What is Underwater Acoustics
Underwater Acoustics encompasses all communications performed in an underwater environment using acoustic pressure waves as information carrying signals. Acoustics are well suited to the underwater environment because they do not suffer from the high attenuation experienced by radio waves in a conducting medium, enabling the possibility of long-range communications. However, the field is not without its own set of unique challenges. The low frequencies required for long-range communications, the long propagation times associated with transmission of acoustic waves, motion of the transceivers, and the numerous reflections and scattering caused by the surface and seabed make high data rate communications difficult in this environment.
Why are we Interested
Underwater Acoustics have a number of interesting applications and present a number of complex challenges, which are not faced in the traditional radio environment. Overcoming these challenges is of great interest to the team at UMDCC and our industrial partners. Significant work has been done in this area but there remains a large gap between what is currently available and what is possible; our goal is to close that gap.
How are we Contributing
By starting at the fundamentals we are developing a statistical model, which encompasses all the channel impairments. With this model we will be able to develop an intelligent modem capable of adapting to the ever-changing conditions encountered in the underwater environment. To accomplish this the team is focusing primarily on the development and testing of OFDM signaling methodologies for underwater communications and advanced estimation techniques capable of tracking the constantly changing underwater environment.
- Christian Schlegel, Amir Vaezi, Dmitry Truhachev, and Murwan Bashir, "Iterative Frequency-Domain Receiver Processing in Doubly-Selective Underwater Acoustic Channels," poster, National Science Foundation Workshop on Underwater Acoustics in Washington, D.C., March 2018.
- Murwan Bashir, Dmitry Truhachev, and Christian Schlegel, "Kalman Forward-Backward Channel Tracking and Combining for OFDM in Underwater Acoustic Channels," IEEE Oceans Conference, 2018. This paper applies a bi-directional time-domain Kalman filter to estimating the doubly-spread acoustic channel and presents results based on measurement-based channel modeling for shallow water channel.
- Navid Eskandri, Murwan Bashir, Dmitry Truhachev, Christian Schlegel, and Jean-Francois Bousquet, "Improving the Quality of Underwater Acoustic Channel via Beamforming, " IEEE Oceans Conference, 2018. This paper quantifies how we can condition a channel through beam-forming to reduce its temporal frequencies and make them easier to track.
- Christian Schlegel and Marat Burnashev, "The Interplay Between Error Control Coding and Iterative Signal Cancelation," IEEE Transactions on Signal Processing, Vol. 65, Lo. 11, June 1, 2017. This paper discusses the type of codes that are most effective in cancelation systems, to wit: either low-rate repetition code or high-rate low-density parity-check (LDPC) codes.
- Christian Schlegel, Dmitry Truhachev, and Lukas Krzymien, "A Two-Stage Capacity-Achieving Demodulation/Decoding Method for Random Matrix Channels," IEEE Transactions on Information Theory, Vol. 55, No. 1, January 2009. This paper describes how adaptive modulation is achieved by generalized modulation superposing independent data streams combined with iterative demodulation.
- Christian Schlegel, Marat Burnashev, and Dmitry Tuhachev, "Generalized Superposition Modulation and Iterative Demodulation: A Capacity Investigation," Journal of Electrical and Computer Engineering Volume 2010, August 2010. The paper introduces the concerpt of generalized modulation via superposition of data streams without the requirement of orthogonality between them.