On Space-Time-Frequency Codes For Broadband Wireless Communication Systems

The MIMO (Multiple-Input Multiple-Output) system can equivalent the fading coefficients between transmit-receive antenna pairs to several parallel independent sub-channels, which can be utilized to transmit data as well as to increase spectral utilization ratio. Space-time code designed for multiple antennas systems is an effective way to approach the MIMO channel capacity. Especially, the performance of coding system can be further improved by using space-time-frequency codes through utilizing the frequency diversity from the multi-path fading channels. Having been widely applied due to the feature of effectively overcoming the multi-path frequency selective fading, the OFDM (Orthogonal Frequency Division Multiplexing) technique was integrated with the space-time- frequency code to form a MIMO-OFDM system, which has been one of the most important researches due to its high capacity and high stability under the limited power and bandwidth.In this thesis, the space-time-frequency code and serially concatenated convolutional orthogonal space-time-frequency code are studied. The organization of this thesis is as follows. First, the background and current studies of the techniques of MIMO and OFDM and space-time codes are summarized. Secondly, the model of MIMO channel are constructed, and the capacity of different channels are calculated. Based on the results of comparing the performances of coded system between space-time coded OFDM system and space-frequency coded OFDM system, the performance of space-time-frequency code is analyzed and the design criterions for space-time-frequency are presented, then the coding and decoding algorithms of space-time-frequency block code and space-time-frequency trellis code are given in detail. Finally, an OSTFC(orthogonal space-time-frequency code) which can achieve the maximum diversity gain over frequency selective fading channel is proposed. Using the OSTFC as the inner code, a SCC-OSTFC (Serially Concatenated Convolutional Orthogonal Space-Time-Frequency Code) scheme is designed for MIMO-OFDM system over the frequency-selective fading channels. It is also shown that the SCC-OSTFC scheme can achieve the maximum diversity gain as well as the coding gain while affording low complexity. The significant performance improvement of the design is confirmed by corroborating.