Bandlimited Intensity Modulation

TL;DR

This paper introduces a bandwidth-efficient signaling method for IM/DD channels that transmits without intersymbol interference at the same bandwidth as coherent channels, optimizing power and bandwidth trade-offs.

Contribution

It proposes a novel transmission technique combining Nyquist pulses with bias and higher-order modulation to achieve bandwidth efficiency comparable to coherent channels.

Findings

Achieves transmission without intersymbol interference at the same bandwidth as coherent channels.

Explores power-bandwidth trade-offs for different pulse shapes.

Demonstrates improved power efficiency with specific pulse choices.

Abstract

In this paper, the design and analysis of a new bandwidth-efficient signaling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is presented. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise (AWGN). Due to the nonnegativity constraint, standard methods for coherent bandlimited channels cannot be applied here. Previously established techniques for the IM/DD channel require bandwidth twice the required bandwidth over the conventional coherent channel. We propose a method to transmit without intersymbol interference in a bandwidth no larger than the bit rate. This is done by combining Nyquist or root-Nyquist pulses with a constant bias and using higher-order modulation formats. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. Depending on the bandwidth required, the most power-efficient transmission is obtained by the parametric linear pulse, the so-called "better than Nyquist" pulse, or the root-raised cosine pulse.