Discrete Multitone Modulation System Research Articles

An improved optimal channel shortening algorithm for DMT modulation systems

In Discrete Multi-Tone (DMT) modulation systems, the well-known technique to overcome the Inter-Carrier Interference (ICI)/Inter-Symbol Interference (ISI) caused by the inadequate Cyclic Prefix (CP) length is to use a Time-Domain Equalizer (TDE) at the receiver front-end. An algorithm used to calculate the coefficients of the optimal shortening Time Domain Equalizer (TDE) was given by Melsa. However, this algorithm requires that the length of the TDE must be smaller than or equal to the memory length of the target impulse response. This paper modifies this algorithm and makes it not only fit for calculating the coefficients of the TDE with arbitrary length, but also have a much less computational time.

A Rate Adaptive Bit-Loading Algorithm for In-Building Power-Line Communications Based on DMT-Modulated Systems

This paper deals with a variable rate discrete multitone modulation system for broadband power-line communications, based on the bit-loading algorithm proposed by Leke and Cioffi. In the proposed system a suitable least mean square channel estimator is considered, which is based on the insertion of a training sequence (TS). The proposed approach will be compared with the ideal channel estimates, showing its effectiveness. Moreover, different TS lengths will be compared. The system performance, expressed in terms of bit rate and bit-error rate, is derived by simulation with and without estimation errors. The propagation environment has been assumed as a frequency-selective multipath fading channel with additive colored Gaussian noise, according to the in-building networks model

Performance indicator for DMT systems with non perfect channel estimation

AbstractIn this letter, we analyse the bit error rate (BER) of a discrete multitone modulation system considering the channel estimation error for the frequency equalisation. After having established an approximate relation for the BER, we propose a simple performance indicator, which accounts for the channel estimation error, the power emitted and the noise level. In order to check the validity of the indicator, simulation has been performed. The results prove that it is more adapted to discrete multi‐tone modulation (DMT) systems than the classical mean squared channel estimation error (MSE), above all when the channel additive noise is coloured. Copyright © 2006 AEIT

Fast bit-loading algorithm for DMT systems

In this paper, a novel solution to bit-loading algorithm for Discrete MultiTone modulation (DMT) systems is proposed. Simulation results, using the carrier serving area (CSA) loops in an ADSL environment impaired by crosstalk, show that the proposed algorithm converges more rapidly than the Campello algorithm, which is the fast algorithm that can be efficiently implemented in practice among those proposed in the past.

Unification and evaluation of equalization structures and design algorithms for discrete multitone modulation systems

To ease equalization in a multicarrier system, a cyclic prefix (CP) is typically inserted between successive symbols. When the channel order exceeds the CP length, equalization can be accomplished via a time-domain equalizer (TEQ), which is a finite impulse response (FIR) filter. The TEQ is placed in cascade with the channel to produce an effective shortened impulse response. Alternatively, a bank of equalizers can remove the interference tone-by-tone. This paper presents a unified treatment of equalizer designs for multicarrier receivers, with an emphasis on discrete multitone systems. It is shown that almost all equalizer designs share a common mathematical framework based on the maximization of a product of generalized Rayleigh quotients. This framework is used to give an overview of existing designs (including an extensive literature survey), to apply a unified notation, and to present various common strategies to obtain a solution. Moreover, the unification emphasizes the differences between the methods, enabling a comparison of their advantages and disadvantages. In addition, 16 different equalizer structures and design procedures are compared in terms of computational complexity and achievable bit rate using synthetic and measured data.

Perfect discrete multitone modulation with optimal transceivers

Previously, discrete Fourier transform (DFT)-based discrete multitone modulation (DMT) systems have been widely applied to various applications. In this paper, we study a broader class of DMT systems using more general unitary matrices instead of DFT matrices. For this class, we show how to design optimal DMT systems over frequency-selective channels with colored noise. In addition, asymptotical performance of DFT-based and optimal DMT systems are studied and shown to be equivalent. However, for a moderate number of bands, the optimal DMT system offers significant gain over the DFT-based DMT system, as is demonstrated by examples.

Discrete multitone echo cancelation

Multicarrier transmission methods have long been known to optimize the performance of data transceivers on bandlimited communication channels. One form of multicarrier transmission, known as discrete multitone modulation (DMT), is particularly attractive for its ability to be implemented using efficient digital signal processing techniques. Given a basic DMT system, it is possible to increase the aggregate data rate with full-duplex transmission using echo cancelation. However, DMT echo cancelation at first appears difficult because of the computational complexity required in a straightforward implementation to cancel the cross-echoes produced by each carrier into every carrier. This paper presents high-speed echo cancelation techniques for full-duplex data transmission using DMT systems. The techniques estimate the echo with a method of fast convolution that combines a complex multiply per tone with a short convolution in the time domain. In addition, the frequency-domain update of the echo parameters consists of one complex multiply per tap. As a result, these techniques can achieve much lower complexity than that required by traditional single-carrier technique, such as the least mean square (LMS) algorithm. This approach has been implemented for asymmetric digital subscriber line (ADSL) applications.