POSITION LOCATING SYSTEM

• US 3,774,215 A
• Filed: 11/23/1970
• Issued: 11/20/1973
• Est. Priority Date: 11/23/1970
• Status: Expired due to Term

• Current Assignee: Roger R. Reed
• Original Assignee: Roger R. Reed
• Inventors: Reed, Roger R.
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): McCabe, Denis H.
• Application Number:
  US05/092,017
• Time in Patent Office: 1,093 Days
• Field of Search: 343/15R,1ST,112D,112R 235/150.27
• US Class Current: 342/458
• CPC Class Codes: G01S 1/308 particularly adapted to Omega systems
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A position locating system for a vehicle with an onboard means for detecting differences in phase between a reference frequency and received radio-beacon navigation signals. Phase data representative of the detected phase differences is transmitted from the vehicle to a communication station which has associated therewith a central processing unit time shared with other communication stations for calculation of vehicle position from required phase data. The calculated position locates the vehicle in any of selectable reference frames requested by the vehicle and is compensated for local beacon signal propagation variations. Position data is transmitted back to the vehicle for indicating vehicle position. To accommodate a plurality of vehicles, transmission time at each communication station is time shared. To communicate with a station, a vehicle selects from a series of time blocks the strongest signal and consequently nearest station and seizes an idle time slot within that time block. Acknowledgement and synchronizing procedures insure accurate synchronization between station and vehicle and prevent vehicles from receiving each other'"'"''"'"'s data.

Claims

1. A position locating system for a plurality of movable vehicles operating in cooperation with a system of radio beacons transmitting phase synchronized signals comprising:

at least one communication station of known geographical position;

means for receiving radio beacon transmissions at each said vehicle;

a reference frequency source at each said vehicle;

means at each said vehicle for detecting the difference in phase between said reference frequency and a pLurality of received beacon signals over an interval;

said detecting means including means responsive to detected phase differences for developing data which in combination represents phase differences between said plurality of received beacon signals;

vehicle data transmission means at each said vehicle for transmitting said data representing the phase differences to one of said at least one communication station;

said data being in a form to permit transmission thereof in a substantially shorter time than said interval;

station receiving means at said at least one communication station for receiving vehicle phase data; and

means available to said at least one communication station for calculating at least one possible vehicle position corresponding to phase data received from each vehicle.

2. The position locating system of claim 1 further comprising:

station transmitting means at each of said communication stations for transmitting to a vehicle data representative of its calculated position; and

vehicle data receiving means at each of said vehicles for receiving position data and indicating the vehicle'"'"''"'"'s position therefrom.

3. The position locating system of claim 1 wherein the calculating means available to each said communication station comprises a time-shared central processing unit performing position calculations over a data link from phase data received at a plurality of said communication station.

4. The position locating system of claim 1 wherein at least some of said communication stations are further characterized by having:

means for receiving transmissions of said beacons;

means for detecting the phase relationship of said received beacon signals;

means for communicating the station detected phase relationship to said calculating means; and

said calculating means are adapted to compensate for propagation variations in said beacon transmissions as received at each said communication station and adapted to adjust for said propagation variations in the positions calculated from phase data received by that communication station.

5. The position locating system of claim 1 wherein said calculating means is adapted to calculate the position of each vehicle transmitting phase data in one of a plurality of selectable reference frames.

6. The position locating system of claim 5 wherein each said vehicle has means for selecting one of said plurality of reference frames for the calculation of position and for cummunicating the selection as a reference frame request data word to said calculating means via a communication station.

7. The position locating system of claim 6 wherein said means for selecting one of said plurality of reference frames comprises:

a plurality of reference frame indicating switches; and

means for composing said reference frame request data word representing the selected reference frame in response to the condition of each said reference frame indicating switch;

each said switch providing electrical conduction through a selectable contact which conduction causes said reference frame request data word to be composed.

8. The position locating system of claim 7 wherein:

each said communication station has means for transmitting data to a plurality of vehicles; and

said calculating means is adapted to cause transmission to a predetermined vehicle of a request for a selection of reference frame via a communication station and upon failure to receive a reference frame request data word from said predetermined vehicle is adapted to terminate communication with said predetermined vehicle and to notify said predetermined vehicle of said failure.

9. The position locating system of claim 1 further including means for resolving vehicle position ambiguity comprising:

means associated with said communication station for measuring the propagation delay between a communication station and one said vehicle from which the distance between said communIcation station and said vehicle can be estimated to define an approximate locus for each said vehicle consistent with a limited number of possible positions; and

means within said calculating means responsive to said measured propagation delay for eliminating as possible positions all possible positions inconsistent with said approximate locus.

10. The position locating system of claim 1 including means for resolving vehicle position ambiguity by selecting as each said vehicle'"'"''"'"'s exact known position the calculated position geographically closest to that vehicle'"'"''"'"'s last known position.

11. The position locating system of claim 10 wherein each said vehicle further comprises means for transmitting a current known position for that vehicle to said communication station whereby a last known position is established.

12. The position locating system of claim 1 wherein:

said calculating means is adapted to transmit alert messages in response to an alert condition to selected vehicles via a communication station; and

means are provided at each said vehicle to receive and indicate said alert messages.

13. The position locating system of claim 1 wherein said vehicle transmission means are adapted to transmit vehicle status data via a communication station to said calculating means to provide said calculating means with status data from a plurality of vehicles.

14. The position locating system of claim 1 wherein said vehicle means for transmitting phase data are further adapted to be activated periodically with an intervening inactive period.

15. The position locating system of claim 1 wherein said means for detecting phase differences further includes:

means for selectively inverting said reference adapted to maintain the phase of said reference at least 90* out of phase with each received beacon signal;

means for counting at a predetermined rate during the time when said selectively inverted reference and each received beacon signal are of the same given signs over a preset time period during reception of each received beacon signal to produce an accumulation of counts representing phase differences averaged over said preset time period; and

means for adjusting said accumulation of counts for the selective inversion of said reference with said phase data representing said adjusted accumulation of counts.

16. The position locating system of claim 15 wherein:

means associated with said communication station are provided for causing each said communication station to transmit a request for reference calibration data;

vehicle located means are provided for initiating a calibration period in response to a received request for reference calibration data;

said means for counting is adapted to count during said calibration period at said predetermined rate when said selectively inverted reference and received beacon signal are coincidentally of the same given signs over an interval defined by the first half of said preset time period and to count at said predetermined rate when said selectively inverted reference and received beacon signals are coincidentally of the opposite sign over an interval defined by the second half of said preset time period whereby the accumulated count during said calibration period deviates from a determined count by an amount indicative of long term reference frequency error;

said vehicle data transmission means is adapted to transmit the accumulated count during said calibration period;

said means for detecting phase differences is further characterized by being adapted to detect phase differences for a sequence of received beacon signals from different beacons with at least one set of at least two phase differences detected for the same beacon at different times, whereby differences in phase data for two measurements of the same beacon signal in conjunction with said calibration period accumulated count represents reference frequency error relative to the comMon frequency of said radio beacons; and

said means for calculating position is responsive to the difference in phase data for the same beacon signal and said calibration period accumulated count from each vehicle as received by a communication station to compensate for reference frequency error in the calculated position for each vehicle.

17. The position locating system of claim 1 wherein:

said means for detecting phase differences is adapted to detect phase differences for a sequence of received beacon signals from different beacons with at least one set of at least two phase differences detected for the same beacon at different times whereby differences in phase data for two measurements of the same beacon signal represent reference frequency error relative to the common frequency of said radio beacons; and

said means for calculating position is adapted to compensate for reference frequency drift determinable from the difference in phase data for each set of beacon signals.

18. The position locating system of claim 1 wherein said plurality of vehicles includes vehicles of at least two different classes with at least one of said classes having its data transmission means adapted for automatic periodic transmission of phase data representing phase differences to one of said communication stations with a substantial period between each automatic transmission.

19. The position locating system of claim 1 wherein:

said calculating means is further adapted to assign each of said communication stations a specific time block in a periodic communication plan;

each said time block being divided into a plurality of time slots with each time slot adapted for data communications between a communication station and a single vehicle;

each said vehicle data transmission means is adapted to seek assignment from said calculating means of an unused time slot associated with a nearby communication station for data exchange with that vehicle; and

said calculating means is adapted to assign a requested time slot to the requesting vehicle.

20. The position locating system of claim 19 wherein:

at least two classes of vehicles exist; and

said calculating means are further adapted to transmit indications of idle time slots via said communication stations with a further indication in each said idle time slot that it is available for communication with only one class of said vehicles with said idle time slots divided among the vehicle classes.

21. The position locating system of claim 20 wherein vehicle data transmission means of at least one class of said vehicles are adapted to count the number of idle time slots indicated for use by said at least one class in the time block of a nearby communication station after each transmission of phase data and to commence seeking assignment of an idle time slot for data transmission automatically after a preselected count of the idle time slots for that class of vehicles whereby said at least one class maintains automatic periodic data communication with a nearby communication station.

22. The position locating system of claim 20 wherein said calculating means is further adapted to terminate the assignment of each vehicle of at least one class during predetermined emergency conditions whereby all unterminated class vehicles may have all time slots available for their use during said predetermined emergency conditions.

23. The position locating system of claim 19 wherein:

said calculating means is further adapted to inhibit assignment of a specific time slot to a requesting vehicle and to terminate the assignment of any vehicle in the presence of noise, a weak signal and interference in that time slot as received by a communication station; and

each said data transmission means on each said vehicle is further adapted to randomly select another idle indicated time slot in that time block for subsequent transmission of a request for assignment after it is inhibited from being assigned aN idle indicated time slot.

24. The position locating system 23 wherein all data transmission is via FM modulation and all data reception is by hard-limiting FM detection.

25. The navigation system of claim 19 wherein:

said calculating means are adapted to transmit indications of idle time slots via said communication stations; and

said vehicle data transmission means are adapted to count the number of idle time slots in the time block of a nearby communication station after each transmission of phase data, and to commence seeking assignment of an idle time slot for data transmission automatically after a preselected count of the idle time slots.

26. A position locating system for a plurality of movable vehicles comprising:

at least one communication station of known geographical position;

a plurality of radio beacons phase synchronously transmitting the same precisely controlled common frequency signal during a portion of different time block assignments in a transmission cycle;

means for receiving radio beacon transmissions at each said vehicle;

a reference frequency source at each said vehicle;

means at each said vehicle for detecting the difference in phase between said reference frequency and a plurality of received beacon signals;

vehicle transmission means at each said vehicle for transmitting data representing the detected phase differences to one of said communications stations and for transmitting a communication request;

station transmitting means at each said communication station for transmitting data;

station receiving means for receiving data transmissions from said vehicles;

vehicle receiving means at each said vehicle for receiving data transmitted by communication stations;

first and second means respectively associated with said vehicles and said communication stations for controlling the data transmitting and receiving means respectively of said vehicles and said communication stations to provide two way communication between a vehicle and a communication station during one of a plurality of time slots in a periodic time block assigned to each communication station, and to assign a vehicle a time slot not then in use whenever that vehicle requests communication;

said means controlling said vehicle receiving and transmitting means being adapted to cause transmission from said vehicle only in its assigned time slot and to establish the time of its assigned time slot in predetermined relationship with the time of receipt of data at a vehicle;

means available to each said communication station for measuring the time of reception of data relative to its time for transmission, said time of reception representing the propagation delay between said communication station and each vehicle communicating with it; and

means available to each said communication station for calculating a vehicle position corresponding to phase data received from each vehicle at a communication station and corresponding to the time of reception of data from that vehicle indicative of the distance between the communicating vehicle and communication station.

27. A time shared system for locating the position of a plurality of vehicles by comparing signals received at each vehicle from a plurality of radio beacons on a common frequency comprising:

a plurality of communication stations at known geographical positions, said communication stations having data transmitters and receivers on at least one assigned frequency;

means at each said vehicle for data receiving and transmitting on said at least one frequency assigned to said communication stations;

said plurality of communication stations being subdivided into groups of at least one station each with each said group having assigned to it a unique block of time in a periodic transmission time plan which block differs from the block of time assigned to all stations in other groups;

each time block being subdivied into sequenTial time slots with each slot adapted for time-shared data communications between a single communication station and a single vehicle;

each station of a given group being geographically positioned to provide an area of communication coverage at any point within which a vehicle is within interference free data communication distance of a nearby communication station via said data transmitters and receivers;

means available to each communication station for causing it to transmit an idle indication in each time slot not used in data exchange with a vehicle;

means at each said vehicle for transmitting a vehicle identifier in an idle time slot of a block assigned to a nearby communication station in order to seek assignment of said idle time slot;

means available to each said communication station for causing it to respond to a vehicle'"'"''"'"'s transmitted identifier in an idle indicated time slot to assign that time slot for data communication with that vehicle and to retransmit in that time slot an acknowledgement of assignment of that time slot to that vehicle so identified, each acknowledgement being unique to the vehicle acknowledged;

a reference frequency source at each said vehicle having a frequency substantially equal to the common frequency of said beacons;

means at each said vehicle for receiving said radio beacons and for detecting the difference in phase between said reference frequency and received beacon signals;

means at each said vehicle for detecting acknowledgement of time slot assignment and for transmitting in its assigned time slot phase data representing phase differences detected at said vessel;

means available to each said communication station for calculating vehicle position in response to phase data transmitted by each said vehicle and received by said communication station; and

means for transmitting via a communication station position data representing the calculated position of each said vehicle in the corresponding time slot assigned to each said vehicle.

28. The time shared system for locating the position of a plurality of vehicles according to claim 27 wherein:

each of said vehicle receiving means are adapted to respond only to the strongest received block in said transmission time plan for seeking time slot assignment;

each of said communication stations is adapted to transmit a synchronizing signal at the start of its assigned time block;

means are provided at each of said vehicles responsive to said synchronizing signal in the most strongly received time block for identifying the beginning of that time block assigned to the station with which it is to communicate; and

said means for transmitting in the assigned time slot of each of said vehicles is further characterized by having;

means for registering the number of time slots between said synchronizing signal and its assigned time slot;

means for counting the number of time slots after each synchronizing signal until the count corresponds to the registered number; and

means for transmitting and receiving data only during that time slot occuring when the count corresponds to the registered number.

29. The time shared system for locating the position of a plurality of vehicles according to claim 28 wherein:

said counting means is adapted to count in a predetermined phase synchronization with the data received by said receiving means at each said vehicle;

said communication stations have means for detecting the time of reception of data in each time slot relative to the time for transmission in each time slot at each said station, said time of reception representing range between said station and the corresponding vehicle; and

said calculating means is adapted to calculate position consistent with the range of each vehicle from the communication station selected for data communication in response to said time of reception of data at said communication station.

30. The time shared system For locating the position of a plurality of vehicles of claim 27 further comprising means for evicting a vehicle from an assigned time slot when proper data exchange with the vehicle in that time slot is impeded.

31. The time shared system for locating a plurality of vehicles of claim 27 wherein:

said data transmitters and receivers of said vehicles and stations operate on FM modulation and hard-limiting FM reception respectively;

said communication stations are so placed that signals transmitted from a vehicle can be received at more than one communication station due to traffic demands requiring close geographic placement of each station in the same group; and

each said communication station has means available to it to assign a time slot to a vehicle received by more than one communication station at only one station which is the nearest one to that vehicle;

the FM, hard-limiting characteristics of said data transmitters and receivers eliminating interference at or from other stations in the same group.

32. A time shared system for locating the position of a plurality of vehicles by comparing signals received at each vehicle from a plurality of radio beacons on a common frequency and for communicating the position of the vehicles to a vehicle dispatcher comprising:

a plurality of communication stations at known geographical positions, said communication stations having data transmitters and receivers on at least one assigned frequency;

means at each said vehicle for data receiving and transmitting on said at least one frequency assigned to said communication stations;

said plurality of communication stations being subdivided into groups of at least one station each with each said group having assigned to it a unique block of time in a periodic transmission time plan which block differs from the block of time assigned to all stations in other groups;

each time block being subdivided into sequential time slots with each slot adapted for time shared data communications between a single communication station and a single vehicle;

each station of a given group being geographically positioned to provide an area of communication coverage at any point within which a vehicle is within interference free data communication distance of a nearby communication station via said data transmitters and receivers;

means available to each communication station for causing it to transmit an idle indication in each time slot not used in data exchange with a vehicle;

means at each said vehicle for counting a preselected number of said idle indications in the time block of a nearby communication station;

means at each said vehicle for transmitting a vehicle identifier in the first idle time slot of the time block of said nearby communication station after said preselected number of said idle indications have been counted;

means available to each said communication station for causing it to respond to a vehicle'"'"''"'"'s transmitted identifier in an idle indicated time slot to assign that time slot for data communication with that vehicle and to retransmit in that time slot an acknowledgement of assignment of that time slot to that vehicle so identified, each acknowledgement being unique to the vehicle acknowledged;

a reference frequency source at each said vehicle having a frequency substantially equal to the common frequency of said beacons;

means at each said vehicle for receiving said radio beacons and for detecting the difference in phase between said reference frequency and said received beacon signals;

means at each said vehicle for detecting acknowledgement of time slot assignment and for transmitting in its assigned time slot phase data representing detected phase differences at said vehicle;

means at each said vehicle for recommencing the counting of said preselected number of said idle indications and for terminating data transmission after a preselected number of time slots in which data Is transmitted;

means available to each said communication station for calculating vehicle position in response to phase data transmitted by each said vehicle and received by said communication station;

means for storing each said calculated position and for providing indexing for said stored position data to identify the vehicle to which the position data applies;

means for receiving requests for specific vehicle position from a dispatcher; and

means for communicating to said dispatcher the stored position of the vehicle whose position said dispatcher requested.

33. The time shared system for locating the position of a plurality of vehicles of claim 32 wherein:

said means for receiving requests is adapted to receive messages from a dispatcher, each said message having at least one vehicle as addressee, and to cause transmission of said messages in the time slots assigned the said at least one vehicle addressed from the appropriate communication station;

each said vehicle has means for transmitting vehicle status messages in its assigned time slot and for detecting and displaying message data received in its assigned time block;

said means for receiving requests is further adapted to receive said vehicle status messages; and

said means for communicating is adapted to communicate to said dispatcher said vehicle status messages of each vehicle along with the stored position of that vehicle.

34. The position locating system of claim 1 further including:

means associated with said communication station for transmitting a message for one of said vehicles; and

means associated with said vehicles for receiving said transmitted message.

35. The position locating system of claim 34 wherein said message transmitting means includes:

means for transmitting an alarm message; and

said vehicle receiving means includes means for providing an indication of a received alarm message.