The study on the space time block coding and its application in wireless communications
Among all the systems implementing transmit diversity, Space-Time Block Coding (STBC) has the simplest structure and offers full diversity and linear maximum-likelihood (ML) detection if the design is orthogonal, although the transmission efficiency is less than one for more than two (2+) transmit antennas. To compensate the reduction of transmission efficiency, quasi-orthogonal STBC (QOSTBC) is proposed.
The first part of this thesis proposes an original design of a general class of QOSTBC for four transmit antennas. By analyzing the orthogonal properties of the symbol pairs in the encoding matrix and by checking the rank of the decoding matrix, a complete family with a total of 18432 complex QOSTBC codes has been found, based on the criterion that each symbol is seen through each channel only once. These QOSTBC codes can be decoded pairwisely and are robust over highly correlated channels. Consequently, they have a small decoding complexity but good performance. Based on these QOSTBC, a new family of rate ¾ complex orthogonal STBC (NF-OSTBC) is derived.
The second part presents three applications of STBC in wireless communications. The first one is the combination of STBC with an outer code to enhance its error correction capability. The concatenation of STBC and Block Turbo Code (BTC) is investigated and the upper bound of the resulting bit error rate (BER) is derived. In order to treat the case of Rayleigh frequency-selective fading channels, the orthogonal frequency division multiplexing (OFDM) is added to this combination to obtain an STBC-BTC-OFDM scheme. This scheme shows an improved performance by simulation over that of the STBC-Turbo-OFDM scheme.
The second application of STBC is in the uplink channels of a multi-user system. A genetic algorithm (GA) is proposed to detect the symbols in a collective manner based upon the maximal likelihood (ML) rule. In this GA, the initial seed chromosome is provided by a decorrelating detector (DD) or a minimal mean square error (MMSE) detector. In addition, the objective function is modified to map all the chromosomes into the unit circle to improve the performance further.
The third application of STBC is found in ultra-wide bandwidth (UWB) systems. Three different UWB systems are evaluated: a system without STBC, a system with STBC encoded over one symbol and a system with STBC encoded over two independent symbols. The analysis and simulations demonstrate that the second system has the best BER performance. Furthermore, it is also shown that the conversion of monocycles in UWB from the commonly used Gaussian pulses to the normalized modified Hermite polynomial based pulses (NMHP) can shorten the symbol period and hence increase the data rate and improve the system capacity.