الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
A space-time code (STC) is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may survive the physical path between transmission and reception in a good enough state to allow reliable decoding.
Alamouti discovered a remarkable space time block code STBC scheme for two transmit antennas. This scheme supports linear decoding complexity for maximum-likelihood (ML) decoding. Despite the lower coding gain, Alamouti’s scheme is very appealing in terms of implementation simplicity. Hence it motivates a search for similar schemes for more than two transmit antennas, to achieve diversity level higher than two. As a result, Orthogonal Space-Time Block Code (OSTBC) was introduced by Tarokh. OSTBC is a generalization of the Alamouti’s scheme to an arbitrary number of transmit antennas. It retains the property of having linear maximum-likelihood decoding with full transmit diversity. Although OSTBC can provide full diversity at low computational cost, rate one OSTBC with complex constellation is not possible for more than two transmit antennas. Various non-orthogonal STBC designs have been proposed. An interesting one among them is the Quasi-Orthogonal STBC (QO-STBC), which is designed to achieve a higher code rate than OSTBC by partially instead of fully, as in the case of other non-orthogonal STBCs relaxing the orthogonality of an OSTBC.
The structure and characteristics of some new type of a Quasi-orthogonal space time block codes (QOSTBC) in frequency-flat quasi-static Rayleigh fading channels were discussed, The error performance for these codes for four transmitted antennas over uncorrelated and spatially correlated MIMO channels is also investigated.• Their BER performance is nearly same as that of existing QOSTBCs for four transmit antennas in spatially uncorrelated channel However, in spatially correlated channels one can observe a substantial performance difference due to different values of the self-interference parameter terms.
Decision metric equations for ML decoding of proposed codes are also provided. These proposed codes will enrich the family of QOSTBCs for four transmit antennas A low-complexity linear decoder for QO-STBCs is proposed, where the interference term will be eliminated from the detection matrix, resulting in performance improvement and simple linear decoding by using a rotation matrix which is a matrix transformation that can eliminate any elements of a given matrix.
Numerical results have shown that the proposed decoder can provide a substantially improved trade off between the complexity and performance in comparison to current known decoding schemes.
Also another detection technique was discussed which is a simplified Zero Forcing (ZF) decoder without the use of matrix inversion which reduces its implementation complexity.