Finite Word Length FIR Filter Design Using Integer Programming Over a Discrete Coefficient Space

The article of record as published may be found at http://dx.doi.org/10.1109/TASSP.1982.1163925Published in: IEEE Transactions on Acoustics, Speech, and Signal Processing (Volume: 30 , Issue: 4 , Aug 1982)It is demonstrated that the improvement achieved by using integer programming over simple coefficient rounding in the design of finite impulse response (FIR) filters with discrete coefficients is most significant when the discrete coefficient space is the powers-of-two space or when a specification is to be met with a given coefficient word length by increasing the filter length. Both minimax and least square error criteria are considered

A combined Kalman filter and constant modulus algorithm beamformer for fast-fading channels

Beamformers which use only the constant modulus algorithm (CMA) are unable to track properly time-variant signals in fast-fading channels. The Kalman kilter (KF), however, has significant advantage in time-varying channels but needs a training sequence to operate. A combined CMA and KF algorithm is therefore proposed in order to utilise the advantages of both algorithms. The associated stepsize of the combination is also varied in accordance with the magnitude of the output. Simulations are presented to demonstrate the potential of this new approac

Leaky constant modulus algorithms: sensitivity of local minima

We propose a new family of mixed constant modulus algorithms for the elimination of local minima associated with the fractionally spaced constant modulus algorithm in the presence of channel noise. A special case of this family is the leaky constant modulus algorithm (L-CMA). We show that L-CMA aims to minimise jointly the intersymbol interference (ISI) and the noise gain introduced by the equalizer. Moreover, we derive a suitable range of leakage factors for which all local minima due to large noise amplification are eliminate

Adaptive notch filters from lossless bounded real all-pass functions for frequency tracking and line enhancing

The authors introduce constrained adaptive notch filters which are synthesized from a numerically robust all-pass filter section. This section is realized as a structurally lossless bounded real function which is canonic in both multipliers and delay elements. The notch filter structures admit orthogonal tuning of their notch frequency and bandwidth. For the two structures, frequency tracking and signal enhancement outputs are derived. The mirror image pair of polynomials present in a real all-pass transfer function is shown to yield significant simplification in the generation of the necessary gradient terms used in parameter adaptation. A cascade of such structures is shown to be suitable for tracking multiple sinusoids. Simulation results verify the utility of these structures for frequency trackin

Constant modulus blind equalisation algorithms under soft constraint satisfaction

New constant modulus (CM) algorithms are presented that are based on soft constraint satisfaction. The stationary points of an algorithm in this family are studied for an AR(p) channel and it is shown that Ding-type undesirable local solutions (ULS) do not exist. This is due to the normalisation of the gradient vector and the soft nonlinearity used in these algorithms. Error performance surfaces (EPS) and convergence trajectories from arbitrary initialisations are presented for various channels that support the analytical finding

A novel re-initialization technique for CMA in the presence of channel noise

The error surface associated with the constant modulus algorithm (CMA) is multimodel. Therefore, an equalizer adapted with CMA has the potential to converge to a local minimum that has large noise amplification. A technique is, therefore, proposed based upon a solution of linear and quadratic equations to re-initialise the equalizer parameters. Linear equations are obtained from the fact that the retrieved transmitted signal with various delays which correspond to different minima are uncorrelated. The quadratic equations are obtained from the knowledge of the transmitted signal power. Simulations are included to demonstrate the robustness of this new schem

Finite-precision design and implementation of all-pass polyphase networks for echo cancellation in sub-bands

All-pass polyphase networks (APN) are particularly attractive for acoustical echo cancellation (AEC) arranged in sub-bands. They provide lower inter-band aliasing, delay and computational complexity than their FIR counterparts. Moreover, APNs achieve higher echo return loss enhancement (ERLE) performance and faster convergence than full-band processing. In the paper, the finite precision implementation of APNs is addressed. A procedure is presented for re-optimising the all-pass coefficients of the prototype low-pass filter for finite precision operation. Robust finite precision implementation of a prototype low-pass filter is discussed. The results of a set of AEC experiments are reported with full and 16-bit precision implementatio

Self-contained encrypted image folding

The recently introduced approach for Encrypted Image Folding is generalized to make it self-contained. The goal is achieved by enlarging the folded image so as to embed all the necessary information for the image recovery. The need for extra size is somewhat compensated by considering a transformation with higher folding capacity. Numerical examples show that the size of the resulting cipher image may be significantly smaller than the plain text one. The implementation of the approach is further extended to deal also with color images