Two-stage interference immune blind equaliser which exploitscyclostationary statistics

Since cyclostationarity is inherent in many man-made signals, there is much to be gained in the signal processing and communication areas if this property is properly recognised and exploited. In particular, the authors propose a novel two-stage scheme which exploits second-order cyclostationary statistics for co-channel interference removal and blind equalisation. The first stage adopts the blind adaptive (BA) FRESH filter proposed by Zhang, to remove co-channel interference and channel noise. The second stage is based on a blind equalisation algorithm, proposed by Tong, which operates on the filtered cyclic signal to remove intersymbol interference. Simulation studies have demonstrated that this two-stage blind equalisation scheme has a fast rate of convergence and excellent performance in a high SNR environment     

Optical level equalisation based on gain saturation in fibreoptical parametric amplifier

Optical level equalisation operation based on gain saturation in an optical fibre parametric amplifier is reported. The signal output has been measured as a function of the signal input in a fibre parametric amplifier, with the result that the signal gain saturates as the input power increases and the output power reached a maximum value at a particular input level. Utilising this gain saturation property, optical level equalisation has been demonstrated     

Lattice-reduction-aided equalisation for transmission over intersymbol-interference channels

Transmission over channels that produce intersymbol interference is considered. New equalisation schemes derived from recently proposed lattice-reduction-aided equalisation of multiple-input/multiple-output channels are presented. The schemes exhibit low complexity, require no or only very little channel state information at the transmitter, and channel coding can be immediately applied. The connection to partial-response signalling and state-of-the-art equalisation schemes is explained. Numerical simulations show good performance of the equalisation scheme.     

Frequency-domain equalisation for optical transmission systems

The first optical single-carrier (SC) transmission system to employ frequency-domain equalisation (FDE) is proposed; 25 Gbit/s SC with FDE is demonstrated in severe chromatic dispersion conditions. The results show that SC with FDE is very tolerant of the chromatic dispersion.     

均衡掺铒光纤放大器及8×2.5Gb/s 450km传输实验

　Aiming at the problem of dynamically gain imbalance in cascaded amplification WDM system,a series of dynamically gain equalized Erbium-doped fiber power booster and inline amplifier were designed and built,in which the population inversion was controlled.The equalisation transmission was demonstrated by using this kind of EDFA.     

Transformation of a Rayleigh fading channel into a set of parallelAWGN channels and its advantage for coded transmission

The authors consider transmission over a memoryless Rayleigh fading channel. It is shown that an appropriate orthogonal transformation at the transmit side and block decision feedback equalisation at the receive side transform the Rayleigh fading channel into a set of AWGN channels. The advantage for coded transmission is demonstrated     

Cascade neural networks for multichannel blind deconvolution

The authors present a new simple but efficient and powerful extension of Bussgang-type blind equalisation algorithms which can extract multiple source signals from their unknown convolutive mixtures. A cascade neural network is proposed, where each module consists of an equalisation subnetwork and a deflation subnetwork. This approach can adopt any blind equalisation algorithm (which has been developed for the equalisation of a single channel). It can also be applied when the number of source signals is not known in advance. Extensive computer simulation results confirm the validity and high efficiency of the proposed method     

Histogram equalisation with S and ? functions in detecting X-ray edges

An algorithm consisting of a histogram equalisation technique followed by further enhancement using S and ? membership functions is described to detect the small variation in grey levels of X-ray images. The effectiveness of the algorithm in identifying the different regional contours related to growth of normal bones is demonstrated.     

Optical beam equalisation using degenerate two-wave mixing

Optical beam equalisation using degenerate two-wave mixing with photorefractive crystals is proposed. The relationship between parameters to achieve beam equalisation is derived.     

Colour histogram equalisation of multichannel images

Histogram equalisation works well on single-channel images; however, the technique used is ineffective on multiple channels because there are an infinite number of ways to perform the equalisation. A technique is developed that works on images with any number of channels, and the inadequacy of a direct extension of histogram equalisation to multiple dimensions is shown. A logarithmic metric is developed to express how well the available histogram volume is utilised and how well equalisation is working. Results of using the technique and using it in reverse, i.e. to reduce the histogram utilisation, are shown. Extensions of the technique are used to measure the difference between and conform one multichannel histogram to another, and uses of these techniques are discussed.     

Bandwidth efficient single carrier systems with frequency domain equalisation

A new bandwidth efficient single carrier system with frequency domain equalisation is proposed. Turbo equalisation and cyclic prefix reconstruction are combined together to eliminate the normally required cyclic prefix for such a system. The proposed method achieves much better performance than the residual inter-symbol interference cancellation approach by utilising soft decoded information and introducing turbo equalisation. The performance of the proposed scheme is studied through simulations.     

Low complexity concurrent constant modulus algorithm and soft decision directed scheme for blind equalisation

The recently introduced concurrent constant modulus algorithm (CMA) and decision-directed (DD) scheme provides a state-of-the-art low-complexity blind equalisation technique for high-order quadrature amplitude modulation (QAM) channels. At a small cost of slightly more than doubling the complexity of the standard CMA blind equaliser, this concurrent CMA and DD blind equaliser achieves a dramatic improvement in equalisation performance over the CMA. In the paper, a new blind equalisation scheme is proposed based on concurrent CMA and a novel soft decision-directed (SDD) adaptation. The proposed concurrent CMA and SDD blind equaliser has simpler computational requirements than the concurrent CMA and DD algorithm. Extensive simulation shows that it has the same steady-state equalisation performance as the concurrent CMA and DD algorithm and a faster convergence speed over the latter scheme     

Bayesian channel equalisation and robust features for speechrecognition

The use of a speech recognition system with telephone channel environments, or different microphones, requires channel equalisation. In speech recognition, the speech model provides a bank of statistical information that can be used in the channel identification and equalisation process. The authors consider HMM-based channel equalisation, and present results demonstrating that substantial improvement can be obtained through the equalisation process. An alternative method, for speech recognition, is to use a feature set which is more robust to channel distortion. Channel distortions result in an amplitude tilt of the speech cepstrum, and therefore differential cepstral features provide a measure of immunity to channel distortions. In particular the cepstral-time feature matrix, in addition to providing a framework for representing speech dynamics, can be made robust to channel distortions. The authors present results demonstrating that a major advantage of cepstral-time matrices is their channel insensitive character     

Fuzzy adaptive decision feedback equaliser

As a new approach to the equalisation of nonlinear channels, a fuzzy adaptive decision feedback equaliser based on a fuzzy adaptive filter is proposed. With perfect knowledge of the channel, the proposed method not only improves equalisation performance but also reduces the computational complexity compared with the conventional fuzzy adaptive filter     

PMD compensation in optical coherent single carrier transmission using frequency-domain equalisation

The transmission performance of optical single-carrier (SC) transmission using frequency-domain equalisation (FDE) to counter polarisation mode dispersion (PMD) is evaluated. 25 Gbit/s coherent optical SC transmission using FDE (CO-SC-FDE) is demonstrated in the presence of a significant amount of differential group delay (DGD). The results show that CO-SC-FDE compensates for the influence of the 125 ps DGD; the OSNR penalty is 0.81 dB.     

Application of jacobi algorithm for ISI channels

Here, the Jacobi iterative algorithm is applied to combat intersymbol interference (ISI) caused by frequency-selective channels. The performance bound of the equaliser is analysed in order to gain an insight into its asymptotic behaviour. Because of the error propagation problem, the potential of this algorithm is not reached in an uncoded system. However, its extension to a coded system with the application of the turboprocessing principle results in a new turbo equalisation algorithm, which demonstrates comparable performance with reduced complexity compared with some existing filter-based turbo equalisation schemes; and superior performance compared with some frequency domain solutions, such as orthogonal frequency division multiplexing and single-carrier frequency domain equalisation.     

Efficient two-stage frequency-domain equalisation for mitigating MAI in CDMA systems

An efficient two-stage frequency-domain equalisation (TS-FDE) is proposed, in order to mitigate the effect of multiple access interference (MAI) in code division multiple access (CDMA) systems having no cyclic-prefix (CP). In TS-FDE, the first stage performs channel equalisation and signal detection. Utilising the detected signal and a channel response, the second stage constructs the circularity of a channel matrix for a received signal, and then it performs once more the channel equalisation like an FDE using the CP. The MAI mitigating capability of the TS-FDE is evaluated in a mobile channel.     

Phase equalisation of analogue magnetic recorders by transversal filtering

The `time-reversed-impulse-response? method of phase equalisation is explained theoretically. Experimental results are presented, showing the impulse response of an analogue magnetic recorder before and after phase equalisation. The transversal-filter equaliser (32-tap analogue delay line of 320 ?s length) is adjusted in the time domain so that actual phase-response measurements are not necessary.     

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     

Active feed-forward channel equalisation for chirped pulsewavelength division multiplexing

A channel equalisation scheme for chirped-pulse wavelength-division-multiplexing (CPWDM) is described and implemented. The equalisation is realised using a simple feed-forward circuit that dynamically varies the loss of the modulator, which is used to sequentially encode channels in CPWDM to actively adjust the channel strengths. A 50% increase in the number of channels within 3 dB power variation is achieved for our laser spectrum