Method and device for detecting and interpreting a distress signal
First Claim
1. An emergency telecommunication process for producing a distress signal repeatedly transmitted from a mobile station in successive sequences and for detecting and interpreting the distress signal with a high reliability at a shore terminal, said process comprising the steps of:
- transmitting in each sequence of the distress signal, an alarm signal during a first time interval and a message signal during a second time interval, said alarm signal being only comprised of a carrier phase-modulated by a sub-carrier and said message signal being comprised of a carrier which is phase-modulated by a sub-carrier to which the information is superimposed by binary phase modulation;
detecting the alarm signal at a shore terminal during said first time interval for producing a command signal indicating the occurrence of a distress signal; and
controlling and demodulating the message signal during said second time interval in response to said command signal so as to restore the distress message.
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Accused Products
Abstract
An emergency telecommunications system wherein the distress signals are transmitted repeatedly in successive sequences each comprised of a detect interval during which an alarm signal is transmitted and of a message transmit interval during which the distress message itself is transmitted indicating particularly the identity of the ship, its location and the nature of distress. During the detect interval, the transmitted signal is comprised of a carrier phase modulated by a sub-carrier, the frequency of the latter being a multiple of the information transmission speed. During the message transmit interval, the information is superposed to the sub-carrier by phase binary modulation. The presence of an alarm signal during each detect interval is detected in an alarm receiver monitoring the receive frequency band simultaneously in several channels of different narrow bandwidths so as to generate a control signal which indicates the presence of a distress signal in anyone of the channels. In response to this control signal, the message signal received during the subsequent message transmit interval is controlled accurately, and demodulated and interpreted coherently in a message receiver so as to restore the distress message.
6 Citations
5 Claims
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1. An emergency telecommunication process for producing a distress signal repeatedly transmitted from a mobile station in successive sequences and for detecting and interpreting the distress signal with a high reliability at a shore terminal, said process comprising the steps of:
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transmitting in each sequence of the distress signal, an alarm signal during a first time interval and a message signal during a second time interval, said alarm signal being only comprised of a carrier phase-modulated by a sub-carrier and said message signal being comprised of a carrier which is phase-modulated by a sub-carrier to which the information is superimposed by binary phase modulation; detecting the alarm signal at a shore terminal during said first time interval for producing a command signal indicating the occurrence of a distress signal; and controlling and demodulating the message signal during said second time interval in response to said command signal so as to restore the distress message.
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2. A receive apparatus for distress signals comprising an alarm signal during a first time interval and a message signal during a second time interval, the alarm signal being comprised of a carrier which is phase-modulated by a sub-carrier and the message signal being comprised of a carrier which is phase-modulated by a sub-carrier to which the information is superimposed by binary phase modulation, said receive apparatus comprising:
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alarm receiver means arranged for monitoring a receive frequency band simultaneously in a plurality of channels each having a distinct narrow bandwidth and for producing a detect signal in response to an alarm signal being detected in any of said channels during the first time interval; transfer logic means arranged to respond to the detect signal for producing a command signal which identifies the channel in which the alarm signal is detected; and
message receiver means connected for accepting the distress signal and arranged for responding to said command signal and for controlling and thereafter processing the message signal received during said second time interval so as to restore the distress message. - View Dependent Claims (3, 4, 5)
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Specification