Radio frequency error detection and correction system

• US 5,249,305 A
• Filed: 05/28/1991
• Issued: 09/28/1993
• Est. Priority Date: 09/27/1989
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Mansfield, Terry K., Zdunek, Kenneth J., Wieczorek, Alfred B., Rozanski, Walter J. Jr., Lynk, Charles N. Jr.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): PHAM, CHI H
• Application Number:
  US07/705,875
• Time in Patent Office: 854 Days
• Field of Search: 455/51.1, 455/54.1, 455/54.2, 455/67.1, 455/68-71, 455/75, 455/76, 455/88, 455/183, 455/260, 371/32, 375/97, 375/107, 375/109, 375/111
• US Class Current: 455/517
• CPC Class Codes: H04B 1/405 with multiple discrete channels
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising

Abstract

A radio communication system including a control station and at least one remote station (20) is provided. The control station has a receiver for receiving radio signals, a transmitter for transmitting radio signals and a demodulator for measuring the frequency of the received signals. Responsive to a request for frequency measurement received from the receiver, the control station also has an error signal encoder to provide an error feedback signal containing the polarity and magnitude of the frequency difference for transmission by the transmitter. At least one remote station (20) has a receiver (25), a transmitter (26), a frequency controller (46), an encoder for encoding the request for frequency measurement and for actuating the transmitter (26) to transmit the request, and a decoder (34), responsive to the received error feedback signal for adjusting the frequency control.

Claims

1. A radio communication system comprising:

a control station comprising;

receiver means for receiving radio signals having a frequency error;

transmitter means for transmitting radio signals;

internal frequency reference means to provide a known proper frequency reference;

frequency measuring means for measuring said received signals to produce a signal indicative of the average frequency received;

an analog to digital converter and an arithmetic logic unit for converting said signal indicative of the average frequency received into a first digital word;

memory means for storing a second digital word representing said known proper frequency reference;

logic means for comparing said first and second digital words to result in a third digital word having a sign and magnitude representing a frequency difference between said average frequency received and said known frequency reference; and

error signal encoder means to provide a feedback error signal including said third digital word representing the polarity and magnitude of the frequency error for transmission by said transmitter means, responsive to said frequency measuring means; and

at least one of a plurality of remote stations comprising;

transmitter means for transmitting radio signals having said frequency error;

a frequency synthesizer for providing a local oscillator output to said receiver and transmitter means;

a reference oscillator having a reference frequency for driving said frequency synthesizer;

receiver means for receiving said feedback error signal; and

a digital to analog (D/A) converter, responsive to said feedback error signal, for adjusting said reference oscillator to correct for said polarity and magnitude of the frequency error.

2. The radio communication system of claim 1 wherein said least one of said plurality of remote stations further comprises means for encoding and actuating said transmitter means to transmit a request for frequency measurement.

3. The radio communication system of claim 1 wherein said error signal encoder means detects a pre-determined limit of correction being reached when a correction needed is too large to be corrected and provides a disable signal for transmission by said transmitter means to disable transmission by said remote station in response thereto.

4. The communication system of claim 3, wherein at least one of said plurality of remote stations further comprises an alert means for generating a distinct signal in response to receiving said disabling signal.

5. The communication system of claim 1, wherein said control station further comprises a signal strength detector means for determining a transmission quality of said received signals.

6. The communication system of claim 1, wherein said at least one of said plurality of remote stations further comprises:

a reference memory for storing a fourth digital word representing a frequency reference, said frequency reference containing said frequency error, said fourth digital word for controlling said reference frequency of said reference oscillator.

7. The radio communication system of claim 1, wherein said control station comprises:

said logic means measuring said frequency difference between said known frequency reference and said average frequency received, said average frequency received related to said local oscillator output of at least one of said remote stations; and

wherein said at least one of said plurality of remote stations comprises;

said digital to analog (D/A) converter, responsive to said third digital word for generating an output voltage having a polarity and magnitude indicative of said difference, and means for applying a control output voltage to control said reference frequency of said reference oscillator.

8. The communication system of claim 7, wherein said at least one of said plurality of remote stations further comprises:

control logic means for programming said fourth digital word and storing said fourth digital word in said reference memory which is used for controlling said reference frequency; and

said reference oscillator comprising a voltage controlled oscillator (VCO) for receiving said control output voltage to control said reference frequency.

9. The communication system of claim 1, wherein

said logic means measuring said difference between said known frequency reference and said average frequency received, said average frequency received is related to said local oscillator output of said frequency synthesizer for at least one of said remote stations to transmit said radio signals.

10. The communication system of claim 1, wherein said frequency measuring means comprises:

a master oscillator coupled to said receiver means; and

frequency shift keying (FSK) averaging means, responsive to an output of said master oscillator of said control station, for producing said signal indicative of the average frequency received.

11. An addressable remote station for use in a communication system having a control station, said remote station comprising:

controllably tuned transmitter means, having a transmit frequency, for transmitting an radio frequency signal at said transmit frequency;

controllably tuned receiver means, having a receive frequency, for receiving radio frequency signal transmissions at said receive frequency;

a frequency synthesizer for providing said transmit frequency to said transmitter means and said receive frequency to said receiver means;

a reference oscillator having a reference frequency for driving said frequency synthesizer;

a reference memory for storing a first digital word representing a frequency reference for setting said reference frequency, said frequency reference containing a frequency error;

means for encoding a request for frequency measurement, coupled to said transmitter means, for generating and sending a frequency measurement request, including said frequency error, to said control station;

identification means, coupled to said transmitter means for generating and sending a predetermined identification signal in conjunction with said request signal; and

a digital to analog converter, coupled to said receiver means for receiving a transmitted error signal including a second digital word, representing the polarity and magnitude of the frequency error, from said control station and, in response thereto, controllably tuning said reference oscillator to correct for said polarity and magnitude of the frequency error.

12. A method of correcting a frequency of a remote station by a control station having receiving and transmitting means, the method comprising the steps of:

in said control station;

receiving radio signals having a frequency error and a request for frequency measurement;

providing a known proper frequency reference;

measuring said received signals to produce a signal indicative of the average frequency received;

converting said signal indicative of the average frequency received into a first digital word;

storing a second digital word representing said known proper frequency reference;

comparing said first and second digital words to result in a third digital word having a sign and magnitude representing a frequency difference between said average frequency received and said known frequency reference; and

transmitting a feedback error signal including said third digital word representating the polarity and magnitude of the frequency error of said error signal, responsive to the request for frequency measurement; and

in said remote station;

storing a fourth digital word representing a frequency reference, said frequency reference containing said frequency error;

converting, in a digital to analog converter, said fourth digital word into a control output voltage;

applying said control output voltage to a reference oscillator, having a reference frequency, to control said reference frequency of said reference oscillator;

synthesizing a transmit frequency relative to said reference frequency;

encoding said request for frequency measurement;

transmitting said request including said frequency error at said transmit frequency;

correcting said frequency reference, in response to said feedback error signal for adjusting said fourth digital word in relationship to said third digital word to provide a resultant word, and substituting said resultant word as a new fourth digital word representing said frequency reference, to correct for said polarity and magnitude of the frequency error;

converting, in said digital to analog converter, said new fourth digital word into a corrected control output voltage; and

applying said corrected control output voltage to said reference oscillator to adjust said reference frequency of said reference oscillator.

13. The method of claim 12 further comprising the steps of:

in said control station;

receiving identifying information in said radio signals;

determining a quality indication of said radio signals;

measuring said received signals if said quality indication is acceptable;

generating said third digital word, said feedback error signal including a correction command to said remote station to change said frequency reference of said remote station if said error does not exceed a limit of correction; and

transmitting identifying information of said remote station and said third digital word to said remote station.

14. The method of claim 13 wherein said generating step comprises the steps of:

comparing said frequency error in an error limit range; and

generating a disable code if said frequency error is greater than the maximum correctable frequency error in said error limit range.

15. The method of claim 13, comprising the steps of:

in said remote unit;

transmitting said request comprising an inbound signalling word (ISW), said ISW requesting frequency correction and providing its identification;

in said control station;

receiving said ISW to determine which remote station is requesting correction; and

transmitting said feedback error signal comprising an outbound signalling word (OSW) to said remote unit, said OSW constituting frequency correction information including said third digital word.

16. The method of of claim 12 further comprising the steps of:

matching a received address from said control station with the address of the remote station;

decoding said feedback error signal to provide a decoded feedback error signal; and

adjusting said fourth digital word in response to said decoded feedback error signal.

17. A radio communication calibration system for a control station comprising:

receiver means for receiving radio signals;

a known external calibration sourcing means for connecting to said receiver means to provide a known frequency reference to said control station;

frequency measuring means for measuring said known frequency reference to produce a signal indicative of the average frequency received;

an analog to digital converter and an arithmetic logic unit for converting said signal indicative of the average frequency received into a first digital word;

memory means for storing a second digital word representing a known proper frequency reference;

logic means for comparing said first and second digital words to result in a third digital word having a sign and magnitude representing a frequency difference between said average frequency received and said known frequency reference for providing an error signal;

logic means for detecting whether said third digital word is within an allowable limit;

encoder means to provide said first digital word, if said third digital word is within said allowable limit, for substituting said first digital word in said memory means as said second digital word representing said known proper frequency reference; and

transmitter means, connected to said logic means, for transmitting radio signals, if said third digital word is within said allowable limit.

18. A radio communication and calibration system comprising:

a control station comprising;

receiver means for receiving radio signals having a frequency error and for receiving a request for frequency measurement;

a known external calibration sourcing means, for connecting to said receiver means to provide a known frequency reference to said control station;

frequency measuring means for measuring one of a group, comprising said known frequency reference and said received signals, in response to said request, to produce a signal indicative of the average frequency received;

an analog to digital converter and an arithmetic logic unit for converting said signal indicative of the average frequency received into a first digital word;

memory means for storing a second digital word representing a known proper frequency reference;

first logic means for comparing said first and second digital words to result in a third digital word having a sign and magnitude representing a frequency difference between said average frequency received and said known frequency reference for providing an error signal;

second logic means for detecting whether said third digital word is within an allowable limit;

reference encoder means to provide said first digital word, if said third digital word is within said allowable limit, for substituting said first digital word in said memory means as said second digital word representing said known proper frequency reference; and

transmitter means, connected to said logic means, for transmitting radio signals, if said third digital word is within said allowable limit; and

error signal encoder means to provide a feedback error signal including a representation of the polarity and magnitude of the frequency error of said error signal for transmission by said transmitter means, responsive to said request for frequency measurement received from said receiver means and said frequency measuring means; and

at least one of a plurality of remote stations comprising;

transmitter means for transmitting said request;

frequency control means having a reference memory for storing a fourth digital word representing a frequency reference, said frequency reference containing said frequency error;

means for encoding said request for frequency measurement and for actuating said transmitter means to transmit said request including said frequency error;

receiver means for receiving said feedback error signal; and

frequency error correction means, responsive to said feedback error signal for adjusting said fourth digital word in said reference memory, in relationship to said third digital word, to provide a resultant word, and for substituting said resultant word in said reference memory as a new fourth digital word representing said frequency reference, to correct for said polarity and magnitude of the frequency error.

19. A control station comprising:

receiver means for receiving radio signals having a frequency error and for receiving a request for frequency measurement;

internal frequency reference means to provide a known proper frequency reference;

frequency measuring means for measuring said received signals to produce a signal indicative of the average frequency received;

an analog to digital converter and an arithmetic logic unit for converting said signal indicative of the average frequency received into a first digital word;

memory means for storing a second digital word representing said known proper frequency reference;

logic means for comparing said first and second digital words to result in a third digital word having a sign and magnitude representing a frequency difference between said average frequency received and said known frequency reference;

transmitter means for transmitting radio signals; and

error signal encoder means for providing a reference oscillator correction signal, said correction signal, including said third digital word representing the polarity and magnitude of the frequency error, for transmission by said transmitter means to a remote station, responsive to said request for frequency measurement received and responsive to said frequency measuring means.

20. A trunked radio communication system comprising:

a control station comprising;

receiver means for receiving radio signals having a frequency error and for receiving an inbound signalling word containing a request for frequency measurement;

an internal frequency reference means to provide a known proper frequency reference;

frequency measuring means for measuring said received signals to produce a signal indicative of the average frequency received;

an analog to digital converter and an arithmetic logic unit for converting said signal indicative of the average frequency received into a first digital word;

memory means for storing a second digital word representing said known proper frequency reference;

logic means for comparing said first and second digital words to result in a third digital word having a sign and magnitude representing a frequency difference between said average frequency received and said known frequency reference;

transmitter means for transmitting radio signals; and

error signal encoder means for encoding a responsive outbound signal word containing an error word having polarity and magnitude of frequency error information, for transmission by said transmitter means, in response to said inbound signalling word containing said request; and

at least one of a plurality of remote stations comprising;

transmitter means, having a transmit frequency, for transmitting said inbound signalling word at said transmit frequency;

a frequency synthesizer for providing said transmit frequency to said transmitter means;

a reference oscillator having a reference frequency for driving said frequency synthesizer;

a reference memory for storing a fourth digital word representing a frequency reference, said frequency reference containing said frequency error, said fourth digital word for controlling said reference frequency of said reference oscillator;

means for encoding said request for frequency measurement and for actuating said transmitter means to transmit said request in said inbound signalling word, said request including said frequency error;

receiver means for receiving said outbound signalling word;

control logic means, responsive to said outbound signal word for adjusting said fourth digital word, in said reference memory, in relationship to said error word, received from said control station, to provide a resultant word, and for substituting said resultant word in said reference memory as a new fourth digital word representing said frequency reference, to correct for said polarity and magnitude of the frequency error; and

a digital to analog (D/A) converter, responsive to said new fourth digital word, for adjusting said reference oscillator to correct for said polarity and magnitude of the frequency error.