Ranging by sequential tone transmission

• US 5,220,332 A
• Filed: 05/04/1992
• Issued: 06/15/1993
• Est. Priority Date: 05/04/1992
• Status: Expired due to Fees

• Current Assignee: Cyberdynamics, Inc.
• Original Assignee: Cyberdynamics, Inc.
• Inventors: Ingram, Darrell K., Beckner, Frederick L.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/877,869
• Time in Patent Office: 407 Days
• Field of Search: 342/125, 342/50, 342/127
• US Class Current: 342/125
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement

Abstract

A range finding system uses non-simultaneous measurements between two communicating and cooperating instruments such that a single carrier frequency is used to exchange information between the instruments with non-simultaneous transmission using the same transmission channel. The range finding system may be considered to be an interrogator/transponder arrangement in which the results of a phase measurement against a local clock is made at one transponder station during one time interval, and then the transponder transmits both a tone derived from the transponder'"'"'s local clock and the measurement results back to the interrogator station during a second time interval. The interrogator then has everything it needs to accurately compute the range while eliminating local delays in clock differences, while permitting the interrogator and the transponder to share a single frequency intermittently.

Claims

1. A method for measuring the distance between two cooperating instruments, Unit A and Unit B, which compute range by using non-simultaneous signals and measurements, comprising the steps:

transmitting from Unit A on a predetermined carrier frequency a first time or phase modulation signal derived from the local time or phase reference of Unit A;

receiving the first modulated carrier signal at Unit B and recovering the time or phase reference signal of Unit A;

performing a sequence of measurements at Unit B on either the time of arrival of the modulated carrier signal relative to a local clock at Unit B or the phase of the modulated carrier signal relative to a local phase reference at Unit B;

storing the results of the Unit B measurements in a random access memory in Unit B;

after a predetermined time sufficient to allow the sequence of measurements to be made at Unit B, terminating the transmission of the modulated carrier signal from Unit A;

transmitting from Unit B on the same predetermined carrier frequency a second time or phase modulation signal derived from the local time or phase reference of Unit B;

receiving the second modulated carrier signal at Unit A and recovering the time or phase reference signal of Unit B;

performing a sequence of measurements at Unit A on either the time of arrival of the second modulated carrier signal relative to a local clock at Unit A or the phase of the second modulated carrier signal relative to a local phase reference at Unit A;

storing the results of the Unit A measurements in a random access memory in Unit A;

after a predetermined time sufficient to allow the sequence of measurements to be made at Unit A, terminating the transmission of the second modulated carrier signal from Unit B;

transmitting the results stored in Unit B to Unit A on the same predetermined carrier frequency; and

,

computing the range from Unit A to Unit B as a function of the two sets of stored measurements, those made by Unit B relative to Unit B'"'"'s local time or phase reference and the measurements made by Unit A relative to its own local time or phase reference.

2. A method for measuring the distance between two cooperating instruments, Unit A and Unit B, which compute range by using non-simultaneous signals and measurements, comprising the steps:

transmitting a first range tone from Unit A to Unit B;

receiving the first range tone at Unit B;

measuring and storing the phase of the first range tone relative to a second range tone W2;

transmitting the second range tone from Unit B to Unit A;

receiving the second range tone at Unit A;

measuring and storing the phase of the second range tone relative to the first range tone;

transmitting the stored phase measurements in Unit B to Unit A;

receiving in Unit A the stored phase measurements from Unit B;

storing the phase measurements received from Unit B in Unit A; and

,

computing the range from Unit A to Unit B as a function of the two sets of stored phase measurements.

3. A method for measuring the distance between an interrogator and a transponder comprising the steps:

transmitting from the interrogator on a predetermined carrier frequency a first time or phase modulation signal derived from the local time or phase reference of the interrogator;

receiving the first modulated carrier signal at the transponder and recovering the time or phase reference signal of the interrogator;

comparing the results of the time or phase reference measurement against a local clock at the transponder station during one time interval;

transmitting a tone derived from the transponder'"'"'s local clock or phase reference and the measurement results back to the interrogator station during a second time interval; and

,

computing the range from the interrogator to the transponder by processing the two sets of measurements, those made by the transponder relative to the transponder'"'"'s local time or phase reference, and those made by the interrogator relative to its own local time or phase reference.

4. A method for measuring the distance between two cooperating instruments, Unit A and Unit B, which compute range by using non-simultaneous signals and measurements, comprising the steps:

transmitting from Unit A a message packet of serial data containing a request for measured data and the identification code of the transponder unit from which a response is desired;

after transmitting the digital data packet, transmitting from the interrogating unit a sequence of one or more fixed frequency tones during a fixed time interval;

comparing the reference frequency of the responding unit with the received range tone signal;

commanding a frequency correction to the reference source to reduce the received frequency error within a predetermined tolerance value;

performing a series of phase measurements on the received range tone relative to the transponder'"'"'s local reference;

after a predetermined time interval from reception of the identification code, switching the responding unit from measure phase mode to send range tone mode;

sending a sequence of range tones from the responding unit for a predetermined period of time during which the interrogating unit receives the range tones and makes a sequence of phase measurements relative to its local reference;

storing the measurements in a random access memory in the interrogating unit;

transmitting the stored phase measurements and calibration data from the responding unit to the interrogating unit; and

,

processing the phase and calibration data in the memory of the interrogating unit to yield the distance from Unit A to Unit B.