The availability of multiple transmit antennas allows for two dimensional channel codes that exploit the spatial transmit diversity. These codes were referred to as space-time codes by Tarokh et al. (see IEEE Trans. Inform. Theory, vol.44, no.2, p.744-65, March 1998). Thus far the main thrust has been to construct space-time codes that achieve maximum spatial diversity in quasi-static fading channels. In this paper, we extend the theory developed by Hammons et al. (see IEEE Trans. Inform. Theory, vol.46, no.2, p.524-42, March 2000) to block fading channels. We present base-band design criteria for space-time codes in block fading channels that encompass as special cases the quasi-static and fast fading design rules. Following the approach of Hammons et al., the diversity advantage base-band criterion is then translated into binary rank criteria for PSK modulated codes. Based on these criteria, we construct space-time codes that strive to optimally exploit the spatial and temporal diversity available in block fading channels. We also introduce the notion of universal space-time codes as a generalisation of the smart-greedy design approach proposed by Tarokh et.al.
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