Wireless Communication Systems Hollow Time / Frequency Code Technology Research

Space-time block coding (STBC) can fully exploit the spatial diversity gain provided by multiple-input multiple-output (MIMO) systems and significantly enhance the reliability of information transmission. The well-structured encoding and low-complexity decoding are its main advantages. Therefore, STBC has attracted extreme attention from both academic and industry field in the past decade. It will potentially become one of the key technologies of the future wireless communications.This thesis focuses on the design of STBC in the narrowband systems and the encoding and decoding technologies of space-time/-frequency coding in the broadband systems. Our topics mainly cover the following aspects:1. To improve the transmission rate of orthogonal STBC in MIMO systems, quasi-orthogonal and semi-orthogonal STBCs are detailedly investigated. To resolve the problem that STBC can't exploit time diversity, a time-separated STBC is proposed to exploit time diversity in time-variant wireless channels. Its separated time interval is greater than channel coherence time. Furthermore, a rotation matrix is devised to fully exploit time diversity. However, the separation property of this code destroys its orthogonality and its decoding complexity is significantly increased. Thus, sphere decoding is adopted to reduce the decoding complexity. Simulation shows:the performances of time-separated STBC and time-continuous STBC are almost equivalent in uncorrelated MIMO channels; when the spatial correlation coefficient is larger than 0.4,the performance of time-separated STBC will exceed that of the time-continuous STBC.2. In the broadband systems, combining the orthogonal STBC and orthogonal frequency division multiplexing (OFDM) technology can form two codes:space-time coded OFDM (ST-OFDM) and space-frequency coded OFDM (SF-OFDM), which can achieve a better performance has been always a controversial topic. In this paper, by changing normalized Doppler spread (NDS) and normalized coherence bandwidth (NCBW). they are compared thoroughly and deeply. Simulation shows:ST-OFDM is more sensitive to NDS.as NDS is larger than 0.05. the performance of ST-OFDM will be inferior than that of SF-OFDM; SF-OFDM is more sensitive to NCBW, when NCBW is bigger than 51 and NDS is bigger than 0.001. the performance of SF-OFDM will be better than that of ST-OFDM.