Optimum DMT-based transceivers for multiuser communications

European Transactions on Telecommunications, 2006

In 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.

2003

The design of optimal DMT transceivers for distorted channel with colored noise has been of great interest. Of particular interest is the class of block based DMT (BDMT), where the transmitter and the receiver consist of constant matrices. For a given channel and channel noise spectrum, the optimal DBMT transceiver that minimizes the transmission power for a fixed probability of error and transmission rate will be derived. The optimal biorthogonal transmitter is in fact orthogonal. That is, there is no loss of generality in using the orthogonal transmitter for the design optimal BDMT.

IEEE Transactions on Signal Processing, 2008

IEEE Transactions on Communications, 2005

This letter presents a new bit-loading algorithm for discrete multitone systems that converges faster to the same bit allocation as the optimal discrete bit-filling and bit-removal methods. The algorithm exploits the differences between the subchannel gain-to-noise ratios in order to determine an initial bit allocation and then performs a multiple-bits loading procedure for achieving the requested target rate. Numerical results using asymmetric digital subscriber test loops demonstrate the computational efficiency of the proposed algorithm.

IEEE Transactions on Signal Processing, 2005

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.

2017 25th European Signal Processing Conference (EUSIPCO), 2017

In discrete multitone (DMT) modulation systems, the channel duration can be longer than the cyclic prefix, yielding both inter-block and inter-carrier interference. In order to avoid these effects, time-domain equalization (TEQ) techniques are usually employed before DMT demodulation. This letter introduces a modification of the iterative minimum delay spread (MDS) method proposed by Lopez-Valcarce in [1] to adapt the TEQ coefficients to the channel. The proposed solution is based on a) the approximation to the solution of a set of equation, and b) a new reference time selection. The resulting scheme requires only a single matrix inversion at the last iteration rather than one per iteration, achieving a significantly lower implementation complexity than iterative MDS, while performing similarly in terms of spectral efficiency.

2011

This article presents a new time domain equaliser (TEQ), which can be used in discrete multi-tone (DMT) systems to maximise the bit rate. The proposed TEQ is tested in the fast Fourier transform based discrete multi-tone (FFT-DMT) system, and in a proposed discrete cosine transform based discrete multi-tone (DCT-DMT) system. The objective of the proposed DCT-DMT system is to make use of the energy compaction property of the DCT to reduce the channel effects on the transmitted signals. A mathematical model of the proposed TEQ is presented. Simulation experiments have been carried out to test the effect of the proposed TEQ with the FFT-DMT system and the proposed DCT-DMT system. The results show that the performance of the DCT-DMT system with the proposed TEQ is better than the FFT-DMT system with this TEQ over the eight standard carrier serving area (CSA). The results also show that employing the proposed TEQ in the DCT-DMT system can achieve a high bit rate, ranging from 2.899 Mbps to 5.369 Mbps.

Wireless Communications and Mobile Computing, 2006

The performance of a DMT system, which transmits information over channels with varying characteristics through the frequency zones, is improved when the subchannels of the system are loaded with variable data rate. In this study, we meet the bit loading problem of the subcarriers of a DMT system. We propose two new optimumloading algorithms with low computational complexity. These algorithms assign integer number of bits successively until a target bit rate is fulfilled. We compare them with several existing algorithms in terms of transmitting energy versus data rate and complexity versus system's characteristics i.e. number of subcarriers and target data rate. Simulations prove that without sacrificing optimality both our proposals present a lower complexity level.

IEEE Transactions on Communications, 2000

This letter first reviews the multiuser bit-loading algorithms for discrete multitone systems. Then an improved algorithm is proposed, which allows several users to get additional bits in parallel. It reduces the number of iterations dramatically. A new fairness coefficient is also introduced to reduce the variance of the data rate among users.