation complexity. For example, by sacrificing spectral efficiency, one could transmit symbols separated far enough in time and/or frequency to avoid interference, thereby guaranteeing simple optimal reception. However, since low spectral efficiency cannot usually be tolerated, the properties of DD-induced interference play a fundamental role in communication performance and complexity.
We can identify two major approaches to the design of coherent communication schemes for the DD channel. In the so-called maximum-diversity linear precoding (MDLP) approach [1], linear modulation waveforms are designed to maximize the exploitable diversity at t
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