Dr. Ali Bassam

In underwater communication systems, the underwater acoustic (UWA) channel is among the most challenging and complex to work with. The UWA channel is both an overspread and doubly spread one so it exhibits severe dispersion in both time and frequency. This has ramifications on communications between mobile underwater nodes.

To recover signals transmitted through UWA channels, Doppler compensation and channel equalization are key elements in the receiver. The Doppler effect underwater is significant compared to channels in other environments like above‐water radio. Radio motions are extremely small compared to the speed of light. By comparison, the time‐variations in the water column due to waves, density differences, mixing, etc. are large relative to the nominal speed of sound.

Doppler effects are further exacerbated when transmitters and receivers are in relative motion as on mobile platforms like underway autonomous underwater vehicles (AUV). Consequently, the propagating signal is significantly affected by the underway motion, and if left untreated, could be unrecoverable.

This presentation will provide: (i) a brief background on UWA channels; (ii) how the Doppler effect makes their treatment unique and the receiver designs that mitigate Doppler effects with emphasis on compensation, and (iii) their applicability to strongly time‐varying channels like those with AUVs. Finally, the presentation will conclude with remarks on current developments in the lab and future directions.

Biography:

Dr. Ali Bassam is a Post‐Doctoral Fellow with the Intelligent Systems Laboratory at Dalhousie University. His research interests are in the areas of underwater acoustic communications, signal processing, digital communications and estimation theory. He received his BEng in Electrical and Computer Engineering from Dalhousie University. His Ph.D. thesis at Dalhousie University was on a novel receiver that efficiently and accurately performs Doppler estimation, tracking and compensation in underwater acoustic applications. His post‐doctoral work involves designing algorithms for underwater modems, with focus on adaptive channel estimation and Doppler analysis. Throughout his career, he has worked with industrial partners and sponsors like Thales R&T and Ultra Electronics Maritime Systems Inc. Dr. Bassam is also a part‐time instructor at the Atlantic Naval Fleet School.