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     

Variable group-delay dispersion equaliser based on a lattice-formprogrammable optical filter

The authors report the first realisation of an integrated-optic variable group-delay dispersion equaliser using a lattice-form programmable optical filter. The equaliser consists of seven tunable couplers and six asymmetrical Mach-Zehnder interferometers cascaded alternately in series. The dispersion can be varied step by step from -923 ps/nm to +653 ps/nm     

PLC-based dynamic gain equaliser consisting of integratedMach-Zehnder interferometers with C- and L-band equalising range

The simultaneous spectral equalisation of the C- and L-bands, achieved using a planar lightwave circuit (PLC)-based dynamic gain equaliser consisting of 10 cascaded Fourier-series Mach-Zehnder interferometers, is described. Gain flattening over 68 nm with a 0.9 dB ripple for an Er³⁺-doped tellurite fibre amplifier was realised     

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     

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.     

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     

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.     

Performance of adaptive multisensor decision feedback equaliser fortime-varying frequency selective radio channels

A multisensor decision feedback equaliser based on the minimum mean squared error (MMSE) criterion is studied. The superiority of the performance of the multisensor equaliser is shown by simulation of a whole communication system in which the adaptive equaliser is incorporated. The recursive least squares (RLS) algorithm is used to update the coefficients. From the results obtained for a time-varying urban terrain channel model, the extremely interesting tracking capability of the multisensor equaliser is shown     

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     

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     

Code-aided adaptive equaliser for mobile communication systems

A new structure for a code-aided adaptive equaliser is proposed for mobile communication systems. The structure aims to improve the tracking capability of a receiver that combines equalisation and coding. Simulation results show that the code-aided adaptive equaliser performs particularly well over mobile channels that fade at a moderate rate. Compared to a conventional equaliser, an order of magnitude reduction in bit error rate is achieved     

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     

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/.     

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.<>     

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.<>     

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     

Noncoherent adaptive linear MMSE equalisation for 16DAPSK signals

A novel adaptive noncoherent linear minimum mean squared error equaliser for 16-level differential amplitude/phase shift keying signals is proposed. A novel modified least mean square algorithm is derived which allows an efficient equaliser adaptation. Simulations confirm the high performance of the proposed noncoherent equaliser and its robustness against carrier phase variations     

2-D adaptive CPWL filter for 2-D nonlinear channel equalisation and image restoration

A 2-D adaptive piecewise-linear equaliser is proposed. As an alternative of the 2-D adaptive Volterra equaliser, the proposed equaliser has advantages in its suitability for cases of strong nonlinearity and saving implementation and computation cost. An experiment examples is presented which demonstrates the superior behaviour of this method over either a linear method or the Volterra method in inverse modelling an unknown 2-D channel with blurring and a common point-wise nonlinearity and restoring images degraded by this channel.<>     

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.     

Turbo-equalisation for symbol-spread block transmission system

The authors consider coded block transmission over a memoryless Rayleigh fading channel based on an orthonormal transform. A new block-turbo equaliser is designed and its performance investigated and compared to an improved iterative block decision feedback equaliser