In frequency-selective media, orthogonal space-time block codes (or alternatively their space-frequency counterparts) fail to achieve the maximum possible space-frequency diversity. This paper first proposes block-orthogonal multisensor codes (i.e., either space-time or space-frequency codes) for frequency-selective channels by considering data blocks rather than symbols as transmission units. These codes can be derived from their narrowband versions, namely the orthogonal space-time block codes proposed by Alamouti, Tarokh et al, and Ganesan and Stoica, and maximally exploit the available space-frequency diversity. For 3- and 4-transmit sensor configurations, the block orthogonal codes derived from the recently proposed rate-(3/4) symbol orthogonal codes have structures that are especially convenient for channel response estimation.
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