Estudio experimental de algoritmos espacio-temporales para sistemas multiantena en túneles

[SPA] Las comunicaciones inalámbricas se han convertido hoy en día en una herramienta imprescindible en la sociedad en la que vivimos. En la actualidad los hábitos de consumo en las comunicaciones inalámbricas exigen aumentar la capacidad para transmitir contenidos multimedia. Día a día se trabaja en conseguir mejorar las prestaciones de estos sistemas inalámbricos y así poder afrontar dichas necesidades. Por ello, surgen los sistemas conocidos como Multiple-Input Multiple-Output (MIMO), que utilizan múltiples antenas en transmisión y múltiples antenas en recepción, permitiendo así alcanzar eficiencias espectrales mucho mayores a las alcanzadas en los sistemas convencionales. Por otro lado, en los últimos años se ha dado mucha importancia a poder comunicarse en entornos especiales, como es el caso de los túneles donde la naturaleza de los fenómenos físicos que permiten la propagación de las ondas es diferente al de otros entornos. En este tipo de entornos la energía es conducida por un medio guiado, de tal forma que la energía llega al receptor con un ángulo muy reducido en comparación con otros entornos. Además, la comunicación debe ser continua, fiable y de alta capacidad. Así pues, para cubrir dichas necesidades esta tesis está enmarcada en el estudio de los entornos tipo túnel, centrándose en el comportamiento y el rendimiento de los algoritmos espacio-temporales, ya que en este tipo de entornos se ha investigado muy poco sobre ello. Por ello, el objetivo principal de esta tesis es estudiar detalladamente, tanto de forma teórica como experimental, el comportamiento de los sistemas MIMO en túneles. Para ello se estudian los algoritmos más representativos de los sistemas multiantena: el algoritmo Vertical Bell Labs Space Time (VBLAST), los códigos Orthogonal Space Time Block Codes (OSTBC) y los códigos Quasy-Orthogonal Space Time Block Codes (QSTBC). El rendimiento de estos algoritmos, según la tasa de error de bit (BER, Bit Error Rate), se relaciona con las propiedades intrínsecas del canal radio tanto en banda estrecha como en banda ancha. [ENG] Wireless communications have become an indispensable tool in the society in which we live. In fact, the consumption habits of wireless communications require increasing capacity to transmit multimedia contents. Therefore, in order to meet these needs, work is continually being carried out in order to achieve the best performance possible from these wireless systems. The Multiple-Input Multiple-Output (MIMO) systems appear to achieve greater spectral efficiencies than the convectional systems. Furthermore, in recent years, communications in special contexts have acquired great importance. This thesis is focused on an environment type tunnel where the nature of the physical phenomena is different from other contexts. The energy is driven by a guided environment, therefore the energy arrives at the receiver with a smaller angle than in other environments. In addition, a continuous, reliable and effective communication is demanded. To meet the needs mentioned above, this thesis analyses the performance of space-time algorithms in tunnels. The main objective of this thesis is to study in detail both theoretically and experimentally the behaviour of the MIMO systems in tunnels combined with space-time algorithms. Moreover, this study covers both narrow and wide bands. The studied algorithms are the most representative: the Vertical Bell Labs Space Time (VBLAST), the Orthogonal Space Time Block Code (OSTBC) and the Quasy-Orthogonal Space Time Block Code (QSTBC). The performances in terms of Bit Error Rate (BER) have been compared, assuming a fixed bit rate, and interpreted from the MIMO channel characteristics.[ENG] Wireless communications have become an indispensable tool in the society in which we live. In fact, the consumption habits of wireless communications require increasing capacity to transmit multimedia contents. Therefore, in order to meet these needs, work is continually being carried out in order to achieve the best performance possible from these wireless systems. The Multiple-Input Multiple-Output (MIMO) systems appear to achieve greater spectral efficiencies than the convectional systems. Furthermore, in recent years, communications in special contexts have acquired great importance. This thesis is focused on an environment type tunnel where the nature of the physical phenomena is different from other contexts. The energy is driven by a guided environment, therefore the energy arrives at the receiver with a smaller angle than in other environments. In addition, a continuous, reliable and effective communication is demanded. To meet the needs mentioned above, this thesis analyses the performance of space-time algorithms in tunnels. The main objective of this thesis is to study in detail both theoretically and experimentally the behaviour of the MIMO systems in tunnels combined with space-time algorithms. Moreover, this study covers both narrow and wide bands. The studied algorithms are the most representative: the Vertical Bell Labs Space Time (VBLAST), the Orthogonal Space Time Block Code (OSTBC) and the Quasy-Orthogonal Space Time Block Code (QSTBC). The performances in terms of Bit Error Rate (BER) have been compared, assuming a fixed bit rate, and interpreted from the MIMO channel characteristics.Universidad Politécnica de CartagenaTecnologías de la Información y Comunicacione

Location-aware and Cooperative Communication in an OFDM based Ultra-wideband Radio System

Die auf dem orthogonalen Frequenzmultiplex (OFDM, Orthogonal Frequency Division Multiplexing) basierende Ultra-Breitband-(UWB, Ultra-wideband) Technologie stellt eine verheißungsvolle Technologie dar, um hohe Datenübertragungsraten und Lokalisierungs- und deren Tracking-Anwendungen zu realisieren. Im Gegensatz zu anderen Systemen ist die Reichweite von OFDM UWB Systemen durch eine strenge Regulierung sehr stark begrenzt. Darüber hinaus ist die Lokalisierung nicht zufriedenstellend. Damit sind bereits die beiden größten Nachteile im Bezug auf bestehende OFDM UWB System benannt. Die Motivation und Hauptaufgabe dieser Arbeit ist damit die Lösung der eben genannten Nachteile. Es wird ein OFDM UWB System vorgestellt, das Space Frequency Block Coding (SFBC) und FFH OFDM miteinander verbindet. Dieses vereinte System wertet die räumliche und frequentielle Diversität eines OFDM-Symbols aus und zeigt dabei eine hohe Güte in der Punkt-zu-Punkt Kommunikation. Beim Design von kooperativen UWB-Systemen wird ein AF-(Amplify-and-Forward) basiertes echtzeitfähriges SFBC-TFC (Time Frequency Code) Protokoll vorgestellt. In Kombination mit den oben genannten Strategien, kann eine Erhöhung in den Reichweite von OFDM UWB Systemen erreicht werden. In den Ausführungen zur Ortung anhand von OFDM UWB Signalen wird ein Algorithmus entwickelt, der aufgrund einer Kanalschätzung eine Minimierung des Phasenversatzes zwischen geschätztem und realem Kanal im Frequenzbereich durchführt. Diese Minimierung erwirkt eine Unterdrückung der Energie am Ende der Kanalimpulsantwort (CIR, Channel Impulse Response) im Zeitbereich. Zum Zweck der einfachen Implementierbarkeit wird das RTT (Round-Trip-Time) Messprotokoll in WiMedia UWB Systemen dahingehend verändert, dass das mobile Gerät keine Minimierung vornimmt. Es leitet seine Informationen an das mit ihm Kommunizierende, stationäre Gerät weiter, das direkt den gesamten Zeitversatz innerhalb des RTT berechnet. Der vorgeschlagene Algorithmus und das vorgeschlagene Protokoll haben ein besseres Ortungsvermögen als bekannte UWB Lokalisierungsprozeduren und bedürfen nur etwas zusätzlicher Berechnungsleistung. Diese Arbeit zeigt, dass Systeme mit hohen Datenraten wie OFDM UWB auch eine gute Lokalisierungsgenauigkeit erreichen können. Zusätzlich ist die Schwachstelle einer limitierten Reichweite ebenso kompensiert worden. Diese Erweiterungen dienen der Entwicklung von nützlichen UWB-Applikationen und sichern den Anteil der OFDM UWB Technik im Markt der drahtlosen Kommunikationssysteme der Zukunft.The Orthogonal Frequency Division Multiplexing (OFDM) based Ultra-wideband (UWB) is one of the most promising technologies for high data rate transmission and localization and tracking applications. However, the restricted transmit power causes a shorter communication range compared to other indoor radio systems. In addition, the ranging functionality is still not well supported by the current OFDM based UWB technology. These two drawbacks are the main disadvantages existing in the current OFDM UWB systems. To get rid of the two drawbacks, is the motivation and main task of this thesis. Within the scope of this thesis, a joint design of Space Frequency Block Coding (SFBC) with Fast Frequency Hopping (FFH) OFDM scheme is investigated in a multiple antenna OFDM UWB system. The joint scheme is able to exploit spatial and frequency domain diversity within one OFDM symbol, and can improve the data transmission quality in point-to-point communication. To the cooperative communication in UWB systems, an Amplify-and-Forward (AF) based distributed SFBC-TFC (Time Frequency Code) protocol is designed. In combination with the aforementioned strategies an increase in the communication range is achieved. Within the scope of this thesis, accurate ranging schemes for the OFDM UWB systems are designed. Fine ToA detection method based on the estimated channel is developed. The fine ToA is estimated by minimizing the accumulated energy of the tail taps of the estimated Channel Impulse Response (CIR). For the purpose of a feasible implementation, the Round-Trip-Time (RTT) measurement protocol in [WiM09] is modified in a way that the complicated computational tasks are burden onto the powerful device. The proposed fine ToA detection method and modified RTT protocol provides an accurate ranging capability and ensures feasible implementation to the MB-OFDM UWB systems. In carrying out this scheme, only some computational tasks are needed, no extra hardware support is required. It is shown in this thesis, OFDM UWB systems with very high data rate transmission and good ranging capability could be achieved, and the weakness of limited communication range is also compensated. These improvements will cause the rise of more valuable UWB applications for customers and ensures a bright future for the OFDM UWB technique

Order-4 Quasi-Orthogonal Cooperative Communication in STFC MB-OFDM UWB

Recently, cooperative communication and Space-Time-Frequency-Codes (STFCs) have been introduced into the Multiband OFDM Ultra-Wideband (MB-OFDM UWB) to improve the reliability, data rate and system capacity. This paper proposes a cooperative communication scheme for a four source node MB-OFDM UWB system using Quasi-Orthogonal STFCs, which is referred to as order-4 Quasi-Orthogonal Cooperative Communication Scheme (4-QOCCS). Simulation results show that the proposed 4-QOCCS provides significantly better error performance over the conventional MB-OFDM UWB and our order-2 Orthogonal Cooperative Communication Scheme (2-OCCS) using the Alamouti STFCs, and even better than the order-4 Orthogonal Cooperative Communication Scheme (4-OCCS), which we have been recently proposed, in the high spectral efficiency cases

Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions

The Error Performance and Fairness of CUWB Correlated Channels

AbstractThe symbol period becomes smaller compared to the channel delay in multiband orthogonal frequency division multiplexing (MB-OFDM) cognitive ultra wideband (CUWB) wireless communications, the transmitted signals experiences frequency-selective fading and leads to performance degradation. In this paper, a new design method for space-time trellis codes in MB-OFDM systems with correlated Rayleigh fading channels is introduced. This method converts the single output code symbol into several STTC code symbols, which are to be transmitted simultaneously from multiple transmitter-antennas. By using Viterbi optimal soft decision decoding algorithm, we investigate both quasi-static and interleaved channels and demonstrate how the spatial fading correlation affects the performance of space–time codes over these two different MB-OFDM wireless channel models. Simulation results show that the performance of space–time code is to be robust to spatial correlation. When the system bandwidth increases, the long term fairness quality will gradually become better and finally converges to 1

Unitary differential space-time-frequency codes for MB-OFDM UWB

In a multiple-input multiple-output (MIMO) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system, coherent detection where the channel state information (CSI) is assumed to be exactly known at the receiver requires the transmission of a large number of symbols for channel estimation, thus reducing the bandwidth efficiency. This paper examines the use of unitary differential space-time frequency codes (DSTFCs) in MB-OFDM UWB, which increases the system bandwidth efficiency due to the fact that no CSI is required for differential detection. The proposed DSTFC MB-OFDM system would be useful when the transmission of multiple channel estimation symbols is impractical or uneconomical. Simulation results show that the application of DSTFCs can significantly improve the bit error performance of conventional differential MB-OFDM system (without MIMO). ©2009 IEEE

Comprehensive performance analysis of fully cooperative communication in WBANs

© 2013 IEEE. While relay-based cooperative networks (widely known in the literature as cooperative communication), where relays only forward signals from the sources to the destination, have been extensively researched, fully cooperative systems have not been thoroughly examined. Unlike relay networks, in a fully cooperative network, each node acts as both a source node sending its own data and a relay forwarding its partner's data to the destination. Mutual cooperation between neighboring nodes is believed to improve the overall system error performance, especially when space-time codes are incorporated. However, a comprehensive performance analysis of space-time-coded fully cooperative communication from all three perspectives, namel,y error performance, outage probability, and energy efficiency, is still missing. Answers to the commonly asked questions of whether, in what conditions, and to what extent the space-time-coded fully cooperative communication is better than direct transmission are still unknown. Motivated by this fact and inspired by the increasing popularity of healthcare applications in wireless body area networks (WBANs), this paper derives for the first time a comprehensive performance analysis of a decode-and-forward space-time coded fully cooperative communication network in Rayleigh and Rician fading channels in either identically or non-identically distributed fading scenario. Numerical analysis of error performance, outage probability, and energy efficiency, validated by simulations, show that fully cooperative communication is better than direct transmission from all three aspects in many cases, especially at a low-power and low signal-to-noise ratio regime, which is a typical working condition in WBANs

Performance Enhancement in SU and MU MIMO-OFDM Technique for Wireless Communication: A Review

The consistent demand for higher data rates and need to send giant volumes of data while not compromising the quality of communication has led the development of a new generations of wireless systems. But range and data rate limitations are there in wireless devices. In an attempt to beat these limitations, Multi Input Multi Output (MIMO) systems will be used which also increase diversity and improve the bit error rate (BER) performance of wireless systems. They additionally increase the channel capacity, increase the transmitted data rate through spatial multiplexing, and/or reduce interference from other users. MIMO systems therefore create a promising communication system because of their high transmission rates without additional bandwidth or transmit power and robustness against multipath fading. This paper provides the overview of Multiuser MIMO system. A detailed review on how to increase performance of system and reduce the bit error rate (BER) in different fading environment e.g. Rayleigh fading, Rician fading, Nakagami fading, composite fading