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The digital Laguerre network has been studied as a means of implementing filters with a much smaller number of coefficients compared to Finite Impulse Response (FIR) filters. This paper considers the selection of the optimum pole for the Laguerre network. We propose a new effective algorithm for solving the optimum pole selection problem. Simulation results are presented, and comparison between the Laguerre structure and FIR filter structure are given.

The difference routing digital filter (DRDF) consists of an FIR filter followed by a first-order integrator. This structure with power-of-two coefficients has been studied as a means of achieving low complexity, high sampling rate filters which can be implemented efficiently in hardware. The optimisation of the coefficients has previously been based on a time-domain least-squares error criterion. A new design method is proposed that includes a frequency-domain least-squares criterion with arbitrary frequency weighting and an improved method for handling quantisation of the filter coefficients. Simulation studies show that the new approach yields an improvement of up to 7 dB over existing methods and that oversampling can be used to improve performance.

This paper presents a new normalized frequency domain approach for adaptive blind equalization for multiple-input multiple-output (MIMO) communication systems. We first develop a time domain block based algorithm that updates the equalizer coefficients once per block of data symbols. As the time domain algorithm involves infinite summations in the separation cost function, an approximation is then proposed to reduce the cost function to finite summations. As a consequence, the block based time domain algorithm can be implemented in the frequency domain to reduce the computational complexity associated with the conventional symbol-by-symbol time domain update. Furthermore, by recognizing that the signals in the frequency domain are orthogonal, it is possible to significantly improve the convergence rate by normalizing the update equations with respect to the signal power in each frequency bin. Simulation results show that the proposed algorithm can successfully equalize the received signals while maintaining low computational complexity. Moreover, the presented normalized frequency domain blind equalization algorithm for MIMO systems significantly improves the convergence rate

The multi-rate subband equaliser converts the computationally complex fullband equaliser structure into several parallel low complexity subband equalisers, each operating independently. The fullband equaliser has a minimum mean square error (MMSE) dependent upon the filter coefficients and the relative delay between the desired symbol and received signal. The subband equalisers MMSE performance is also dependent upon the subband adaptive filter (SAF) coefficients and the relative delay between the desired and received subband signal components, referred herein as the alignment delay. We propose a new structure allowing implementation of independent alignment delays for each subband to achieve the MMSE with respect to both the SAF coefficients and the alignment delay. Simulation results show that the use of independent alignment delays in each subband provides significant improvement over the standard subband transversal equaliser.

In this paper, we consider the design of a class of unified complex Hadamard transform (UCHT) sequences. An efficient modification is imposed to those sequences to better suit applications in asynchronous code-division multiple-access (CDMA) systems. These modified UCHT sequences preserve the orthogonality of the original UCHT sequences and offer increased design options due to an increased number of parameters. The design of UCHT, modified UCHT, and Oppermann sequences is then formulated with reference to optimizing the maximum nontrivial aperiodic correlation value. These optimization problems can then be solved efficiently using a genetic algorithm with the maximum nontrivial aperiodic correlation value serving in the definition of a fitness function. Numerical examples illustrate the benefits of modified UCHT sequences over the original UCHT sequences

Broadband wireless systems require powerful equalizers which can cope with long channel impulse responses and severe intersymbol interference (ISI). In this paper, a frequency domain modified constant modulus algorithm (PD-MCMA) is presented. The employed modified CMA (MCMA) is chosen to confine the phase ambiguity of the conventional CMA to a 90/spl deg/ phase shift solution. On this foundation, a block MCMA algorithm which updates the equalizer coefficients on a block-by-block basis is proposed. The advantage of this block MCMA is that it can be equivalently implemented in the frequency domain. This approach offers a large reduction in computational complexity compared to time domain algorithms. For an equalizer with 256 coefficients, the number of real multiplications required by the FD-MCMA is only 9.5% of that required by the MCMA. Furthermore, convergence of the proposed FD-MCMA is significantly improved by properly normalizing the update equations. Simulations show that the normalized FD-MCMA converges much faster than the MCMA and the FD-MCMA while maintaining approximately the same bit error rate (BER) performance.