Space-frequency-time coded OFDM for broadband wireless communications

In this paper, we propose and analyze an efficient space-frequency-time coded OFDM technique for high-speed transmission over wireless links. Joint use of space-time trellis coding and space-time block coding is considered. It is shown that the maximum achievable diversity order increases linearly not only with the number of transmit and receive antennas but also with the number of multiple paths provided that a proper joint coding scheme is employed. Because of the orthogonality of space-time block codes, space-time trellis codes with low trellis complexity can be used to efficiently achieve the full diversity provided by the fading channel. This is in contrast to traditional space-frequency coded OFDM systems, where we need to design space-time trellis codes with very high trellis complexity to exploit the maximum achievable diversity of the fading channel. Numerical results are provided to demonstrate the significant performance improvement achieved by the proposed space-frequency-time coded OFDM technique