Frequency agile radio

• US 5,377,222 A
• Filed: 08/10/1993
• Issued: 12/27/1994
• Est. Priority Date: 05/08/1992
• Status: Expired due to Term

• Current Assignee: M&FC Holding, LLC (Xylem, Inc.)
• Original Assignee: Axonn LLC (Globalstar Incorporated)
• Inventors: Sanderford, H. Britton Jr.
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US08/103,993
• Time in Patent Office: 504 Days
• Field of Search: 375/1, 342/18, 370/50, 380/34
• US Class Current: 375/131
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 1/715 Interference-related aspects
• CPC Class Codes: H04B 2001/7152 with means for suppressing interference
• CPC Class Codes: H04B 2001/7154 with means for preventing interference
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal

Abstract

A frequency agile spread spectrum radio system which uses a frequency-agile receiver that adaptively learns which frequencies to avoid as being occupied or jammed. The transmitter sends redundant transmissions on widely separated pseudo-random carrier frequencies to overcome jammed channels. A coded preamble is used to provide a greatly enhanced hybrid form of Time Division Multiple Access/Frequency Division Multiple Access for co-existence and frequency re-use with nearby systems. Anti-jam margins of 60 to 90 dB can be inexpensively achieved, far exceeding that of traditional direct sequence systems. The receiver scans the radio spectrum, identifies occupied portions, stores information on these occupied portions, skips over the occupied portions for a set period of time while scanning for radio signals, detects a repetitive preamble code in a received radio signal, maintains the frequency of the received radio signal, and receives and decodes message data in the received radio signal.

Claims

1. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from at least one transmitter transmitting on a plurality of pseudo-random frequencies, comprising the steps of:

a. scanning a radio spectrum;

b. identifying occupied portions of the ratio spectrum;

c. storing information identifying the occupied portions of the radio spectrum;

d. skipping over, in response to the information and while receiving with the frequency-agile receiver, the occupied portions of the radio spectrum;

e. detecting the presence of a radio carrier;

f. frequency locking, responsive to detecting the radio carrier, for compensating for transmitter and receiver frequency drift;

g. receiving message data on the radio carrier; and

h. repeating, responsive to not detecting the presence of the radio carrier, steps a through d.

2. A method, using a frequency-agile receiver in a frequency-agile radio system, with a plurality of transmitters, each of said plurality of transmitters transmitting independently, for increasing receipt of signals and message data transmitted in a radio spectrum from the plurality of transmitters, comprising the steps of:

scanning the radio spectrum;

identifying occupied portions of the radio spectrum;

updating information identifying the occupied portions;

storing, in memory means, the updated information;

associating a time-out period with the stored occupied portions;

skipping over, during the time-out period, in response to the updated information and while receiving with the frequency-agile receiver, the occupied portions of the radio spectrum; and

receiving a radio signal on a single frequency from one of the plurality of transmitters.

3. The method as set forth in claim 2, wherein the step of skipping over the occupied portions of the radio spectrum during the time-out period is initiated after a plurality of failed attempts to identify occupied portions of the radio spectrum have occurred.

4. The method as set forth in claim 2, wherein the step of skipping over the occupied portions of the radio spectrum during the time-out period is performed throughout the frequency-agile radio system.

6. The method as set forth in claim 2 or 5, wherein the sweep time of the sweeping of the radio spectrum is reduced by the steps of:

measuring received energy at an initially wide intermediate frequency band;

detecting a repetitive PREAMBLE SYSTEM CODE in the radio signal; and

narrowing, upon detection of the PREAMBLE SYSTEM CODE, the bandwidth of the intermediate frequency band prior to detecting data to improve carrier to noise ratio.

7. The method as set forth in claim 2 or 5, further including the steps of:

detecting the presence of a radio carrier; and

frequency locking, responsive to detecting the radio carrier, for compensating for transmitter and receiver frequency drift.

5. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a plurality of transmitters, transmitting on a plurality of pseudo-random frequencies, comprising the steps of:

sweeping a radio spectrum;

determining if a repetitive PREAMBLE SYSTEM CODE is present in a radio signal on a single frequency continuous in time;

detecting the repetitive PREAMBLE SYSTEM CODE in the radio signal;

maintaining, respective to detecting the repetitive PREAMBLE SYSTEM CODE, the single frequency;

decoding,responsive to detecting the repetitive PREAMBLE SYSTEM CODE, message-data; and

continuing, responsive to not detecting the repetitive PREAMBLE SYSTEM CODE, to sweep the radio spectrum.

8. A method, using a frequency-agile receiver in a frequency-agile radio system for increasing receipt of message data transmitted in a radio spectrum, comprising the steps of:

scanning the radio spectrum;

identifying occupied portions of the radio spectrum;

updating information identifying the occupied portions;

storing, in memory means, the updated information;

associating a time-out period with the stored occupied portions;

skipping over, during the time-out period, in response to the updated information and while receiving with the frequency-agile receiver, the occupied portions of the radio spectrum;

measuring received energy at an initially wide intermediate frequency band;

detecting a repetitive PREAMBLE SYSTEM CODE in a radio signal; and

narrowing, upon detection of the PREAMBLE SYSTEM CODE, the bandwidth of the intermediate frequency band prior to detecting data to improve carrier to noise ratio.

9. A method, using a frequency-agile receiver in a frequency-agile radio system, comprising the steps of:

measuring received energy at an initially wide intermediate frequency band;

sweeping a radio spectrum;

determining if a repetitive PREAMBLE SYSTEM CODE is present in a radio signal;

detecting the repetitive PREAMBLE SYSTEM CODE;

narrowing, upon a signal detection, the bandwidth of the intermediate frequency band prior to detecting data to improve carrier to noise ratio;

decoding, responsive to detecting the repetitive PREAMBLE SYSTEM CODE, message-data; and

continuing, responsive to not detecting the repetitive PREAMBLE SYSTEM CODE, to sweep the radio spectrum.

10. A method, using a frequency-agile receiver in a frequency-agile radio system, comprising the steps of:

sweeping a radio spectrum;

detecting the presence of a radio carrier;

determining if a repetitive PREAMBLE SYSTEM CODE is present in a radio signal on a single frequency of the radio carrier;

detecting the repetitive PREAMBLE SYSTEM CODE on the single frequency;

frequency locking, responsive to detecting the PREAMBLE SYSTEM CODE, for compensating for transmitter and receiver frequency drift;

decoding, responsive to detecting the repetitive PREAMBLE SYSTEM CODE, message-data; and

continuing, responsive to not detecting the repetitive PREAMBLE SYSTEM CODE, to sweep the radio spectrum.

11. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a plurality of transmitters transmitting information messages on a plurality of pseudo-random frequencies, comprising the steps of:

sweeping an available frequency band;

logging to memory occupied portions of the frequency band;

transferring a list of the occupied portions to the plurality of transmitters;

setting a wide received signal detection bandwidth;

sweeping the wide received signal detection bandwidth using a voltage controlled oscillator;

skipping, responsive to the list of occupied portions, the occupied portions of the frequency band during a time out period;

detecting a radio signal from a transmitter;

ceasing to sweep the wide received signal detection bandwidth;

reducing the wide received signal detection bandwidth for increasing signal to noise ratio;

enabling a frequency locked loop for reducing frequency drift between the receiver and the transmitter;

decoding a PREAMBLE SYSTEM CODE; and

decoding data.

12. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from at least one transmitter transmitting information messages on a plurality of pseudo-random frequencies, comprising the steps of:

sweeping an available radio spectrum;

identifying occupied portions of the radio spectrum;

storing the occupied portions in a memory;

skipping, responsive to the memory, the occupied portions;

detecting a radio signal from a transmitter on a channel;

ceasing a sweep the available radio spectrum;

determining if at least one of a repetitive preamble system code and a transmitter identifier is present in the radio signal;

decoding data;

continuing, responsive to at least one of detecting jamming and failing to detect data, to sweep the radio spectrum; and

storing updated information in the memory identifying the channel as jammed.

13. The method as set forth in claim 12, further including the steps of:

sweeping the available radio spectrum using voltage-controlled oscillating means; and

setting a sweep time less than a transmitted preamble time and greater than a bit time.

14. The method as set forth in claim 12, further including the step of:

reducing received signal detection bandwidth to increase signal to noise ratio.

15. The method as set forth in claim 12, further including the step of:

enabling a frequency locked loop to reduce frequency drift between the receiver and the transmitter.

16. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a plurality of transmitters transmitting information messages on a plurality of pseudo-random frequencies, comprising the steps of:

sweeping an available radio spectrum;

setting a sweep time less than a transmitted preamble time and greater than a bit time;

measuring at least one of signal strength, quieting, and phase lock loop (PLL) lock detect output of the receiver;

skipping over, responsive to a table in a memory, occupied portions of the available radio spectrum;

detecting a radio signal from a transmitter on a channel;

ceasing to sweep the available radio spectrum;

determining if at least one of a repetitive preamble system code and a transmitter identifier is present in the radio signal;

decoding at least one of the repetitive preamble system code and the transmitter identifier;

continuing, responsive to not detecting at least one of the repetitive preamble system code and the transmitter identifier, to sweep the radio spectrum; and

storing updated information in the memory.

17. The method as set forth in claim 16, further including the steps, after the step of sweeping the available radio spectrum, of:

logging, to a table in the memory, a list of occupied areas in the available band; and

transferring the list of occupied areas to the plurality of transmitters.

18. The method as set forth in claim 16, further including the step, after the step of detecting a radio signal from a transmitter, of:

reducing received signal detection bandwidth for increasing signal to noise ratio.

19. The method as set forth in claim 16, further including the step, after the step of detecting a radio signal from a transmitter, of:

enabling a frequency locked loop for reducing frequency drift between the receiver and the transmitter.

20. The method as set forth in claim 16, further including the step, after the step of storing updated information in the memory, of:

identifying the channel as jammed.

21. The method as set forth in claim 16, further including the step, after the step of storing updated information in the memory, of:

associating a time out period with occupied channels.

22. A method, using a frequency-agile receiver in a frequency-agile radio system,for receiving signals from a plurality of transmitters transmitting information messages on a plurality of pseudo-random frequencies,comprising the steps of:

sweeping an available radio spectrum using voltage controlled oscillating means;

setting a sweep time less than a transmitted preamble time and greater than a bit time;

calibrating the voltage controlled oscillating means with a divider and crystal;

measuring at least one of signal strength, quieting, and phase lock loop (PLL) lock detect output of the receiver;

skipping over, responsive to a table in a memory, occupied portions of the available radio spectrum marked as jammed;

detecting a radio signal from a transmitter in a portion of the available radio spectrum not marked as jammed;

ceasing to sweep the voltage controlled oscillating means;

matching at least one of a repetitive preamble system code and a transmitter identifier with at least one of a preamble system code and a identifier of the receiver; and

decoding data.

23. The method as set forth in claim 22, further including the steps, after the step of sweeping the available radio spectrum, of:

logging, to a table in the memory, a list of occupied areas in the available band; and

transferring the list of occupied areas to the plurality of transmitters.

24. The method as set forth in claim 22, further including the step of:

setting a wide received signal detection bandwidth for rapid local oscillator sweep rate.

25. The method as set forth in claim 24, further including the steps of:

sweeping a bandwidth including transmitted guard bands;

associating a time out period with occupied channels; and

skipping over, responsive to an associated table entry in the memory, occupied portions of the available radio spectrum during the time output period.

26. The method as set forth in claim 22, further including the step, after the step of detecting a radio signal from a transmitter, of:

reducing received signal detection bandwidth for increasing signal to noise ratio.

27. The method as set forth in claim 22, further including the steps, after the step of detecting a radio signal from a transmitter, of:

enabling a frequency locked loop for reducing frequency drift between the receiver and the transmitter; and

verifying data using error detection means.

28. The method as set forth to claim 22, further including the steps, after the step of decoding data, of:

storing, responsive to at least one of failing to decode data and detecting jamming, updated information in the memory; and

associating a time out period with occupied channels.

29. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a plurality of transmitters transmitting information messages on a plurality of pseudo-random frequencies, comprising the steps of:

sweeping an available radio spectrum;

measuring at least one of signal strength, quieting, and phase lock loop (PLL) lock detect output of the receiver;

skipping over, responsive to a table in a memory, occupied portions of the available radio spectrum marked as jammed;

detecting a radio signal from a transmitter on a channel in a portion of the available radio spectrum not marked as jammed;

ceasing to sweep the available radio spectrum;

enabling a frequency locked loop for reducing frequency drift between the receiver and the transmitter;

decoding at least one of a repetitive preamble system code and a transmitter identifier;

matching at least one of the repetitive preamble system code and the transmitter identifier with at least one of a preamble system code and a identifier of the receiver;

decoding data;

verifying data using error detection means; and

storing, responsive to at least one of detecting jamming and failing to detect data, updated information in the table identifying the channel as jammed.

30. The method as set forth in claim 29, further including the steps, after the step of sweeping the available radio spectrum, of:

logging, to a table in the memory, a list of occupied areas in the available band; and

transferring the list of occupied areas to the plurality of transmitters.

31. The method as set forth in claim 29, further including the step of:

setting a wide received signal detection bandwidth using voltage controlled oscillating means.

32. The method as set forth in claim 31, further including the steps of:

setting a sweep time less than a transmitted preamble time and greater than a bit time;

calibrating the voltage controlled oscillating means with a divider and crystal;

sweeping a bandwidth including transmitted guard bands;

associating a time out period with occupied channels; and

skipping over, responsive to an associated table entry in the memory, occupied portions of the available radio spectrum during the time out period.

33. The method as set forth in claim 29, further including the step, after the step of detecting a radio signal from a transmitter, of:

reducing received signal detection bandwidth for increasing signal to noise ratio.

34. The method as set forth in claim 29, further including the step, after the step of decoding data, of:

storing, responsive to at least one of failing to decode data and detecting jamming, updated information in the memory; and

associating a time out period with occupied channels.

35. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a plurality of transmitters transmitting information messages on a plurality of pseudo-random frequencies, comprising the steps of:

setting a wide received signal detection bandwidth;

sweeping an available radio spectrum using voltage controlled oscillating means;

setting a sweep time less than a transmitted preamble time and greater than a bit time;

measuring at least one of signal strength, quieting, and phase lock loop (PLL) lock detect output of the receiver;

skipping over, responsive to a table in a memory, occupied portions of the available radio spectrum during a time out period;

detecting a radio signal from a transmitter on a channel in a portion of the available radio spectrum not marked as jammed;

ceasing to sweep the available radio spectrum;

reducing received signal detection bandwidth for increasing signal to noise ratio;

decoding at least one of a repetitive preamble system code and a transmitter identifier;

matching at least one of the repetitive preamble system code and the transmitter identifier with at least one of a preamble system code and a transmitter identifier of the receiver;

decoding data; and

storing, responsive to at least one of detecting jamming and failing to detect data, updated information in the memory associating a time out period with occupied channels.

36. The method as set forth in claim 35, further including the steps, after the step of sweeping the available radio spectrum, of:

logging, to a table in the memory, a list of occupied areas in the available band; and

transferring the list of occupied areas to the plurality of transmitters.

37. The method as set forth in claim 35, further including the step of:

calibrating the voltage controlled oscillating means with a divider and crystal.

38. The method as set forth in claim 35, further including the step of:

sweeping a bandwidth including transmitted guard bands.

39. The method as set forth in claim 35, further including the step, after the step of ceasing to sweep the available radio spectrum, of:

enabling a frequency locked loop for reducing frequency drift between the receiver and the transmitter.

40. The method as set forth in claim 35, further including the steps, after the step of decoding data, of:

verifying the data using error detection means.