Optimizing Constellations for Single-Subcarrier Intensity-Modulated Optical Systems
Journal article, 2012

We optimize modulation formats for the additive white Gaussian noise channel with nonnegative input, also known as the intensity-modulated direct-detection channel, with and without confining them to a lattice structure. Our optimization criteria are the average electrical, average optical, and peak power. The nonnegative constraint on the input to the channel is translated into a conical constraint in signal space, and modulation formats are designed by sphere packing inside this cone. Some dense packings are found, which yield more power-efficient modulation formats than previously known. For example, at a spectral efficiency of 1.5 bit/s/Hz, the modulation format optimized for average electrical power has a 2.55 dB average electrical power gain over the best known format to achieve a symbol error rate of 10-6 . The corresponding gains for formats optimized for average and peak optical power are 1.35 and 1.72 dB, respectively. Using modulation formats optimized for peak power in average-power limited systems results in a smaller power penalty than when using formats optimized for average power in peak-power limited systems. We also evaluate the modulation formats in terms of their mutual information to predict their performance in the presence of capacity-achieving error-correcting codes, and finally show numerically and analytically that the optimal modulation formats for reliable transmission in the wideband regime have only one nonzero point.

fiber-optical communications

noncoherent communications

free-space optical communications

mutual information

Direct detection

infrared communications

sphere packing

lattice codes

intensity modulation

Author

Johnny Karout

Chalmers, Signals and Systems, Communication and Antenna Systems, Communication Systems

Erik Agrell

Chalmers, Signals and Systems, Communication and Antenna Systems, Communication Systems

Krzysztof Szczerba

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Magnus Karlsson

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

IEEE Transactions on Information Theory

0018-9448 (ISSN)

Vol. 58 7 4645-4659

Areas of Advance

Information and Communication Technology

Subject Categories

Electrical Engineering, Electronic Engineering, Information Engineering

DOI

10.1109/TIT.2012.2193374

More information

Latest update

3/29/2018