A Robust and Low-Complexity Timing Synchronization Algorithm for ADSRC System

In this paper, a robust, low-complexity timing synchronization algorithm suitable for 5.9 GHz Dedicated Short Range Communications (DSRC) system is proposed. The proposed method uses cross-correlation technique to detect the starting point of both a short training symbol and the guard interval of the first long training symbol. This allows the proposed algorithm to have low-complex architecture. Compared to the scheme proposed by Chang and Kelly, the proposed algorithm attains considerably higher timing synchronization performance and significantly reduced computational complexity. Simulation results show that the proposed algorithm is robust and efficient in high-mobility environments and low signal-to-noise ratio (SNR) conditions

Implementation of uplink network-coded modulation for two-hop networks

With the fast growing number of wireless devices and demand of user data, the backhaul load becomes a bottleneck in wireless networks. Physical layer network coding (PNC) allows Access Points (APs) to relay compressed, network coded user data, therefore reducing the backhaul traffic. In this paper, an implementation of uplink Network Coded Modulation (NetCoM) with PNC is presented. A 5-node prototype NetCoM system is established using Universal Software Radio Peripherals (USRPs) and a practical PNC scheme designed for binary systems is utilised. An orthogonal frequency division multiplexing (OFDM) waveform implementation and the practical challenges (e.g. device synchronisation and clock drift) of applying OFDM to NetCoM are discussed. To the best of our knowledge this is the first PNC implementation in an uplink scenario in radio access networks and our prototype provides an industrially-applicable implementation of the proposed NetCoM with PNC approach

Interference Mitigation in Wireless Communications

The primary objective of this thesis is to design advanced interference resilient schemes for asynchronous slow frequency hopping wireless personal area networks (FH-WPAN) and time division multiple access (TDMA) cellular systems in interference dominant environments. We also propose an interference-resilient power allocation method for multiple-input-multiple-output (MIMO) systems. For asynchronous FH-WPANs in the presence of frequent packet collisions, we propose a single antenna interference canceling dual decision feedback (IC-DDF) receiver based on joint maximum likelihood (ML) detection and recursive least squares (RLS) channel estimation. For the system level performance evaluation, we propose a novel geometric method that combines bit error rate (BER) and the spatial distribution of the traffic load of CCI for the computation of packet error rate (PER). We also derived the probabilities of packet collision in multiple asynchronous FH-WPANs with uniform and nonuniform traffic patterns. For the design of TDMA receivers resilient to CCI in frequency selective channels, we propose a soft output joint detection interference rejection combining delayed decision feedback sequence estimation (JD IRC-DDFSE) scheme. In the proposed scheme, IRC suppresses the CCI, while DDFSE equalizes ISI with reduced complexity. Also, the soft outputs are generated from IRC-DDFSE decision metric to improve the performance of iterative or non-iterative type soft-input outer code decoders. For the design of interference resilient power allocation scheme in MIMO systems, we investigate an adaptive power allocation method using subset antenna transmission (SAT) techniques. Motivated by the observation of capacity imbalance among the multiple parallel sub-channels, the SAT method achieves high spectral efficiency by allocating power on a selected transmit antenna subset. For 4 x 4 V-BLAST MIMO systems, the proposed scheme with SAT showed analogous results. Adaptive modulation schemes combined with the proposed method increase the capacity gains. From a feasibility viewpoint, the proposed method is a practical solution to CCI-limited MIMO systems since it does not require the channel state information (CSI) of CCI.Ph.D.Committee Chair: Professor Gordon L. StBe

Design and theoretical analysis of advanced power based positioning in RF system

Accurate locating and tracking of people and resources has become a fundamental requirement for many applications. The global navigation satellite systems (GNSS) is widely used. But its accuracy suffers from signal obstruction by buildings, multipath fading, and disruption due to jamming and spoof. Hence, it is required to supplement GPS with inertial sensors and indoor localization schemes that make use of WiFi APs or beacon nodes. In the GPS-challenging or fault scenario, radio-frequency (RF) infrastructure based localization schemes can be a fallback solution for robust navigation. For the indoor/outdoor transition scenario, we propose hypothesis test based fusion method to integrate multi-modal localization sensors. In the first paper, a ubiquitous tracking using motion and location sensor (UTMLS) is proposed. As a fallback approach, power-based schemes are cost-effective when compared with the existing ToA or AoA schemes. However, traditional power-based positioning methods suffer from low accuracy and are vulnerable to environmental fading. Also, the expected accuracy of power-based localization is not well understood but is needed to derive the hypothesis test for the fusion scheme. Hence, in paper 2-5, we focus on developing more accurate power-based localization schemes. The second paper improves the power-based range estimation accuracy by estimating the LoS component. The ranging error model in fading channel is derived. The third paper introduces the LoS-based positioning method with corresponding theoretical limits and error models. In the fourth and fifth paper, a novel antenna radiation-pattern-aware power-based positioning (ARPAP) system and power contour circle fitting (PCCF) algorithm are proposed to address antenna directivity effect on power-based localization. Overall, a complete LoS signal power based positioning system has been developed that can be included in the fusion scheme --Abstract, page iv

Identification of Technologies for Provision of Future Aeronautical Communications

This report describes the process, findings, and recommendations of the second of three phases of the Future Communications Study (FCS) technology investigation conducted by NASA Glenn Research Center and ITT Advanced Engineering & Sciences Division for the Federal Aviation Administration (FAA). The FCS is a collaborative research effort between the FAA and Eurocontrol to address frequency congestion and spectrum depletion for safety critical airground communications. The goal of the technology investigation is to identify technologies that can support the longterm aeronautical mobile communication operating concept. A derived set of evaluation criteria traceable to the operating concept document is presented. An adaptation of the analytical hierarchy process is described and recommended for selecting candidates for detailed evaluation. Evaluations of a subset of technologies brought forward from the prescreening process are provided. Five of those are identified as candidates with the highest potential for continental airspace solutions in L-band (P-34, W-CDMA, LDL, B-VHF, and E-TDMA). Additional technologies are identified as best performers in the unique environments of remote/oceanic airspace in the satellite bands (Inmarsat SBB and a custom satellite solution) and the airport flight domain in C-band (802.16e). Details of the evaluation criteria, channel models, and the technology evaluations are provided in appendixes

Urban, suburban and rural channel models based on cellular and wireless area network signals for positioning purposes

Location information is becoming more and more useful in everyday life. The cellular- based and wireless area network based positioning are being used to predict the location of users in environments such as indoors and densely urban, where the Global Navigation Satellite Systems often fail. The Received Signal Strength (RSS) is used more and more due to its wide availability on any mobile device and based on various signals. However, studies about the availability of signal measurements in various urban and sub-urban scenarios and about the RSS fluctuations in various terrain types are still lacking in the current literature. The main objective of this thesis is to analyze method wide range of measurement-based RSS in urban, suburban and rural environments. The thesis is divided in two parts. In the literature study part, issues related to cellular and wireless local area networks (WLANs) such as frequency bands, system architectures, radio interfaces and RSS measurements are described. Also the propagation channel characteristics and the different path-loss models existing in the literature are exposed. The information explained in this part was useful in order to be able to process the available data measurements. In the measurements and analysis part, the collected results were evaluated. The different parameters of cellular and WLAN signals were studied and compared. Availability of signals in various scenarios, density of the transmitters and path loss coefficients were deeply analyzed, by dividing the measured scenarios into seven distinct environments: airport areas, Seaside or beach areas, Mountain or forest areas, suburban areas, densely urban areas, lake areas, and other urban areas. The obtained results provide more insight into the availability of RSS signal measurements on mobile devices nowadays and into the possibility of creating generic and unified RSS-based positioning algorithms (based on the similarities between different types of signals and different types of environments)

Optimisation of wireless communication system by exploitation of channel diversity

Communication systems are susceptible to degradation in performance because of interference received through their side lobes. The interference may be deliberate electronic counter measure (ECM), Accidental RF Interference (RFI) or natural noise. The growth of interference communication systems have given rise to different algorithms, Adaptive array techniques offer a possible solution to this problem of interference received through side lobes because of their automatic null steering in both spatial and frequency domains. Key requirement for space-time architecture is to use robust adaptive algorithms to ensure reliable operation of the smart antenna. Space division multiple access (SDMA) involves the use of adaptive nulling to allow two or more users (mobiles) in the same cell to share same frequency and time slot. One beam is formed for each user with nulls in the direction of other users. Different approaches have been used to identify the interferer from desired user. Thus a basic model for determining the angle of arrival of incoming signals, an appropriate antenna beam forming and adaptive algorithms are used for array processing. There is an insatiable demand for capacity in wireless data networks and cellular radio communication systems. However the RF environment that these systems operate in is harsh and severely limits the capacity of traditional digital wireless networks. With normal wireless systems this limits the data rate in cellular radio environments to approximately 200 kbps whereas much higher data rates in excess of 25Mbps are required. A common wireless channel problem is that of frequency selective multi-path fading. To combat this problem, new types of wireless interface are being developed which utilise space, time and frequency diversity to provide increasing resilience to the channel imperfections. At any instant in time, the channel conditions may be such that one or more of these diversity methods may offer a superior performance to the other diversity methods. The overall aim of the research is to develop new systems that use a novel combination of smart antenna MIMO techniques and an advanced communication system based on advanced system configuration that could be exploited by IEEE 802.20 user specification approach for broadband wireless networking. The new system combines the Multi-input Multi-output communication system with frequency diversity in the form of an OFDM modulator. The benefits of each approach are examined under similar channel conditions and results presented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Algoritmos en transmisión y recepción para OFDM en entornos multi-usuario

Desde su incursión en la vida de los ciudadanos de forma cotidiana, las comunicaciones móviles han ido adquiriendo cada vez más protagonismo. Lo que hace unos años era un elemento de lujo o causa de envidias, hoy es algo tan habitual como coger el autobús. Este auge en las comunicaciones móviles ha llevado consigo un aumento del número de usuarios de estos servicios, así como una mayor exigencia por parte de éstos en cuanto a velocidad de transmisión, seguridad, servicios, calidad ... Por este motivo, se han ido introduciendo nuevas redes, así como mejoras en las ya existentes. Actualmente estamos asistiendo al inicio de la implantación de las redes denominadas de tercera generación (3G). No obstante, estas redes 3G fueron de nidas a mediados de los años 90. En la actualidad nos encontramos en la de nición de lo que será la cuarta generación móvil (4G) a la que probablemente preceda una intermedia, tal vez Super 3G. Muchas son las tecnologías candidatas para esta Super 3G o para la 4G, pero es OFDM (Multiplexación por División en Frecuencias Ortogonales - Orthogonal Frequency Division Multiplexing) una de las más prometedoras para terminar siendo la tecnología elegida, debido principalmente a la robustez que ofrece frente al multi-trayecto, la flexibilidad que proporciona por el hecho de dividir el ancho de banda en sub-portadoras que pueden ser moduladas independientemente para adaptarse a las condiciones específicas de los canales móviles y al aprovechamiento de la diversidad multi-usuario cuando se combina en OFDMA (Acceso múltiple por división en frecuencias ortogonales - Orthogonal Frequency Division Multiple Access). Sin embargo, para que estos sistemas OFDMA sean una realidad en redes futuras como la Super 3G o la 4G, es preciso reducir la complejidad que ellos conllevan, en aspectos como la sincronización multi-usuario o la implementación de la modulación adaptativa. Esta Tesis está enfocada a reducir la complejidad de implementación para que la tecnología OFDMA pueda ser un hecho en las futuras redes inalámbricas. La sincronización en sistemas OFDMA, principalmente en escenarios ad-hoc plantea un reto importante a la hora de implementarla en este tipo de redes. Dado que existe una literatura extensa dedicada a resolver el problema de la sincronización en entornos OFDM mono-usuario, en esta Tesis se propone un procedimiento para reducir el problema de la sincronización multiusuario al caso mono-usuario, lo que permite la re-utilización de todas las técnicas propuestas en la literatura. Además de las buenas prestaciones incluso en situaciones de saturación de la red, permite un ahorro de la energía necesaria para la realización de las tareas de sincronización. Asimismo, a la vez que se resuelve la sincronización multi-usuario, también en esta Tesis se aporta un algoritmo para realizar el seguimiento de la desviación de frecuencia en sistemas tanto OFDM como OFDMA, de una forma sencilla y eficiente. Este algoritmo utiliza las sub-portadoras piloto de los símbolos, y ofrece unas prestaciones razonables, incluso cuando el número de estas sub-portadoras piloto es reducido. La modulación adaptativa u otras técnicas avanzadas de comunicaciones como MIMO (Multiple Input Multiple Output) o el conformado de haz (beamforming), que se hacen más atractivas cuando se combinan con OFDM u OFDMA, requieren de cierta realimentación hacia el transmisor por parte del receptor, además de un conocimiento del canal bastante preciso. En esta Tesis se aportan algoritmos para la compresión de esta información (que puede ser muy elevada dependiendo de la granularidad de la adaptación y la variabilidad del canal), lo que permite un mejor aprovechamiento de los recursos radio, y simpli ca la implementación de este tipo de sistemas. Se consiguen reducciones superiores a cuatro veces la tasa original, lo que implica grandes ventajas en todos los sentidos. Además, se realiza un estudio teórico sobre cómo afectan los errores en la estimación de canal en la capacidad del sistema, obteniéndose dos cotas numéricas para ésta. Gracias a estas cotas se puede concluir que las técnicas actuales de estimación de canal son su cientemente buenas como para que las pérdidas producidas por los errores en esta estimación no sean muy significativas; No obstante, estas pérdidas aumentan a medida que se incrementa la relación señal a ruido, y, por tanto, es conveniente seguir mejorando la estimación de canal si se pretende que estos sistemas trabajen a altas relaciones señal a ruido. Por último, destacar que las simulaciones llevadas a cabo para examinar las prestaciones de los algoritmos desarrollados han proporcionado datos prácticos que ayudarán al diseño e implementación de futuras redes móviles 4G.Nowadays mobile communications are common in our society. In less than two decades they have changed the way people understand personal communications. This interest is still growing and makes users (every day larger in number) ask for more and more services, speed, security and quality, at least comparable to the wired technologies. For this reason, new networks have been introduced in the scene, as well as improvements in the already existing ones. At the moment we are witnessing the beginning of the deployment of the so-called third generation networks (3G). However, these 3G networks were defined in the middle of years 90. At the present time we are in the definition of what will be the fourth mobile generation, which is called the 4G and probably an intermediate stage as Super 3G could be defined first. Many different technologies are in consideration, but OFDM (Orthogonal Frequency Multiplexing Division) is one of most promising candidates to end up becoming the technology to be used, due mainly to the robustness that it others to the multi-path channel, the flexibility that it provides by the fact that it divides the bandwidth into sub-carriers which can be modulated independently to adapt the signal to the specific channel conditions and to the advantage of the multi-user diversity when it is used to multiplex several users in the form of OFDMA (Orthogonal Frequency Division Multiple Access). Nevertheless, in order for these OFDMA systems to be a reality in future networks as Super 3G or 4G, the reduction in complexity has to be considered, in aspects such as the multi-user synchronization or the implementation of the Adaptive Modulation. This doctoral Thesis is focused on reducing the implementation complexity in both multi-user synchronization and Adaptive Modulation so that OFDMA technology can be a fact in the near future radio networks. The synchronization in OFDMA systems, specially in ad-hoc scenarios, raises an important challenge at the time of implementing this technology. Since an extensive literature is devoted to solve the problem of the synchronization in single-user OFDM systems, in this Thesis we have designed and proposed a procedure to reduce the multi-user synchronization problem to the single-user case, and therefore it allows the reuse of all the already proposed techniques in the literature. The procedure exhibits a good performance even in network saturation situations, and in addition it does not incur in a high power consumption when performing the synchronization tasks. Besides, solving the multi-user synchronization problem, the Thesis also proposes an algorithm for frequency offset tracking in an efficient and simple way, for both OFDM and OFDMA systems. This algorithm uses the pilot sub-carriers scattered in each OFDM symbol, and o ers reasonable performance, even when the number of these pilot sub-carriers is small. Adaptive Modulation and other advanced techniques as MIMO (Multiple Input Multiple Output) or beamforming become more attractive when they are combined with OFDM or OFDMA. However they require certain feedback information from receiver to the transmitter, and in addition, a quite precise knowledge about channel conditions. In this Thesis several algorithms for compressing the feedback information have been developed. This feedback information can be very highly demanding (depending on the granularity of the adaptation and the variability of the channel), and therefore this compression allows a better use of the resources, and simplifies the implementation of this kind of systems. Reductions of more than four times the original flow are obtained, which implies great advantages. In addition, a theoretical study is made on how errors in channel estimation affect the channel capacity, and several upper-bounds (one of them very tight) for this effect are obtained. One of the conclusions is that the actual state of the art in channel estimation techniques is good enough to be used without too much loss; However, the loss increases as the signal to noise ratio increases, and therefore, it is suggested to continue improving channel estimation algorithms for improving performance in high signal to noise ratio scenarios. Finally, thanks to simulations and designs carried out in order to examine the performance of the developed algorithms, some practical data are provided that will help in the future design of new mobile networks as 4G