Unitary space-time modulation for multiple-antenna communications in Rayleigh flat fading

Motivated by information-theoretic considerations, we propose a signaling s cheme, unitary space-time modulation, for multiple-antenna communication li nks. This modulation is ideally suited for Rayleigh fast-fading environment s, since it does not require the receiver to know or learn the propagation coefficients. Unitary space-time modulation uses constellations of T X M space-time signa ls {Phi(l), l = 1, ..., L}, where T represents the coherence interval durin g which the fading is approximately constant, and M < T is the number of tr ansmitter antennas. The columns of each Phi(l) are orthonormal. When the re ceiver does not know the propagation coefficients, which between pairs of t ransmitter and receiver antennas are modeled as statistically independent, this modulation performs very well either when the signal-to-noise ratio (S NR) is high or when T much greater than M. We design some multiple-antenna signal constellations and simulate their ef fectiveness as measured by bit-error probability with maximum-likelihood de coding. We demonstrate that two antennas have a 6-dB diversity gain over on e antenna at 15-dB SNR.