Study Of Quasi-Orthogonal Space-Time Block Code Technology

With the development of mobile communications services, frequency resources are becoming more and more scarce. To improve new technologies of wireless communications mainly focus on how to efficiently make use of the limited communication resources. Space-Time Coding (STC), which is a new coding/signal processing technique that combines channel coding with antenna diversity techniques, greatly increases data rate and the capacity of wireless communication system with no need of additional bandwidth and transmitting power, accordingly provides far more higher frequency band utilization than traditional single antenna system.Space-Time Codes mainly include two parts, Space-Time Trellis Code and Space-time Block Code. In this paper, we compare the performances of the two Space-Time Codes in many aspects, such as design criterion, coding and decoding methods. The coding rate is less than one for Orthogonal Space-Time Block Code with two or more transmit antennas, it can't ensure the data transmission with full rate. In this paper, attention is paid to Quasi-Orthogonal Space-Time Block Codes. From which we propose an improved Quasi-Orthogonal Space-Time Block Code which the number of transmission antennas is two to some power. Simulation results demonstrate that the new method doesn't increase the decoding complexity, therefore, it allows a wide latitude of generality.The complexity of quasi-orthogonal codes is an important cause of limiting its application to industry. Based on the thorough research on Sphere Decoding (SD) algorithm, a new improved method is introduced which combines Quasi-Orthogonal Space-Time Block Code with Sphere Decoding algorithm, which narrows detection range, increases respond speed and reduces the complexity to decode for systems with four or more transmit antennas, compared with the conventional SD algorithm.