Nelson L. Esteves

On frequency-domain equalization and diversity combining for broadband wireless communications

This paper is concerned with the use of frequency-domain equalization (FDE) and space diversity within block transmission schemes for broadband wireless communications. The expected performance with both multicarrier (MC) and single-carrier (SC) modulations is emphasized, when a cyclic prefix, long enough to cope with the maximum relative channel delay, is appended to each transmitted block. A set of numerical results is presented and discussed, with the help of appropriate, analytical performance bounds which are conditional on a given channel realization. These bounds are used to explain the performance advantage of the SC/FDE option, the benefits of space diversity, and the impact of the criterion for computing the FDE parameters.

A Turbo FDE Technique for Reduced-CP SC-Based Block Transmission Systems

For conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP is recommendable, since it allows good performances through the use of simple frequency-domain equalization (FDE) techniques. In this letter, a soft-decision-directed correction (SDDC)-aided turbo FDE technique is presented for reduced-CP SC-based block transmission systems using conventional frame structures. The relations with some already known iterative FDE techniques are established, and a set of performance results is reported and discussed. The advantages of the proposed approach are emphasized, namely, the possibility of approximately achieving (besides the obvious bandwidth efficiency gain) the maximum power efficiency gain that a strong CP reduction allows

Adaptive HARQ schemes using punctured RS codes for ATM-compatible broadband wireless communications

This paper considers the use of an adaptive error control, based on punctured Reed-Solomon codes, for an ATM-compatible mobile broadband system. Several alternative HARQ schemes are considered and their performance is evaluated through a semi-analytical method which resorts to an appropriate signal flow graph technique. A set of performance results is presented and discussed.

IIR echo canceller using a dual error criterion and incorporating a lattice structure

Abstract A new recursive echo cancellor (EC) for data transmission is proposed, where the output-error criterion and the equation-error criterion are used simultaneously. The combination of these two error criteria allows a fast initial convergence and leads to error surfaces with a single (global) minimum corresponding to unbiased parameter estimates, provided that the EC structure is not underspecified. The proposed EC includes an all-pole lattice structure, which greatly simplifies the control of the poles position to ensure stability. The transversal-to-lattice conversion is used to update the reflection coefficients, but the total amount of signal processing is reduced, because those coefficients need not be updated at every iteration. The results of a computer simulation show that the new echo canceller, when compared to commonly used conventional structures, can give a better performance.

An adaptive IIR echo canceller combining output-error and equation-error criteria

An echo canceller structure which permits the combined use of the equation error and the output error criteria in the adaptation of the coefficients is presented. A method is described for the smooth transition between the two criteria in such a way that the advantages of both are retained and their drawbacks are eliminated. Further improvement is obtained by using lattice structures in the realization of some of the cancellers blocks. Computer simulation results are presented which confirm the superior performance of the echo canceller with respect to other realizations.<<ETX>>

New IIR echo canceller using a dual error criterion and lattice structures

An adaptive IIR echo canceller for data transmission is presented, where the output-error criterion and the equation-error criterion are used simultaneously. The combined use of these two error criteria provides a fast initial convergence and leads to unbiased parameter estimates, even in the presence of noise. The poles of the echo path transfer function are modelled by means of lattice structures, which greatly simplifies the stability monitoring. The performance of the proposed echo canceller, as updated by LMS-type algorithms, is evaluated by computer simulation.