Please read the abstract in the section 00front of this document / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

Spread Spectrum Communication techniques have been widely used in mobile and wireless communications. They have very beneficial features like antijam and security (noise-like character, pseudorandom codes usage). At first, the features of Spread Spectrum systems are described with emphasis on the Direct Sequence Spread Spectrum (DS-SS) scheme. Main specifications of UMTS system are also introduced. The goal of this thesis was to create the model of a physical layer UMTS suitable for investigation of disturbing signals influences in Matlab Simulink. This model was used to measure how the Bit error rate (BER) is affected by the Processing gain and the Signal-to-noise ratio. Finally, two important charts which describe the relation of Bit error rate versus the Processing gain and the Signal-to-noise ratio have been plotted.

The aim of this dissertation thesis is an optimization of access to CDMA networks. To be more specific, this thesis deals with an optimization of admission control in UMTS network. The first part of the thesis deals with the present progress of the particular topic. Thereinafter there is an analysis of admission control in UMTS system. An own UMTS simulation program was created in MATLAB. This program enables implementation and simulation of the selected admission control algorithms. The thesis is focused on load factor based, fuzzy logic based and genetic algorithms. The created UMTS simulator was used for the mutual comparison of all algorithms. The aims of this thesis are the suitable UMTS model design, evaluation and possible optimization of selected algorithms.

The number of mobile wireless devices on the market has increased substantially over the last decade. The frequency spectrum has become crowded due to the number of devices demanding radio traffic and new modulation schemes have been developed to accommodate the number of users. These new modulation schemes have caused very poor efficiencies in power amplifiers for wireless transmission systems due to high peak-to-average power ratios (PAPR). This thesis first presents the issue with classical power amplifiers in modern modulation systems. A brief overview of current attempts to mitigate this issue is provided. A new RF power amplifier topology is then presented with supporting simulations. The presented amplifier topology utilizes the concept of negative conductance and load modulation. The amplifier operates in two stages, a low power stage and a high power stage. A negative conductance amplifier is utilized during peak power transmission to modulate the load presented to the input amplifier. This topology is shown to greatly improve the power added efficiency of power amplifiers in systems with high PAPR.

En este trabajo se analiza cual es el equipamiento más apropiado para dar cobertura de telefonía móvil celular a la localidad de Laredo, distrito de Laredo provincia Trujillo departamento La Libertad; una estación Base Celular y/o un Repetidor Celular tomando como objetos de análisis la cobertura celular radioeléctrica, la capacidad de tráfico esperada y análisis económico.

La presente tesis abarca el diseño de una red de acceso inalámbrica utilizando tecnología CDMA en la frecuencia de 450 Mhz para el distrito de Ahuac, provincia Chupaca, Departamento Junín. El primer capítulo presenta el estudio de la problemática de la red de acceso de telecomunicaciones en dicho distrito, teniendo en cuenta sus condiciones geográficas y características socio-económicas. El segundo capítulo muestra los conceptos generales de una red de acceso inalámbrica para zonas rurales, describiendo los sistemas de comunicaciones rurales, las centrales telefónicas, los sistemas de transmisión y las tecnologías de acceso inalámbrica para zonas rurales. El tercer capítulo presenta los datos para el análisis de la red de acceso inalámbrica, se define la hipótesis, los objetivos, el universo, el procedimiento para el análisis de datos, las definiciones operativas y se muestra la propuesta del diseño de la red. El cuarto y último capítulo describe el diseño de la red de acceso, analizando diversos factores como: cálculo del radio de cobertura de la estación base, cálculo del link budget, cálculo del número de canales, el cálculo del enlace entre la estación base y la central de conmutación, infraestructura a utilizar, costo del proyecto y su viabilidad económica.

El presente trabajo tiene como objetivo mostrar el diseño de una red de tercera generación con tecnología WCDMA en la ciudad de Tacna para lo cual se utilizará el estándar UMTS Release 99 aprobado por la IMT2000.

El presente trabajo de tesis se ha sido realizado con la finalidad de exponer los principales conceptos que se deben tener en consideración al afrontar el problema de dimensionar la etapa de conmutación dentro de una red celular llegando a determinar la solución conceptual y su posterior ejecución, para mayor claridad se presentan casos prácticos de dimensionamiento y el desarrollo de un proyecto. Por consiguiente y con la finalidad de brindar un concepto teórico general, en el capítulo 1, se presenta el esquema de una red celular CDMA mostrando los principales equipos que componen esta red, describiendo las funciones fundamentales, capacidades y elementos internos de los principales equipos. En el marco teórico, capítulo 2, se describen los principales conceptos referentes a tráfico telefónico y la descripción de los parámetros que indican el estado de una red celular, con el objetivo de caracterizar el comportamiento de llamadas de los usuarios y por ende de la misma red. En el capítulo 3 se muestra la aplicación de los conceptos teóricos en casos prácticos de dimensionamiento de tráfico, determinación de estructura de la red y control de la capacidad de equipos. El objetivo es que tomando en consideración todas las reglas de dimensionamiento y parámetros de control de calidad, en cada uno de los tres casos expuestos en este capítulo, se debe plantear para cada caso una solución de ingeniería factible de aplicar. Teniendo ya planteada la solución de un problema se debe ejecutar, por lo que en el capítulo 4 se ha descrito las principales consideraciones que se deben tener en la ejecución de un proyecto, como ejemplo, y para un mejor entendimiento, se ha tomado al segundo caso del capítulo 3. Finalmente el Capítulo 5 muestra muy brevemente un análisis de los costos involucrados en el caso 1 del capítulo 3.

A new class of Wireless Sensor Networks (WSNs) is emerging within the Internet of Things (IoT) that features extremely high node density, low data rates per node, and high network dependability. Applications such as industrial IoT, factory automation, vehicular networks, aviation, spacecraft and others will soon feature hundreds of low power, low data rate (1-15 kbps) wireless sensor nodes within a limited spatial environment. Existing Medium Access Control (MAC) layer protocols, namely IEEE 802.15.4, may not be suitable for highly dense, low rate networks. A new MAC protocol has been proposed that supports a Receiver-Assigned Code Division Multiple Access (RA-CDMA) physical (PHY) layer multiple access technique, which may enable higher network scalability while maintaining performance and contributing additional robustness. This thesis presents a comparison of the contention mechanisms of IEEE 802.15.4 non- beacon enabled mode and RA-CDMA along with a Matlab simulation framework used for end-to-end simulations of the protocols. Simulations suggest that IEEE 802.15.4 networks begin to break down in terms of throughput, latency, and delivery ratio at a relatively low overall traffic rate compared to RA-CDMA networks. Results show that networks using the proposed RA-CDMA multiple access can support node densities on the order of two to three times higher than IEEE 802.15.4 within the same bandwidth. Furthermore, features of a new MAC layer protocol are proposed that is optimized for RA-CDMA, which could further improve network performance over IEEE 802.15.4. The protocol's simple and lightweight design eliminates significant overhead compared to other protocols while meeting performance requirements, and could further enable the deployment of RA-CDMA WSNs. / Master of Science / Factories, automobiles, planes, spacecraft and other systems in the future will require hundreds of sensors within a relatively small area for data gathering purposes. The sensors, which form Wireless Sensor Networks (WSNs), must have some method of wireless communication that allows each of them to transmit information when needed without obstructing other sensors’ transmissions. Wireless communication protocols provide a method for doing so. Some recognizable examples of wireless communication protocols include Bluetooth, WiFi, 3G and LTE. For WSNs in the future, the industry’s leading candidate protocol is called IEEE 802.15.4, but it may not be most suitable because it is known to break down as large amounts of sensors are added to its networks. Because of this, a new protocol has been proposed around a channel sharing technique called Receiver-Assigned Code Division Multiple Access (RACDMA), which uses a different strategy to efficiently distribute network resources among sensors. This work analyzes the differences between IEEE 802.15.4 and RA-CDMA, focusing specifically on how each protocol allows sensors to transmit without conflicting with one another. A simulation framework is introduced for complete simulations of each protocol. The result of the simulations shows that IEEE 802.15.4 breaks down in dense sensor networks. RACDMA, however, is able to support very large networks, on the order of two to three times the size of IEEE 802.15.4. This result could be an enabling technology for large wireless sensor networks in the future. Additionally, a new protocol optimized for RA-CDMA is presented. Its simple design could further enable the deployment of RA-CDMA WSNs.

Asynchronous multiplexing schemes are efficient than synchronous schemes, in a bursty traffic environment of multiple access local area network (LAN), as fixed bandwidth is not allocated among the users and there is no access delay. Fiber- Optic Code-Division Multiple Access (FO-CDMA) is one such asynchronous multiplexing scheme suitable for high speed LAN networks. While FO-CDMA offers potential benefits it also faces challenges in three diverse areas which are 1) coding algorithms and schemes 2) advanced encoding and decoding hardware and 3) network architecture. In this thesis, as a solution to the first challenge, we propose the design and construction of a new family of codes, wavelength/time multiple-pulses-per-row (W/T MPR) codes. These codes have good cardinality, spectral efficiency and minimal cross-correlation values. Performance analysis of the W/T MPR codes is carried out and found to be superior to other codes. In unipolar 1-D Optical Orthogonal Codes (OOCs) proposed by Salehi et al., the ratio of code length/code weight grows rapidly as the number of users is increased for a reasonable weight. Hence, for a given pulse width, the data rate decreases or in other words for a given data rate very narrow pulses have to be used, because of which dispersion effects will be dominant. To overcome the drawbacks of non-linear effects in large spread sequences of 1-D unipolar codes in FO-CDMA networks, several two-dimensional codes have been proposed. Wavelength-time (W/T) encoding of the two-dimensional codes is practical in FO-CDMA networks. W/T codes reported so far can be classified mainly into two types: 1) hybrid sequences, where one type of sequence is crossed with another to improve the cardinality and correlation properties and 2) matrix codes, 1-D sequences converted to 2-D codes or 2-D codes by construc- tion, to reduce the ’time’ spread of the sequences/codes. Prime-hop and eqc/prime W/T hybrid codes have been proposed where one type of sequence is crossed with another to improve the cardinality and correlation properties. Other constructions deal with conversion of 1-D sequences to 2-D codes either by using Chinese remainder theorem or folding GoLomb rulers. W/T single-pulse-per-row (W/T SPR) codes are 2-D codes constructed using algebraic method Addition Modulo Group operation. Motivation for this work: To design a family of 2-D codes which have the design choice of length of one dimension over the other, and also have better cardinality, spectral efficiency and also low cross-correlation values (thereby have low BER) than that of the reported unipolar 2-D codes. In this thesis, we describe the design principles of W/T MPR codes, for in- coherent FO-CDMA networks, which have good cardinality, spectral efficiency and minimal cross-correlation values. Another feature of the W/T MPR codes is that the aspect ratio can be varied by trade off between wavelength and temporal lengths. We lay down the necessary conditions to be satisfied by W/T MPR codes to have minimal correlation values of unity. We analytically prove the correlation results and also verify by simulation (of the codes) using Matlab software tool. We also discuss the physical implementation of the W/T MPR FO-CDMA network with optical encoding and decoding. We show analytically that when distinct 1-D OOCs of a family are used as the row vectors of a W/T MPR code, it will have off-peak autocorrelation equal to ‘1’. An expression for the upper bound on the cardinality of W/T MPR codes is derived. We also show that 1-D OOCs and W/T SPR codes are the limiting cases of W/T MPR codes. Starting with distinct 1-D OOCs, of a family, as row vectors, we propose a greedy algorithm, for the construction of W/T MPR codes and present the repre- sentations of the results. An entire W/T MPR code family, generated using greedy algorithm, is simulated for various number of interfering users. Performance analysis of the W/T MPR codes and their limiting cases is carried out for various parameter variations such as the dimensions of wavelength, time and weight of the code. We evaluate the performance in terms of BER, capacities of the networks, temporal lengths needed (to achieve a given BER). Multiple access interference (MAI) signal can be reduced, by using a bistable optical hard-limiter device in the W/T MPR code receiver, by eliminating those signal levels which exceed a certain preset level. Performance analysis of the W/T MPR codes and their limiting cases is studied for various parameter variations. For given wavelength × time dimensions, we compare various W/T codes, whose cardinalities are known, and show that W/T MPR family of codes have better cardinality and spectral efficiency than the other (reported) W/T codes. As W/T MPR codes are superior to other W/T codes in terms of cardinality, spectral efficiency, low peak cross-correlation values and at the same time have good performance, makes it a suitable coding scheme for incoherent FO-CDMA access networks.