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Bibliography: leaves 116-7., The last decade has shown a very rapid increase in the application of digital computers to virtually all walks of life. This has resulted in a demand for better and faster digital communication links, at reasonable prices. Trellis coded modulation is a fairly recent development in the technology of digital communications that has helped to meet an aspect of this demand. The Department of Electrical Engineering at the University of Cape Town had not undertaken any research in the field of trellis coded modulation at the time this thesis was started. From what was understood of the topic at the time, it was deemed important to develop a foundation of skills and tools for working with trellis coded modulation. It was hoped that such a foundation will give current and future members of the department sufficient background to spot potential applications for the principles of trellis coded modulation.

Includes bibliographical references., This thesis investigates the use of partial response signalling as a modulation scheme in a modem structure. The modem structure consists of transmitter modulation and receiver demodulation sections only. The modem is designed to operate at data rates of 2400, 4800 and 9600 bps. The signalling format replaces the CCITT Recommendation V.29 format. The transmitted signal is required to conform to the bandwidth limitations of CCITT Recommendation M.1020 leased telephone circuits.

Bibliography: leaves 78-79., Partial response signaling ( PRS) has been used successfully to improve the spectral properties of Pulse Amplitude Modulated (PAM) digital transmission systems. This thesis investigation studied the effect of PRS on frequency- and phase-modulated carrier systems, in particular on their spectral performance and their maintenance of constant envelope.

Includes bibliographical references.

Includes bibliographical references., This thesis investigates high-speed digital transmission over a conditioned, voice-grade telephone circuit (M.1020), using a technique known as partial response signaling, or PRS. In particular, the case where 4800 bps, full-duplex transmission is required in a CCI'PT V. 22 type format is investigated. The main v.22 criterion to be adhered to, is that frequency-division multiplexing (FDM) is to be used as the means of separating thetransmit and receive channels. The carrier frequencies should be 1200 Hz and 2400 Hz respectively. The investigation concerns the modulation and demodulation sections only.

Includes bibliography., An investigation into the analysis of Digital Microwave Radio Paths was conducted. The causes and effects of multipath fading on the propagation of microwave signals are of particular interest here. A study is made of the theory of link engineering, including an examination of fading and distortion, and the instrumentation used in the analysis of link performance. Multipath fading, the different categories, as well as the causes and effects thereof, are reviewed. The Tellurometer Method of distance measurement is described and its suitability to path analysis discussed.

This thesis concerns itself with the study of the Minimum Shift Keying (MSK) modulation scheme. The aspects considered are its operation under non-linear conditions as well as an investigation into the hardware implementation of both coherent and non-coherent MSK modems. The literature on digital data transmission and MSK in particular is surveyed, and a comprehensive theoretical description of MSK is given. In addition, papers on the operation of MSK under non-linear conditions were studied, and their major findings are presented. Due to the lack of theory on the effects of incorrect modulation index on the error performance of MSK, an investigation into this avenue was performed. The design of a correction mechanism for maintaining the modulation index at its correct value is described, and aspects of its implementation are considered. Using the available literature, various modules of which a coherent MSK modem is comprised were developed, and their design is discussed. The design of a non-coherent MSK demodulator is also described.

This thesis concerns itself with the development of a real-time automatic Network Analyzer measurement system based on Hewlett Packard's manual HP8410C. The major limitation in non real-time systems is the time required to perform a measurement. Real-time systems have greater measurement speed than their non real-time counterparts, but are also generally less accurate. The main objectives of the thesis are to survey literature on high frequency measurements, to develop hardware and software for a real-time Analyzer and to perform tests with the system.

The purpose of this dissertation is to investigate the effects of non-linear propagation on a proposed digital microwave radio link which employs MSK modulation, in order to specify a suitable form of adaptive equalization. MSK is a coherent modulation technique, having improved spectral roll-off over FSK because it avoids the abrupt phase changes at the bit transitions. However computer simulations and field results indicate that MSK digital radio links do suffer from intersymbol interference and crosstalk. Software and hardware simulations of multipath propagation are based on Rummlers simplified three path model and statistics. The results obtained from the computer simulations of the MSK link and multipath propagation confirm that there is no simple relationship between the multipath parameters and the BER degradation which could be used in the design of an equalizer. The choice of adaptive equalizer is made based on criteria such as construction cost, circuit complexity, and performance improvement. It is known from ray model analysis that at a transmitting frequency of 23 GHz deep fading will only occur on links longer than 5.24 kms. However even on hops of length 5 km' s the fade time is-in the order of 1612 seconds/month (calculated using Rummlers model). A ldB increase in theoretical Eb/No will also be required to overcome potential modem imperfections. It is necessary to have a time domain equalizer which can compensate for both amplitude and phase distortions simultaneously by acting directly on the ISI. The equalizer structure chosen is a 2-by-2, fractionally spaced, decision feedback, complex adaptive equalizer with zero forcing control algorithm.

Includes bibliographical references., The work in this thesis is primarily directed toward the design, construction and testing of an experimental multilevel partial response signalling baseband system. The system will find practical application in existing frequency division multiplexed-frequency modulated microwave links. The basic supergroup bandwidth of these links is 240 kHz. The design requires a transmission rate of 1.024 Mb/s in this bandwidth. Class-4 15 partial response signalling is the coding technique suitable to achieve this. A pilot tone scheme is used to facilitate symbol timing recovery at the demodulator. A sixth order Butterworth low pass filter approximates the ideal raised-cosine Nyquist channel. A theoretical discussion on impairments caused by deviation from this channel is given. Since the experimental system was non-ideal, it produced a degradation in the channel signal to noise ratio. This degradation, coupled with other factors, showed that further development was necessary for the system to be suitable for connection into an existing microwave link.