Let an M-transmitter-antenna, N-receiver-antenna Rayleigh flat fading channel be characterized by an M x N matrix of independent propagation coefficients, distributed as zero-mean, unit-variance complex Gaussian random variables. This propagation matrix is unknown to the transmitter, it remains constant during a T-symbol coherence interval, and there is a fixed total transmit power. Let the coherence interval and number of transmitter antennas be related as T=b*M for some constant b. A T x M matrix-valued signal, associated with R * T bits of information for some rate R is transmitted during the T-symbol coherence interval. Then there is a positive space-time autocapacity C_a such that for all R < C_a, the block probability of error goes to zero as the pair (T,M) go to infinity such that T/M = b. The autocoding effect occurs whether or not the propagation matrix is known to the receiver, and C_a = N*log(1+SNR) in either case, independently of b, where SNR is the expected signal-to-noise ratio at each receiver antenna. Lower bounds on the cutoff rate derived from random Unitary Space-Time signals suggest that the autocoding effect manifests itself for relatively small values of T and M. For example, within a single coherence interval of duration T=16, for M=7 transmitter antennas and N=4 receiver antennas, and an 18 dB expected SNR, a total of 80 bits (corresponding to rate R=5) can theoretically be transmitted with a block probability of error less than 10^{-9}, all without any training or knowledge of the propagation matrix.

Status: Bell Labs Technical Memorandum, 1999. Submitted to IEEE Transactions on Information Theory.

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