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En el presente trabajo de tesis, se ha realizado un análisis del esquema de cooperación de usuarios, con el objetivo de obtener la menor probabilidad de error de bit del sistema. Este análisis es efectuado sobre la implementación CDMA detallada en el articulo User Cooperation Diversity-Part II, escrito por Sendonaris et al. Sin embargo, la probabilidad de error obtenida en este articulo sólo es válido para canales fijos, y sabemos que en la realidad este canal esta expuesto a diferentes tipos de desvanecimiento, lo cual lo hace variable. En este caso, el desvanecimiento multitrayectoria es lo que causa los mayores daños en la recuperación de la información y obedece a una distribución de probabilidad Rayleigh. En tal sentido, una expresión exacta para la probabilidad de error de bit media fue obtenida para el detector λ-MRC (maximal-ratio combining), sobre un canal con desvanecimiento Rayleigh. Sin embargo, dada la complejidad de la expresión exacta, una aproximación muy cercana fue obtenida para calcular la probabilidad de error de bit media, en el caso de cualquier esquema de asignación de potencia. Con esta aproximación, podemos hacer un análisis más exhaustivo y más real del sistema, en el sentido de conocer cuándo la cooperación es beneficiosa y cuándo no la es. Una vez identificado cuando cooperar, la idea es hacerlo con los parámetros adecuados para que la probabilidad de error del sistema sea la mínima. Nuestro análisis, consiste precisamente, en encontrar estos parámetros para tener un sistema de cooperación de usuarios óptimo. Aún con nuestra aproximación, manejar tantas variables resulta complejo. Por tal motivo, simplificaremos el análisis usando una asignación de potencia uniforme, ya que nuestro objetivo es demostrar que podemos llegar a tener un mejor sistema con el manejo adecuado de todas las variables involucradas. Aquí también, debemos considerar que el esfuerzo computacional demandado no debe ser alto, ya que esto le quitará eficiencia a nuestro análisis. Los resultados presentados, muestran que nuestra expresión permite investigar las diferentes situaciones del canal y con esta información crear estrategias, haciendo que el esquema de cooperación de usuarios sea más eficiente.

El presente trabajo consiste en diseñar una red rural de telecomunicaciones con tecnología CDMA en 450 MHz, que pueda brindar servicio a los distritos de Pacarán, Zúñiga, Catahuasi, Tupe, Chocos, Huangascar, Manden, Viñac, ubicados a orillas del rio Cañete y sus alrededores. En el primer capítulo se muestra el estudio de la tecnología celular CDMA 2000 en frecuencias de 450 MHz, sus características y ventajas favorables para la aplicación en redes rurales. También se describe las características adversas en zonas rurales y la situación normativa actual en este escenario. El segundo capítulo muestra la información obtenida del estudio en sitio de la zona donde se pretende dar cobertura de voz y datos. Con dicha información y datos estadísticos del Instituto Nacional de Estadística e Informática (INEI), se realizan estimaciones y cálculos para obtener la demanda potencial. En el tercer capítulo se realiza el diseño la de red rural, plasmando la topología de red en el valle de cañete. Luego mediante la estimación realizada en el capitulo anterior, dimensionamos la capacidad de los equipos en la red, asegurando la cobertura de la zona y el escalamiento de la red en el futuro; basado en estos requerimientos se presenta el equipamiento elegido. En el último capítulo se detalla los costos de inversión inicial de los activos y servicios necesarios de mayor importancia para iniciar las operaciones de red. También se muestra los costos de operación más importantes. Por último, luego de adquirir en el presente trabajo nuevos conocimientos e interiorizar la problemática de la zona rural del Valle de Cañete, se presentan conclusiones y recomendaciones.

El desarrollo de las comunicaciones requiere la utilización de tecnologías de punta que se adecuen a la especial topografía de nuestro País y que permitan ejecutar los enlaces de larga distancia en corto tiempo. El uso de tecnologías como VSAT, basada en accesos satelitales de pequeña apertura; MAR, basada en enlaces de microondas con línea de vista y CDMA 450, basada en celdas de telefonía móvil sobre portadoras en banda UHF (450 MHz), permitirá una solución de la problemática de los servicios de telecomunicación del ámbito rural peruano. El presente trabajo tiene como principal objetivo el de mostrar cual de las tres tecnología sería recomendable usar en una determinada región (las 7 regiones habitables: Costa, Yunga, Quechua, Suni, Puna, Rupa Rupa y Omagua) del Perú basándose para ello en aspectos económicos y técnicos. Al término de este se mostrara cuadros comparativos que mostrara los resultados obtenidos.

The research presented in this dissertation is on the development and application of advanced reduced rank adaptive signal processing techniques for high data rate wireless code division multiple access (CDMA) communications systems. This is an important area of research in the field of wireless communications. Current systems are moving towards the use of multiple simultaneous users in a given channel to increase system capacity as well as spatial and/or temporal diversity for improved performance in the presence of multipath and fading channels. Furthermore, to accommodate the demand for higher data rates, fast signal processing algorithms are required, which often translate into blind signal detection and estimation and the desire for optimal, low complexity detection techniques. The research presented here shows how minimum mean square error (MMSE) receivers implemented via the multistage Wiener filter (MWF) can be employed at the receiving end of a CDMA system to perform multiuser detection (MUD) or interference suppression (IS) with no loss in performance and significant signal subspace compression better than any previous reduced rank techniques have shown. This is important for optimizing performance because it implies a reduction in the number of required samples, so it lessens the requirement that the channel be stationary for a time duration long enough to obtain enough samples for an accurate MMSE estimate. The structure of these receivers is derived for synchronous and asynchronous systems for a multipath environment, and then it is shown that implementation of the receiver in a reduced rank subspace results in no loss in performance over full rank methods. It is also shown in some instances that reduced rank exceeds full rank performance. Multiuser detectors are also studied, and the optimal reduced rank detector is shown to be equivalent to a bank of parallel single user detectors performing interference suppression (IS). The performance as a function of rank for parallel and joint multiuser detectors are compared. The research is then extended to include joint space-code (i.e. a joint multiuser detector) and joint space-time processing algorithms which employ receiver diversity for low complexity diversity gain. Non-linear techniques, namely serial interference cancellation (SIC) and parallel interference cancellation (PIC), will also be studied. The conventional matched filter correlator will be replaced by the MWF, thereby incorporating IS at each stage of the interference canceller for improved performance. A closed form expression is derived for the probability of error, and performance gains are evaluated. It will be further shown how the receiver structure can be extended when space-time codes are employed at the transmitter for additional diversity gain with minimal impact on complexity. The MMSE solution is derived and implemented via the MWF with some examples. It is believed that these new techniques will have a significant impact on the design of fourth generation (4G) and beyond cellular CDMA systems. / Ph. D.

The focus of this dissertation is the study of advanced processing techniques for multiuser interference cancellation in direct sequence code division multiple access communications. Emphasis is placed on the development of efficient techniques that are practical to implement. The work begins with a study of several sub-optimal multiuser detection techniques under a variety of conditions. Multistage parallel interference cancellation is identified as a practical and robust approach for mitigating multiple access interference. In order to reduce the effect of biased decision statistics inherent to parallel cancellation, a low-complexity modification to parallel interference cancellation that significantly improves performance is derived. Based on this approach, two real-time DSP implementations are devised, one fully coherent and one non-coherent. Multi-symbol differential detection is then explored as an alternative for improving the performance of the non-coherent approach. Additionally, dual-antenna diversity techniques are also investigated as a means for improving performance in multipath environments. / Ph. D.

Multiple-input/multiple-output (MIMO) systems with the adaptive array processing technique, also referred to as smart antennas, have received extensive attention in wireless communications due to their ability to combat multipath fading and co-channel interference, two major channel impairments that degrade system performance. However, when smart antennas are deployed in wireless networks, careful attention is required since any defective or imperfect operation of smart antennas can severely degrade the performance of the entire network. Therefore, the evaluation of network performance under ideal and imperfect conditions is critical in the process of system design and should precede deploying smart antennas on the wireless network. This work focuses on the development of an analytical framework to evaluate the performance of wireless networks based on popular DS/CDMA cellular systems equipped with antenna arrays. Spatial diversity at both the base station (BS) and the mobile station (MS) is investigated through both analytical analysis and simulation. The main contribution of this research is to provide a comprehensive analytical framework for examining the system level performance with multiple antennas at both the BS and the MS. Using the framework developed in this research, system capacity and coverage of the uplink (or reverse link) are investigated when antenna arrays are implemented at both the BS and the MS. In addition, the system capacity and soft handoff capability of the downlink (or forward link) are examined taking into account MIMO. Furthermore, various physical and upper layer parameters that can affect the system level performance are taken into account in the analytical framework and their combined impact is evaluated. Finally, to validate the analytical analysis results, a system level simulator is developed and selective results are provided. / Ph. D.

The inadequacy of conventional CDMA receivers in a multiple access interference-limited mobile radio environment has spurred research on advanced receiver technologies. This research investigates the use of adaptive receivers for single user demodulation to overcome some of the deficiencies of a conventional receiver and, hence, enhance the system capacity. Several new adaptive techniques are proposed. The new techniques and some existing schemes are analyzed. The limitation of existing blind algorithms in multipath channels is analyzed and a new blind algorithm is proposed that overcomes this limitation. The optimal receiver structure for multi-rate spread spectrum systems is derived and the performance of this receiver in various propagation channels is investigated. The application of coherent and differentially coherent implementations of the adaptive receiver in the presence of carrier frequency offsets is analyzed. The performance of several new adaptive receiver structures for frequency offset compensation is also studied in this research. Analysis of the minimum mean-squared error receiver is carried out to provide a better understanding of the dependence of its performance on channel parameters and to explain the near-far resilience of the receiver. Complex differentially coherent versions of the sign algorithm and the signed regressor algorithm, algorithms that have a much lower computational complexity than the least-means square algorithm, are proposed and applied for CDMA interference rejection. / Ph. D.

This research investigates the application of multiuser detection to Code Division Multiple Access for cellular communications. This investigation focuses on the use of multiuser receivers at the base station of mobile radio systems. The first two chapters are dedicated to multiuser detection in general. An extensive literature survey is performed on the research concerning multiuser receivers to date. Six major receiver structures are chosen for extensive simulation studies. The bit error rate performance of these receivers is investigated in several system environments. Additionally, practical issues are considered such as computational complexity and robustness to code tracking errors. From this work, one receiver structure is identified for further study, namely multistage interference cancellation. The theoretical performance of this receiver is analyzed using a standard Gaussian Approximation and an Improved Gaussian Approximation for AWGN and fading environments. Additionally, the resistance of the receiver to interference energy levels is explored. Parameter estimation is an important issue for interference cancellation. Simple methods of improving parameter estimation are examined, as is the effect of parameter estimation error on system performance. A baseband hardware implementation is detailed and several design challenges are presented. Results are given for the performance of the implemented receiver and shown to match well with theory and computer simulation. Finally, the implications of this research are discussed. / Ph. D.

After Qualcomm's proposal of the IS-95 standard, <i>code-division multiple access</i> (CDMA) gained popularity as an alternative multiple-access scheme in cellular and <i>personal communication systems</i> (PCS). Besides the advantage of allowing asynchronous operation of the users, CDMA <i>direct-sequence spread spectrum</i> (DS-SS) offers resistance to frequency selective fading and graceful degradation of the performance as the number of users increases. Orthogonality of the signals in time-division multiple access and frequency-division multiple access is inherent from the nature of the multiple access scheme. In a CDMA system, orthogonality of the signals is not guaranteed in general. Consequently, the performance of conventional correlation receivers suffers. Sub-optimum receivers which use knowledge of the interfering signals have been investigated by other researchers. These receivers attempt to cancel the multi-user interference by despreading the interfering users. Hence, these receivers require knowledge about all the spreading codes, amplitude levels, and signal timing, and are, in general, computationally intensive. In this thesis, a technique is presented for which a high degree of interference rejection can be obtained without the necessity of despreading each user. It is shown that exploiting spectral correlation can help mitigate the effects of the multiple-access interference. If <i>code-on-pulse</i> DS-SS modulation is used, a cyclic form of the Wiener filter provides substantial improvements in performance in terms of bit error rate and user capacity. Furthermore, it is shown, that a special error-criterion should be used to adapt the weights of the filter. The computational complexity of the receiver is equivalent to that of conventional equalizers. / Master of Science