### Browsing by Author "Braun, Robin"

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- ItemOpen AccessDecoding algorithms for continuous phase modulation(2002) Kleyn, Werner Frederick; Braun, RobinContinuous Phase Modulation (CPM) possesses characteristics that make it very attractive for many applications. Efficient non-linear power amplifiers can be used in the transmitters of constant envelope CPM schemes. CPM also allows for the use of simple limiters in the demodulator rather than linear receivers with gain control. These characteristics not only increases the life of the power source, but it improves circuit reliability since less heat is generated. In some applications, such as satellite transmitters, where power and circuit failure is very expensive, CPM is the most attractive choice. Bandwidth efficiency, also, is very attractive, and improves as the order of the scheme increases (together with reduction in modulation index). Still further improvement is obtained through pulse shaping which normally result in partial response schemes as opposed to full-response (CPFSK) schemes. The inherent memory or coding gain of CPM increases the minimum distance, which is a figure of merit for a scheme's error performance. The length of the inherent memory is the constraint length of the scheme. Successful extraction of this inherent memory result in improved power efficiency. By periodic variation of the modulation index as in multi-h CPFSK, a sub class of CPM, coding gain or inherent memory can be significantly improved. CPM demodulation is also less sensitive to fading channels than some other comparable systems. Well-known schemes such as GSM digital mobile systems, DECT and Iridium all use some form of CPM to transport their information. These implementations are normally pulse-shaped FSK or MSK and are used for the reasons above, except that their receivers do not always exploit the inherent memory. Unfortunately, though, when one wants to exploit the inherent memory of higher level CPM schemes, all these attractive characteristics are offset by the complexity of the receiver structures which increases exponentially in complexity as the order or constraint length is increased. Optimum receivers for binary CPFSK were first described by Osborne and Luntz [19] in 1974 and their research was later extended by Schonhoff [26] to include M-ary CPFSK. These receivers evaluate likelihood functions after observing the received signal for a certain number of symbol intervals, say N, then calculate a set of likelihood parameters on which a likelihood ratio test regarding the first symbol is based. These receivers are complex and impractical but does provide valuable insight. This is called maximum likelihood sequence estimation (MLSE). Another way to do MLSE would be to correlate all possible transmitted sequences (reference signals at the demodulator) over a period of N symbol intervals with the received sequence. The first symbol of the reference sequence with which the received sequence has the largest correlation, is decoded as the most likely symbol. The number of reference sequences required at the receiver grow very fast as the observation period increases. Up to now, only the lowest order CPM schemes have feasible optimal receiver structures. The only practical solution thus far for the MLSE of higher order schemes is the use of software implementations of which the Viterbi algorithm is the most popular. Through recursive or sequential processing of data per interval, the number of matched filters required can be reduced. However, for schemes beyond a certain order and constraint length, the Viterbi algorithm's consumption of computational resources reduces its feasibility. Research into CPM is focused mainly on the quest for simpler demodulators and decoders or lower order schemes with better coding gain. In order to gain further insight into CPM, research is approached from different angles.
- ItemOpen AccessDesign and testing of a real time simulation for Trellis Coded Modulation(1995) Benzakein, Allon; Braun, RobinThe aim of this project is to build and test a real time simulation for Trellis Coded Modulation(TCM). The tests to be performed are a comparison between Ungerboeck and pragmatic codes and varying and observing different Viterbi decoder parameters for coded 8PSK. TCM is coded modulation which means the choice of modulation scheme is linked with the encoding technique. Convolutional codes are important for an understanding of TCM. They are described by the rate (which is the number of inputs over the number of outputs) and the number of memory elements, v. For TCM schemes, soft decision decoding, based on euclidean distance, rather than hard decision decoding, based on hamming distance, is used. Ungerboeck developed a mapping of encoder bits to channel signals on a constellation diagram. The mapping is called mapping by set partitioning and aims to find the smallest free euclidean distance for a given code. The free euclidean distance is the minimum euclidean distance between output sequences in a code. The asymptotic coding gain is a measure of coding gain based on the free euclidean distance.
- ItemOpen AccessDesign of a simulation for trellis coded modulation(1992) Lindebaum, Theo; Braun, RobinThe 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.
- ItemOpen AccessThe development of a novel modem structure for connection of rural to diginet(1990) Courtenay, Timothy D; Braun, RobinThis 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.
- ItemOpen AccessDevelopment of a real-time automatic network analyzer measurement system(1989) Murray, James John; Braun, RobinThis 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.
- ItemOpen AccessThe development of an ultrasonic Doppler bed-load velocimeter(1989) Lazarus, Mark Doron; Braun, RobinA instrument has been developed for measuring the velocity of solid particles adjacent to the pipe wall in a solids-liquid pipeline. It has been based on the Doppler shift principle and employs ultrasonic methods for detecting the bed-load particle velocity. Its application is in the mining industry for measuring the bed-load velocity of high concentration slurries such as in tailings and backfill hydraulic pipelines. Analyses have been conducted to investigate methods for increasing the accuracy of detecting the bed-load particle velocity. These methods have been implemented in the design of the transducer and the electronic circuitry. The system was tested using a simulation test-rig, hydraulic test-loops and at two industrial mining locations.
- ItemOpen AccessAn investigation into a DSP implementation of partial response signaling for 4800 bits per second full-duplex data communications over M.1020 telephone lines(1990) Horwitz, Russel; Braun, RobinThis 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.
- ItemMetadata onlyAn investigation into path analysis for line-of-sight microwave radio(1989) Gale, David James; Braun, RobinAn 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.
- ItemOpen AccessInvestigation into PRS-precoded, constant-envelope, continuous-phase digital modulation schemes(1990) Golby, John N A; Braun, RobinPartial 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.
- ItemOpen AccessAn investigation into the performance of a power-of-two coefficient transversal equalizer in a 34Mbit/s QPSK digital radio during frequency-selective fading conditions(1997) Archer, Brindsley Broughton; Braun, RobinUnder certain atmospheric conditions, multipath propagation can occur. The interaction of radio waves arriving at a receiver, having travelled via paths of differing length, results in the phenomenon of frequency-selective fading. This phenomenon manifests as a notch in the received spectrum and causes a severe degradation in the performance of a digital radio system. As the total power in the received bandwidth may be unaffected, the Automatic Gain Control is not able to correct for this distortion, and so other methods are required. The dissertation commences with a summary of the phenomenon of multipath as this provides the context for the investigations which follow. The adaptive equalizer was developed to combat the distortion introduced by frequency-selective fading. It achieves this by applying an estimate of the inverse of the distorting channel's transfer function. The theory on adaptive equalizers has been well established, and a summary of this theory is presented in the form of Wiener Filter theory and the Wiener-Hopf equations. An adaptive equalizer located in a 34MBit/s QPSK digital radio is required to operate at very high speed, and its digital hardware implementation is not a trivial task. In order to reduce the cost and complexity, a compromise was proposed. If the tap weights of the equalizer could be represented by power-of-two binary numbers, the equalizer circuitry can be dramatically simplified. The aim of the dissertation was to investigate the performance of this simplified equalizer structure and to determine whether a power-of-two equalizer was a viable consideration.
- ItemOpen AccessInvestigation into variable shift keying using direct sequence spread spectrum techniques(1997) Whaits, Clive Vivian; Braun, RobinThis thesis reports the research done into a relatively unknown modulation scheme called VPSK (Variable Phase Shift Keying) and the use of DSSS (Direct Sequence Spread Spectrum) techniques to achieve carrier synchronization and hence coherent demodulation in the receiver. VPSK is a new and relatively unknown modulation scheme in which data bits are encoded using patented algorithms designed by Millerand Walker. VPSK modulation is a SSBSC (Single Sideband Suppressed Carrier) modulation scheme with good bandwidth efficiency. Data is coherently demodulated in the receiver. In existing VPSK systems, the locally generated carrier in the receiver is synchronized to an integer multiple of the symbol clock frequency to allow coherent demodulation. This coherent method of demodulation is not optimum if the channel over which information must be transmitted is a non-Gaussian channel, or has multi-path characteristics.
- ItemOpen AccessMulti-h synchronisation for codes with long constraints-length(1997) Nel, EugÃ©ne Johannes; Braun, RobinThis dissertation investigates the synchronisation of Multi-h signals with a long constraint length. However, Multi-h codes exhibiting a long constraint length invariably also exhibit a large denominator q. Since traditional methods for synchronising Multi-h signals utilises a q-th power law device, where the frequency spectrum of the qth power of the signal renders all the necessary frequencies for synchronisation, we suspect that a large q could be detrimental. When simulated, it turns out that the qth power law device fails to deliver distinct (and useable) frequency components at a q size of about 8. Unfortunately, the most useful codes have denominators starting at a size of q equals 32. This called for a novel approach to synchronisation. One device that shows much potential is the new Massey-Hodgart coherent MSK demodulator. In a significant departure from standard quadrature structures, this MSK demodulator uses matched filter detection with a pair of reference signals at the two MSK signaling frequencies; an optimal maximum-likelihood bit decision is then formed over two bit intervals. The reference signals are recovered by a pair of decision-switched Costas loops, which are tightly integrated with the demodulator structure. The goal was to modify the Massey-Hodgart MSK demodulator into a Multi-h synchroniser that contained matched filter detection for all the frequencies in the Multi-h signal. The reference frequencies would still be decision switched and recovered by Costas loops.
- ItemOpen AccessThe study of an adaptive bit rate modem for meteor scatter communications(1990) Meyerowitz, Graham John; Braun, Robin
- ItemOpen AccessA study of multilevel partial response signalling for transmission in a basic supergroup bandwidth(1989) Joffe, Neil Raymond; Braun, RobinThe 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.