A step by step educational guide to designing and testing an underwater acoustic modem

Abstract

We examine the design and systematic implementation of a receiver system for underwater acoustic communication. The system includes, but is not limited to, passband filter, down converter, matched filter, and detection logic. Our final implementation target is a frame-based system to minimize memory use and system latency. The matched filter uses the overlap-save method in frequency domain to reduce computational cost. Initially, the system is designed and tested for performance using the MATLAB platform in a non-real time vector-based implementation. The code is then restructured to a MATLAB frame-based model. The code contains several functions; each function performs a specific task and maintains its own histories as needed. Once the performance of the frame-based model is measured to be identical to the vector-based model, we systematically move each function to C + +. Each C + + function is individually substituted into the frame-based model using MEX files and verified for performance. Once all C + + functions are verified for performance, the entire C + + implementation is uploaded to the Popoto Modem™ real-time hardware and performs real-time transmission and reception in both air and underwater environments, with known and tested performance characteristics. [Work supported in part by NSF, Grant IIP-1500123, the INTERN program.]