Adaptive estimation and equalisation of the high frequency communications channel

SIGLEAvailable from British Library Document Supply Centre- DSC:D94945 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

QR factorization equalisation scheme for mode devision multiplexing transmission in fibre optics

Optical communication systems play a major role in handling worldwide Internet traffic. Internet traffic has been increasing at a dramatic rate and the current optical network infrastructure may not be able to support the traffic growth in a few decades. Mode division multiplexing is introduced as a new emerging technique to improve the optical network capacity by the use of the light modes as individual channels. One of the main issues in MDM is mode coupling which is a physical phenomenon when light modes exchange their energy between each other during propagation through optical fiber resulting in inter-symbol interference (ISI). Many studies based on Least Mean Square (LMS) and Recursive Least Square (RLS) have taken place to mitigate the mode coupling effect. Still, most approaches have high computational complexity and hinders high-speed communication systems. Blind equalisation approach does not need training signals, thus, will reduce the overhead payload. On the other hand, QR factorization shows low computational complexity in the previous research in the radio domain. The combination of these two concepts shows significant results, as the use of low complexity algorithms reduces the processing needed to be done by the communication equipment, resulting in more cost effective and smaller equipment, while having no training signal saves the bandwidth and enhances the overall system performance. To the best knowledge of the researcher, blind equalisation based on QR factorization technique has been not used in MDM equalisation to date. The research goes through the four stages of the design research methodology (DRM) to achieve the purpose of the study. The implementation stage is taken two different simulators has been used, the first one which is the optical simulator is used to collect the initial optical data then, MATLAB is used to develop the equalisation scheme. The development starts with the derivation of the system’s transfer function (H) to be used as the input to the developed equalizer. Blind equalisation based on QR factorization is chosen as a way to introduce an efficient equalization to mitigate ISI by narrowing the pulse width. The development stages include a stage where the channel estimation is taken place. Statistical properties based on the standard deviation (STD) of the powers of the input and output signals has been used for the blind equalisation’s channel estimation part. The proposed channel estimation way has the ability in estimating the channel with an overall mean square error (MSE) of 0.176588301 from the initial transmitted signal. It is found that the worst channel has an MSE of 0.771365 from the transmitted signal, while the best channel has and MSE of 0.000185 from the transmitted signal. This is done by trying to avoid the issues accompanied with the development of the previous algorithms that have been utilized for the same goal. The algorithm mentioned in the study reduces the computational complexity problem which is one of the main issues that accompany currently used tap filter algorithms, such as (LMS) and (RLS). The results from this study show that the developed equalisation scheme has a complexity of O(N) compared with O(N2) for RLS and at the same time, it is faster than LMS as its calculation CPU time is equal to 0.005242 seconds compared with 0.0077814 seconds of LMS. The results are only valid for invertible and square channel matrices

Evolving Optimal IIR and Adaptive Filters

In this thesis, current digital filter design techniques are critically reviewed and problems associated with computational cost, complexity, frequency response and speed of convergence, identified. Based on this, a globally optimal, fine- tuned and efficient evolutionary hybrid technique has been developed to automate and optimise infinite impulse response (HR) and adaptive filter design. The proposed hybrid design approach employs an evolutionary algorithm (EA) as a global search tool and a least mean square (LMS) algorithm, whenever appropriate, as a fine-tuner. This permits optimal and real-time tracking of time varying changes in nonstationary environments as widely encountered in telecommunications. In the development, various improvements on existing algorithms are made, including those on components of EAs, LMS algorithm and the filter structures. The aims are to be able to evolve direct form HR structures using simple stability monitoring techniques, to improve local hue-tuning performance and to avoid premature convergence. To evolve complex phenotype chromosomes that are needed by complex HR. filters, a novel method of crossover operation is developed. This is a variation of the standard uniform crossover in which the split points are considered to combine uniquely as indivisible floating-point complex valued genes. The split-point crossover operation produces more new members than the standard crossover operation, and hence provides a faster rate of convergence and avoids premature convergence. The EAs have been particularly designed for small population sizes and to reduce premature convergence, a new operator is designed to introduce new members into the population during evolution. Two techniques are investigated in the design of linear adaptive HR digital filters, namely, the pole design method and the coefficient design method. The pole design method provides filter stability throughout the genetic search without requiring a variety of stability monitoring techniques. The coefficient design method uses simple stability guaranteeing techniques, which also improves the rate of convergence of the EAs. With the hybrid technique, complex-coefficient filters have been designed successfully and globally optimal and adaptive filters have been achieved. The developed methodologies and designs are verified using higher order complex HR systems and, for adaptation, inverse system modelling that is synonymous with channel equalising filters operating in multipath environments. Here adaptive complex parameters become possible to equalise amplitude and phase distortions of the received signals. Various stability-ensuring techniques are investigated extensively and their convergence performances are compared with the proposed method. The proposed hybrid, global and fine design technique is applied to solve adaptive channel equalisation and noise cancellation problems commonly existing in telecommunications