Super-orthogonal space-time turbo coded OFDM systems.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.The ever increasing demand for fast and efficient broadband wireless communication services requires future broadband communication systems to provide a high data rate, robust performance and low complexity within the limited available electromagnetic spectrum. One of the identified, most-promising techniques to support high performance and high data rate communication for future wireless broadband services is the deployment of multi-input multi-output (MIMO) antenna systems with orthogonal frequency division multiplexing (OFDM). The combination of MIMO and OFDM techniques guarantees a much more reliable and robust transmission over a hostile wireless channel through coding over the space, time and frequency domains. In this thesis, two full-rate space-time coded OFDM systems are proposed. The first one, designed for two transmit antennas, is called extended super-orthogonal space-time trellis coded OFDM (ESOSTTC-OFDM), and is based on constellation rotation. The second one, called super-quasi-orthogonal space-time trellis coded OFDM (SQOSTTCOFDM), combines a quasi-orthogonal space-time block code with a trellis code to provide a full-rate code for four transmit antennas. The designed space-time coded MIMO-OFDM systems achieve a high diversity order with high coding gain by exploiting the diversity advantage of frequency-selective fading channels. Concatenated codes have been shown to be an effective technique of achieving reliable communication close to the Shannon limit, provided that there is sufficient available diversity. In a bid to improve the performance of the super orthogonal space-time trellis code (SOSTTC) in frequency selective fading channels, five distinct concatenated codes are proposed for MIMO-OFDM over frequency-selective fading channels in the second part of this thesis. Four of the coding schemes are based on the concatenation of convolutional coding, interleaving, and space-time coding, along multiple-transmitter diversity systems, while the fifth coding scheme is based on the concatenation of two space-time codes and interleaving. The proposed concatenated Super-Orthogonal Space-Time Turbo-Coded OFDM System I. B. Oluwafemi 2012 vii coding schemes in MIMO-OFDM systems achieve high diversity gain by exploiting available diversity resources of frequency-selective fading channels and achieve a high coding gain through concatenations by employing the turbo principle. Using computer software simulations, the performance of the concatenated SOSTTC-OFDM schemes is compared with those of concatenated space-time trellis codes and those of conventional SOSTTC-OFDM schemes in frequency-selective fading channels. Simulation results show that the concatenated SOSTTC-OFDM system outperformed the concatenated space-time trellis codes and the conventional SOSTTC-OFDM system under the various channel scenarios in terms of both diversity order and coding gain

Blind channel estimation for space-time block codes : novel methods and performance Studies

[abstract] This work is based on a study of blind source separation techniques in order to estimate coe cients in transmission systems using Alamouti codi cation with two transmit antennas and one receive antenna. Most of present standards include pilot symbols to estimate the channel in reception. Since these symbols do not deliver user's data, their use decrease transferring quantity and also the system capacity. On the other hand, algorithms of blind separation are less precise when estimating channel coe cients than those supervised, but achieving a higher transferring rate. In this work we will deal with Alamouti codi cation system as a typical problem of blind sources separation where the signals transmitted and the channel coe cients must be estimated according to lineal and instantaneous mixtures (observations). Orthogonal structure required by Alamouti codi cation allows us to solve this problem by decomposing eigenvalues and eigenvectors of matrices calculated from di erent statistics of the observations. These algorithms could be classi ed as those using second order statistics and those using higher order statistics. Algorithms based on second order statistics work with correlation matrix of observations. They are computationally less expensive, but require a lineal precoder in order to balance the power of the signals transmitted. One of our contributions is being able to determine in an empirical way how the power decompensation should be done in order to reduce the proabibility of error in the system. On the other hand, algorithms dealing with high level statistics are based on diagonalize one or several high level cumulant matrices deriving into a major computational cost in the receiver. As an advantage we must point out that they do not require to include a lineal precoder to do the power decompensation. In this work we will prove that the output of these techniques depends on the level of eigenvalue of the diagonalized matrix spreading. This idea will be used by us in order to achieve the optimal cumulant matrix and also to propose a new algorithm that increases the output in relation to those already proposed by other authors. Another important contribution of this present study is to propose a detailed comparison between channel estimation techniques in simulated scenarios, considering channels with Rayleigh and Rice distribution, and in real scenarios in ISM of 2.4 GHz band, by using a MIMO testbed developed in Universidade da Coruña. [Resumen] En este trabajo se realiza un estudio de técnicas de separación ciega de fuentes para la estimación de los coeficientes en sistemas de transmisión que emplean la codificación de Alamouti con 2 antenas transmisoras y 1 antena receptora. La mayoría de los estándares actuales incluyen símbolos piloto para estimar el canal en recepción. Dado que estos símbolos no transportan datos del usuario, su utilización decrementa la tasa de transferencia y degrada el rendimiento del sistema. Por otro lado, los algoritmos de separación ciega son menos precisos en la estimación de los coeficientes de canal que los supervisados pero consiguen una tasa de transferencia mayor. En el presente trabajo, modelaremos el sistema de codificación de Alamouti como un problema típico de separación ciega de fuentes donde las se~nales transmitidas y los coeficientes del canal deben ser estimados a partir de mezclas lineales e instantáneas (observaciones). La estructura ortogonal impuesta por la codificación de Alamouti permite resolver este problema mediante la descomposición de autovalores y autovectores de matrices calculadas a partir de diferentes estadísticos de las observaciones. Estos algoritmos pueden ser clasificados en aquellos que utilizan estadísticos de segundo orden y aquellos que emplean estadísticos de orden superior. Los algoritmos que emplean estadísticos de segundo orden trabajan con la matriz de correlación de las observaciones, son computacionalmente poco costosos pero requieren de un precodificador lineal para descompensar la potencia de las se~nales transmitidas. Una de nuestras aportaciones es la de determinar de forma empírica cómo debe realizarse la descompesación de potencia de cara a reducir la probabilidad de error del sistema. Por otro lado, los algoritmos que trabajan con estadísticos de orden superior se basan en diagonalizar una o varias matrices de cumulantes de orden superior, lo que conlleva un mayor coste computacional en el receptor. Como ventaja debe resaltarse que no requieren incluir un precodificador lineal que realice la descompensación de potencia. En este trabajo mostraremos que el rendimiento de estas técnicas depende del grado de dispersión de los autovalores de la matriz que se diagonaliza. Utilizaremos esta idea para obtener la matriz de cumulantes óptima y para formular un nuevo algoritmo que supera en rendimiento a los propuestos previamente por otros autores. Otra aportación relevante del presente trabajo es presentar una detallada comparación de las técnicas de estimación de canal en entornos simulados, considerando canales con ditribución Rayleigh y Rice, y en entornos reales en la banda ISM de 2.4 GHz mediante el empleo de una plataforma de transmisión MIMO desarrollada en la Universidade da Coruña