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To reduce pattern-dependent jitter in four-level pulse-amplitude modulation (PAM-4) signalling, a transition-aware feed-forward equaliser (TFFE) is proposed. By allowing the transition time to vary according to the transition types of the PAM-4 symbols, switching jitter in TFFE-based PAM-4 transmitters can be greatly suppressed, down to the non-return-to-zero (NRZ) level. Simulation results confirm that a PAM-4 transmitter that employs a TFFE can reduce the jitter level by 0.18 unit interval peak-to-peak, and this proposed equaliser can achieve nearly identical eye height as the conventional PAM-4 feed-forward equalisers design without introducing any signal-to-noise ratio penalty.

An analogue equaliser with a novel digitally tuned variable degeneration resistance is realised in a 65 nm CMOS technology. Implemented with three parallel resistance branches and one serial resistance branch to well fit the optimal conductance curve, the proposed variable degeneration resistance is exploited to achieve a wide boost range while significantly improving the linearity of the tuned boost factors compared with the equaliser with a traditional degeneration resistance structure.

The design of a 4× blind analogue-to-digital converter (ADC)-based receiver implemented in 65 nm CMOS technology is presented. The ADC, which has three levels with two adjustable thresholds, effectively implements a speculative decision-feedback equaliser. By reducing the ADC resolution and by simplifying the digital clock and data recovery design, the power consumption is reduced by a factor of 2 compared with previous works. Measurement results confirm a bit error rate of

We propose a 10-Gb/s Wavelength-Division-Multiplexed Passive Optical Network (WDM-PON) scheme with upstream transmission employing Reflective Semiconductor Optical Amplifier (RSOA) and Fibre Bragg Grating (FBG) optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2-GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-km standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pumped Erbium-Doped Fibre Amplifier (RP-EDFA), where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.

The authors consider the channel estimation problem in the context of a linear equaliser designed for a frequency selective channel, which relies on the minimum bit-error-ratio (MBER) optimisation framework. Previous literature has shown that the MBER-based signal detection may outperform its minimum-mean-square-error (MMSE) counterpart in the bit-error-ratio performance sense. In this study, they develop a framework for channel estimation by first discretising the parameter space and then posing it as a detection problem. Explicitly, the MBER cost function (CF) is derived and its performance studied, when transmitting binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) signals. It is demonstrated that the MBER based CF aided scheme is capable of outperforming existing MMSE, least square-based solutions.

In this study, the authors propose a novel equalisation digital on-channel repeater (EDOCR) with a feedback interference canceller (FIC) for a single frequency network of the advanced television systems committee terrestrial digital television system. The proposed EDOCR with an FIC not only has high output power by the cancellation of feedback signals caused by insufficient antenna isolation through the FIC, but also shows better quality of output signals than conventional digital on-channel repeaters (DOCRs) by removing multipath signals existing between the main transmitter and DOCR, as well as residual feedback signals through an equaliser. Computer simulation results are provided to demonstrate the superior performance of the proposed EDOCR with an FIC.

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 indu...

The maximum data rate that can be achieved in diffuse indoor optical wireless communication (OWC) is limited due to the effect of intersymbol interference (ISI). The adverse effect of ISI on the system performance can be minimised using a channel equaliser at the receiver. In this study, digital signal detection is formulated as a classification problem and hence a classifier is adopted at the receiver. The bit error performance of classifiers with non-linear decision boundary including a multilayer perceptron (MLP), a support vector machine (SVM), the radial basis function (RBF), and the Bayesian classifier is studied along with traditional equaliser and reported here. The MLP offers the best performance; however there is trade-off between the performance and complexity especially at highly diffuse channel.

The explosive increase in data traffic requires networks to provide higher capacity and long-haul transmission capabilities. This paper introduces new results on high-order modulation and efficient Digital Signal Processing algorithms to reduce various transmission limitations in coherent receiving systems. Polarization Division Multiplexed Quadrature Phase Shift Keying (PDM-QPSK) is deployed to reach high bit rates, provides modified digital clock recovery, and allows BER-Aided Constant Modulus Algorithm (BA-CMA) equalising. A Soft Decision-Forward Error Correction (SD-FEC) algorithm and a joint scheme with timing recovery and adaptive equaliser are used to achieve better performance. A compact coherent transceiver is also developed. These techniques have been applied in the largest 100 G Optical Transport Network (OTN) deployment in the world, the backbone expansion project for Phase 3 of the China Education and Research Network (CERNET), with a total transmission length of 10 000 km.

Batteries play an important role in sustainable energy systems because the energy stored in batteries can be dispatched at any time. Series-connected batteries can furnish a load with higher voltage and consequently reduce the I 2 R loss during power conversion and transmission. However, if imbalanced voltage occurs, a battery with high state of charge (SOC) would react more drastically than that with lower SOC under both charging and discharging conditions. Imbalanced charge or discharge would give rise to potential damage to the battery and also shorten the battery life cycle. This study presents a modified charge equaliser (CE) along with an optimal charge equalisation algorithm (CEA). The proposed circuit scheme can distribute an imbalanced charge in a more efficient way without increasing additional circuit cost. To further expedite charge equalisation among a battery string, the activated CE duty ratio is fixed at the upper limits throughout the charge equalisation phase. An optimal CEA with a view towards maximising the final battery string voltage is developed to resolve the CE operating sequence and length. The proposed equalisation strategy is realised using a peripheral interface controller that uses a buck–boost converter as the CE. The experimental results confirm the performance of the proposed strategy.

A low-complexity channel estimation algorithm is proposed to improve performance of two high frequency standardised waveforms: MIL-STD-188-110B Appendix C standard and STANAG 4285. In the proposed estimation algorithm, the channel impulse response is modelled as a linear-time function within a frame and the least square criterion is adopted. With the estimated CIRs, the authors study and compare bit-error-rate (BER) performance and complexity of three turbo equalisation (TEQ) schemes, including the minimum mean-square error (MMSE), the MMSE with decision feedback equalisation (DFE) (MMSE-DFE) and the soft-feedback interference-cancellation (SFIC) turbo receivers. The authors then propose a hybrid TEQ scheme that uses the MMSE-DFE equaliser for the first iteration and the SFIC equaliser for the rest. Simulation results show that the proposed channel estimation algorithm performs well and the TEQ schemes realise a significant performance improvement as compared with a non-iterative receiver. Moreover, the proposed hybrid TEQ scheme achieves the best trade-off between BER and complexity for the MIL-STD-188-110B Appendix C standard, whereas the SFIC-TEQ scheme is optimal for the STANAG 4285 standard.

A clock and data recovery (CDR) circuit has been developed for a clock-forwarded 3.4-Gbps serial link. The loss of the signal channel is compensated by a linear equaliser whose output is applied to eight samplers which provides edge- and data-samples of the serial data input. Based on the edge- and data-samples, the phase of a voltage-controlled oscillator (VCO) running at one-fourth of the data rate is adjusted to get the optimum eight-phase sampling clocks. Implemented in a 0.13-μm standard CMOS process, the CDR circuit shows the bit-error rate (BER) less than 10−15.

SUMMARY Nonlinear equalisers based on minimum BER are proposed for the equalisation of nonlinear time-varying channels. To train the equalisers online, a sliding-window-based hybrid quasi-Newton algorithm is proposed. Switching between sliding-window stochastic gradient algorithm and sliding-window quasi-Newton algorithm makes the new algorithm significantly stabler with a fast convergence rate. Results from extensive simulation tests show that performance of nonlinear equalisers based on minimum BER is better than the equaliser based on minimum mean square error. The proposed algorithm demonstrates high efficiency as well. Copyright © 2013 John Wiley & Sons, Ltd.

RESUMEN: Los radiómetros son los receptores de radioastronomía usados para detectar el fondo cósmico de microondas (CMB), el eco del Big Bang, la huella que explica el origen de nuestro Universo. El amplificador de bajo ruido (LNA) es un subsistema clave puesto que un nivel de amplificación alto junto con un nivel de ruido muy bajo incrementa el ancho de banda de medida y la sensibilidad del receptor. En esta tesis se ha mejorado las prestaciones del LNA en cuanto a nivel de ruido, aumento de ancho de banda, y entrega de potencia. Se han explorado diferentes topologías y tecnologías de diseño, y se ha integrado las soluciones en amplificadores pertenecientes a un radiómetro funcionando a 40 GHz. Se ha caracterizado el receptor completo, enfriando el LNA a temperaturas criogénicas. Por último, se ha propuesto un esquema de radiómetro funcionando en una nueva ventana de observación del CMB en la frecuencia de 90 GHz. ABSTRACT: The radiometers are the radio astronomy receivers used to detect the cosmic microwave background (CMB), the Big Bang echo, the footprint that explains the origin of our Universe. The low noise amplifier (LNA) is a key subsystem because a high gain level with a very low noise level increases the measurement effective bandwidth and receiver sensitivity. In this thesis, the LNA performance has been improved in terms of noise level, increase of effective bandwidth, and power delivered. Different design topologies and technologies have been studied, and the amplifier solutions have been integrated in a radiometer working at 40 GHz frequency band. The radiometer has been full characterised, cooling down to cryogenic temperatures the LNA. Finally, a new radiometer scheme has been proposed in a new CMB observation window at 90 GHz frequency band.

Rackların Çaprazlanmış Modüllerinin Kategoriksel Özellikleri başlıklı bu doktora tezi, altı bölümden oluşmaktadır. Birinci bölümde rack kavramıyla ilgili genel tanımlar ve örnekler verildi. Ayrıca bu bölümde, alt rack, normal alt rack, bölüm rack ve serbest rack kavramları tanıtıldı. İkinci bölümde rack kategorisinin kategoriksel özelliklerinden çarpım, eş-çarpım, geri çekme, ileri itme, eşitleyici ve eş-eşitleyici objeler ayrıntılı olarak incelendi. Üçüncü bölümde rackların çaprazlanmış modül kavramı tanıtılarak rackların çaprazlanmış modül örneklerine yer verildi. Dördüncü bölümde rackların çaprazlanmış modül kategorisinin çarpım, eş-çarpım, geri çekme, ileri itme, eşitleyici ve eş-eşitleyici objelere sahip olduğu gösterildi. Beşinci bölümde rackların serbest çaprazlanmış modülü tanımlandı. Altıncı ve son bölümde ise elde edilen sonuçlar yorumlanarak “sonuç ve öneriler” başlığı altında sunulmuştur. This Ph.D. thesis, titled Some Categorical Construction of Crossed Modules of Racks, consists of six chapters. In the first chapter, the definition of rack is given and general examples about this concept are examined. Also in this chapter, the notions of subrack, normal subrack, quotient rack and free rack are introduced. In the second chapter, the categorical properties of the category of rack, product, coproduct, pullback, pushout, equaliser and coequaliser, are investigated in detail. In the third chapter, the crossed module concept of racks is introduced and examples of crossed modules of racks are given. In the fourth chapter, it is shown that the category of crossed modules of racks have product, coproduct, pullback, pushout, equaliser and coequaliser objects. In the fifth section, the free crossed module of racks is defined. In the last chapter, the results obtained and suggestion are given under the heading ”results and suggestions”.

This paper demonstrates a 10 Gbit/s wavelength converting access network utilising a centralised optical processing unit that consolidates multiple low cost PONs onto a DWDM backhaul. The centralised processing unit functions as an amplifier, wavelength converter, pre-chirping stage and optical burst equaliser to map legacy PONs onto a DWDM grid for efficient backhaul transmission and to ease the dynamic range requirement of the 10 Gbit/s burst-mode receiver at the optical line termination (OLT). The dispersion limited performance, wavelength tolerance, and burst-mode dynamic range are evaluated demonstrating a maximum range of 62 km for 20 nm of input wavelength variation and a dynamic range of up to 22 dB.

MIMO-OFDM is considered as a fast growing technology now days. OFDM is a multi carrier modulation technique in which the carriers are Orthogonal to each others as a result of which it provides high bandwidth efficiency and multiple carriers share the data among themselves. During the research equalizer is always a matter of strategies. When a signal is transmitted over a radio channel, it is subject to reflection, refraction and diffraction and also the type of modulation technique selected at transmitter. In this paper Bit Error Rate performance of OFDM under Rayleigh fading channel is analysed, and compared with Additive White Gaussian Noise Channel.

To improve performance in step-index plastic optical fiber (SI-POF), spectral efficient modulation Scheme like multilevel pulse amplitude modulation (M-PAM) with equalisers have recently been studied. The adaptive equalisers used for POF in recent literature are the conventional linear transversal equalisers (LTE) and decision feedback equaliser (DFE). In this paper, we investigate the performance of multi-layer perceptron (MLP), which is a feed-forward neural network architecture, as an adaptive equaliser for minimizing intersymbol interference (ISI) in SI-POF using M-PAM schemes. The bit-error rate (BER) performance for the MLP equaliser is compared with that of conventional equaliser (LTE and DFE) for theoretical POF channels with Gaussian Profile. In comparison to LTE and DFE, we show in this paper that under severe ISI, MLP achieves better BER performance.

Equalisation is one of the most commonly-used tools in sound production, allowing users to control the gains of different frequency components in an audio signal. In this paper we present a model for mapping a set of equalisation parameters to a reduced dimensionality space. The purpose of this approach is to allow a user to interact with the system in an intuitive way through both the reduction of the number of parameters and the elimination of technical knowledge required to creatively equalise the input audio. The proposed model represents 13 equaliser parameters on a two-dimensional plane, which is trained with data extracted from a semantic equalisation plug-in, using the timbral adjectives warm and bright. We also include a parameter weighting stage in order to scale the input parameters to spectral features of the audio signal, making the system adaptive. To maximise the efficacy of the model, we evaluate a variety of dimensionality reduction and regression techniques, assessing the performance of both parameter reconstruction and structural preservation in low-dimensional space. After selecting an appropriate model based on the evaluation criteria, we conclude by subjectively evaluating the system using listening tests.

A new low peak-to-average power ratio (PAPR) transceiver is proposed for the coded single-carrier frequency division multiple access (SC-FDMA) system over frequency selective fading channels. By exploiting the constant envelope of the Chu-sequence in both frequency and time domains, the parallel spreading scheme and M-ary cyclic shift mapping technique can support the coded SC-FDMA system with a low PAPR for transmission at a high data rate. Interleaved time and frequency domain orthogonal modulation can increase the frequency diversity gain through the frequency domain equaliser and the time domain despreader. Moreover, the maximum likelihood rule is designed to detect the M-ary mapping data, which can provide M-ary gain to improve system performance. Simulation results reveal that the proposed high-rate coded SC-FDMA system can provide a lower PAPR and a better bit error rate (BER) performance than the conventional interleaved SC-FDMA system.

The author proposed soft decision feedback equalisation for orthogonal frequency division multiplexing (OFDM) transmission over doubly selective channels which is used for turbo equalisation. The doubly selective channel is approximated using the basis expansion model (BEM). The decision feedback equaliser (DFE) is obtained and updated for every sub-carrier which results in a per-tone DFE. On the basis of the Gaussian approximation, expressions for the a priori, the a posteriori and the extrinsic information have been derived for quadrature phase shift keying (QPSK) modulation. For turbo equalisation, where iterative joint channel equalisation and channel decoding is executed, in the first iteration, estimates are based on the feed-forward filter which are fed to the channel decoder. These estimates are not reliable and may incur error propagation and poor turbo equalisation performance. For more reliable estimates in the first iteration, the DFE is initialised as a linear minimum mean square error (LMMSE) equaliser. The per-tone LMMSE soft-output equaliser is also derived, and expressions for the a priori, a posteriori and extrinsic information are obtained viewing the LMMSE equaliser as a special case of the DFE. The extrinsic information in both cases was derived based on the Gaussian approximation. Numerical results for bit-error rate performance assuming the BEM channel model and Jakes’ channel model are shown to confirm our findings.

A low peak-to-average-power-ratio (PAPR) modulation technique is proposed for discrete Fourier transform precoded orthogonal frequency division multiple access (DFT-precoded-OFDMA) systems. This technique reduces the PAPR by introducing a phase rotation between successive modulation symbols along with partial response (PR) precoding before feeding the data to a DFT-precoded-OFDMA modulator. The PAPR reduction is shown to be quite significant for amplitude-shift-keying systems based on real constellations employing π/2 phase rotation. In particular, for the special case of binary modulation, the combination of phase rotation and PR precoding produces a signal with low amplitude variations. We show that the class of PR precoders obtained by sampling the linearised Gaussian-minimum-shift-keying pulse provides low PAPR and a small degradation in bit-error-rate (BER) performance. In particular, the widely linear minimum-mean-square-error (WL-MMSE) estimation and WL MMSE decision feedback equaliser (WL MMSE-DFE) methods that jointly filter the signal and its complex conjugate are shown to be useful in mitigating the additional intersymbol interference introduced by the PR precoder. The BER performance is comparable with that of conventional DFT-precoded-OFDMA systems employing conventional equalisers. The proposed technique is also suitable for reducing the PAPR of Q-ary phase-shift-keying systems based on complex constellations employing a phase rotation of π/Q. Introduction of Type A-2 PR precoder that is obtained from the linearised Gaussian-minimum-shift-keying pulse reduces the PAPR by 3.0 dB for quadrature phase-shift keying, and 2.5 dB reduction is observed for Q-ary phase-shift keying with Q ≥ 8. The intersymbol interference created by the PR precoder causes bit-error-rate degradation in the range of 2.0-2.5 dB when conventional MMSE-DFE receiver is used for symbol detection

In this paper, we consider a single-carrier modulation combined with frequency-domain equalisation block transmission with residual frequency errors. We employ a frequency-domain iterative decision feedback equalisation (DFE) denoted iterative block-decision feedback equalisation (IB-DFE), which is combined with a decision-directed carrier frequency offset (CFO) estimator. This estimator produces a CFO estimate within each iteration of the equaliser, which is used to compensate for the CFO. As the analytical study of the IB-DFE is very hard because of the feedback chain, IB-DFE receivers with joint symbol detection and carrier frequency synchronisation are also very difficult to tackle. To address this problem, we propose three new models. One models the decision-directed CFO estimator, another models the IB-DFE and finally one makes use of the previous two models to jointly characterise equalisation and carrier frequency synchronisation. In addition, a novel graphical tool for the convergence evaluation of the iterative receiver is included. Finally, we validate our models using Monte Carlo simulations and conclude that they are accurate for small and moderate residual CFO values. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, equalization algorithms applying soft–decision feedback, designed for quaternary phase–shift keying (QPSK) and 8PSK (phase–shift keying) transmission are introduced. The method employed is a minimum mean– squared error (MMSE) in which each iteration is done in order to refine the data estimates. The rule for generating soft decisions is adapted continuously to the current state of the algorithm. We show that standard Decision Feedback Equalization (DFE-Non linear Equaliser) methods are clearly outperformed the minimum mean–squared error (MMSE linear Equaliser). We use the MATLAB to show that the MMSE-DFE provide better performance with the increasing value of SNR in scattering environment.

Optimal power allocation (PA) and sub-carrier pairing (SP) strategies for a dual-hop amplify-and-forward single-carrier frequency division multiple access network are derived. Frequency domain equalisers based on minimum mean square error (MMSE) and zero forcing (ZF) criteria are considered. For each equaliser, the problem of joint PA and SP is solved to maximise the system capacity subject to the total network power constraint. The optimality of ordered SP (OSP) and reverse OSP scenarios for MMSE and ZF equalisers, respectively, is proved.

A semi-blind adaptive space–time equaliser (STE) has recently been proposed based on a concurrent gradient-Newton (GN) constant modulus algorithm (CMA) and soft decision-directed (SDD) scheme for dispersive multiple-input multiple-output (MIMO) systems that employ high-throughput quadrature amplitude modulation signalling. A minimum number of training symbols, approximately equal to the dimension of the STE, is used to provide a rough initial estimate of the STE's weight vector. The concurrent GN based CMA and SDD blind adaptive scheme is then adopted to adapt the STE. This semi-blind STE has a complexity similar to that of the training-based recursive least squares (RLS) algorithm. For stationary MIMO channels, it has been demonstrated that this semi-blind adaptive STE is capable of converging fast to the optimal minimum mean square error STE solution. In this contribution, we investigate the performance of this semi-blind adaptive STE operating in Rayleigh fading MIMO systems. Our results obtained show that the tracking performance of this semi-blind adaptive algorithm is close to that of the training-based RLS algorithm. Thus, this semi-blind adaptive STE offers an effective and practical means to successfully operate under the highly dispersive and fading MIMO environment.

Block transmission techniques, with appropriate cyclic prefixes and employing frequency-domain equalisation techniques, have been shown to be suitable for high data rate transmission over severely time-dispersive channels. The most popular techniques based on this concept are orthogonal frequency division multiplexing (OFDM) and single-carrier with frequency-domain equalisation (SC-FDE). In this paper, we consider OFDM and SC-FDE transmission schemes and study the impact of the number of multipath components and the diversity order on their performance. It is shown that when we have a high number of separable multipath components, the asymptotic performance of both schemes approaches the matched filter bound, even without diversity. When we have diversity, the performance approaches the matched filter bound faster, with a small number of separable multipath components. It was also observed that the SC-FDE has an overall performance advantage over the OFDM option, especially when employing the iterative block decision feedback equaliser with turbo equalisation and for high code rates. Copyright © 2011 John Wiley & Sons, Ltd.

The authors study the spatial-temporal minimum mean square error decision-feedback equaliser (ST-DFE) to combat dispersive interference over fading channels. The proposed ST-DFE consists of an anticausal fractionally spaced feedforward filter (FFF) on each antenna branch to perform co-channel interference (CCI) and precursor intersymbol interference (ISI) cancellation, followed by a symbol-spaced feedback filter to remove postcursor ISI. An optimum ST-DFE with a double-sided symbol-spaced FFF demonstrates excellent CCI/ISI cancellation ability, but occupies wider time span and is too complicated to implement in practice. Several ST-DFE schemes using the anticausal symbol-spaced FFF were proposed, but the simulation reveals that such an approach is unable to eliminate dispersive CCI efficiently and even performs substantially worse than spatial-temporal linear equalisers, when the continuous transmitted pulse shape is considered. The performance might become worse owing to the error propagation. The proposed ST-DFE is capable of improving the performance significantly, and even outperforms the double-sided symbol-spaced ST-DFE. The algorithm for computing the fractionally spaced coefficients is presented and then applied to the fast error probability calculation using the Gauss quadrature rule which can approximate the probability of the density function of the residual ISI and CCI. Such an approach avoids the interference characteristic of the inaccurate Gaussian method.

This article presents a new time domain equaliser (TEQ), which can be used in discrete multi-tone (DMT) systems to maximise the bit rate. The proposed TEQ is tested in the fast Fourier transform based discrete multi-tone (FFT–DMT) system, and in a proposed discrete cosine transform based discrete multi-tone (DCT–DMT) system. The objective of the proposed DCT–DMT system is to make use of the energy compaction property of the DCT to reduce the channel effects on the transmitted signals. A mathematical model of the proposed TEQ is presented. Simulation experiments have been carried out to test the effect of the proposed TEQ with the FFT–DMT system and the proposed DCT–DMT system. The results show that the performance of the DCT–DMT system with the proposed TEQ is better than the FFT–DMT system with this TEQ over the eight standard carrier serving area (CSA). The results also show that employing the proposed TEQ in the DCT–DMT system can achieve a high bit rate, ranging from 2.899 Mbps to 5.369 Mbps.

We proposed the support vector machine (SVM)-based equalisation schemes for direct-sequence ultra wideband (UWB) systems. The severe intersymbol interference caused by the UWB channel was formulated as a pattern classification problem in the SVM-based equaliser, which operates in two main modes: training and detection. We also applied the least squares support vector classifiers (LS-SVCs) to reduce the training complexity and sparse LS-SVCs to reduce the detection complexity, with little performance loss compared to SVCs. Simulation results confirm the outperformance of the proposed equalisers over the conventional rake receiver with the same order of complexity for detection, especially when no channel information is known at the receiver. Also, the SVM-based equalisers in the line-of-sight scenario provide a performance close to the case with additive white Gaussian noise only. Copyright © 2011 John Wiley & Sons, Ltd.

Similar to the orthogonal frequency division multiple access (OFDMA) system, the single-carrier frequency division multiple access (SC-FDMA) system also suffers from frequency mismatches between the transmitter and the receiver. As a result, in this system, the carrier frequency offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to inter-carrier interference (ICI) and multiple access interference (MAI) among users. The authors present a new minimum mean square error (MMSE) equaliser, which jointly performs equalisation and carrier frequency offsets (CFOs) compensation. The mathematical expression of this equaliser has been derived taking into account the MAI and the channel noise. A low complexity implementation of the proposed equalisation scheme using a banded matrix approximation is presented here. From the obtained simulation results, the proposed equalisation scheme is able to enhance the performance of the SC-FDMA system, even in the presence of estimation errors.

To combat the linear and non-linear distortions for time-invariant and time-variant channels, a novel adaptive joint process equaliser based on a pipelined decision feedback recurrent neural network (JPDFRNN) is proposed in this paper. The JPDFRNN consists of a number of simple small-scale decision feedback recurrent neural network (DFRNN) modules and a linear combiner. The cascaded DFRNN provides pre-processing for the linear combiner. Moreover, each DFRNN can provide a local interpolation for M sample points; the final linear combiner presents a global interpolation with good localisation properties. Furthermore, since those modules of non-linear subsection can be performed simultaneously in a pipelined parallelism fashion, this would result in a significant improvement in the total computational efficiency. Simulation results show that the performance of the JPDFRNN using the modified real-time recurrent learning (RTRL) algorithm is superior to that of the DFRNN and RNN for the non-linear time-invariant and time-variant channels.

It is well known that for constant modulus (i.e., magnitude) signals the famous constant modulus (CM) blind equalisation algorithm implemented in a fractionally spaced equaliser can present a zero steady-state mean square error (MSE), which means completely eliminating the distortions introduced in transmitting signals through channels. But for non-constant modulus signals it suffers a large steady-state MSE. In order to overcome this defect, a segment cost function according to the CM criterion is suggested. The distinctive feature of the segment cost function is that the equalised signals (of the non-constant modulus signals) are divided into three segments to form a s shape where the ideal signals have a constant modulus instead of non-constant. And then a new blind equalisation algorithm seeks to minimise this segment cost function by applying a stochastic gradient method is proposed. When employing the proposed algorithm to equalise the 4-PAM or 16-QAM non-constant modulus signals, just as using the CM blind equalisation algorithm to equalise the 4-QAM constant modulus signal, a zero steady-state MSE can be obtained, which is derived. Compared to the classical bind equalisation algorithms, such as CMA, MMA, MCMA, or CMA+SDD, the proposed algorithm yields improved performance, especially for higher SNR.

A simple method for dynamically adjusting the tap-length adaptation step-size of a variable tap-length linear equaliser based on the fractional tap-length algorithm is presented. Simulations show that the technique provides a fast convergence of tap-length and small steady-state tap-length fluctuation.

An adaptive frequency-domain equaliser for the single carrier frequency division multiple access (SC-FDMA) system using the particle swarm optimisation (PSO) technique is proposed. Unlike the stochastic gradient and recursive least squares algorithms, the PSO is known to have fast convergence which does not depend on the underlying structure. The cost function used in a PSO is formulated based on the respective structure of the equaliser, whether it is a linear equaliser or a decision feedback equaliser. The robustness of the proposed PSO algorithm is demonstrated on a high Doppler scenario. Furthermore, it is shown that the performance improves more when using re-randomisation. Finally, it is shown that the PSO-based frequency-domain equaliser is more computationally efficient than its time-domain counterpart.

In orthogonal frequency division multiplexing (OFDM) systems, channels' rapid variations cause intercarrier interference (ICI), resulting in performance degradation. Although ICI caused by channels' variations makes the reliable signal detection difficult, it also introduces Doppler diversity, which can be exploited to improve the system performance. In this paper, an ICI mitigation and Doppler-multipath diversity technique based on fractionally sampling at the receiver is proposed for OFDM systems over time-varying multipath fading channels. To reduce the computation burden of minimum mean-square error (MMSE) equaliser with successive detection (SD), an efficient algorithm is presented by using the property of matrix decomposition. The algorithm avoids direct or recursive computation of matrix inversion, thereby reducing the computation complexity and ensuring numerical stability. Simulations show that the proposed techniques can collect both Doppler and multipath diversity gains with moderate complexities. Copyright © 2010 John Wiley & Sons, Ltd.

Adaptive equalisation in digital communication systems is a process of compensating the disruptive effects caused mainly by intersymbol interference in a band-limited channel and plays a vital role for enabling higher data rate in modern digital communication system. Designing efficient equalisers having low structural complexity and faster learning algorithms is also an area of much research interest in the present scenario. This paper presents a novel technique of improving the performance of conventional multilayer perceptron (MLP)-based decision feedback equaliser (DFE) of reduced structural complexity by adapting the slope of the sigmoidal activation function using fuzzy logic control technique. The adaptation of the slope parameter increases the degrees of freedom in the weight space of the conventional feedforward neural network (CFNN) configuration. Application of this technique provides faster learning with less training samples and significant performance gain. This research work also proposes adaptive channel equalisation techniques on recurrent neural network framework. Exhaustive simulation studies carried out prove that by replacing the conventional sigmoid activation functions in each of the processing nodes of recurrent neural network with multilevel sigmoid activation functions, the bit error rate performance has significantly improved. Further slopes of different levels of the multilevel sigmoid have been adapted using fuzzy logic control concept. Simulation results considering standard channel models show faster learning with less number of training samples and performance level comparable to the their conventional counterparts. Also, there is scope for parallel implementation of slope adaptation technique in real-time implementation, which saves the computational time.

In search for faster and more reliable communication, multiple-input multiple-output (MIMO) in conjuction with Orthogonal Frequency Division Multiplexing (OFDM) are subject of extensive research. In spatial multiplexing transmission an instantaneous rise of data rates governed by the number of transmit antennas can be realised. The system performance depends highly on signal-to-interference-plus-noise ratios (SINR) at the receiver. The receiver's equaliser is supposed to maximize the SINR by mitigating the spatial interference and thus separating the transmitted signals. For this problem several solutions exist such as linear and nonlinear, per subcarrier or OFDM symbol-based. An overview of common algorithms is given and complexity is discussed. Bit error rate (BER) performance evaluations are presented. Another aspect is the impact of the equalisation strategy on the performance of bit-interleaved soft information-based channel coding schemes. As a representative, LDPC codes are chosen. Simulation results show a significant BER performance loss for symbol decision-based equalisers compared to the uncoded performance. To overcome this problem a modification of the Maximum Likelihood algorithm is proposed which yields good performance for low SNR applications.

In this paper, we consider a time division multiple access (TDMA) transmission of coded symbols over a time and frequency selective channel. At the receiver, a turbo-detector composed of a maximum a posteriori (MAP) equaliser and a MAP decoder is used. We give the expression of the MAP iterative burst-by-burst channel estimation algorithm using the Expectation-Maximisation (EM) algorithm. Since the obtained algorithm is complex, we propose to simplify it by neglecting the inter-symbol interference (ISI) term. In order to reduce the error caused by this simplification, we propose to use a candidate precoder at the transmitter chosen among a given set of precoders such that the selected precoded sequence leads to the minimum mean square value of the ISI neglected term. Simulations show that the performance of the approximate algorithm with precoding are almost similar to the performance of the exact algorithm. Copyright © 2010 John Wiley & Sons, Ltd.

Continuous Active SONAR (CAS) systems allow duty cycles up to 100% and so lower target association errors are possible as compared to Pulse Active Sonar (PAS). Large time-bandwidth product Linear Frequency Modulated (LFM) signals are the de facto standard for this type of SONAR systems, yet, these signals suffer from low processing gains when the ocean exhibits low-spatio temporal coherence. In this work, we depart from the typical sub-band matched filter processing and propose to adopt signal processing techniques used in underwater acoustic communications. In particular, we analyze Binary Phase Shift Keying (BPSK) signals via an adaptive Decision-Feedback Equaliser (DFE). The DFE is able to adapt to environmental changes based on the known transmitted bits. The operational bandwidth is 1500–4000 Hz and the BPSK signals are transmitted in two non-overlapping bands to avoid transmit interference during reception. The performance of the proposed system is demonstrated based on field data recorded during a sea experiment off the Coast of La Spezia in October 2017. The key result here is that the Doppler measurement update rate of the echoes is as fast as the bit rate of the transmitted BPSK signal.Continuous Active SONAR (CAS) systems allow duty cycles up to 100% and so lower target association errors are possible as compared to Pulse Active Sonar (PAS). Large time-bandwidth product Linear Frequency Modulated (LFM) signals are the de facto standard for this type of SONAR systems, yet, these signals suffer from low processing gains when the ocean exhibits low-spatio temporal coherence. In this work, we depart from the typical sub-band matched filter processing and propose to adopt signal processing techniques used in underwater acoustic communications. In particular, we analyze Binary Phase Shift Keying (BPSK) signals via an adaptive Decision-Feedback Equaliser (DFE). The DFE is able to adapt to environmental changes based on the known transmitted bits. The operational bandwidth is 1500–4000 Hz and the BPSK signals are transmitted in two non-overlapping bands to avoid transmit interference during reception. The performance of the proposed system is demonstrated based on field data recorded during a ...

Equalisation is necessary in a digital communication system to mitigate the effect of inter-symbol interference and other nonlinear distortions. A new reduced complexity approach to digital communication channel equalization is proposed based on a single generalised neuron (GN). Since it uses only a single GN, there is no problem of selection of initial architecture of the neural network giving optimum performance. It has less computational requirements giving rise to reduced training and computation time. The simulation results show that proposed equaliser bit error rate (BER) performance approaches to optimal Bayesian solution. Defence Science Journal, 2009, 59(5), pp.524-529 , DOI:http://dx.doi.org/10.14429/dsj.59.1559

The key design approaches and results in the field of compensation of optical impairment distortion by electronic means, as an outcome of the studies and research innovations developed within the joint project on mitigation of optical transmission impairments by electronic means work group of the ePhoton/ONe+ European project are presented. The research topics addressed are related to chromatic and polarisation mode dispersion, with particular reference to feed-forward/decision-feedback equaliser and maximum-likelihood sequence estimation-based equalisers as well as pre-distortion schemes. Additionally, the use of electronic compensation in metro/access applications is examined with reference to studies related to the performance enhancement of directly modulated laser transmitters, the compensation of the square-law characteristics of receivers and the equalisation of multi-level format schemes.

This paper proposes a new classification network, the fuzzy C-means based support vector machine (FCM–SVM) and applies it to channel equalisation. In contrast to a kernel-based SVM, the FCM–SVM has a smaller number of parameters while retaining the SVM's good generalisation ability. In FCM–SVM, input training data is clustered by FCM. The output of FCM–SVM is a weighted sum of the degrees where each input data belongs to the clusters. To achieve high generalisation ability, FCM–SVM weights are learned through linear kernel based SVM. Computer simulations illustrate the performance of the suggested network, where the FCM–SVM is used as a channel equaliser. Simulations with white Gaussian and coloured Gaussian noise are performed. This paper also compares simulation results from the FCM–SVM, the Gaussian kernel based SVM and the optimal equaliser.

A thorough study on the beneficial use of electronic distortion equalisation (EDE) in the transmission performance enhancement of conventional low-cost directly modulated lasers (DMLs) is provided. The studies focus first on the compensation of the chromatic dispersion effect and then on the compensation of cascaded filtering effects of DML generated transmission signals in a system, by means of the feed-forward and decision-feedback equalisers (FFE/DFE). The reported studies consider DMLs with different chirp characteristics operating at 2.5 and 10 Gb/s, using parameters that have been extracted from real lasers, previously verified by simulations and experiments. The performance efficiency of EDE is evaluated in terms of eye-opening penalty degradation associated with the signal transmission over a standard single mode fibre. Extensive simulations reveal significant performance improvement for all the examined cases by using the FFE/DFE. Furthermore, the results show that the equalisation efficiency strongly depends on the chirp characteristics of DMLs.

Decision feedback equaliser (DFE) for dispersion compensation is a cost-effective element in optical communication OOK systems. The most common but sub-optimal optimisation criterion for the DFE weights is based on minimising the mean square error (MSE). Here, we derive an analytical expression for the probability of error with DFE and examine the optimal optimisation criterion, minimum bit-error rate (MBER) for DFE in optical communication system. A BER performance comparison analysis shows that the MBER optimisation criterion introduces improvements over the conventional minimum MSE optimisation criterion.

Turbo equalisation (TEQ) is an iterative detection and decoding technique that has been shown to be successful in mitigating the effects of intersymbol interference (ISI) introduced by partial response modems and by dispersive channels. In this paper, we propose a fuzzy filter-assisted decision-feedback equaliser (DFE)-based TEQ scheme that not only is comparable in performance to the Jacobian radial basis function (RBF) DFE-based TEQ but also is low-complexity. The per iteration computation of both the fuzzy filter DFE TEQ using product inference and maximum defuzzification and the fuzzy filter DFE TEQ using minimum inference and maximum defuzzification is much lower than that of the Jacobian RBF DFE TEQ for binary phase-shift keying (BPSK) modulation, 4 quadrature amplitude modulation (QAM), and 16 QAM. Notably, the computational complexity of the Jacobian RBF DFE TEQ is exponentially related to the feedforward order, but the fuzzy filter DFE TEQ using minimum inference and maximum defuzzification is independent of that. Previous TEQ research has shown that the Jacobian RBF DFE TEQ considerably reduces the computational complexity compared to the logarithmic maximum a posteriori (Log-MAP) TEQ with similar performance. In this present study, the proposed fuzzy filter DFE TEQ further reduces the computational complexity with slight performance degradation in contrast to the Jacobian RBF DFE TEQ. With this, the materialisation of the TEQ scheme becomes more feasible. Copyright © 2007 John Wiley & Sons, Ltd.

This paper investigates a blind space–time equaliser (STE) designed for single-input multiple-output (SIMO) systems that employ high-throughput quadrature amplitude modulation schemes. A constant modulus algorithm (CMA) aided soft decision-directed (SDD) scheme, originally derived for low-complexity blind equalisation of single-input single-output channels, is extended to the SIMO scenario. Simulations are conducted to compare the performance of this blind adaptive scheme with another low-complexity blind STE referred to as the CMA aided decision directed (DD) scheme. The results obtained demonstrate that for SIMO systems the CMA aided SDD scheme exhibits advantages over the CMA aided DD arrangement, in terms of its faster convergence speed and lower computational complexity.

To compensate the performance degradation induced by polarisation mode dispersion (PMD) in high-speed optical transmission, a single-input multiple-output (SIMO) decision feedback equaliser (DFE) technique is proposed to combat all orders of PMD-induced distortion. The scheme is based on a new SIMO PMD channel model which utilises information embedded in both polarisation states. The performance analysis of the proposed PMD SIMO DFE scheme is provided along with explicit expressions for the filter coefficients. The analysis results show that the new scheme provides a significant improvement over using a first-order optical compensator and conventional DFE.

A novel system-level simulation environment is presented for the evaluation of step-index polymer optical fibre transmission systems. Key element is a new fibre model, which incorporates the three major attributes describing light propagation in SI-POF: the mode-dependent attenuation, the modal dispersion and the mode coupling process. Inter-symbol interference (ISI) due to modal dispersion can be mitigated in the receiver by means of electronic dispersion compensation. In this work, we present the performance of an analog equaliser scheme based on a (sub-)optimal a-posteriori-probability (APP) technique, which increases the achievable fibre length for error-free transmission at 1 Gbit/s from 11 to 53m. Copyright © 2007 John Wiley & Sons, Ltd.

The RDE for M-ary QAM equalisation is modified using a low-complexity probabilistic update algorithm. Performance is investigated in simulation and experiment for 8 GBd DP-64QAM and DP-256QAM. DP-64QAM improved by 3.2 dB Q2-factor for a dynamic channel with high OSNR.