An improved multiple access scheme for chaos-based digital communications using adaptive receivers

Author name used in this publication: Francis C.M. LauAuthor name used in this publication: Chi K. TseRefereed conference paper2003-2004 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

A multiple access scheme for chaos-based digital communication systems utilizing transmitted reference

Author name used in this publication: Francis C. M. LauAuthor name used in this publication: Chi K. Tse2004-2005 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Bit error performance of diffuse indoor optical wireless channel pulse position modulation system employing artificial neural networks for channel equalisation

The bit-error rate (BER) performance of a pulse position modulation (PPM) scheme for non-line-of-sight indoor optical links employing channel equalisation based on the artificial neural network (ANN) is reported. Channel equalisation is achieved by training a multilayer perceptrons ANN. A comparative study of the unequalised `soft' decision decoding and the `hard' decision decoding along with the neural equalised `soft' decision decoding is presented for different bit resolutions for optical channels with different delay spread. We show that the unequalised `hard' decision decoding performs the worst for all values of normalised delayed spread, becoming impractical beyond a normalised delayed spread of 0.6. However, `soft' decision decoding with/without equalisation displays relatively improved performance for all values of the delay spread. The study shows that for a highly diffuse channel, the signal-to-noise ratio requirement to achieve a BER of 10−5 for the ANN-based equaliser is ~10 dB lower compared with the unequalised `soft' decoding for 16-PPM at a data rate of 155 Mbps. Our results indicate that for all range of delay spread, neural network equalisation is an effective tool of mitigating the inter-symbol interference

Chaotic communications with correlator receivers: theory and performance limits

This paper provides a review of the principles of chaotic digital communications using correlator receivers. Modulation schemes using one and two chaotic basis functions, as well as coherent and noncoherent correlation receivers, are discussed. The performance of differential chaos shift keying (DCSK) in multipath channels is characterized. Results are presented for DCSK with multiuser capability and multiple bits per symbol

Multi user chaotic communication systems sing orthogonal chaotic vectors

Due to quasi orthogonal nature of chaotic spreading sequences, the co-channel interference will be introduced and increases with the increase in number of users and limits the number of simultaneous users transmitting information. In this dissertation the application of orthogonal chaotic vector (OCV) for spreading information bits is presented. The bit error rate of the multi user chaotic communication system is analysed through simulation and analytical expressions. Two main types of communication scenarios are considered, multi user chaotic communication system with coherent receiver and training assisted non coherent multi user chaotic communication system with adaptive receiver. The first case deals with ideal scenario where it is assumed that exact replica of chaotic vector used to spread data is available at the receiver and the information is extracted without synchronisation error. Thus lacks practical realisation but, the results obtained will provide a lower bound for comparison with other practical counter parts. The second scenario deals with more practical approach where a reference chaotic sequence is also transmitted by modulating with training bits so that the chaotic vector required for correlation can be recovered at the receiver

Symmetric complex-valued RBF receiver for multiple-antenna aided wireless systems

A nonlinear beamforming assisted detector is proposed for multiple-antenna-aided wireless systems employing complex-valued quadrature phase shift-keying modulation. By exploiting the inherent symmetry of the optimal Bayesian detection solution, a novel complex-valued symmetric radial basis function (SRBF)-network-based detector is developed, which is capable of approaching the optimal Bayesian performance using channel-impaired training data. In the uplink case, adaptive nonlinear beamforming can be efficiently implemented by estimating the system’s channel matrix based on the least squares channel estimate. Adaptive implementation of nonlinear beamforming in the downlink case by contrast is much more challenging, and we adopt a cluster-variationenhanced clustering algorithm to directly identify the SRBF center vectors required for realizing the optimal Bayesian detector. A simulation example is included to demonstrate the achievable performance improvement by the proposed adaptive nonlinear beamforming solution over the theoretical linear minimum bit error rate beamforming benchmark