Demodulation of Underwater OFDM Transmissions by Time Reversal and Basis Pursuit Methods

Konferenz: European Wireless 2011 - Sustainable Wireless Technologies
27.04.2011 - 29.04.2011 in Vienna, Austria

Tagungsband: European Wireless 2011

Seiten: 9Sprache: EnglischTyp: PDF

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Gomes, João (Institute for Systems and Robotics, Instituto Superior Técnico, 1049-001 Lisboa, Portugal)
Berger, Christian R. (Dept. of Electr. & Comp. Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA)
Silva, António (SiPLAB, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal)

In this paper we discuss a channel shortening approach based on passive time reversal (PTR) for underwater acoustic communication using OFDM. PTR exploits the physics of acoustic propagation to mitigate intersymbol interference in a simple and robust way, reducing the need for long OFDM symbols and prefixes. We adopt recent basis pursuit methods for identification of sparse responses from PTR channel probes. This effectively discards unstable or insignificant estimated channel coefficients, improving the performance relative to PTR with directly observed channel responses. We present results for data collected during the CALCOM’10 sea trial with 4.5 kHz bandwidth, 4.1-6.4 kbit/s raw data rates (2-3.2 kbit/s before convolutional coding), and 3 km communication range. Channel responses are sparse, with delay spreads of 20-30 ms that PTR reduces to 5-10 ms. Subsequent OFDM demodulation attains good results in much of the signal bandwidth, although some seemingly source-related issues remain that lead to overall higher error rates than using plain OFDM with multichannel combining.