In this study, two optical wireless indoor multiple‐input–multiple‐output systems using on–off keying and pulse position modulation are studied. Then, by using the Matlab curve‐fitting, the training parts of the experimental results are fitted and evaluation models are developed, where root mean squared error and additional testing data are used to verify the accuracy of the evaluation models.

In this paper, we analyze the performance of a prism-array receiver in a multiple-input multiple-output (MIMO) intensity-modulated direct-detection optical wireless communication system. The elements of the MIMO channel matrix depend on the geometry of each prism and the orientation of the prism relative to the optical transmitter. An expression is derived for each channel gain as a function of the angle of the prism, the aspect ratio and area of the receiving surface of the prism, and the orientation and distance between the transmitter and receiver. Results are presented for the directionality and overall field of view (FOV) of a receiver comprising six prisms, showing that compact receivers can be designed, which combine well-conditioned channel matrices with wide FOVs. Simulation results are presented for a typical indoor visible light communication system where four light-emitting diode lights transmit information using asymmetrically clipped optical orthogonal frequency division multiplexing and linear equalizers are used in the receiver. It is shown that the overall bit error rate depends very strongly on the angle of the prisms and on the position of the receiver, but that a simple six-prism receiver can successfully decouple the four transmitted signals at typical receiver positions within the room.

The authors propose a model for estimating the response of an ultrasonic communication channel, where a specific type of capacitive transreceivers was used to give an effective bandwidth of over 1 MHz. Apart from the responses of transreceivers, the channel response at each location within the radiated field can be determined by attenuation response and special field response. The driving signal used to verify the model was a quadrature phase shift keying (QPSK) signal centred at 300 kHz, and with a signalling rate of 400 kbps. Simulations were firstly carried out to identify the variations in waveform as well as spectrum caused by predicted response at several coordinates. This is then compared with experimental results, and good agreements were found between the two.

New low-complexity adaptive receivers are proposed for time-hopping binary phase shift keying ultra-wide bandwidth systems with multiple users. Both additive white Gaussian noise and multipath fading channels are considered. Numerical results show that the new adaptive receivers outperform the conventional matched-filter receivers in both additive white Gaussian noise and multipath fading channels, when the multiple-access interference is present. Moreover, the performance gain increases when the number of users decreases or the signal-to-noise ratio increases.

A genetic algorithm controlled multispot transmitter is demonstrated that is capable of optimising the received power distribution for randomly aligned single element receivers in multiple fully diffuse optical wireless communications systems with multiple mobile users. Using a genetic algorithm to control the intensity of individual diffusion spots, system deployment environment changes, user movement and user alignment can be compensating for, with negligible impact on the bandwidth and root mean square delay spread. It is shown that the dynamic range, referenced against the peak received power, can be reduced up to 27% for empty environments and up to 26% when the users are moving. Furthermore, the effect of user movement, that can perturb the channel up to 8%, can be reduced to within 5% of the optimised case. Compared to alternative bespoke designs that are capable of mitigating optical wireless channel drawbacks, this method provides the possibility of cost-effectiveness for mass-produced receivers in applications where end-user friendliness and mobility are paramount.

An overview of the developments in optical wireless systems viewed from the traditional communications viewpoint of transmitter, channel and receiver is presented. The trends in modulation formats that match information to the optical wireless channel are considered. This is followed by the discussion of recent transmitter and receiver innovations, particularly the utilisation of diversity transceivers. As a preliminary to the following treatment, the nature and modelling of the optical wireless channel are introduced, with particular emphasis on its unique features in terms of transmitted power constraints and non-negativity. From the examination of modulation formats, on-off‐keying remains the format of choice for basic binary transmission, whereas pulse-position modulation and its derivatives are preferred for more sophisticated requirements. The recent introduction of techniques from radio systems employing subcarriers is seen to be the most promising development in modulation techniques at present. In receiver technology, quasi-diffuse systems employing multispot diffusion and angular diversity are significant developments. They offer lower path loss and less multipath dispersion, at a lower transmission power compared to ‘conventional’ wide-angle diffuse systems, while providing a high level of user mobility compared to line-of-sight transmission. These developments are helping optical wireless systems to fulfil their promise by adopting a philosophy inspired by the radio domain to accommodate operation within a hostile channel.

Performance of optical wireless communication (OWC) systems can be optimised using constant optical power transmission in conjunction with forward error control coding. A new family of constant power error correcting codes using multiple pulse position modulation optical transmission are introduced. This doubly featured technique may extend the capability of many difficult wireless optical links beyond their existing barriers and may enable a higher error performance for OWC networks. The potential and design of look-up table codes are investigated. The Monte Carlo methods provide supportive data for the performance and code word search.

This paper aims to illustrate for the first time the applicability of emergence within the design, modeling and simulation of wireless routing protocols for the security of information exchange in the presence of a malicious node. Our methodology focuses on the black hole problem and delivers a set of results that describe a protocol prototype within a number of set characteristic pairs. For this purpose, and motivated by the ever growing number of protocol implementations, we define an adaptive system that, through a set of simple rules, has the capability of selecting the fittest structure within a well defined environment capable of dealing with the problem under question.

A new simplified approach for QAM signal error analysis in hybrid AM/QAM lightwave systems is proposed. The method allows fast and accurate BER calculation.

Content based indexing and retrieval of images and video requires a proper semantic description for image content. The paper discusses the mapping of high level, application specific features to the visual primitives that are accessible through image processing techniques. A major difficulty is that there are currently no established methodologies for describing the contents of an image in terms of semantic features, and we suggest that semiotic approaches could be adapted to the task of image description in limited areas of expertise. After reviewing current trends in the mapping of high level to low level features, we present preliminary results that suggest a possible strategy for mapping semiotic descriptions to image processing primitives.

Analogue video cavalcade services in cable access television (CATV) networks usually require a very high carrier-to-noise ratio (CNR) in order to provide a good quality picture. In consequence, practical lightwave hybrid amplitude modulation (AM) M-ary quadrature amplitude modulation (M-QAM) systems are found to suffer only infrequent clipping impulse noise, which can be provably modeled as a Poisson arriving pulse train. Based on this knowledge, a new expression for the probability density function (PDF) of the clipping noise at the output of a QAM demodulation matched filter is given which can be numerically evaluated with high accuracy. The bit-error rate (BER) performance prediction is then carried out for M-QAM signals within the hybrid system in the presence of an additive mixture of Gaussian and clipping impulse noise. The agreement between the analytical results and the experimental data is quite good.

An automatic off-line character recognition system for handwritten cursive Arabic characters is presented. A robust noise-independent algorithm is developed that yields skeletons that reflect the structural relationships of the character components. The character skeleton is converted to a tree structure suitable for recognition. A set of fuzzy constrained character graph models (FCCGM's), which tolerate large variability in writing, is designed. These models are graphs, with fuzzily labeled arcs used as prototypes for the characters. A set of rules is applied in sequence to match a character tree to an FCCGM. Arabic handwritings of four writers were used in the learning and testing stages. The system proved to be powerful in tolerance to variable writing, speed, and recognition rate.>

The objective signal-to-noise performance of component colour video signals is analysed in this paper for FM and AM-VSB video transmission systems. In the analysis, the effect of splitting the composite video signal into its components, by subcarrier demodulation and colour decoding, is taken into consideration. The effect of non linearity of the display is also included in the analysis. An expression for objective component signal-to-noise ratio is derived for both the transmission systems. A relationship between the conventional composite video SNR and the component video SNR is established. Effective noise transfer, between the input and various stages of video signal processing, is discussed in detail. Noise spectral density analysis, for fully saturated primary colours, is evaluated quantitatively for a PAL-I video system. Finally, SNR performance of various hues at constant luminance is evaluated, and the results obtained are compared with the subjective noise visibility tests first carried out in 1957.>