Study On The Differential Space-Time Coded Diversity System

Among the effective methods to mitigate the fading in wireless communications is transmit diversity, which can utilize the space diversity of transmit antennae to generate the receive diversity and improve the performance of the forward link. Space time coding was proposed by combining transmit diversity and coding technology to improve the system performance, such as error bit rate, data rate, and system capacity. In particular, Space-time block coding (STBC) schemes, proposed originally by Alamouti were adopted by the 3G standardization committees as one key technique in 3G wireless systems.According to the channel state information (CSI), transmit diversity was classified into coherent transmit diversity and non-coherent transmit diversity. Coherent transmit diversity usually depends on the accurate CSI, which is difficult to acquire as the channel varies relatively fast. So the non-coherent transmit diversity becomes more interesting. Among the non-coherent transmit diversity technologies, differential transmit diversity is a remarkable technique.In this thesis we consider the combining diversity of the differential transmit diversity and receive diversity. The potential of space diversity was discussed and the error performance of combining diversity system was investigated. The main results are as follows. (1) A generalized detection algorithm was proposed for all the 3 combining methods. (2) According to the simulations and the analysis, the error performance of the easiest equal gain combing (EGC) was found to be as good as maximal ratio combining (MRC) and better than selective combining. (3) The effect of fading parameter, correlation coefficient and carrier frequency offset on the system performance was also investigated. Some available regions of parameters were acquired according to the error threshold.To extend the investigation of the performance of combining diversity system to Nakagami fading channels, we summarized the Nakagami channel simulation theory, Nakagami fading parameter estimation theory and the Nakagami channel simulation algorithm. On this condition, we proposed 3 indicators to evaluate the validity of the Nakagami simulation channel. They are fading parameter consistency, probability density function consistency and covariance matrix consistency.