Satellite-based position determining and message transfer system with monitoring of link quality

• US 4,744,083 A
• Filed: 09/14/1984
• Issued: 05/10/1988
• Est. Priority Date: 09/14/1984
• Status: Expired due to Term

• Current Assignee: COMSAT Corporation (Reorganized ISA SA)
• Original Assignee: Geostar Corp.
• Inventors: Snively, Leslie O., O'Neill, Gerard K.
• Primary Examiner(s): Fleming, Michael R.
• Application Number:
  US06/650,493
• Time in Patent Office: 1,334 Days
• Field of Search: 371/5, 371/30, 371/31, 371/32, 371/33, 371/34, 371/43, 371/44, 371/45, 370/104, 370/84, 370/92, 375/10, 375/100
• US Class Current: 714/704
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G01S 19/38 Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
• CPC Class Codes: H04B 17/40 of relay systems
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/1855 using a telephonic control signal, e.g. propagation delay variation, Doppler frequency variation, power variation, beam identification
• CPC Class Codes: H04B 7/18567 Arrangements for providing additional services to the basic mobile satellite telephony service

Abstract

A radio position determination and message transfer system is implemented using a number of satellites in geostationary orbit for relaying interrogation and reply signals between a ground station and a user-carried transceiver. Message information can be exchanged between a given user transceiver and the ground station, as well as between different user transceivers. The user transceiver is provided with means for monitoring the quality of the radio communication link between the transceiver and one or more of the satelites, based on errors detected in the received interrogation signals. The transmission of a reply signal by the transceiver is enabled only when the link quality is found to be acceptable. The reply signal may contain message information or may constitute a request for a position fix. In the latter case, the transceiver may be configured to await favorable link quality to more than one satellite before the reply signal is transmitted.

Claims

1. A radio communication system comprising:

a central station for transmitting interrogation signals over a radio communication link which is subject to variations in signal propagation quality;

a remote transceiver for receiving interrogation signals from the central station over said radio communication link, and for transmitting reply signals to the central station in response to the interrogation signals; and

control means in said remote transceiver for measuring the quality of the radio communication link between the central station and the remote transceiver, and for allowing the transmission of a reply signal by the transceiver only when said communication link has at least a predetermined minimum quality.

2. A radio communication system as claimed in claim 1, wherein said control means is effective to detect errors in the received interrogation signals, and to derive from the absence or presence of said errors a measurement of the quality of the communication link.

3. A radio communication system as claimed in claim 2, wherein:

said control means maintains a running count of errors detected in a number of recently received interrogation signals; and

said control means is effective to compare said count with a predetermined threshold value in order to determine whether the communication link has at least the predetermined minimum quality required for the transmission of a reply signal by the transceiver.

4. A radio communication system as claimed in claim 3, wherein said transceiver further includes display means connected to said control means for displaying the measured quality of the communication link.

5. A radio communication system as claimed in claim 2, wherein:

said interrogation signals comprise binary digital signals incorporating error detection codes; and

said control means includes decoding means responsive to said error detection codes for measuring the quality of the communication link.

6. A radio communication system as claimed in claim 5, wherein:

said error detection codes comprise parity check bits; and

said decoding means comprises a parity decoder.

7. A radio communication system as claimed in claim 1, wherein said radio communication link includes at least one satellite.

8. A radio communication system comprising:

a central station for transmitting a sequence of interrogation signals containing error detection codes;

a remote transceiver for receiving said interrogation signals over a radio communication link between the central station and the remote transceiver, said radio communication link being subject to variations in signal propagation quality, and for transmitting reply signals containing message information to the central station in response to said interrogation signals; and

control means in the remote transceiver for utilizing said error detection codes to provide an indication of the quality of the communication link between the central station and the remote transceiver, and for suppressing the transmission of a reply signal by the remote transceiver until at least a predetermined minimum quality of the communication link is indicated.

9. A radio communication system as claimed in claim 8, wherein:

said control means maintains a running count of errors detected in a number of recently received interrogation signals; and

said control means is effective to compare said count with a predetermined threshold value in order to determine whether the communication link has at least the predetermined minimum quality required for the transmission of a reply signal by the transceiver.

10. A radio communication system as claimed in claim 8, wherein said remote transceiver further includes display means connected to said control means for displaying an indication of the quality of the communication link to a user.

11. A radio communication system as claimed in claim 8, wherein:

said interrogation signals comprise binary digital signals in which said error detection codes comprise parity check bits; and

13. A radio communication system as claimed in claim 8, wherein said communication link includes at least one satellite for relaying interrogation signals from the central station to the remote transceiver, and for relaying reply signals from the remote transceiver to the central station.

15. A radio communication system as claimed in claim 13, wherein said monitoring means is effective to detect errors in the received interrogation signals, and to derive from the presence or absence of said errors an indication of the quality of the radio communication link.

12. said control means includes a parity decoder.

14. A radio communication system comprising:

a central station for transmitting interrogation signals over a radio communication link which is subject to variations in signal propagation quality;

a remote transceiver for receiving interrogation signals from the central station by means of said radio communication link, and for transmitting reply signals to the central station in response to the interrogation signals;

monitoring means in said remote transceiver for monitoring the quality of the radio communication link between the central station and the remote transceiver as a function of the received interrogation signals; and

display means connected to said monitoring means for displaying an indication of the quality of the communication link.

16. A remote transceiver for receiving and responding to error-coded interrogation signals transmitted by a central station over a communication link which is subject to variations in signal propagation quality, comprising:

receiving means for receiving interrogation signals;

monitoring means for monitoring the quality of communication link as a function of errors detected in the received interrogation signals; and

transmitting means connected to said monitoring means for transmitting reply signals in response to the interrogation signal only when said communication link has at least a predetermined minimum quality.

17. A remote transceiver for receiving and responding to error-coded interrogation signals transmitted by a central station over a communication link which is subject to variations in signal propagation quality, comprising:

receive and transmit means for receiving interrogation signals and for transmitting reply signals in response to said interrogation signals;

monitoring means for monitoring the quality of the communication link as a function of errors detected in the received interrogation signals; and

display means connected to said monitoring means for displaying to a user an indication of the quality of the communication link.

19. A radio communication system as claimed in claim 17, wherein:

said control means maintains a running count of errors detected in a number of recently received interrogation signals; and

said control means is effective to compare said count with a predetermined threshold value in order to determine whether the communication link has at least the predetermined minimum quality required for the transmission of a reply signal by the transceiver.

20. A radio communication system as claimed in claim 17, wherein said remote transceiver further includes display means connected to said control means for displaying an indication of the quality of the communication link to a user.

21. A radio communication system as claimed in claim 17, wherein:

said interrogation signals comprise binary digital signals in which said error detection codes comprise parity check bits; and

said control means includes a parity decoder.

18. A radio communication system for sending messages to a ground station from a remote transceiver by means of a satellite, comprising:

a remote transceiver for receiving interrogation signals containing error detection codes and for transmitting reply signals carrying message information in response to said interrogation signals;

a ground station for transmitting interrogation signals containing error detection codes and for receiving reply signals from the remote transceiver;

at least one relay satellite for relaying interrogation signals from the ground station to the remote transceiver over a radio communication link which is subject to variations in signal propagation quality, and for relaying reply signals from the remote transceiver to the ground station; and

control means in the remote transceiver for utilizing the error detection codes in the received interrogation signals to provide an indication of the quality of the radio communication link to the remote transceiver, and for suppressing the transmission of a reply signal by the remote transceiver until at least a predetermined minimum quality of the communication link is indicated.

22. A radio communication system for sending messages to a ground station from a remote transceiver by means of a satellite, comprising:

a remote transceiver for receiving interrogation signals containing error detection codes and for transmitting reply signals carrying message information in response to said interrogation signals;

a ground station for transmitting interrogation signals containing error detection codes and for receiving reply signals from the remote transceiver;

at least one relay satellite for relaying interrogation signals from the ground station to the remote transceiver over a radio communication link which is subject to variations in signal propagation quality, and for relaying reply signals from the remote transceiver to the ground station;

monitoring means in the remote transceiver for monitoring the quality of the radio communication link to the remote transceiver as a function of errors detected in the received interrogation signals; and

display means connected to said monitoring means for displaying an indication of the quality of the communication link.

23. A method for sending messages to a central station from a remote transceiver over a radio communication link which is subject to variations in signal propagation quality, comprising the steps of:

transmitting a sequence of interrogation signals containing error detection codes from the central station;

receiving said interrogation signals at the remote transceiver;

utilizing the error detection codes in the received interrogation signals to provide the remote transceiver with an indication of the quality of the radio communication link between the central station and the remote transceiver;

transmitting reply signals containing message information from the remote transceiver to the central station when at least a predetermined minimum quality of the radio communication link is indicated; and

suppressing the transmission of reply signals from the remote transceiver when the indicated quality of the radio communication link is less than a predetermined minimum value.

24. A method for sending messages to a ground station from a remote transceiver over a radio communication link including a satellite, said radio communication link being subject to variations in signal propagation quality, said method comprising the steps of:

transmitting a sequence of interrogation signals containing error detection codes from the ground station;

relaying said interrogation signals through the satellite to the remote transceiver;

receiving said interrogation signals at the remote transceiver;

utilizing the error detection codes in the received interrogation signals to provide the remote transceiver with an indication of the quality of the radio communication link between the satellite and the remote transceiver;

transmitting reply signals containing message information from the remote transceiver to the ground station through the relay satellite when at least a predetermined minimum quality of the radio communication link is indicated; and

suppressing the transmission of reply signals by the remote transceiver when the indicated quality of the radio communication link is less than a predetermined minimum value.

26. A method as claimed in claim 24, wherein the simultaneous interrogation signals transmitted by the ground station are distinguished by different pseudo-noise coding, and wherein the step of receiving the interrogation signals at the remote transceiver includes the step of distinguishing the interrogation signals according to pseudo-noise code.

27. A method as claimed in claim 24, comprising the further steps of:

relaying the transceiver reply signals to the ground station through each of the satellites; and

calculating the position of the remote transceiver based on the arrival times of the reply signals at the ground station.

29. A method as claimed in claim 27, wherein the first and second interrogation signals transmitted by the ground station are distinguished by different pseudo-noise coding, and wherein the step of receiving at least one of the first and second interrogation signals at the remote transceiver includes the step of decoding at least one of the pseudo-noise codes.

25. A method for establishing radio communication between a ground station and a remote transceiver through at least two relay satellites, each of said relay satellites communicating with the remote transceiver over a radio communication link which is subject to variations in signal propagation quality, said method comprising the steps of:

simultaneous transmitting from the ground station at least two mutually distinguishable interrogation signals containing error detection codes;

relaying each of said interrogation signals to the remote transceiver through a different satellite;

receiving said interrogation signals at the remote transceiver;

utilizing the error detection codes in each received interrogation signal to provide the remote transceiver with an indication of the quality of the radio communication links between the remote transceiver and each of the satellites;

transmitting reply signals from the remote transceiver to the ground station through the satellites when at least a predetermined minimum quality of the radio communication link is indicated for all satellites; and

suppressing the transmission of reply signals by the remote transceiver when the indicated quality of the radio communication link is less than a predetermined value for one or more of the satellites.

28. A method for sending messages to a ground station from a remote transceiver over a radio communication link including first and second satellites, comprising the steps of:

transmitting first and second mutually distinguishable interrogation signals from the ground station;

relaying the first interrogation signal to the remote transceiver through the first satellite;

relaying the second interrogation signal to the remote transceiver through the second satellite;

retransmitting the first and second interrogation signals from the ground station;

relaying the first interrogation signal to the remote transceiver through the second satellite;

relaying the second interrogation signal to the remote transceiver through the first satellite;

receiving at least one of said first and second interrogation signals at the remote transceiver; and

transmitting reply signals containing message information from the remote transceiver to the ground station through at least one of the satellites in response to the received interrogation signal.

30. A method for sending messages to a remote transceiver from a central station over a radio communication link which is subject to variations in signal propagation quality, comprising the steps of:

transmitting a sequence of pseudo-noise coded interrogation signals containing error detection codes from the central station, said sequence including a repeating series of interrogation signals employing different spread ratios in the pseudo-noise codes;

receiving said interrogation signals at the remote transceiver;

utilizing the error detection codes in the received interrogation signals to provide the remote transceiver with an indication of the quality of the radio communication link between the central station and the transceiver for each of said pseudo-noise code spread ratios;

selecting the lowest pseudo-noise code spread ratio for which the indicated quality of the radio communication link at the remote transceiver is above a predetermined threshold value;

transmitting a reply signal from the remote transceiver to the central station, said reply signal containing an indication of the selected pseudo-noise code spread ratio; and

transmitting message information to the remote transceiver from the central station using a pseudo-noise code having the spread ratio selected by the remote transceiver.

31. A method for sending messages from a sending transceiver to a destination transceiver through a central station, comprising the steps of:

transmitting message information from the sending transceiver to the central station;

in response to the receipt of said message information at the central station, transmitting a first acknowledgement from the central station to the sending transceiver;

transmitting the message information from the central station to the destination transceiver;

in response to the receipt of the message information at the destination transceiver, transmitting a second acknowledgement from the destination transceiver to the central station;

relaying the second acknowledgement from the central station to the sending transceiver;

in response to a user input at the destination transceiver indicating that the message information has been read by the user, transmitting a third acknowledgement from the destination transceiver to the central station; and

relaying the third acknowledgement from the central station to the sending transceiver.