Enhanced frequency agile radio

• US 5,668,828 A
• Filed: 09/23/1994
• Issued: 09/16/1997
• Est. Priority Date: 05/08/1992
• Status: Expired due to Term

• Current Assignee: Sensus Spectrum, LLC (Xylem, Inc.)
• Original Assignee: Sanconix Inc.
• Inventors: Rouquette, Robert E., Sanderford, H. Britton Jr., Davis, Robert J.
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US08/311,774
• Time in Patent Office: 1,089 Days
• Field of Search: 375/202
• US Class Current: 375/136
• CPC Class Codes: H03J 1/0091 provided with means for scanning over a band of frequencies H03J1/0058 takes precedence
• 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

An enhanced frequency-agile radio for avoiding undesired signal energy, based on a prediction, by scanning an available radio spectrum, measuring a receiver output, identifying an occupied portion of the available spectrum, predicting a level of undesired signal energy in a future scan, and storing the prediction. Enhancements provided by the frequency-agile radio include lowered implementation complexity appropriate for very low cost receivers and transceivers, reduced size due to elimination of larger components allowing for physically small pocket pager applications, increased anti-jam performance appropriate for wide area networks, increased receiver sensitivity and frequency tracking desirable for voice applications, enhanced signal coding error tolerance allowing operation within congested portions of the radio band and additional signal verification means which allow correct data reception from thousands of concurrently operating, collision prone transmit-only devices such as power utility meters and long range security systems.

Claims

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating, based at least in part on the measurement, a prediction of a level of interference signal energy, within the portion of the available radio spectrum, expected in a future scan of said available radio spectrum by said frequency-agile receiver; and

storing the prediction of the level of interference signal energy in a memory location associated with the portion of the scanned available radio spectrum.

20. The method as set forth in claim 1, 2, 3, 4, 6, 8, 13, 14, 15, 17 or 19, further including the steps of:

receiving a transmission by said freguency agile receiver;

associating portions of a bandwidth received by said frequency agile receiver with levels of interference signal energy;

storing information on the levels of interference signal energy in a memory means;

transmitting on a transmitter portion of said frequency agile receiver, data representing the information to a remotely located transceiving device; and

transmitting, by the remotely located transceiving device and responsive to the information, on frequencies with levels of interference signal energy below an interference signal energy threshold.

24. The method as set forth in claim 1, 2, 3, 4, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

dwelling, by said frequency-agile receiver, on a portion of an available radio spectrum; and

aborting a dwell on said portion of an available radio spectrum if at least one of a type of modulation performed on a signal on said portion of the scanned available radio spectrum, data encoding performed on a signal on said portion of the scanned available radio spectrum, and a sequence of data of a signal on said portion of the scanned available radio spectrum is not of a type or value intended to be received by said freguency-agile receiver.

25. The method as set forth in claim 1, 2, 3, 4, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

computing an adaptive trip level by using at least one of percent message throughput indicating a percentage of successfully and decoded messages at a previous trip level, attack variables that predict a rate of increase in interference signal level, decay variables that indicate an amount of decrease in interference signal level, and false trip historic information indicating previous false trips; and

dwelling, responsive to future measurements exceeding at least one of an adaptive trip level and an adaptive trip level plus a shunt level, on a portion of the scanned available radio spectrum.

29. The method as set forth in claim 1, 2, 3, 4, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

dwelling, by said frequency-agile receiver, on a portion of the scanned available radio spectrum; and

controlling, responsive to at least one of an initial carrier frequency error occurring as a result of a difference between transmitted and received frequencies and a carrier frequency drift error resulting from a separation of transmitted and received frequencies caused by variances within said transmitter and frequency agile receiver, at least one of a voltage controlled oscillator, a numerically controlled oscillator, a frequency synthesizer, and a reference frequency to minimize frequency error.

30. The method as set forth in claim 1, 2, 3, 4, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

receiving a transmission from a transmitter system which locks a carrier to a data clock;

dwelling, by said frequency-agile receiver, on a portion of the available radio spectrum; and

controlling, responsive to at least one of an initial carrier frequency error occurring as a result of a difference between transmitted and received frequencies and a carrier frequency drift error resulting from a separation of transmitted and received frequencies caused by variances within said transmitter and frequency agile receiver, a system reference frequency for cancelling carrier frequency drift and data clock drift.

31. The method as set forth in claim 1, 2, 3, 4, 6, 7, 12, 13, 14, 15, 17, 18 or 19, wherein the step of generating the prediction, responsive to a level of interference signal energy on said portion of the available radio spectrum remaining constant, includes the step of generating by said frequency agile receiver a prediction equal to an average level of interference signal energy.

32. The method as set forth in claim 1, 2, 3, 4, 6, 7, 12, 13, 14, 15, 17, 18 or 19, wherein the steps of generating the prediction, responsive to at least one of variation above an interference variation threshold or faster than a rate of change threshold in the level of interference signal energy, includes the step of generating the prediction equal to an average level interference signal energy in which said average is calculated with said variation in the level of interference signal energy weighted by a multiplication factor.

33. The method as set forth in claim 1, 2, 3, 4, 6, 7, 12, 13, 14, 15, 17, 18 or 19, wherein the step of generating the prediction, equal to the measurement falling within a specified hysterisis range of plus or minus a signal energy level encompassing a previous interference signal energy prediction, includes the step of generating the prediction equal to an average of past readings from the portion of the available radio spectrum.

34. The method as set forth in claim 1, 2, 3, 4, 6, 7, 12, 13, 14, 15, 17, 18 or 19, wherein the step of generating the prediction, responsive to the measurement falling outside of a specified hysterisis range of plus or minus a signal energy level encompassing a previous interference signal energy production, includes the step of generating the prediction at least one of equal to and closer to the present measurement than a previous prediction.

35. The method as set forth in claim 1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, wherein the step of generating the prediction responsive to the measurement, includes the step of generating the prediction resulting from attack variables that predict a rate of increase in interference signal level, and decay variables that indicate an amount of decrease in interference signal level based on previous measurements.

36. The method as set forth in claim 1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further comprising the step of updating at least one of the prediction and the shunt level predicated upon more than one false trip signal level above either the shunt level or the prediction plus a trip level on at least one of a same frequency bin representing a received frequency, and a same portion of the available radio spectrum occurring in consecutive scans of a radio spectrum.

37. The method as set forth in claims 1, 2, 3, 4, 6, 7, 8, 12, 13, 14, 15, 17, 16 or 19, wherein the step of scanning includes the steps of:

generating a next local oscillator frequency by frequency generation means;

discharging energy storing elements of at least one of a most narrow bandwidth IF filter and a baseband filter; and

delaying an amount of time to allow filter settling.

38. The method as set forth in claim 1, 2, 3, 4, 6, 7, 8, 12, 15, 17, 18 or 19, further including the steps of:

selecting at least one of a chirp filter and a filter which has a bandwidth greater than that of transmitted data to filter incoming signals, while scanning an available radio spectrum;

measuring at least one of signal strength and quieting and signal lock quality as a measurement;

ceasing, responsive to the measurement exceeding a threshold, to scan the available radio spectrum;

selecting at least one of an IF filter and a baseband filter having a bandwidth similar to a bandwidth of the transmitted data; and

attempting to decode at least one of data and voice modulation and a preamble system code and a transmitter identifier and voice modulation and data.

39. The method set forth in claim 37 wherein the step of discharging energy storing elements of at least one of the most narrow bandwidth IF filter and the baseband filter achieves a sharp leading edge in a frequency swept application while causing minimal peak signal attenuation.

40. The method as set forth in claims 1, 2, 3, 4, 6, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

delaying scanning for a period of time;

calculating a reduction factor based upon a decay variable that indicates an amount of decrease in interference signal level;

subtracting the calculated reduction factor from a shunt-level to yield a new shunt level; and

storing the new shunt level in memory means.

42. The method as set forth in claim 1, 2, 3, 4, 6, 7, 12, 13 or 14, further including the steps of:

outputting at least one of a shunt level representing an interference prediction and a portion of a shunt level to an AGC circuit;

measuring at least one of receiver signal strength and quieting and signal lock quality, as a measurement; and

comparing the measurement to at least one of a, trip level a shunt level less the portion of the shunt level output to the AGC circuit, and a shunt level plus a trip level representing an amount of signal energy less the portion of the shunt level output to the AGC circuit.

43. The method as set forth in claim 1, 2, 3, 4, 6, 7, 12, 13 or 14, further including the step of:

disabling, responsive to at least one of a prediction of undesired signal energy and a shunt level exceeding an amount equal to an attenuation caused by disabling at least one gain stage of said frequency-agile receiver plus an amount equal to signal strength required to achieve a desired bit error rate, at least one gain stage of said frequency-agile receiver.

44. The method as set forth in claims 1 and 3, further including the steps of:

identifying a segment of the available radio spectrum as occupied;

marking the segment of the available radio spectrum as occupied; and

avoiding, responsive to the segment of the radio spectrum being marked as occupied, the occupied segment of the radio spectrum.

45. The method of claim 44, further comprising the step of:

identifying, utilizing at least one of percent data throughput indicating a percentage of successfully received and decoded messages at a previous trip level, shunt level, attack variables that predict a rate of increase in interference signal level, and decay variables that indicate an amount of decrease in interference signal level, whether the portion of the scanned available radio spectrum fails to provide a recognizable coded signal.

2. A method, using a frequency-agile receiver in a frequency-agile-radio system, for receiving signals from a transmitter transmitting information message on a plurality of frequencies, comprising the steps of:

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating, using the measurement, a prediction of a level of interference signal energy, within the portion of the scanned available radio spectrum, expected in a future scan of said available radio spectrum by the frequency-agile receiver;

storing the prediction of the level of interference signal energy in a memory location associated with the portion of the scanned available radio spectrum; and

avoiding the portion of the scanned available radio spectrum in future signal receptions if the stored prediction indicates a level of interference above an interference threshold.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating a prediction, using the measurement and information derived from previous measurements, of a level of interference signal energy, within the portion of the available radio spectrum, expected in a future scan of said frequency agile receiver; and

storing the prediction in a memory location associated with the portion of the available radio spectrum.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

comparing the measurement to a threshold stored in a memory location associated with the portion of the scanned available radio spectrum;

ceasing, responsive to the measurement exceeding the threshold, to scan the available radio spectrum; and

decoding, responsive to said ceasing step, on the portion of the scanned available radio spectrum at least one of a preamble system code that modulates a carrier frequency in said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and a transmitter identifier transmitted on the carrier frequency.

5. The method as set forth in claim 4, wherein the step of comparing the measurement to the threshold includes the step of comparing the measurement to at least one of a shunt level representing an interference prediction and a shunt level plus a trip level representing a margin of signal energy above said shunt level such that a coded signal would be recognizable against an interference level equivalent to said shunt level.

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

(a) scanning an available radio spectrum;

(b) measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

(c) comparing the measurement to a prediction of interference on said portion of the scanned available radio spectrum stored in a memory location associated with the portion of the available radio spectrum;

(c1) performing, when said comparing step indicates the measurement exceeds at least one of the prediction and the prediction plus a trip level representing a margin of signal energy above said prediction such that a coded signal would be recognizable against an interference level equivalent to said prediction, the following steps,

(c1i) ceasing to scan the available radio spectrum, and

(c1ii) attempting to decode at least one of a preamble system code that modulates a carrier frequency in said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and a transmitter identifier transmitted on the modulated carrier frequency;

(c2) continuing, responsive to the measurement not exceeding at least one of the prediction and the prediction plus a trip level, to scan the available radio spectrum and returning to step (b);

(d) identifying whether the portion of the scanned available radio spectrum measured in step (b) failed to provide a recognizable preamble system code and a transmitter identification matching an identification stored in said frequency agile receiver;

(e) generating, responsive to said portion of the scanned available radio spectrum failing to provide a recognizable preamble system code and a transmitter identification matching an identification stored in said frequency agile receiver, using at least one of the measurement, history of said portion of the scanned available radio spectrum and other information regarding said portion of the scanned available radio spectrum, a prediction of a level of interference signal energy, within the portion of the scanned available radio spectrum, expected in a future scan of said available radio spectrum by said frequency-agile receiver; and

(f) updating, responsive to said generating step, the prediction in a memory location associated with the portion of the scanned available radio spectrum.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating, using the measurement, a prediction of a level of interference signal energy, within the portion of the scanned available radio spectrum, expected in a future scan of said available radio spectrum by said frequency-agile receiver;

storing the prediction in a memory location associated with the portion of the scanned available radio spectrum;

avoiding, responsive to the stored prediction, future scans of said portion of the scanning available radio spectrum if the prediction indicates interference signal energy exceeding an interference signal energy threshold;

attempting to decode at least one of a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and a transmitter identifier; and

decoding, responsive to decoding of a preamble system code and transmitter identification, at least one of voice modulation and data transmitted on said carrier frequency.

8. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a transmitter information messages on a plurality of frequencies, comprising the steps of:

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating, using at least one of the measurement and other information regarding said portion of the scanned available radio spectrum, a prediction of a level of interference signal energy within the portion of the scanned available radio spectrum expected in a future scan of said available radio spectrum by said frequency-agile receiver, the prediction, responsive to an average level of interference signal energy remaining constant, including at least one of an average prediction and an average signal shunt level representing previous predictions of interference signal energy; and

storing the prediction in a memory location associated with the portion of the scanned available radio spectrum.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating, using at least one of the measurement and other information regarding said portion of the scanned available radio spectrum, a prediction of a level of interference signal energy within the portion of the scanned available radio spectrum expected in a future scan of said available radio spectrum by said frequency-agile receiver, the prediction, responsive to at least one of amplitude variation and speed of variation in the level of interference signal energy, including at least one of a prediction and a shunt level representing previous interference predictions which approximates the level of interference signal energy on said portion of the scanned available radio spectrum; and

storing the prediction in a memory location associated with the portion of the scanned available radio spectrum.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating using at least one of the measurement and other information regarding said portion of the scanned available radio spectrum, a prediction of a level of interference signal energy, within the portion of the scanned available radio spectrum, expected in a future scan of said available radio spectrum by said frequency-agile receiver, the prediction, responsive to the measurement falling within a specified hysterisis range of plus or minus a signal energy level encompassing a previous interference signal energy prediction, including an average of past readings from the portion of the scanned available radio spectrum; and

storing the prediction in a memory location associated with the portion of scanned available radio spectrum.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

generating using at least one of the measurement and other information regarding said portion of the available radio spectrum, a prediction of a level of interference signal energy within the portion of the scanned available radio spectrum expected in a future scan of said available radio spectrum by said frequency-agile receiver, the prediction, responsive to the measurement falling within a specified hysterisis range of plus or minus a signal energy level encompassing a previous interference signal energy prediction, including a value equal to the present measurement; and

storing the prediction in a memory location associated with the portion of the scanned available radio spectrum.

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

scanning an available radio spectrum;

measuring, in a portion of the scanned available radio spectrum, at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

comparing the measurement to a threshold stored in a memory location associated with the portion of the scanned available radio spectrum, the threshold including at least one of a shunt level representing an interference prediction and shunt level plus an adaptive trip level representing an amount of signal energy;

ceasing, responsive to the measurement exceeding the threshold, to scan the available radio spectrum; and

attempting to decode at least one of a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system, a transmitter identifier, voice modulation, and data.

21. The method as set forth in claim 4, 6, 12, 13, 14, 15, 17 or 19, further including the steps of:

accepting a preamble system code as matching that of said frequency-agile receiver; and

comparing successive remaining repetitions of the preamble system code to continue verifying a correct match.

22. The method as set forth in claim 4, 6, 12, 13, 14, 15 or 19 further including the steps of:

comparing successive remaining repetitions of a preamble system code to continue verifying a correct match; and

verifying that a system code identifying a specific receiver matches a system code of said frequency-agile receiver.

23. The method as set forth in claim 4, 6, 12, 13, 14, 15 or 19 further including the steps of:

comparing successive remaining repetitions of a preamble system code to continue verifying a correct match; and

verifying that a transmitted ID code identifying said transmitter matches a sub-group of desired transmitter IDs.

26. The method as set forth in claim 4, 7, 8, 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

identifying a segment of the available radio spectrum as occupied;

marking the segment of the available radio spectrum as occupied; and

avoiding, responsive to the segment of the radio spectrum being marked as occupied, the segment of the radio spectrum.

27. The method as set forth in claim 26, wherein the step of identifying utilizes at least one of percent data throughput indicating a percentage of successfully received and decoded messages at a previous trip level, shunt level, attack variables that predict a rate of increase in interference signal level, and decay variables that indicate an amount of decrease in interference signal level.

28. The method as set forth in claim 26 wherein the step of avoiding the occupied portion of the radio spectrum includes the step of avoiding the occupied portion of the radio spectrum by at least one of skipping over and blanking and utilizing wider band width filters and discharging the energy storing elements of either a most narrow bandwidth IF filter or a most narrow bandwidth baseband filter.

41. The method as set forth in claim 12, 13, 14, 15, 17, 18 or 19, further including the steps of:

generating, using a present measurement and historical information derived from past measurements, a prediction of a level of interference signal energy, within a portion of the available radio spectrum; and

updating the prediction in a memory location associated with the portion of the available radio spectrum.

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

(a) selecting one of a bank of chirp filters to filter incoming signals and having a bandwidth matching said incoming signals while scanning an available radio spectrum;

(b) receiving a signal limited in bandwidth by the selected chirp filter on a portion of the scanned available radio spectrum;

(c) measuring at least one of signal strength and quieting and signal lock quality as a measurement of the received signal;

(c1) performing, when said measurement exceeds at least one of a shunt level representing an interference prediction and a shunt level plus a trip level representing an amount of signal energy, the following steps;

(c1i) ceasing to scan the available radio spectrum;

(c1ii) selecting at least one of an intermediate frequency (IF) filter and a baseband filter having a bandwidth similar to a bandwidth of the received signal; and

(c1iii) attempting to decode at least one of data and voice and a preamble system code that modulates a carrier freguency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and a transmitter identifier transmitted on said carrier frequency from the received signal passed through the selected IF or baseband filter.

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

(a) scanning an available radio spectrum;

(b) receiving a signal having transmitted data on said scanned available radio spectrum;

(c) selecting a filter with a bandwidth greater than that of the transmitted data and filtering the received signal with the selected filter;

(d) measuring at least one of signal strength and quieting and signal lock quality as a measurement of the received signal passed through said selected filter;

(e1) performing, when said measurement exceeds at least one of a shunt level representing an interference prediction and a shunt level plus a trip level representing an amount of signal energy, the following steps;

(e1i) ceasing to scan the available radio spectrum;

(e1ii) selecting at least one of an IF filter and a baseband filter having a bandwidth similar to a bandwidth of the transmitted data; and

(e1iii) decoding at least one of data and voice modulation and a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and a transmitter identifier transmitted on said carrier frequency from the received signal passed through the selected IF or baseband filter.

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

generating a local oscillator frequency;

selecting a next frequency to be received and adjusting said oscillator frequency by processor means to output a frequency equivalent to said next frequency;

reading a shunt level representing an interference prediction associated with the next frequency from a table stored in memory means;

outputting at least one of the shunt level and a portion of the shunt level to an automatic gain control (AGC) circuit to control gain of signals received at said next frequency;

measuring at least one of receiver signal strength and quieting and signal lock quality, as a measurement;

comparing the measurement to a threshold; and

decoding, responsive to the measurement exceeding the threshold, at least one of a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and voice and data and a transmitter identifier.

16. The method as set forth in claim 15, wherein the step of comparing the threshold includes the step of comparing the threshold to at least one of a trip level representing an amount of signal energy, and a shunt level representing an interference prediction less the portion of the shunt level output to the AGC circuit, and a shunt level plus a trip level less the portion of the shunt level output to the AGC circuit.

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

scanning an available radio spectrum;

reading a shunt level representing an interference prediction associated with a portion of the scanned available radio spectrum from a table stored in memory means;

outputting at least one of the shunt level and a portion of the shunt level to an automatic gain control (AGC) circuit to control gain of signals received at said portion of the scanned available radio spectrum;

measuring at least one of receiver signal strength and quieting and signal lock quality, of said portion of the scanned available radio spectrum, as a measurement;

comparing the measurement to at least one of a trip level representing an amount of signal energy, a shunt level less the portion of the shunt level output to the AGC circuit, and a shunt level plus a trip level less the portion of the shunt level output to the AGC circuit; and

decoding, responsive to the measurement exceeding the at least one of a trip level, a shunt level less the portion of the shunt level output to the AGC circuit, and a shunt level plus a trip level less the portion of the shunt level output to the AGC circuit, at least one of a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to particular system and voice modulation and data and a transmitter identifier transmitted on said carrier frequency.

18. A method, using a frequency-agile receiver in a frequency-agile radio system, for receiving signals from a transmitter transmitting information messages on an imperfectly known frequency, comprising the steps of:

scanning an available radio spectrum;

reading a shunt level representing an interference prediction associated with a portion of the scanned available radio spectrum from a table stored in memory means;

outputting at least one of a shunt level and a portion of the shunt level to an automatic gain control (AGC) circuit to control gain of signals received at said portion of the scanned available radio spectrum;

measuring at least one of receiver signal strength and quieting and signal lock quality, at said portion of the scanned available radio spectrum as a measurement;

comparing the measurement to at least one of a trip level representing an amount of signal energy, a shunt level less the portion of the shunt level output to the AGC circuit, and a shunt level plus a trip level less the portion of the shunt level output to the AGC circuit; and

decoding, responsive to the measurement exceeding the at least one of a trip level, a shunt level less the portion of the shunt level output to the AGC circuit and a shunt level plus a trip level less the portion of the shunt level output to the AGC circuit, at least one of a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and voice modulation and data and a transmitter identifier transmitted on said carrier frequency.

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

generating a local oscillator frequency by processor means;

selecting a-next frequency to be received and adjusting said local oscillator by processor means to output a frequency equivalent to said next frequency;

reading a shunt level representing an interference prediction associated with the next frequency from a table stored in memory means;

disabling, responsive to the shunt level exceeding a level equal to an attenuation caused by disabling a gain stage of said frequency-agile receiver plus a signal level required to establish a carrier-to-noise ratio to achieve a desired bit error rate (BER), a gain stage of said frequency-agile receiver;

measuring at least one of receiver signal strength and quieting and signal lock quality, of said next frequency, as a measurement;

comparing the measurement to at least one of a shunt level less the attenuation, and a shunt level plus a trip level representing an amount of signal energy less the attenuation; and

decoding, responsive to the measurement exceeding at least one of a shunt level less the attenuation, and a shunt level plus a trip level less the attenuation, at least one of a preamble system code that modulates a carrier frequency within said portion of the scanned available radio spectrum and identifies a transmitter as belonging to a particular system and voice modulation and data and a transmitter identifier transmitted on said carrier frequency.