The space-time autocoding effect implies that arbitrarilyudreliable communication is possible within a singleudcoherence interval in Rayleigh flat fading as theudsymbol-duration of the coherence interval and theudnumber of transmit antennas grow simultaneously. Forudrelatively short (e.g., 16-symbol) coherence intervals, uda codebook of isotropically random unitary space-timeudsignals theoretically supports transmission ratesudthat are a significant fraction of autocapacity withudan extremely low probability of error. Howeveruda constellation of the required size (typically L = 280)udis impossible to generate and store, and due to lackudof structure there is little hope of finding a fastuddecoding scheme. We propose a random, but highly structured,udconstellation that is completely specified by log,udL independent isotropically distributed unitary matrices.udThe distinguishing property of this constructionudis that any two signals in the constellation areudpairwise statistically independent and isotropicallyuddistributed. Thus, the pairwise probability of error, udand hence the union bound on the block probabilityudof error, of the structured constellation is identicaludto that of a fully random constellation of independentudsignals.
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