133 research outputs found
WHOI acoustic telemetry project interim report 12/1/88 - 6/1/89
This interim report covers the progress of the acoustic telemetry project
during the period 12/1/88 to 5/15/89. In general, the work followed the
format specified in WHOI proposal No. 5674.1. The major exception was
the deletion of the transmitter array development task and a corresponding
funding decrease from 170,000. In addition, the period for the
funding was extended to June 30, partly due to a two month delay in project
startup.
The telemetry project was centered around the construction, programming
and testing of a digital receiver prototype capable of supporting future
signal processing algorithms in real-time over ocean acoustic channels. The
baseline receiver consists of a two-channel analog quadrature demodulator,
and interface to a multiprocessor receiver for digital signal processing.
The software developed includes routines for command and control of the
analog demodulator, data handling and formatting, and minimal software
to digitally implement an incoherent MFSK demodulator, synchronizer and
data decoder. Data storage and display programs were also completed to
facilitate the performance analysis of the unit during testing.
The system was tested in Woods Hole harbor at data rates up to 4800
bits/sec. The acoustic channel was time-dispersive Rayleigh fading, and
performance close to theoretical expectations was achieved. We are confident
that the system error behavior is arising from channel-caused effects and
known deficiencies in system performance, such as excessive synchronizer
steady-state jitter.Funding was provided by the Office of Naval Research
under contract Number N00014-86-K-0751, and
by the Charles Stark Draper Laboratory Inc
Leveraging Spatial Diversity to Mitigate Partial Band Interference in Undersea Networks through Waveform Reconstruction
Many acoustic channels suffer from interference which is neither narrowband nor impulsive. This relatively long duration partial band interference can be particularly detrimental to system performance. We survey recent work in interference mitigation as background motivation to develop a spatial diversity receiver for use in underwater networks. The network consists of multiple distributed cabled hydrophones that receive data transmitted over a time-varying multipath channel in the presence of partial band interference produced by interfering active sonar signals as well as marine mammal vocalizations. In operational networks, many “dropped” messages are lost due to partial band interference which corrupts different portions of the received signal depending on the relative position of the interferers, information source and receivers due to the slow speed of propagation. Our algorithm has been tested on simulated data and is shown to work on an example from a recent undersea experiment
Report on the Acoustic Network Arctic Deployment, March 1994
This report describes the March 1994 Arctic deployment undertaken by the Acoustic Telemetry Group of WHOI. The
deployment was a part of the 1994 Sea Ice Mechanics Initiative (SIMI) project and was based at the west SIMI camp,
approximately 150 nautical miles north-east of Prudhoe Bay, Alaska. The goal of the deployment was to install a network of
six high-performance acoustic modems, developed at WHOI, and to obtain a data set demonstrating the communications
and acoustic monitoring capabilties of the network.
The six modems in the network were deployed over an area of 22 square km and communicated via radio Ethernet with a
computer at the SIMI camp. Each model had a global positioning system, an acoustic source and an 8 element receiving
array. The network was operated in a round-robin broadcast mode (i.e., each modem in turn transmitted a packet of data
while the others received). The transmissions were 5000 bits-per-second QPSK with a 15kHz carrier. An extensive data set
including raw acoustic data source localization information, and modem position was collected during the deployment.
An additional function of the acoustic network was to communicate with, and track, the Odyssey, an autonomous
underwater vehicle operated by the MIT group at the SIMI camp. To this end, the Odyssey was equipped with a Datasonics
modem configured for periodic QPSK transmission to the network. A data set was obtained from which both the up-link
communication and localization capabilties of the network can be determined.Funding was provided by the Office of Naval Research under Contract No. N00014-93-1-0988
and the Advanced Research Projects Agency under Contract Nos. MDA972-91-j-1004 and
MDA972-93-1-0019
Recommended from our members
Structure of the substrate-engaged SecA-SecY protein translocation machine.
The Sec61/SecY channel allows the translocation of many proteins across the eukaryotic endoplasmic reticulum membrane or the prokaryotic plasma membrane. In bacteria, most secretory proteins are transported post-translationally through the SecY channel by the SecA ATPase. How a polypeptide is moved through the SecA-SecY complex is poorly understood, as structural information is lacking. Here, we report an electron cryo-microscopy (cryo-EM) structure of a translocating SecA-SecY complex in a lipid environment. The translocating polypeptide chain can be traced through both SecA and SecY. In the captured transition state of ATP hydrolysis, SecAs two-helix finger is close to the polypeptide, while SecAs clamp interacts with the polypeptide in a sequence-independent manner by inducing a short β-strand. Taking into account previous biochemical and biophysical data, our structure is consistent with a model in which the two-helix finger and clamp cooperate during the ATPase cycle to move a polypeptide through the channel
Applying Spatial Diversity to Mitigate Partial Band Interference in Undersea Networks
Many acoustic channels suffer from interference which is neither narrowband nor impulsive. This relatively long duration partial band interference can be particularly detrimental to system performance. We survey recent work in interference mitigation and orthogonal frequency division multiplexing (OFDM) as background motivation to develop a spatial diversity receiver for use in underwater networks. The network consists of multiple distributed cabled hydrophones that receive data transmitted over a time-varying multipath channel in the presence of partial band interference produced by interfering active sonar signals as well as marine mammal vocalizations. In operational networks, many “dropped” messages are lost due to partial band interference which corrupts different portions of the received signal depending on the relative position of the interferers, information source and receivers due to the slow speed of propagation
A Comparison of a Single Receiver and a Multi-Receiver Techniques to Mitigate Partial Band Interference
Many acoustic channels suffer from interference which is neither narrowband nor impulsive. This relatively long duration partial band interference can be particularly detrimental to system performance. We survey recent work in interference mitigation as background motivation to develop a spatial diversity receiver for use in underwater networks and compare this novel multi-receiver interference mitigation strategy with a recently developed single receiver interference mitigation algorithm using experimental data collected from the underwater acoustic network at the Atlantic Underwater Test and Evaluation Center. The network consists of multiple distributed cabled hydrophones that receive data transmitted over a time-varying multipath channel in the presence of partial band interference produced by interfering active sonar signals. In operational networks, many dropped messages are lost due to partial band interference which corrupts different portions of the received signal depending on the relative position of the interferers, information source and receivers due to the slow speed of propagation
Diagnoses of Suicidum and Tentamen Suicidi in The Registers of Patients of The Kingdom of Yugoslavia’s Banovina Public General Hospital in Bjelovar from 1931–1940
Suicide has been a subject of research of philosophy, ethics, religion and medicine for centuries. Attitudes towards it changed during the history, from condemnation of suicide as an unethical act to the theory of suicide as the utmost expression of a human as an individual. Croatia, with the annual suicide rate above 20 percent belongs to the high-risk countries. Suicide frequency varies from region to region, while the suicide rates for the County Bjelovarsko-bilogorska have been well above Croatia’s average for decades. The aim of this retrospective study was to establish some epidemiological features of hospital patients with the diagnoses of »suicidum« and »tentamen suicidi« on the basis of records available in the registers of patients of General Hospital in Bjelovar in the period between 1931 and 1940. In the observed period, thirty-three people were treated in hospital for suicide attempt, seven of them dying. An equal number of men and women attempted suicide (13:13), while in the group of those who died, the ratio was more in favour of women (4:3). Suicide incidence was highest in November, followed by May and June, with the most common method for suicide being acetic acid
Multiple convergence zone acoustic telemetry feasibility test report
This report describes a multiple CZ acoustic telemetry experiment conducted off the coast of California 1/28/90-2/2/90. The goal
was to design a maximally robust high speed underwater modem suitable for data telemetry for submerged platforms and moorings.
Six modulation methods were used to transmit data at rates from 1 to 1000 baud corresponding to bit rates up to 3kbit/sec.
In addition, a large number of channel probe sequences was transmitted in order to estimate channel multipath, fluctuation
dynamics and spatial diversity characteristics relevant to acoustic data telemetry.
The data was transmitted from a 1 kHz source suspended from the R/V McGaw, and received on a multichannel vertical array
tended by the RV Point Sur. The multichannel data was digitally recorded using floating-point digitizers and stored on optical disk for further processing. Approximate transmission ranges were 70, 140, 200 and 250km. Approximtely 8 hrs of transmission were recorded at each data range.Funding was provided by the Office of Naval Technology under Grant No. N00014-90-C-0098
VOICE - a spectrogram computer display package
A real-time spetrogram instrument has been developed to provide an inexpensive and field-portable instrument for the
analysis of animal sounds. The instrument integrates a computer graphics display package with a PC-AT computer equipped with
an A/D board and a digital signal processing board. It provides a real-time spectrogram display of frequencies up to 50kHz in a
variety of modes: a running display, a signal halted on screen, successive expanded views of the signal. The signal amplitude may
also be displayed. Portions of the scrolled data may be saved to disk file for future viewing, or as part of a database collection. The
screen display may be manipulated to adapt to special needs. Program source listings are included in the text.Funding was provided by the Office of Naval Research through
Grant Nos. N00014-88-K-0273 and N00014-87-K-0236,
the National Institutes of Health through Grant No.1 R29 NS25290,
and the Andrew W. Mellon Foundation
Sensor Network Architectures for Monitoring Underwater Pipelines
This paper develops and compares different sensor network architecture designs that can be used for monitoring underwater pipeline infrastructures. These architectures are underwater wired sensor networks, underwater acoustic wireless sensor networks, RF (Radio Frequency) wireless sensor networks, integrated wired/acoustic wireless sensor networks, and integrated wired/RF wireless sensor networks. The paper also discusses the reliability challenges and enhancement approaches for these network architectures. The reliability evaluation, characteristics, advantages, and disadvantages among these architectures are discussed and compared. Three reliability factors are used for the discussion and comparison: the network connectivity, the continuity of power supply for the network, and the physical network security. In addition, the paper also develops and evaluates a hierarchical sensor network framework for underwater pipeline monitoring
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