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no abstract provided by author / Master of Science

Satellite systems in the 20/30 GHz band are very susceptible to outages due to rain-induced fades. In order to reduce the impact of these fades, it has been proposed that the power of the uplink station transmitter be adjusted during the fade to compensate. This dissertation will explore some of the issues involved in implementing this uplink power control (ULPC). Fade slope is examined as a parameter to predict signal strength during a fade. A fade slope model based on fade physics is presented, but it strongly suggests that fade slope is not an appropriate parameter for ULPC. Real time scaling of attenuation from the downlink to the uplink shows more promise for ULPC. Differences in drop size distributions during a rain storm will result is different scaling factors. If the downlink attenuation is limited to 6 dB at 20 GHz, real time scaling can be accomplished. A scaling type ULPC algorithm driven by downlink attenuation is tested on 66 hours of OLYMPUS 20/30 GHz fade data. A similar algorithm driven by uplink attenuation is tested and the performance of the two algorithms is presented and compared. / Ph. D.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy in the School of Electrical and Information Engineering, 2016 / Reliable and e cient data transmission have been the subject of current research, most especially in realistic channels such as the Rayleigh fading channels. The focus of every new technique is to improve the transmission reliability and to increase the transmission capacity of the communication links for more information to be transmitted. Modulation schemes such as M-ary Quadrature Amplitude Modulation (M-QAM) and Orthogonal Frequency Division Multiplexing (OFDM) were developed to increase the transmission capacity of communication links without additional bandwidth expansion, and to reduce the design complexity of communication systems. On the contrary, due to the varying nature of communication channels, the message transmission reliability is subjected to a couple of factors. These factors include the channel estimation techniques and Forward Error Correction schemes (FEC) used in improving the message reliability. Innumerable channel estimation techniques have been proposed independently, and in combination with di erent FEC schemes in order to improve the message reliability. The emphasis have been to improve the channel estimation performance, bandwidth and power consumption, and the implementation time complexity of the estimation techniques. Of particular interest, FEC schemes such as Reed-Solomon (RS) codes, Turbo codes, Low Density Parity Check (LDPC) codes, Hamming codes, and Permutation codes, are proposed to improve the message transmission reliability of communication links. Turbo and LDPC codes have been used extensively to combat the varying nature of communication channels, most especially in joint iterative channel estimation and decoding receiver structures. In this thesis, attention is focused on using RS codes to improve the message reliability of a communication link because RS codes have good capability of correcting random and burst errors, and are useful in di erent wireless applications. This study concentrates on symbol level soft decision decoding of RS codes. In this regards, a novel symbol level iterative soft decision decoder for RS codes based on parity-check equations is developed. This Parity-check matrix Transformation Algorithm (PTA) is based on the soft reliability information derived from the channel output in order to perform syndrome checks in an iterative process. Performance analysis verify that this developed PTA outperforms the conventional RS hard decision decoding algorithms and the symbol level Koetter and Vardy (KV ) RS soft decision decoding algorithm. In addition, this thesis develops an improved Distance Metric (DM) method of deriving reliability information over Rayleigh fading channels for combined demodulation with symbol level RS soft decision decoding algorithms. The newly proposed DM method incorporates the channel state information in deriving the soft reliability information over Rayleigh fading channels. Analysis verify that this developed metric enhances the performance of symbol level RS soft decision decoders in comparison with the conventional method. Although, in this thesis, the performance of the developed DM method of deriving soft reliability information over Rayleigh fading channels is only veri ed for symbol level RS soft decision decoders, it is applicable to any symbol level soft decision decoding FEC scheme. Besides, the performance of the all FEC decoding schemes plummet as a result of the Rayleigh fading channels. This engender the development of joint iterative channel estimation and decoding receiver structures in order to improve the message reliability, most especially with Turbo and LDPC codes as the FEC schemes. As such, this thesis develops the rst joint iterative channel estimation and Reed- Solomon decoding receiver structure. Essentially, the joint iterative channel estimation and RS decoding receiver is developed based on the existing symbol level soft decision KV algorithm. Consequently, the joint iterative channel estimation and RS decoding receiver is extended to the developed RS parity-check matrix transformation algorithm. The PTA provides design ease and exibility, and lesser computational time complexity in an iterative receiver structure in comparison with the KV algorithm. Generally, the ndings of this thesis are relevant in improving the message transmission reliability of a communication link with RS codes. For instance, it is pertinent to numerous data transmission technologies such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Digital Subscriber Line (DSL), WiMAX, and long distance satellite communications. Equally, the developed, less computationally intensive, and performance e cient symbol level decoding algorithm for RS codes can be use in consumer technologies like compact disc and digital versatile disc. / GS2016

by Wong Chun Kau, Jolly. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 84-88). / ABSTRACT --- p.1 / ACKNOWLEDGEMENT --- p.3 / Chapter 1. --- INTRODUCTION --- p.7 / Chapter 1.1 --- Land Mobile Radio (LMR) Communications / Chapter 1.2 --- Paramilitary Communications Security / Chapter 1.3 --- Voice Scrambling Methods / Chapter 1.4 --- Digital Voice Encryption / Chapter 1.5 --- Digital Secure LMR / Chapter 2. --- DESIGN GOALS --- p.20 / Chapter 2.1 --- System Concept and Configuration / Chapter 2.2 --- Operational Requirements / Chapter 2.2.1 --- Operating conditions / Chapter 2.2.2 --- Intelligibility and speech quality / Chapter 2.2.3 --- Field coverage and transmission delay / Chapter 2.2.4 --- Reliability and maintenance / Chapter 2.3 --- Functional Requirements / Chapter 2.3.1 --- Major system features / Chapter 2.3.2 --- Cryptographic features / Chapter 2.3.3 --- Phone patch facility / Chapter 2.3.4 --- Mobile data capability / Chapter 2.4 --- Bandwidth Requirements / Chapter 2.5 --- Bit Error Rate Requirements / Chapter 3. --- VOICE CODERS --- p.38 / Chapter 3.1 --- Digital Speech Coding Methods / Chapter 3.1.1 --- Waveform coding / Chapter 3.1.2 --- Linear predictive coding / Chapter 3.1.3 --- Sub-band coding / Chapter 3.1.4 --- Vocoders / Chapter 3.2 --- Performance Evaluation / Chapter 4. --- CRYPTOGRAPHIC CONCERNS --- p.52 / Chapter 4.1 --- Basic Concepts and Cryptoanalysis / Chapter 4.2 --- Digital Encryption Techniques / Chapter 4.3 --- Crypto Synchronization / Chapter 4.3.1 --- Auto synchronization / Chapter 4.3.2 --- Initial synchronization / Chapter 4.3.3 --- Continuous synchronization / Chapter 4.3.4 --- Hybrid synchronization / Chapter 5. --- DIGITAL MODULATION --- p.63 / Chapter 5.1 --- Narrowband Channel Requirements / Chapter 5.2 --- Narrowband Digital FM / Chapter 5.3 --- Performance Evaluation / Chapter 6. --- SYSTEM IMPLEMENTATION --- p.71 / Chapter 6.1 --- Potential EMC Problems / Chapter 6.2 --- Frequency Planning / Chapter 6.3 --- Key Management / Chapter 6.4 --- Potential Electromagnetic Compatibility (EMC) Problems / Chapter 7. --- CONCLUSION --- p.80 / LIST OF ILLUSTRATIONS --- p.81 / REFERENCES --- p.82 / APPENDICES --- p.89 / Chapter I. --- Path Propagation Loss(L) Vs Distance (d) / Chapter II. --- Speech Quality Assessment Tests performed / by Special Duties Unit (SDU)

In the first part of this thesis, the information capacity of time-varying fading channels is analysed using finite-state Markov channel (FSMC) models. Both fading channel amplitude and fading channel phase are modelled as finite-state Markov processes. The effect of the number of fading channel gain partitions on the capacity is studied (from 2 to 128 partitions). It is observed that the FSMC capacity is saturated when the number of fading channel gain partitions is larger than 4 to 8 times the number of channel input levels. The rapid FSMC capacity saturation with a small number of fading channel gain partitions can be used for the design of computationally simple receivers, with a negligible loss in the capacity. Furthermore, the effect of fading channel memory order on the capacity is studied (from first- to fourth-order). It is observed that low-order FSMC models can provide higher capacity estimates for fading channels than high-order FSMC models, especially when channel states are poorly observable in the presence of channel noise. To explain the effect of memory order on the FSMC capacity, the capacities of high-order and low-order FSMC models are analytically compared. It is shown that the capacity difference is caused by two factors: 1) the channel entropy difference, and 2) the channel observability difference between the high-order and low-order FSMC models. Due to the existence of the second factor, the capacity of high-order FSMC models can be lower than the capacity of low-order FSMC models. Two sufficient conditions are proven to predict when the low-order FSMC capacity is higher or lower than the high-order FSMC capacity. In the second part of this thesis, a new implicit (blind) channel estimation method in time- varying fading channels is proposed. The information source emits bits ???0??? and ???1??? with unequal probabilities. The unbalanced source distribution is used as a priori known signal structure at the receiver for channel estimation. Compared to pilot-symbol-assisted channel estimation, the proposed channel estimation technique can achieve a superior receiver bit error rate performance, especially at low signal to noise ratio conditions.

Technological progress in the field of wireless communications over the past few years has only been matched by the increasing demand for sophisticated services at lower costs. A significant breakthrough was achieved in the design of efficient wireless communication systems with the advent of the diversity concept. Spatial diversity exploits the availability of multiple spatial paths between the transmitter and receiver by placing antenna arrays at either end. In addition to improving the reliability of communication by creating redundant copies of the transmitted information at the receiver, wireless transceivers with multiple antennas exploit the spatial degrees of freedom to multiplex multiple streams of data and achieve significant gains in spectral efficiencies. In this thesis, we design spatial diversity techniques for slow-fading wireless channels. There are two parts to this thesis: In Part I we propose spatial diversity techniques for point-to-point single-user wireless systems, while in Part II we propose multiuser cooperative diversity techniques for multiuser wireless communication systems. In the first part, we propose a set of new wireless communication techniques for multiple-input, multiple-output (MIMO) channels over Rayleigh slow-fading wireless channels. We introduce MIMO transceivers that achieve high data rates and low error rates using a class of MIMO systems known as layered space-time (ST) architectures, which use low complexity, suboptimal decoders such as successive cancellation (SC) decoders. We propose a set of improved layered space-time architectures and show that it is possible to achieve near-optimal error performance over MIMO channels while requiring just SC decoding at the receiver. We show that these architectures achieve high rate and diversity gains. We also show that some of the proposed layered space-time architectures could find applications in multiple-access communications as low-complexity solutions for achieving near-optimum performance. In the second part of this thesis, we propose novel techniques for cooperative communication between terminals in multiuser wireless communication systems. Cooperative communication is a concept where neighboring terminals share their antennas and signal processing resources to create a virtual transmit array . In addition to transmitting their own information, users in a cooperative communication system listen to transmission from other users and relay this information to the destination, thus creating multiple paths between transmitter and receiver. This form of diversity, known as cooperative diversity, helps improve the overall reliability of all the users in a network. We start with a simple three node multiple-access system where two users are communicating with a common destination. We propose new high-rate cooperation strategies which achieve the full diversity gain offered by the cooperative channel for this simple system. We propose a new framework to address the tradeoff between cooperation and independent transmission over a multiple access channel and determine the conditions under which each idea is better than the other. Finally, we propose a high rate cooperation protocol which achieves the maximum diversity over a multiple access system with an arbitrary number of users and achieves high rates which scale favorably as the number of users increases.

Switching frequency modulation techniques, an inductor current sensing circuit for fast switching converter, and a dual converter are proposed, and the simulation results and experimental results are drawn. The experimental results for monotonic and pseudo-random modulation techniques show that the switching noise peak was effectively reduced as much as -19 dBc. The inductor current sensing circuit accurately tracks the output current of the switching converter that switches up to 30MHz. This current sensing circuit is used to drive the slow converter in the dual converter. The dual converter consists of a fast converter and a slow converter. The fast converter provides only the high frequency conponents in the output current, and the slow converter provides the majority portion of the output current with a higher efficiency. Therefore, the dual converter can have a fast transient response without sacrificing its efficiency. All chips are fabricated in a standard CMOS 0.18um process.

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Quality-of-service (QoS) guarantees have become critically important for the transmission of real-time multimedia traffic in next generation mobile wireless networks. The aim of this dissertation is to investigate the cross-layer design for support of delay bound QoS guarantees over fading channels. Providing diverse QoS guarantees presents a challenge due to the time-varying fading nature of wireless channels. Existing physical layer modelling is inadequate in supporting real time QoS metrics such as delay, hence adaptive techniques need to be extended to the upper-protocol layers. The first objective of this dissertation is to introduce a cross-layer design framework which investigates the impact of the physical layer on the data link delay bound QoS performance. At the physical layer, adaptive modulation and coding (AMC) is utilized for transmission over block fading channels. At the data link layer, the effective capacity approach is used to model the delay bound QoS performance subject to physical layer variations. The effects of varying physical layer parameters, such as average signal-to-noise ratio (SNR), the fading parameter for the kagami- model, and target packet-error rate (PER), on the analytical delay bound performance are investigated and then validated by the simulation of a queuing system. Due to the cross-layer design framework, the system’s throughput has a significant impact on bounded delay at the data link layer. The switching levels of the conventional AMC scheme used in the first objective were fixed, subject to a target PER. However, fixed switching levels results in the system’s throughput limiting the delay bound performance. The second objective of this dissertation is to optimize the switching levels of the AMC scheme employed at the physical layer, by maximizing the average throughput, while maintaining the target PER constraint. The analytical and simulated results show that by optimizing the switching levels, a superior delay bound performance is achieved, when compared to the deterministic switching levels of the conventional AMC scheme used in the first objective. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.