497 research outputs found

    Fast antijamming timing acquisition using multilayer synchronization sequence

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    Pseudonoise (PN) sequences are widely used as preamble sequences to establish timing synchronization in military wireless communication systems. At the receiver, searching and detection techniques, such as the full parallel search (FPS) and the serial search (SS), are usually adopted to acquire correct timing position. However, the synchronization sequence has to be very long to combat jamming that reduces the signal-to-noise ratio (SNR) to an extremely low level. In this adverse scenario, the FPS scheme becomes too complex to implement, whereas the SS method suffers from the drawback of long mean acquisition time (MAT). In this paper, a fast timing acquisition method is proposed, using the multilayer synchronization sequence based on cyclical codes. Specifically, the transmitted preamble is the Kronecker product of Bose–Chaudhuri-Hocquenghem (BCH) codewords and PN sequences. At the receiver, the cyclical nature of BCH codes is exploited to test only a part of the entire sequence, resulting in shorter acquisition time. The algorithm is evaluated using the metrics of MAT and detection probability (DP). Theoretical expressions of MAT and DP are derived from the constant false-alarm rate (CFAR) criterion. Theoretical analysis and simulation results show that our proposed scheme dramatically reduces the acquisition time while achieving similar DP performance and maintaining a reasonably low real-time hardware implementation complexity, in comparison with the SS schem

    Advanced Wireless LAN

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    The past two decades have witnessed starling advances in wireless LAN technologies that were stimulated by its increasing popularity in the home due to ease of installation, and in commercial complexes offering wireless access to their customers. This book presents some of the latest development status of wireless LAN, covering the topics on physical layer, MAC layer, QoS and systems. It provides an opportunity for both practitioners and researchers to explore the problems that arise in the rapidly developed technologies in wireless LAN

    Transceiver architectures and sub-mW fast frequency-hopping synthesizers for ultra-low power WSNs

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    Wireless sensor networks (WSN) have the potential to become the third wireless revolution after wireless voice networks in the 80s and wireless data networks in the late 90s. This revolution will finally connect together the physical world of the human and the virtual world of the electronic devices. Though in the recent years large progress in power consumption reduction has been made in the wireless arena in order to increase the battery life, this is still not enough to achieve a wide adoption of this technology. Indeed, while nowadays consumers are used to charge batteries in laptops, mobile phones and other high-tech products, this operation becomes infeasible when scaled up to large industrial, enterprise or home networks composed of thousands of wireless nodes. Wireless sensor networks come as a new way to connect electronic equipments reducing, in this way, the costs associated with the installation and maintenance of large wired networks. To accomplish this task, it is necessary to reduce the energy consumption of the wireless node to a point where energy harvesting becomes feasible and the node energy autonomy exceeds the life time of the wireless node itself. This thesis focuses on the radio design, which is the backbone of any wireless node. A common approach to radio design for WSNs is to start from a very simple radio (like an RFID) adding more functionalities up to the point in which the power budget is reached. In this way, the robustness of the wireless link is traded off for power reducing the range of applications that can draw benefit form a WSN. In this thesis, we propose a novel approach to the radio design for WSNs. We started from a proven architecture like Bluetooth, and progressively we removed all the functionalities that are not required for WSNs. The robustness of the wireless link is guaranteed by using a fast frequency hopping spread spectrum technique while the power budget is achieved by optimizing the radio architecture and the frequency hopping synthesizer Two different radio architectures and a novel fast frequency hopping synthesizer are proposed that cover the large space of applications for WSNs. The two architectures make use of the peculiarities of each scenario and, together with a novel fast frequency hopping synthesizer, proved that spread spectrum techniques can be used also in severely power constrained scenarios like WSNs. This solution opens a new window toward a radio design, which ultimately trades off flexibility, rather than robustness, for power consumption. In this way, we broadened the range of applications for WSNs to areas in which security and reliability of the communication link are mandatory

    Direct sequence spread spectrum techniques in local area networks

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    This thesis describes the application of a direct sequence spread spectrum modulation scheme to the physical layer of a local area networks subsequently named the SS-LAN. Most present day LANs employ erne form or another of time division multiplexing which performs well in many systems but which is limited by its very nature in real time, time critical and time demanding applications. The use of spread spectrum multiplexing removes these limitations by providing a simultaneous multiple user access capability to the channel which permits each and all nodes to utilise the channel independent of the activity being currently supported by that channel. The theory of spectral spreading is a consequence of the Shannon channel capacity in which the channel capacity may be maintained by the trading of signal to noise ratio for bandwidth. The increased bandwidth provides an increased signal dimensionality which can be utilised in providing noise immunity and/or a simultaneous multiple user environment: the effects of the simultaneous users can be considered as noise from the point of view of any particular constituent signal. The use of code sequences at the physical layer of a LAN permits a wide range of mapping alternatives which can be selected according to the particular application. Each of the mapping techniques possess the general spread spectrum properties but certain properties can be emphasised at the expense of others. The work has Involved the description of the properties of the SS-LAN coupled with the development of the mapping techniques for use In the distribution of the code sequences. This has been followed by an appraisal of a set of code sequences which has resulted in the definition of the ideal code properties and the selection of code families for particular types of applications. The top level design specification for the hardware required in the construction of the SS-LAN has also been presented and this has provided the basis for a simplified and idealised theoretical analysis of the performance parameters of the SS-LAN. A positive set of conclusions for the range of these parameters has been obtained and these have been further analysed by the use of a SS-LAN computer simulation program. This program can simulate any configuration of the SS-LAN and the results it has produced have been compared with those of the analysis and have been found to be in agreement. A tool for the further analysis of complex SS-LAN configurations has therefore been developed and this will form the basis for further work

    An Assessment of Indoor Geolocation Systems

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    Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance

    Adaptive CFAR PN Code Acquisition for DSSS Systems

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    The communication between transmitter and receiver in Direct Sequence Spread Spectrum (DSSS) systems starts with synchronisation, which can be carried out in two steps: acquisition and tracking. Acquisition is the coarse searching of the delay of PN code in transmitted signal, and tracking is to find the exact delay of PN code in transmitted signal and maintain the alignment of the two PN codes.This thesis “Adaptive PN code Acquisition for DSSS Systems” presents research on PN code acquisition in DSSS systems. The research focused on the adapitve threshold optimisation with Constant False Alarm Rate (CFAR) techniques in different noise background. Both homogeneous and non-homogeneous noise background are analysed to check the performance of different CFAR techniques, in the terms of Probability of detection ( Pd), Probability of false alarm (Pja) and Mean Acquisition Time (MAT). Thelimitations of general CFAR techniques in non-homogeneous noise background are disclosed in the research, and adaptive censoring technique is applied into general CFAR techniques, showing significant improvement in performance. In the research, MATLAB is used for mathematical simulations, and Monte Carlo simulation is used for independent validation of the theoretical results obtained. ISE, Modelsim, and System generator are used for the hardware implementation in Field Programmable Gate Array (FPGA).Results show that all the kinds of CFAR techniques perform well in homogeneous noise background, with high Pd and short MAT, however, the general CFAR techniques without automatic censoring suffer serious degradation in non-homogeneous noise background. In this thesis, after disclosing the limilation of general CFAR techniques, Greatest-Of/ Smallest-Of CFAR (GO/SO-CFAR) was introduced to solve the problem in non-homogeneous noise background. The simulation results show that GO/SO-CFAR has much better performance than the general CFAR in non-homogeneous noise background, especially in noise background with high interferences, GO/SO-CFAR can maintain high Pd and short MAT. FPGA is used to analyse the complexity of achievement for GO/SO- CFAR detector, and the results illustrate that GO/SO-CFAR is only slightly more complex and slower than the CA-CFAR and OS-CFAR detectors. Therefore, GO/SO- CFAR is much more suitable than general CFAR techniques in non-homogeneous noise background, when the noise condition is unknown

    Infrared ranging in multipath environments for indoor localization of mobile targets

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    Esta tesis aborda el problema de la medida de diferencias de distancia mediante señales ópticas afectadas por multicamino, aplicada a la localización de agentes móviles en espacios interiores. Los avances en robótica, entornos inteligentes y vehículos autónomos han creado un campo de aplicación específico para la localización en interiores, cuyos requerimientos de precisión (en el rango de los cm) son muy superiores a los demandados por las aplicaciones de localización orientadas a personas, en cuyo contexto se han desarrollado la mayor parte de las alternativas tecnológicas. La investigación con métodos de geometría proyectiva basados en cámaras y de multilateración basados en medida de distancia con señales de radiofrecuencia de banda ancha, de ultrasonido y ópticas han demostrado un rendimiento potencial adecuado para cubrir estos requerimientos. Sin embargo, todas estas alternativas, aún en fase de investigación, presentan dificultades que limitan su aplicación práctica. En el caso de los sistemas ópticos, escasamente estudiados en este contexto, los trabajos previos se han basado en medidas de diferencia de fase de llegada de señales infrarrojas moduladas sinusoidalmente en intensidad. Una infraestructura centralizada computa medidas diferenciales, entre receptores fijos, de la señal emitida desde el móvil a posicionar, y calcula la posición del móvil mediante trilateración hiperbólica a partir de éstas. Estas investigaciones demostraron que se pueden alcanzar precisiones de pocos centímetros; sin embargo, las interferencias por multicamino debidas a la reflexión de la señal óptica en superficies del entorno pueden degradar esta precisión hasta las decenas de centímetros dependiendo de las características del espacio. Así pues, el efecto del multicamino es actualmente la principal fuente de error en esta tecnología, y por tanto, la principal barrera a superar para su implementación en situaciones reales. En esta tesis se propone y analiza un sistema de medida con señales ópticas que permite obtener estimaciones de diferencias de distancia precisas reduciendo el efecto crítico del multicamino. El sistema propuesto introduce una modulación con secuencias de ruido pseudoaleatorio sobre la modulación sinusoidal típicamente usada para medida de fase por onda continua, y aprovecha las propiedades de ensanchamiento en frecuencia de estas secuencias para reducir el efecto del multicamino. El sistema, que realiza una doble estimación de tiempo y fase de llegada, está compuesto por una etapa de sincronización que posibilita la demodulación parcialmente coherente de la señal recibida, seguida de un medidor diferencial de fase sobre las componentes desensanchadas tras la demodulación. Las condiciones de multicamino óptico típicas en espacios interiores, con una componente de camino directo claramente dominante, permiten que el proceso de demodulación recupere más potencia del camino directo que del resto de contribuciones, reduciendo el efecto del multicamino en la estimación final. Los resultados obtenidos demuestran que la aplicación del método propuesto permitiría realizar posicionamiento a partir de señales ópticas con el rendimiento adecuando para aplicaciones de robótica y guiado de vehículos en espacios interiores; además, el progresivo aumento de la potencia y el ancho de banda de los dispositivos optoelectrónicos disponibles permite esperar un incremento considerable de las prestaciones de la propuesta en los próximos años
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