Contents 1. INTRODUCTION
Space-time (ST) coding offers an attractive means of achieving high data rate wireless transmissions with diversity and coding gains [1], [2]. However, space-time codes are originally designed for flat-fading channels. In order to maintain decoding simplicity, most works on ST coding for frequency selective channels employ orthogonal frequency division multiplexing (OFDM) to convert a frequency-selective channel to a set of flat fading channels [3], [4]. Some ST-OFDM uses codes designed for flat channels but does not exploit the multipath diversity. Some combine space-time coding, space-frequency coding, and space-time-frequency coding across multiple antennas with OFDM technique to provide full diversities (both spatial and multipath diversities) over frequency-selective channels [5], [6], [7]. However, their computational complexity can be very high or the full diversity gain cannot be guaranteed, especially for systems with a large number of antennas. In practice, some existing redundancies, such as channel coding, can also be exploited in the space-time codes design, but they are ignored in the existing literature.
