Direction finding and mobile location system for trunked mobile radio systems

• US 5,592,180 A
• Filed: 10/26/1994
• Issued: 01/07/1997
• Est. Priority Date: 08/20/1992
• Status: Expired due to Fees

• Current Assignee: Nexus 1994 Limited
• Original Assignee: Nexus1994 Limited
• Inventors: Harel, Haim, Peleg, Shimon, Meiman, Yehouda, Yokev, Hanoch
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US08/329,549
• Time in Patent Office: 804 Days
• Field of Search: 342/450, 342/457, 342/446, 342/460
• US Class Current: 342/450
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/043 Receivers
• CPC Class Codes: G01S 3/10 Means for reducing or compensating for quadrantal, site, or like errors
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04B 1/7156 Arrangements for sequence synchronisation
• CPC Class Codes: H04B 7/2681 Synchronisation of a mobile station with one base station
• CPC Class Codes: H04B 7/2693 Centralised synchronisation, i.e. using external universal time reference, e.g. by using a global positioning system [GPS] or by distributing time reference over the wireline network
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04L 5/0062 Avoidance of ingress interference, e.g. ham radio channels
• CPC Class Codes: H04L 5/0091 Signaling for the administration of the divided path
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 84/025 with acknowledge back capability
• CPC Class Codes: H04W 88/022 Selective call receivers

Abstract

A special mobile radio mobile, vehicle or personal location system is described where the system operates to locate any one of a the transmitters in an SMR system. The present invention operates by identifying the received signals, removing the modulation information to reconstruct a demodulated carrier and analyzing the carrier signals for multipath distortion. The multipath disruptions are removed to calculate the true incident angle of the transmitted signal at a base station. A plurality of base stations are used to simultaneously calculate the incident angle of the transmitted SMR signal and a central location calculates the most probable location of the transmitter based upon triangulation. The incident angle of the transmitted SMR signal at each base station is performed by calculating the phase differences of the incoming voice signal with phase ambiguity minimized by using a plurality of dipole antennas spaced at an irregular distance to eliminate phase ambiguity error.

Claims

1. A mobile radio location system, comprising:

a mobile radio having a unique identifier, and having a transmitter for sending a message on one or more selected frequency channels selected from a set of available frequency channels and for coordinating selection of the one or more selected frequency channels on a control channel;

a first base station having a first array of irregularly spaced antennas operable for receiving the message on the one or more selected frequency channels, operable for receiving control information on the control channel and capable of determining a first direction of origin of the message by phase differences measurements on the array of irregularly spaced antennas using interferometric direction finding;

a second base station having a second array of irregularly spaced antennas operable for receiving the message on the one or more selected frequency channels, operable for receiving control information on the control channel and capable of determining a second direction of origin of the message by phase differences measurements on the second array of irregularly spaced antennas using interferometric direction finding; and

a central station connected to the first base station and the second base station, and operable for;

1.) receiving the first direction of origin of the message from the first base station;

2.) receiving the second direction of origin of the message from the second base station;

3.) triangulating the first direction with the second direction to determine the location.

2. The special mobile radio location system according to claim 1 wherein a reference station operates periodically to transmit a reference signal of known origin and location to calibrate the first and second base stations and the central station.

3. The special mobile radio location system according to claim 1 wherein the first base station and the second base station both include a reference antenna such that the phase difference of the one or more selected channel frequencies between each antenna of the array of irregularly spaced antennas and the reference antenna is determined.

7. The mobile location system according to claim 1 wherein the central site received the most probable values from the first and second base stations and applies a spatial filter to only use the most probable values which lie within a preselected distance of the average location of all most probable values.

4. A special mobile radio location system, comprising:

a special mobile radio having a unique identifier, and having a transmitter for sending a message on one or more selected frequency channels selected from a set of available frequency channels and for coordinating selection of the one or more selected frequency channels on a control channel;

a first base station having an array of irregularly spaced antennas operable for receiving the message on the one or more selected frequency channels, operable for receiving control information on the control channel and capable of determining a first direction of origin of the message;

a second base station also having an array of irregularly spaced antennas operable for receiving the message on the one or more selected frequency channels, operable for receiving control information on the control channel and capable of determining a second direction of origin of the message;

a central station connected to the first base station and the second base station, and operable for;

1.) receiving the first direction of origin of the message from the first base station;

2.) receiving the second direction of origin of the message from the second base station;

6. The mobile location system according to claim 4 wherein the first base station and the second base station both generate a histogram of the probable values and sending the two most probable values to the central station.

5. ) triangulating the first direction with the second direction to determine the location;

and

wherein the first base station and the second base station both operate to reduce the ambiguity of the direction of arrival of the incoming signal by calculating a multidimensional ambiguity space having lines indicating the only possible angles of the direction of arrival of the signal and determining the probable points of these lines which are closest to the observed value.

8. A method of locating a trunked mobile transmitter, comprising the steps of:

a.) receiving at a first base station a trunked radio frequency signal on a plurality of irregularly spaced antennas;

b.) removing the modulation information to produce a demodulated radio frequency carrier signal;

c.) calculating the observed angle of arrival of the demodulated radio frequency carrier signal by comparing the phase difference of the demodulated radio frequency carrier signal between pairs of the plurality of irregularly spaced antennas;

d.) determining the most probable angle of arrival of the demodulated radio frequency carrier signal by comparing the observed angle of arrival to ambiguity lines in an n-dimensional space where the number of antennas is n+1;

e.) repeating steps a.-d. for each of a plurality of base stations to produce a plurality of most probable angles of arrivals;

f.) calculating an histogram of the plurality of most probable angles of arrivals and selecting the strongest most probable values; and

g.) applying a spatial filter to the strongest most probable values from each base station and selecting the location based on the closest grouping of the strongest most probable values.