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Abstract: In this paper, the required amount of feedback overhead for multiple-inputmultiple-output MIMO beamforming over time-varying channels is presented interms of the entropy of the feedback messages. In the case that each transmitantenna has its own power amplifier which has individual power limit, it hasbeen known that only phase steering information is necessary to form theoptimal transmit beamforming vector. Since temporal correlation exists forwireless fading channels, one can utilize the previous reported feedbackmessages as prior information to efficiently encode the current feedbackmessage. Thus, phase tracking information, difference between two phasesteering information in adjacent feedback slots, is sufficient as a feedbackmessage. We show that while the entropy of the phase steering information is aconstant, the entropy of the phase tracking information is a function of thetemporal correlation parameter. For the phase tracking information, upperboundson the entropy are presented in the Gaussian entropy and the von-Mises entropyby using the theory on the maximum entropy distributions. Derived results canquantify the amount of reduction in feedback overhead of the phase trackinginformation over the phase steering information. For application perspective,the signal-to-noise ratio SNR gain of phase tracking beamforming over phasesteering beamforming is evaluated by using Monte-Carlo simulation. Also we showthat the derived entropies can determine the appropriate duration of thefeedback reports with respect to the degree of the channel variation rates.



Autor: Jaewon Kim, Jonghyun Park

Fuente: https://arxiv.org/



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