Abstract
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.
Highlights
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 [1,2,3,4,5,6]
A criterion that balances between intersymbol interference (ISI) plus intercarrier interference (ICI) and the stopband attenuation was proposed for designing NPR prototype filters for cosine-modulated multitone (CMT)
CMT was compared with zipper discrete multitone (z-discrete multitone (DMT)) and filtered multitone (FMT), the two candidate modulation schemes for very-high-speed digital subscriber lines (VDSLs) [16]
Summary
Multicarrier modulation (MCM) has attracted considerable attention as a practical and viable technology for high-speed data transmission over spectrally shaped noisy channels [1,2,3,4,5,6]. In order to avoid interference among various subcarriers, FMT adopts a filter bank with very sharp transition bands and allocates sufficient excess bandwidth, typically in the range from 0.05 to 0.125 This introduces significant intersymbol interference (ISI) that is dealt with by using a separate decision feedback equalizer (DFE) for each subcarrier [23]. In DWMT, it is proposed that channel equalization in each subcarrier be performed by combining the signals from the desired band and its adjacent bands These equalizers that have been referred to as postcombiner equalizers impose significant load on the computational complexity of the receiver. In [36], a receiver structure that combines signals from a CMFB and a sine-modulated filter bank (SMFB) is proposed to avoid cross-filters.
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