Lee E Freitag

US Patent:

7859944, Dec 28, 2010

Filed:

Jun 18, 2008

Appl. No.:

12/141527

Inventors:

Shengli Zhou - Mansfield CT, US
Baosheng Li - Willington CT, US
Peter Willett - Coventry CT, US
Milica Stojanovic - Boston MA, US
Lee Freitag - Falmouth MA, US

Assignee:

Massachusetts Institute of Technology - Cambridge MA
University of Connecticut - Farmington CT
Woods Hole Oceanographic Institution - Woods Hole MA

International Classification:

H04B 11/00

US Classification:

367134

Abstract:

Advantageous OFDM-based underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. In general, OFDM transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among OFDM subcarriers. The disclosed apparatus, systems, and methods use a two-step approach to mitigate frequency-dependent Doppler drifts for zero-padded OFDM transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling to convert a “wideband” problem into a “narrowband” problem; and (2) high-resolution uniform compensation on the residual Doppler. The disclosed apparatus, systems and methods are based on block-by-block processing and do not rely on channel dependence across OFDM blocks. Thus, the disclosed apparatus, systems and methods are advantageously applicable for fast-varying UWA channels.

US Patent:

7953326, May 31, 2011

Filed:

Feb 6, 2006

Appl. No.:

11/348726

Inventors:

Norman E. Farr - Woods Hole MA, US
Lee Freitag - Falmouth MA, US
James Preisig - Falmouth MA, US
Dana R. Yoerger - North Falmouth MA, US
Sheri N. White - East Falmouth MA, US
Alan D. Chave - Falmouth MA, US

Assignee:

Woods Hole Oceanographic Institution - Woods Hole MA

International Classification:

H04B 13/02
H04B 10/00

US Classification:

398104, 398118, 398128, 398130

Abstract:

The systems and methods of the invention provide for improved underwater communication systems. In particular, the systems and methods of the invention provide for improved underwater optical modems including optical transmitters and optical receivers that allow omni-directional transmission and reception of optical signals underwater and having a range of about 100 m and allowing data rates greater than 1 Mbit/s. The systems and methods of the invention also provide for underwater communication networks having a plurality of optical modems communicating with each other.

US Patent:

20110229141, Sep 22, 2011

Filed:

May 27, 2011

Appl. No.:

13/117867

Inventors:

Alan D. Chave - Falmouth MA, US
Norman E. Farr - Woods Hole MA, US
Lee Freitag - Falmouth MA, US
James Preisig - Falmouth MA, US
Dana R. Yoerger - North Falmouth MA, US
Sheri N. White - East Flamouth MA, US

Assignee:

WOODS HOLE OCEANOGRAPHIC - Woods Hole MA

International Classification:

H04B 13/02
B23P 11/00

US Classification:

398104, 29428

Abstract:

The systems and methods of the invention provide for improved underwater communication systems. In particular, the systems and methods of the invention provide for improved underwater optical modems including optical transmitters and optical receivers that allow omni-directional transmission and reception of optical signals underwater and having a range of about 100 m and allowing data rates greater than 1 Mbit/s. The systems and methods of the invention also provide for underwater communication networks having a plurality of optical modems communicating with each other.

US Patent:

20120170935, Jul 5, 2012

Filed:

Jan 5, 2012

Appl. No.:

13/344430

Inventors:

Casey Machado - Woods Hole MA, US
Lee Freitag - Falmouth MA, US
Andy Bowen - Woods Hole MA, US
Norman E. Farr - Woods Hole MA, US

Assignee:

WOODS HOLE OCEANOGRAPHIC INSTITUTION - Woods Hole MA

International Classification:

H04J 14/00

US Classification:

398 58

Abstract:

The systems and methods described herein provide a reconfigurable, long-range, optical modem-based underwater communication network. In particular, the network provides a low power, low cost, and easy to deploy underwater optical communication system capable of being operated at long distances. Optical modem-based communication offer high data rate, omni-directional spatial communication in the visual spectrum. The omni-directional aspect of communication is advantageous because precise alignment of communication units may not be required. The optical modems may be deployed via unmanned underwater vehicles (UUVs) and physically connected by tethers.

US Patent:

55597572, Sep 24, 1996

Filed:

Feb 9, 1994

Appl. No.:

8/195965

Inventors:

Josko A. Catipovic - Woods Hole MA
Lee E. Freitag - Woods Hole MA

International Classification:

H04B 1100

US Classification:

367134

Abstract:

An underwater acoustic telemetry system uses spatially distributed receivers with aperture sizes from 0. 35 to 20 m. Output from each receiver is assigned a quality measure based on the estimated error rate, and the data, weighted by the quality measure, is combined and decoded. The quality measure is derived from a Viterbi error-correction decoder operating on each receiver. The quality estimator exploits the signal and noise differential travel times to individual sensors. The spatial coherence structure of the shallow-water acoustic channel shows relatively low signal coherence at separations as short as 0. 35 m. Increasing receiver spacing beyond 5 m offers additional benefits in the presence of impulsive noise and larger scale inhomogeneities in the acoustic field. Diversity combining, even with only two receivers, can lower uncoded error rates by up to several orders of magnitude while providing immunity to transducer jamming or failure.

US Patent:

20150372769, Dec 24, 2015

Filed:

May 12, 2015

Appl. No.:

14/710456

Inventors:

- Woods Hole MA, US
Lee Freitag - Falmouth MA, US
James Preisig - Falmouth MA, US
Dana Yoerger - North Falmouth MA, US
Sheri N. White - East Falmouth MA, US
Alan D. Chave - Falmouth MA, US

International Classification:

H04B 10/80
H04B 13/02

Abstract:

An underwater system including at least one input device that is in sensory communication with water and generates input signals. The system further includes at least one optical transmitter and at least one optical receiver that allow omni-directional transmission and reception through water of optical signals representing the input signals, and allow data rates greater than 1 Mbps.