Improving the Link Availability of an Underwater Wireless Optical Communication System Using Chirped Pulse Compression Technique

Abstract

The effect of frequency chirping on the link availability of an underwater wireless optical communication (UWOC) system is studied theoretically using a simple and realistic model. It is observed, both theoretically and numerically, that a light pulse can be compressed in temporal axis when propagating in the water medium and can attain the minimum value at a prespecified location by appropriately choosing the initial pulse chirp parameter. The pulse compression takes place due to the interplay between the initial frequency chirp and the group velocity dispersion (GVD) effect. An increase in peak intensity, due to pulse compression, at the prespecified receiver location results in an improvement in the link availability compromised due to both attenuation and turbulence. The link availability is quantified by estimating the fading probability for various cases of initially chirped (+ve, 0, and -ve) Gaussian pulses under the influence of attenuation and turbulence and the results are compared for different scenarios. To have a complete channel description, the effect of particulate scattering on the GVD-induced pulse compression and hence on the fading probability is studied and quantified using the Monte Carlo numerical simulation technique. It is shown that, for the same system and channel parameters, the fading probability of a UWOC system is a few orders of magnitude lower (at a prespecified location) for the case with the negatively chirped pulse than for the cases when the initial pulse chirp is either zero or positive. In addition, the analytical expressions for estimating the focus distance and minimum pulse length, as functions of the channel properties, incident pulse length, and initial chirp parameters, are presented and discussed.