The Research On Multisymbol-Decodable Space-Time Code And Design Of Its Precoding Matrix In MIMO Systems

In recent years, Multiple-Input Multiple-Output(MIMO) technology becomes one of the hot spot of research on the field of wireless communication because of improving the efficiency of spectrum greatly. Space-time coding as an important technique in the MIMO system, causing widespread concern, it can provide both diversity gain and coding gain. In order to make its performance better, people have done a great deal of improvement. At the same time, the development of precoding technology in the MIMO system is also very rapid, this technology uses channel state information at the transmitter which can adaptive channel state without needing to change the code, so as to enhance the transmit diversity gain and reduce the bit error rate simultaneously, and then improve the quality of the received signal effectively.Based on the study on space-time code technology and precoding technology, the multisymbol-decodable space-time block code (CUW-g-SD) which we foucus on is improved and then combined with precoding technology to improve the BER(bit error rate) performance of MIMO systems. The specific research works are as follows:First of all, on the basis of reviewing relevant literature, this thesis investigates a CUW-g-SD which has high rate and full diversity in the MIMO system, discusses specific method of construction and structure of coding, then focuses on analyzing its performance, it has higher transmission rate than other general orthogonal space-time coding (OSTBC) and quasi-orthogonal space-time coding (QOSTBC), and can be applied to systems with any number of transmitting antennas, and has the characteristics of full diversity and lower decoding complexity due to employing group decoding at the receiver.Secondly, we deeply analyze QOSTBC which has full diversity based on the rotation of constellation, compare the performance of CUW-g-SD and quasi-orthogonal space-time coding. On this basis, according to the fact that diversity of obtaining the optimal rotation angle of constellation, we apply the optimal rotation angle of QOSTBC which comes from the theoretical derivation of the CUW-g-SD so as to increase diversity gain and coding gain, and then improve its BER performance.Finally, we study the design of optimal linear precoding matrix based on orthogonal space-time block coding, expound the process of design for precoding matrix. Since non-orthogonality of CUW-g-SD, we apply the objective function which is relaxed properly during designing to the CUW-g-SD, the result obtains the linear precoding matrix based on multisymbol-decodable space-time block coding. Simulation results show that the BER of CUW-g-SD which combined with precoding techniques is decreased.