optical channel with a per-antenna peak-power constraint and a sum

(over all antennas) average-power constraint is studied. The

asymptotic low-signal-to-noise-ratio (low-SNR) capacity is

determined exactly and close upper and lower bounds are presented

in the low- and moderate-SNR regimes. The asymptotic low-SNR

limit is achieved by having each transmit antenna signal either

with zero or with the maximally allowed peak power, and the latter

only if all stronger antennas also send at maximum peak power. In

particular, for almost all channel gains, the input to achieve the

asymptotic low-SNR capacity is such that its projection on the

channel-gain vector has only two or three positive probability

point masses, one of them being at zero. The lower bounds at

finite SNR are numerical and are obtained using input

distributions whose projection on the channel-gain vector has

either two, three, or four positive probability masses. Finally,

the paper presents two analytic upper bounds on the capacity of

the MISO channel: the first one closely follows the proposed

numerical lower bounds in the low-SNR regime, and the second one

can improve on previous bounds in the moderate-SNR regime.

-||- _|_ _|_ / __|__ Stefan M. Moser

[-] --__|__ /__\ /__ Senior Scientist, ETH Zurich, Switzerland

_|_ -- --|- _ / / Adjunct Professor, National Yang Ming Chiao Tung University, Taiwan

/ \ [] \| |_| / \/ Web: https://moser-isi.ethz.ch/

Last modified: Tue Feb 4 13:50:42 CET 2020