Approved for public release; distribution is unlimited / The objective of this thesis is to synthesize signals with a dynamically change power spectral density, in a SDR transmitter, utilizing the most appropriate channels, modulation schemes and transmission rates for communication, based on the noise profile (AWGN plus interferences) of the link, in order to achieve performance within some predefined acceptable levels. The objective is obtained by simulation. / Major, Hellenic Army

The results of a feasibility study of some new methods for reducing the bandwidth required for transmission of commercial-quality television are described in this thesis. It is shown that television requires a wide transmission bandwidth because of the broad frequency spectrum obtained in scanning scenes which contain abrupt changes of brightness at edges. An efficient method of coding these edges is therefore sought. The properties of the Gabor-type hologram are studied and it is shown that holograms may be used advantageously to code the picture edge information. A two-channel system is proposed and its construction and testing described. The low-frequency information is transmitted in conventional form on one channel and the high-frequency information in hologram form on the other channel. The test results support the theoretical prediction that the system can transmit television pictures with reduced bandwidth. However, the system is shown to have practical disadvantages largely caused by the necessity of making electro-optical conversions which cannot be performed in real time. In one of the alternative systems proposed here, a reduced bandwidth is made possible by transmitting the low-frequency information conventionally, and the edge pattern is scanned in a vertical direction to transmit the high frequencies. In a practical test, the system gave a bandwidth compression ratio of 6:1. As a basis for another possible system it is shown that because the edge pattern of typical pictures occupies only a small fraction of the raster area and exhibits a high degree of spatial correlation, bandwidth compression could be achieved by transmitting only this edge information. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis is part of a feasibility study concerned with the application of the Gabor Hologram to a proposed method of bandwidth compression of television (video) signals obtainable by scanning a restricted class of two tone pictures: the experimental work consists of producing and improving on the Gabor type Holograms and demonstrating the reconstruction. The proposed television system will employ two channels. One channel would be used to transmit the signal obtained by scanning the picture normally; the bandwidth allowed for this channel, though, would be much less than the normal bandwidth: the other channel of equally reduced bandwidth would be used to transmit the signal obtained, again by normal scanning, from the Hologram. At the receiver, optical superposition of the two pictures obtained from the two channels would be made. For a certain restricted class of two tone pictures the distortion produced at the receiver by this method of picture transmission is anticipated to be negligible. The Fourier transform property of the Hologram is specially developed in order to complement the two channel television system. Considering the transform point of view it has been shown theoretically that the reconstruction lens suggested by Gabor is not necessary for the two step imaging process and a lensless system has been developed. It is demonstrated that better quality results can be obtained by using the modified process. In the experimental setup a positive lens necessary to widen the laser beam is used. The effect of the noisy Airy rings created by this lens is studied and a pinhole method of removing the noise has been suggested and its effectiveness demonstrated experimentally. Finally some examples of two step imaging using the modified lensless system are given. The detailed account of the experimental work is given to facilitate future work. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A diversity combining scheme is examined that utilizes a demodulator's hard decisions in conjunction with knowledge of each decision's reliability. A maximum-likelihood bit decision is made, based on these partial decisions from the demodulator and on measurements of the state of the fading channel. The technique is sub-optimal since hard decisions are processed, but it may find application in low cost receiver design. The technique is optimal in the sense that a minimum probability of bit error is achieved, given a set of partial decisions and knowledge of their reliability. Performance analysis for the case of non-coherent frequency shift keying on a slow Rayleigh fading channel with additive white Gaussian noise includes the derivation of a tight upper bound on the probability of bit error, and estimates of the asymptotic performance relative to standard diversity schemes such as majority-voting, selection diversity, square-law, and maximal ratio combining. These results are supported by simulation results for bit and packet error rates in an example system. With five independent bit repeats and a BER of 10⁻³, the receiver is about 3 dB more efficient than majority-voting, and about 1 dB more efficient than selection diversity. The gain in efficiency, relative to the standard partial decision combination schemes, increases with the number of repeats. The degradation in performance in a practical receiver implementation is addressed, and it is demonstrated that near ideal performance may be obtained with only a few reliability weights quantized to a small number of levels. Furthermore, this performance is maintained over a wide range of average signal to noise ratio without having to adapt the reliability weights. When the reliability estimate is corrupted by additive white Gaussian noise, it is demonstrated that simple low- pass filtering of the signal strength estimate is sufficient to obtain near ideal performance. The performance is degraded in the presence of cochannel interference, but for a moderate level of interference the performance is demonstrated to be superior to majority-voting or selection diversity. Other results include a method to estimate the optimal quantization thresholds, and a method to obtain the probability of error of selection diversity receivers employing signal to noise ratio measurement quantization. The selection diversity analysis is applicable to the more general case of Rician fading. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Call number: LD2668 .T4 1951 B83 / Master of Science

Call number: LD2668 .T4 1950 F85 / Master of Science

by Hung Kwok Wah. / Summary in Chinese and English / Bibliography: leaves 43-46 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

No description available.

Optical signal processing is introduced as a tool for investigations in the field of television compression research. An optical signal processing system is designed, which performs the Fourier transform of a picture signal F[B(x,y)] and its reconstruction F⁻¹ {F [B(x,y)]} . Some basic optical filtering experiments are performed in the spatial frequency plane, and the optical analogue of the frequency sampling theorem is demonstrated. The Fourier transforms of test pattern pictures show large gaps which can be used for compression. Observation of complex spectra of continuous tone pictures is found to be impaired by noise effects. A physiological experiment is carried out, which investigates the relationship between tolerable flicker frequency and spatial frequency of a television picture. It is found that the tolerable flicker rate f decreases as the spatial frequency fx is increased, according to the empirical equation fc = fo exp(-kfx). fo and k are parameters depending on factors like contrast ratio, kind and size of picture, etc. Compression systems using the above results are found to have a limit of obtainable compression ratio of approximately 3 to 1. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Thesis (M.Sc.)--Chinese University of Hong Kong. / Bibliography: leaves 84-86.