On the use of discrete cosine transforms for multicarrier communications

In this correspondence, the conditions to use any kind of discrete cosine transform (DCT) for multicarrier data transmission are derived. The symmetric convolution-multiplication property of each DCT implies that when symmetric convolution is performed in the time domain, an element-by-element multiplication is performed in the corresponding discrete trigonometric domain. Therefore, appending symmetric redun-dancy (as prefix and suffix) into each data symbol to be transmitted, and also enforcing symmetry for the equivalent channel impulse response, the linear convolution performed in the transmission channel becomes a symmetric convolution in those samples of interest. Furthermore, the channel equalization can be carried out by means of a bank of scalars in the corresponding discrete cosine transform domain. The expressions for obtaining the value of each scalar corresponding to these one-tap per subcarrier equalizers are presented. This study is completed with several computer simulations in mobile broadband wireless communication scenarios, considering the presence of carrier frequency offset (CFO). The obtained results indicate that the proposed systems outperform the standardized ones based on the DFT

Investigation of methods for data communication and power delivery through metals

PhD ThesisThe retrieval of data from a sensor, enclosed by a metallic structure, such as a naval vessel, pipeline or nuclear flask is often very challenging. To maintain structural integrity it is not desirable to penetrate the wall of the structure, preventing any hard-wired solution. Furthermore, the conductive nature of the structure prevents the use of radio communications. Applications involving sealed containers also have a requirement for power delivery, as the periodic changing of batteries is not possible. Ultrasound has previously been identified as an attractive approach but there are two key challenges: efficient/reliable ultrasonic transduction and a method of overcoming the inherent multipath distortion resulting from boundary reflections. Previous studies have utilised piezoelectric contact transducers, however, they are impractical due to their reliance on coupling, i.e. the bond between the transducer and the metal surface, which leads to concerns over long term reliability. A non-contact transducer overcomes this key drawback, thus highlighting the electromagnetic acoustic transducer (EMAT) as a favourable alternative. This thesis presents the design and testing of an EMAT with appropriate characteristics for through-metal data communications. A low cost, low power data transmission scheme is presented for overcoming acoustic multipath based on pulse position modulation (PPM). Due to the necessary guard time, the data rate is limited to 50kbps. A second solution is presented employing continuous wave, Quadrature phase shift keying (QPSK) modulation, allowing data rates in excess of 1Mbps to be achieved. Equalisation is required to avoid intersymbol interference (ISI) and a decision feedback equaliser (DFE) is shown to be adept at mitigating this effect. The relatively low efficiency of an EMAT makes it unsuitable for power delivery, consequently, an alternative non-contact approach, utilising inductive coupling, is explored. Power transfer efficiency of ≈ 4% is shown to be achievable through 20mm thick stainless steel.ICS department of BAE Systems Submarine Solutions, EPSR

Underwater Acoustic MIMO OFDM: An experimental analysis

Projecte fet en col.laboració amb Massachusetts Institute of TechnologyResearch e orts over the past several years have provided ample proof that orthogonal frequency division multiplexing (OFDM) represents a viable alternative to single-carrier modulation which has traditionally been used for high rate communications over underwater acoustic channels. The main attraction of OFDM lies in its simplicity of implementation via FFT modulation/demodulation, which makes it a candidate for implementation in the next generation of acoustic modems

Solutions for New Terrestrial Broadcasting Systems Offering Simultaneously Stationary and Mobile Services

221 p.[EN]Since the first broadcasted TV signal was transmitted in the early decades of the past century, the television broadcasting industry has experienced a series of dramatic changes. Most recently, following the evolution from analogue to digital systems, the digital dividend has become one of the main concerns of the broadcasting industry. In fact, there are many international spectrum authorities reclaiming part of the broadcasting spectrum to satisfy the growing demand of other services, such as broadband wireless services, arguing that the TV services are not very spectrum-efficient. Apart from that, it must be taken into account that, even if up to now the mobile broadcasting has not been considered a major requirement, this will probably change in the near future. In fact, it is expected that the global mobile data traffic will increase 11-fold between 2014 and 2018, and what is more, over two thirds of the data traffic will be video stream by the end of that period. Therefore, the capability to receive HD services anywhere with a mobile device is going to be a mandatory requirement for any new generation broadcasting system. The main objective of this work is to present several technical solutions that answer to these challenges. In particular, the main questions to be solved are the spectrum efficiency issue and the increasing user expectations of receiving high quality mobile services. In other words, the main objective is to provide technical solutions for an efficient and flexible usage of the terrestrial broadcasting spectrum for both stationary and mobile services. The first contributions of this scientific work are closely related to the study of the mobile broadcast reception. Firstly, a comprehensive mathematical analysis of the OFDM signal behaviour over time-varying channels is presented. In order to maximize the channel capacity in mobile environments, channel estimation and equalization are studied in depth. First, the most implemented equalization solutions in time-varying scenarios are analyzed, and then, based on these existing techniques, a new equalization algorithm is proposed for enhancing the receivers’ performance. An alternative solution for improving the efficiency under mobile channel conditions is treating the Inter Carrier Interference as another noise source. Specifically, after analyzing the ICI impact and the existing solutions for reducing the ICI penalty, a new approach based on the robustness of FEC codes is presented. This new approach employs one dimensional algorithms at the receiver and entrusts the ICI removing task to the robust forward error correction codes. Finally, another major contribution of this work is the presentation of the Layer Division Multiplexing (LDM) as a spectrum-efficient and flexible solution for offering stationary and mobile services simultaneously. The comprehensive theoretical study developed here verifies the improved spectrum efficiency, whereas the included practical validation confirms the feasibility of the system and presents it as a very promising multiplexing technique, which will surely be a strong candidate for the next generation broadcasting services.[ES]Desde el comienzo de la transmisión de las primeras señales de televisión a principios del siglo pasado, la radiodifusión digital ha evolucionado gracias a una serie de cambios relevantes. Recientemente, como consecuencia directa de la digitalización del servicio, el dividendo digital se ha convertido en uno de los caballos de batalla de la industria de la radiodifusión. De hecho, no son pocos los consorcios internacionales que abogan por asignar parte del espectro de radiodifusión a otros servicios como, por ejemplo, la telefonía móvil, argumentado la poca eficiencia espectral de la tecnología de radiodifusión actual. Asimismo, se debe tener en cuenta que a pesar de que los servicios móviles no se han considerado fundamentales en el pasado, esta tendencia probablemente variará en el futuro cercano. De hecho, se espera que el tráfico derivado de servicios móviles se multiplique por once entre los años 2014 y 2018; y lo que es más importante, se pronostica que dos tercios del tráfico móvil sea video streaming para finales de ese periodo. Por lo tanto, la posibilidad de ofrecer servicios de alta definición en dispositivos móviles es un requisito fundamental para los sistemas de radiodifusión de nueva generación. El principal objetivo de este trabajo es presentar soluciones técnicas que den respuesta a los retos planteados anteriormente. En particular, las principales cuestiones a resolver son la ineficiencia espectral y el incremento de usuarios que demandan mayor calidad en los contenidos para dispositivos móviles. En pocas palabras, el principal objetivo de este trabajo se basa en ofrecer una solución más eficiente y flexible para la transmisión simultánea de servicios fijos y móviles. La primera contribución relevante de este trabajo está relacionada con la recepción de la señal de televisión en movimiento. En primer lugar, se presenta un completo análisis matemático del comportamiento de la señal OFDM en canales variantes con el tiempo. A continuación, con la intención de maximizar la capacidad del canal, se estudian en profundidad los algoritmos de estimación y ecualización. Posteriormente, se analizan los algoritmos de ecualización más implementados, y por último, basándose en estas técnicas, se propone un nuevo algoritmo de ecualización para aumentar el rendimiento de los receptores en tales condiciones. Del mismo modo, se plantea un nuevo enfoque para mejorar la eficiencia de los servicios móviles basado en tratar la interferencia entre portadoras como una fuente de ruido. Concretamente, tras analizar el impacto del ICI en los receptores actuales, se sugiere delegar el trabajo de corrección de dichas distorsiones en códigos FEC muy robustos. Finalmente, la última contribución importante de este trabajo es la presentación de la tecnología LDM como una manera más eficiente y flexible para la transmisión simultánea de servicios fijos y móviles. El análisis teórico presentado confirma el incremento en la eficiencia espectral, mientras que el estudio práctico valida la posible implementación del sistema y presenta la tecnología LDM c

Mobile OFDM communications

Orthogonal frequency division multiplexing (OFDM) has recently received increased attention due to its capability of supporting high-data-rate communications in frequency-selective fading environments with a comparatively simple receiver structure. However, the time variations (high mobility) of the channel during one OFDM symbol destroy the orthogonality of the different subcarriers and generate power leakage among the subcarriers, known as Inter-Carrier Interference (ICI), which will cause degradation in system performance. Therefore, our research emphasis on Doppler sensitivity is especially meaningful given the popularity that fixed wireless/low mobility OFDM systems have experienced (e.g. 802.11a). In this dissertation, we first analyze the theoretical performance degradation of OFDM system due to Doppler spreading by developing a two-dimensional Gram- Charlier representation for the bivariate pdf of the ICI, after the bivariate probability density function (pdf) of the ICI is shown to be a weighted Gaussian mixture. Secondly, in order to suppress ICI in OFDM systems, we describe an MMSE based OFDM detection according to the estimated channel information through a simple and efficient polynomial surface channel estimation technique. Thirdly, we consider filtered multitone (FMT) modulation over frequency-selective time-varying fading channels. Both ICI and ISI are quantified under several different fading channels conditions. An analysis of the C/I ratio of the FMT system is compared with the conventional OFDM system in order to demonstrate the underlying trade-offs between the spectral efficiency and system performance. Finally, a per-channel tap-delay-line equalizer is proposed at the FMT receiver to mitigate the ISI. A closed -form expression of the upper bound for its C/I ratio is derived for the per-channel equalized FMT system and used to evaluate the system performance. Performance comparisons are made with an un-equalized FMT system as well as a standard OFDM syste

Mobile OFDM communications

Orthogonal frequency division multiplexing (OFDM) has recently received increased attention due to its capability of supporting high-data-rate communications in frequency-selective fading environments with a comparatively simple receiver structure. However, the time variations (high mobility) of the channel during one OFDM symbol destroy the orthogonality of the different subcarriers and generate power leakage among the subcarriers, known as Inter-Carrier Interference (ICI), which will cause degradation in system performance. Therefore, our research emphasis on Doppler sensitivity is especially meaningful given the popularity that fixed wireless/low mobility OFDM systems have experienced (e.g. 802.11a). In this dissertation, we first analyze the theoretical performance degradation of OFDM system due to Doppler spreading by developing a two-dimensional Gram- Charlier representation for the bivariate pdf of the ICI, after the bivariate probability density function (pdf) of the ICI is shown to be a weighted Gaussian mixture. Secondly, in order to suppress ICI in OFDM systems, we describe an MMSE based OFDM detection according to the estimated channel information through a simple and efficient polynomial surface channel estimation technique. Thirdly, we consider filtered multitone (FMT) modulation over frequency-selective time-varying fading channels. Both ICI and ISI are quantified under several different fading channels conditions. An analysis of the C/I ratio of the FMT system is compared with the conventional OFDM system in order to demonstrate the underlying trade-offs between the spectral efficiency and system performance. Finally, a per-channel tap-delay-line equalizer is proposed at the FMT receiver to mitigate the ISI. A closed -form expression of the upper bound for its C/I ratio is derived for the per-channel equalized FMT system and used to evaluate the system performance. Performance comparisons are made with an un-equalized FMT system as well as a standard OFDM syste

Channel modeling and estimation for mobile-to-mobile OFDM communications

M.S.Gordon Stübe