On Limits of Wireless Communications in a Fading Environment when UsingMultiple Antennas
Wireless Personal Communications: An International Journal
IEEE Transactions on Information Theory
Space-time block codes from orthogonal designs
IEEE Transactions on Information Theory
A simple transmit diversity technique for wireless communications
IEEE Journal on Selected Areas in Communications
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Many theories of exploiting spatial diversity in wireless communications and more recently space-time coding are results of understanding the spatial channel models for antenna array communication systems. For example, the models for rich scattering environments assume the channel coefficients to be almost independent when the spacing between the antennas is sufficient. This could limit the possibility of extracting direction of the signal propagation with respect to antenna locations (G. Xu et al., IEEE Transactions on Signal Processing, Vol. 42, No. 2, pp. 349–355, 1994). On the other hand, when the scattering is limited to few dominant reflectors, the directions of the signals traveling through the environment can prevail in the channel coefficients. Extracting the propagation direction (beam direction) information from the channel coefficients has been investigated extensively in array signal processing literature. These investigations have led to many algorithms of direction of arrival (DOA) estimation and beamforming. Here, we propose a transmit diversity technique that exploits beam directions in environments with few beam directions. While we present this technique for two-beam Rayleigh fading channels (J.E. Mazo, IEEE Transaction on Communication, Vol. 39, No. 7, pp. 1027–1030, 1991), it can be easily extended to multibeam general fading channels. The proposed method does not require feedback from the receiver.