409 research outputs found

    Calibration and linearity issues for an adaptive antenna system

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    Application of adaptive antenna technology to third generation radio architectures

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    Artificial neural networks for location estimation and co-cannel interference suppression in cellular networks

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    This thesis reports on the application of artificial neural networks to two important problems encountered in cellular communications, namely, location estimation and co-channel interference suppression. The prediction of a mobile location using propagation path loss (signal strength) is a very difficult and complex task. Several techniques have been proposed recently mostly based on linearized, geometrical and maximum likelihood methods. An alternative approach based on artificial neural networks is proposed in this thesis which offers the advantages of increased flexibility to adapt to different environments and high speed parallel processing. Location estimation provides users of cellular telephones with information about their location. Some of the existing location estimation techniques such as those used in GPS satellite navigation systems require non-standard features, either from the cellular phone or the cellular network. However, it is possible to use the existing GSM technology for location estimation by taking advantage of the signals transmitted between the phone and the network. This thesis proposes the application of neural networks to predict the location coordinates from signal strength data. New multi-layered perceptron and radial basis function based neural networks are employed for the prediction of mobile locations using signal strength measurements in a simulated COST-231 metropolitan environment. In addition, initial preliminary results using limited available real signal-strength measurements in a metropolitan environment are also reported comparing the performance of the neural predictors with a conventional linear technique. The results indicate that the neural predictors can be trained to provide a near perfect mapping using signal strength measurements from two or more base stations. The second application of neural networks addressed in this thesis, is concerned with adaptive equalization, which is known to be an important technique for combating distortion and Inter-Symbol Interference (ISI) in digital communication channels. However, many communication systems are also impaired by what is known as co-channel interference (CCI). Many digital communications systems such as digital cellular radio (DCR) and dual polarized micro-wave radio, for example, employ frequency re-usage and often exhibit performance limitation due to co-channel interference. The degradation in performance due to CCI is more severe than due to ISI. Therefore, simple and effective interference suppression techniques are required to mitigate the interference for a high-quality signal reception. The current work briefly reviews the application of neural network based non-linear adaptive equalizers to the problem of combating co-channel interference, without a priori knowledge of the channel or co-channel orders. A realistic co-channel system is used as a case study to demonstrate the superior equalization capability of the functional-link neural network based Decision Feedback Equalizer (DFE) compared to other conventional linear and neural network based non-linear adaptive equalizers.This project was funded by Solectron (Scotland) Ltd

    Minimum power design of RF front ends

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    This thesis describes an investigation into the design of RF front ends with minimum power dissipation. The central question is: "What are the fundamental limits for the power dissipation of telecommunication front ends, and what design procedures can be followed that approach these limits and, at the same time, result in practical circuits?" After a discussion of the state of the art in this area, the elementary operations of a front end are identified. For each of these elementary operations, the fundamental limits for the power dissipation are discussed, divided into technology imposed limits and physics imposed limits. A traditional DECT front end design is used to demonstrate the large difference between the fundamental limits and the power dissipation of existing circuits. To improve this situation, first the optimum distribution of specifications across individual subcircuits needs to be determined, such that the requirements for a specific system can be fulfilled. This is achieved through the introduction of formal transforms of the specifications of subcircuits, which correspond with transforms of the subcircuit itself. Using these transforms, the optimum distribution of gain, noise, linearity and power dissipation can be determined. As it turns out, this optimum distribution can even be represented by a simple, analytical expression. This expression predicts that the power dissipation of the DECT front end can be reduced by a factor of 2.7 through an optimum distribution of the specifications. Using these optimum specifications of the subcircuits, the boundaries for further power dissipation reduction can be determined. This is investigated at the system, circuit and technology level. These insights are used in the design of a 2.5GHz wireless local area network, implemented in an optimized technology ("Silicon on Anything"). The power dissipation of the complete receiver is 3.5mW, more than an order of magnitude below other wireless LAN receivers in recent publications. Finally, the combination of this minimum power design method with a platform based development strategy is discussed

    Improved cryptanalysis of the DECT standard cipher

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    On the modeling of WCDMA system performance with propagation data

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    The aim of this study was to develop calculation methods for estimating the most important system level performance characteristics of the WCDMA radio network (i.e. network capacity and coverage) in the presence of interference from various sources. The calculation methods described in this work enable the fast design of radio systems with a reasonable degree of accuracy, where different system parameters, propagation conditions and networks as well as frequency scenarios can be easily tested. The work also includes the development and verification of a propagation model for a microcellular environment. Traditionally, system level performance figures have been retrieved using system simulations where the radio network has been modeled as accurately as possible. This has included base stations and mobile stations, propagation models, traffic models and mobility models. Various radio resource management (RRM) algorithms, such as power controls and handovers have also been modeled. However, these system simulations are very complex and time consuming and typically the models are difficult to modify. The idea behind this work is to use the main statistical parameters retrieved from accurate, case specific propagation models and to use these statistics as input for the developed analytical radio network models. When used as output from these analytical models we are able to obtain the performance measures of the network. The specific application area for the developed methods is the evaluation of the effect of the interference from the adjacent frequency channels. Adjacent channel interference decreases the efficiency of the usage of the electromagnetic spectrum i.e. the spectral efficiency. The aim of a radio system design is to ensure that the reduction in the spectral efficiency is as low as possible. This interference may originate from the same or a different radio system and from the same or another operator's network. The strength of this interference is dependent on the system parameters and the network layout. The standard questions regarding adjacent system interference between different operators' network are what guard band is needed between the radio carriers in order to maintain the quality of the network or what are the main mobile and network parameters, such as adjacent channel emission levels or adjacent channel selectivity, required in order to achieve satisfactory network performance. With the developed method proposed here it is possible to answer these questions with reasonable accuracy. One important aspect of network performance is the radio wave propagation environment for which the radio systems are designed. This thesis presents methods evaluating radio wave propagation, especially for cases where the base station antenna is below the rooftops, i.e. in the case of microcellular network environments. The developed microcellular propagation model has been developed for network planning purposes and it has been verified using numerous field propagation measurements. The model can be used in cases where the mobile station is located either indoors or outdoors.reviewe

    Design of a GSM phone booth for low cost rural communication

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    The GSM phone booth was designed as a mobile phone with solar arrays on the roof. These arrays are for charging the phone batteries and powering the booth during the day while the batteries which can be bigger, powers the phone at night or in the absence of sunlight. The cell phone platform was integrated into the booth such that when a SIM card is inserted it can be used as if it were a personal phone. The SIM card holder was designed in such a way that the user carries it along to the phone booth and slots it into the provided slot on the booth before making a call. It was also designed to switch on or off the phone booth such that when the card is removed the booth is switched off while the battery continues to charge. This is another mean by which the battery life is extended. The design provides a low cost approach for extending mobile communication to rural areas and also for campuses and public area
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