Study On The Key Technology Of Space-Time Codes

In the system of the third generation mobile communication, the traditional receive diversity is difficult to come true, because of the request of mobile to be smaller size, lighter weight, cheaper price, easier carry and so on. So more and more people have focus on the transmit diversity instead of receive diversity. Space-time codes are new technology of transmit diversity. It uses multiple transmit antennas and multiple receive antennas to improve the capacity and performance of wireless communication system under the multi-path fading channel. Space-time codes can be divide into two mainly parts, one is space-time trellis code, the other is space-time block code. In this paper, we mainly compare the performance of the two space-time codes in many aspects, such as design criterion, transmission rate, diversity gain, code gain and arithmetic complexity etc. Because of the design of space-time block codes are based on the orthogonal theory, so it can also be called orthogonal space-time block codes. If the number of transmit antennas is more than two, the space-time block codes have to at a loss of code rate. This leads up to the deposit of the data at the transmit point. The code rate can be made higher by constructing quasi-orthogonal codes. In this paper, we propose an improved space-time block code based on quasi-orthogonal design, combining constellation rotation(CR) technique. Simulation results demonstrate that the new scheme can improve the performance, while the decoding complexity is the same as other quasi-orthogonal codes.