OPTIMAL SPATIAL MODULATION FOR RECIPROCAL CHANNELS.
MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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The purpose of this research is to find ways of improving optical communication through atmospheric turbulence by using spatial modulation. The performance of a class of adaptive spatially modulated communication systems, in which the antenna pattern at the transmitter is modified in accordance with the knowledge of the channel state obtained from a beacon signal transmitted from the receiving terminal to the transmitter, is examined. For time-invariant channels satisfying a certain reciprocity condition, there exists an adaptive system that achieves the maximum energy transfer possible from transmitter to receiver. This result is applied to the turbulent atmospheric channel by regarding the atmosphere as undergoing a succession of fixed states, and proving that instantaneously the atmosphere is reciprocal. The performance of adaptive spatially modulated systems for the turbulent channel is derived for both point-to-point and deep-space applications. In the deep-space case we find that the turbulence does not increase the average far-field beamwidth attainable with a given diameter aperture, but fluctuations about this average beamwidth do occur as the state of the atmosphere changes. The effects of noise and approximate transmitter implementations on the performance of the adaptive systems under discussion are considered. A hypothetical deep-space system is specified and its performance is evaluated. Author
- Non-Radio Communications