Complexity reduction for a multisensor Viterbi equaliser

A multisensor equaliser based on the Viterbi algorithm is presented. The equaliser consists of a multisensor Viterbi estimator and adaptive channel estimators. Its complexity is described and its performance over mobile channels is analysed. It is concluded that the multisensor Viterbi equaliser is capable of considering truncated channels, thereby allowing a considerable reduction in complexity     

Simplified parallel decision feedback equalisation for CCITT V.32/V.32 bis coded modems

A simplified parallel decision feedback equaliser (SPDFE) with the 32/64/128 AMPM CCITT trellis code is considered. The SPDFE detector consists of a whitened matched filter (WMF) and a reduced parallel decision feedback equaliser incorporated in the Viterbi decoder. The bit error rate simulation results show substantial improvement over the conventional detector with a linear equaliser and a separate Viterbi algorithm, although the implementation complexity remains the same.<>     

Turbo equalisation in non-Gaussian impulsive noise

Turbo equalisation is a state-of-the-art receiving scheme for coded data transmission over channels introducing intersymbol interference (ISI). The author investigates turbo equalisation performance in the presence of ISI and impulsive noise. The design imperfections contributing to the non-robustness of the standard turbo equaliser to outliers are identified, and a novel turbo equaliser, at almost no additional increase in complexity, is proposed for joint mitigation of ISI and impulsive noise. The proposed turbo equaliser incorporates a Talwar penalty function into the maximum a posteriori (MAP) component equaliser to serve two purposes. First, it improves the estimation of the transition probabilities for all transitions through the trellis and for subsequent determination of the a posteriori log-likelihood ratio. Secondly, it absorbs the outliers and prevents them from spreading into the MAP constituent decoder. Simulation results based on Proakis's channel models show that the proposed turbo equaliser achieves a dramatic improvement over the standard turbo equaliser in impulsive noise. At a bit error rate (BER) of 10/sup -2/, the performance gain is as large as 3.5 to 5 dB, and as large as 7 to 8 dB at a BER of 10/sup -3/.     

Recursive single-most-likely-replacement channel equaliser

The paper proposes a recursive single-most-likely-replacement (SMLR) equaliser, that is a fixed-lag block signal processing algorithm indexed by the block size L and the number of decisions N⩽L at each recursion, for channels in the presence of intersymbol interference of finite or infinite length and additive white Gaussian noise. Both computational load and storage required by the proposed recursive SMLR equaliser are linearly proportional to the block size. Two simulation examples illustrate the performance of the proposed recursive SMLR equaliser     

Performance improvement in decision feedback equalisers by using`soft decision'

One method to combat intersymbol interference (ISI) in digital transmission is to use a decision feedback equaliser (DFE). It is well known that a major part of the errors made by a DFE is due to the fact that the equaliser makes instantaneous decisions without taking into account data received later. It is therefore obvious that the performance of a DFE could be improved by allowing some type of `soft decision'. A method to introduce `soft decisions' in a decision feedback equaliser is presented. The method gives a performance improvement in SNR of about 1.5 dB with almost no increase in complexity compared to an ordinary DFE     

Adaptive equalisation for DECT systems operating in low time-dispersive channels

DECT (digital European cordless telecommunication) is the current standard for cordless indoor communication in Europe. In this work the authors present a scheme to increase the coverage area of DECT links in multipath propagation by the application of channel equalisation. The equaliser is a decision feedback equaliser using a recursive least squares algorithm for adaptation. As a training sequence for the equaliser, the standardised packet synchronising word of the DECT TDMA slots is used.<>     

CMOS equaliser for compensating sinc(x) distortion of video D/Aconverters

The authors describe the design and CMOS realisation of a new g _m-C amplitude equaliser for correcting sinc(x) distortion in video D/A converters. Simulated and measured results demonstrate how the equaliser is used to correct distortion in D/A converters with F_s =13.5 MHz to ⩽0.08 dB ripple over 5 MHz bandwidth. Fabricated using a 0.8 μm CMOS process, the equaliser occupies 0.7 mm² and dissipates 20 mW from a 5 V supply     

Asymptotic analysis of stabilisation technique for the blindfractionally spaced equaliser

The authors propose a technique to counteract the ill-conditioning of the blind fractionally spaced equaliser. The technique involves whitening the signal at the equaliser input and introducing a leakage term in the cost function minimised by the equaliser. The result is that, when applied to the Godard quartic cost function and to the infinitely long equaliser, such a technique yields optimal equalisation and actually counteracts the ill-conditioning     

Fabrication of tilted fibre-grating polarisation-dependent lossequaliser

The fabrication of a polarisation-dependent loss (PDL) equaliser using tilted fibre Bragg grating in standard telecommunication fibre is demonstrated. The equaliser has a predetermined level of PDL in a specific wavelength range, which is studied to compensate for the PDL of a component or system     

Robustness evaluation of a minimal RBF neural network fornonlinear-data-storage-channel equalisation

The authors present a performance-robustness evaluation of the recently developed minimal resource allocation network (MRAN) for equalisation in highly nonlinear magnetic recording channels in disc storage systems. Unlike communication systems, equalisation of signals in these channels is a difficult problem, as they are corrupted by data-dependent noise and highly nonlinear distortions. Nair and Moon (1997) have proposed a maximum signal to distortion ratio (MSDR) equaliser for data storage channels, which uses a specially designed neural network, where all the parameters of the neural network are determined theoretically, based on the exact knowledge of the channel model parameters. In the present paper, the performance of the MSDR equaliser is compared with that of the MRAN equaliser using a magnetic recording channel model, under Conditions that include variations in partial erasure, jitter, width and noise power, as well as model mismatch. Results from the study indicate that the less complex MRAN equaliser gives consistently better performance robustness than the MSDR equaliser in terms of signal to distortion ratios (SDRs)     

Enhanced sequence detector in the presence of intersymbol interference and non-Gaussian noise

A new Viterbi equaliser is proposed for joint mitigation of intersymbol interference and impulsive noise. The new equaliser uses a robust branch metric incorporating the Talwar penalty function. It is shown that the proposed equaliser facilitates considerable performance improvements.     

Planar lightwave circuit dispersion equaliser module withpolarisation insensitive properties

The authors report the fabrication of an integrated-optic dispersion equaliser module based on a planar lightwave circuit (PLC). The equaliser consists of five asymmetrical Mach-Zehnder interferometers cascaded in series. Polyimide half waveplates inserted in the interferometers eliminate the polarisation dependent path length differences of the equaliser     

Blind decision feedback equaliser for multichannels with commonzeros

Blind equalisation of a fractionally spaced channel (FSC) is generally difficult if all subchannels have common zeros. A new blind equalisation structure is proposed so that the uncommon part of the FSC is equalised with a fractionally spaced equaliser and the common part of the FSC is equalised with a decision feedback equaliser which operates at the baud rate     

Voltage equaliser for Li–Fe battery

In this article, a voltage equaliser is proposed for a battery string with four Li–Fe batteries. The proposed voltage equaliser is developed from a flyback converter, which comprises a transformer, a power electronic switch and a resonant clamped circuit. The transformer contains a primary winding and four secondary windings with the same number of turns connected to each battery. The resonant clamped circuit is for recycling the energy of leakage inductance of the transformer and for performing zero-voltage switching (ZVS) of the power electronic switch. When the power electronic switch is switched on, the energy is stored in the transformer; and when the power electronic switch is switched off, the energy stored in the transformer will automatically charge the battery whose voltage is the lowest. In this way, the voltage of individual batteries in the battery string is balanced. The salient features of the proposed voltage equaliser are that only one switch is used, the energy stored in the leakage inductance of the transformer can be recycled and ZVS is obtained. A prototype is developed and tested to verify the performance of the proposed voltage equaliser. The experimental results show that the proposed voltage equaliser achieves the expected performance.     

Decision feedback demodulation-based adaptive linear equalisers fordifferentially coherent DPSK systems

The authors propose to combine linear feedback equalisation and decision feedback demodulation for the equalisation of differentially coherent PSK signalling. By modifying the equaliser output based on the decision feedback demodulation before feeding back, the proposed equaliser can be made to behave like one with a decision feedback structure. Indeed, computer simulation results demonstrate that this equaliser performs much better than existing equalisers, such as linear equalisers for differentially coherent detection. Furthermore its performance is even comparable to that of a decision feedback equaliser with coherent detection     

Approach to blind decision feedback equalisation

Based on the fact that a decision feedback equaliser (DFE) can be divided into a linear equaliser and a prediction error filter with feedback, a new blind adaptation method for the DFE is proposed. The proposed method provides reliable convergence and the resulting symbol error rate is very close to that of the DFE using a training sequence     

Adaptive lattice-form IIR blind equaliser

The author describes incorporation of the lattice-form structure in the blind infinite impulse response (IIR) algorithm, based on a cost function which is a modified version of that proposed by Shalvi and Weinstein (1990). The proposed IIR blind equaliser has the advantage of lower complexity; simulation results also indicate that the proposed IIR blind equaliser has a faster convergence rate and a smaller mean square error (MSE)     

Chromatic dispersion compensation with FFE-DFE utilising MZ filter for diverse VSB filtering

Chromatic dispersion compensation of non-return-to-zero on?off keying (NRZ-OOK) signals with a diverse-vestigial-sideband-filtering feed forward equaliser and a decision feedback equaliser (DVSB-FFEDFE) is presented, in which diverse vestigial sideband (VSB) filtering is realised with a Mach-Zehnder (MZ) filter. In a 10.709 Gbit/s NRZOOK system, experiment results show that the standard singlemode fibre transmission distance at 3 dB optical signal-to-noise ratio penalty with DVSB-FFE-DFE is doubled, compared to that with conventional FFE-DFE.     

Planar lightwave circuit dispersion equaliser with a wideoperational frequency range

The authors report an integrated-optic dispersion equaliser with an amplitude flattening circuit on a planar lightwave circuit. The equaliser consists of six asymmetrical Mach-Zehnder interferometers cascaded in series. The operational frequency range of the equaliser is successfully extended from 12.6 to 21.2 GHz by amplitude flattening without deteriorating the delay characteristics     

Adaptive retraining equalisation based on channel change detections

By adaptively detecting abrupt changes in the channel tap coefficients and requesting the training sequence to be transmitted whenever changes are detected, an adaptive retraining equaliser has been designed. The performance of the equaliser is evaluated by numerical simulations, and the results show that the equaliser outperforms the traditional periodical retraining equaliser and requires fewer training sequences.