Symbol Synchronization Techniques In Digital Communications

"Timing synchronization plays an important role in recovering the original transmitted signal in telecommunication systems. In order to have a communication system that operates at the correct time and in the correct order, it is necessary to synchronize to the transmitter’s symbol timing. Synchronization can be accomplished when the receiver clock tracks the periodic timing information in a transmitted signal to reproduce the original signal. In this thesis work, we report the design, implementation and evaluation of a timing synchronization algorithm based on the technique first proposed by Gardner [1], applied to wireless communication using the Alamouti spacetime code [2] under QPSK modulation with halfsine pulses. To achieve this, a mathematical model is introduced which includes software design of communication algorithms. In this modeling, we simulate the Gardner algorithm in MATLAB. Then, five techniques are introduced to improve the performance of the loop filter in the digital receiver, and they are successfully implemented and evaluated in Matlab. These five techniques prove that there is an improvement in digital receiver performance in terms of the convergence speed and the communication system complexity. On the other hand, the optimum decoding of the Alamouti spacetime code, as initially proposed, makes the nontrivial assumption that the communication system is perfectly synchronized. Realistic wireless environments contain additive white Gaussian noise (AWGN), multipath fading, and it is not perfectly synchronized. In this thesis, the Alamouti spacetime code technique is written for QPSK modulation scheme to work in realistic environment that involves a timing synchronization technique. We compare the bit error rate (BER) of the Alamouti decoder when synchronized using the proposed algorithms with the ideal results found in the literature, and we find them to be similar, proving that the synchronization algorithm is in fact achieving optimum synchronization. This thesis presents synchronization algorithms that are necessary for a complete working wireless Alamouti technique. Also, this thesis improves the communication system performance in terms of the convergence speed with reducing the computational complexity of the communication system design."--Abstract.