Cosine-Modulated Multitone for Very-High-Speed Digital Subscriber Lines
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Cosine-Modulated Multitone for Very-High-Speed Digital Subscriber Lines Lekun Lin and Behrouz Farhang-Boroujeny Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT 84112-9206, USA Received 17 November 2004; Revised 24 June 2005; Accepted 22 July 2005 In this paper, the use of cosine-modulated filter banks (CMFBs) for multicarrier modulation in the application of very-high-speed digital subscriber lines (VDSLs) is studied. We refer to this modulation technique as cosine-modulated multitone (CMT). CMT has the same transmitter structure as discrete wavelet multitone (DWMT). However, the receiver structure in CMT is different from its DWMT counterpart. DWMT uses linear combiner equalizers, which typically have more than 20 taps per subcarrier. CMT, on the other hand, adopts a receiver structure that uses only two taps per subcarrier for equalization. This paper has the following contributions. (i) A modification that reduces the computational complexity of the receiver structure of CMT is proposed. (ii) Although traditionally CMFBs are designed to satisfy perfect-reconstruction (PR) property, in transmultiplexing applications, the presence of channel destroys the PR property of the filter bank, and thus other criteria of filter design should be adopted. We propose one such method. (iii) Through extensive computer simulations, we compare CMT with zipper discrete multitone (z-DMT) and filtered multitone (FMT), the two modulation techniques that have been included in the VDSL draft standard. Comparisons are made in terms of computational complexity, transmission latency, achievable bit rate, and resistance to radio ingress noise. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
1.
INTRODUCTION
In recent years, multicarrier modulation (MCM) has attracted considerable attention as a practical and viable technology for high-speed data transmission over spectrally shaped noisy channels [1–6]. The most popular MCM technique uses the properties of the discrete Fourier transform (DFT) in an elegant way so as to achieve a computationally efficient realization. Cyclic prefix (CP) samples are added to each block of data to resolve and compensate for channel distortion. This modulation technique has been accepted by standardization bodies in both wired (digital subscriber lines—DSL) [7–10] and wireless [11, 12] channels. While the terminology discrete multitone (DMT) is used in the DSL literature to refer to this MCM technique, in wireless applications, the terminology orthogonal frequency-division multiplexing (OFDM) has been adopted. The difference is that in DSL applications, MCM signals are transmitted at baseband, while in wireless applications, MCM signals are upconverted to a radio frequency (RF) band for transmission. Zipper DMT (z-DMT) is the latest version of DMT that has been proposed as an effective frequency-division duplexing (FDD) method for very-high-speed DSL (VDSL) applications. Two variations of z-DMT have been proposed:
(i) synchronous zipper [13, 14] and (i
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