System for direction determination

• US 5,990,833 A
• Filed: 11/14/1997
• Issued: 11/23/1999
• Est. Priority Date: 11/15/1996
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Ahlbom, Sten, Andersson, Bengt
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/970,752
• Time in Patent Office: 739 Days
• Field of Search: 342/378, 342/417, 342/444, 367/125, 367/124
• US Class Current: 342/417
• CPC Class Codes: G01S 3/50 the waves arriving at the antennas being pulse modulated and the time difference of their arrival being measured
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 7/021 Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals

Abstract

System for determining the position of radar transmitters where the system includes at least one information center with associated cells and means of communication between the information center and the cells with a restricted transfer rate utilising existing infrastructure in the country, such as for example a national telephone network and also mobile telephone networks and their base stations. Each cell includes at least one sensor in order to be able to detect radar signals. Leading edges of pulses in the radar signals are detected and time-marked after which they are sorted according to PRI (Pulse Repetition Interval). The time of arrival for the first pulse in a pulse train is calculated and data reduced by modulo calculation to a value that as a maximum is the propagation time difference for pulses between two cells in a pair of cells/sensors that are used together for calculating the bearing. Bearings calculated from at least two pairs of cells are correlated in the information center which thereafter calculates the position of the radar transmitter.

Claims

1. A method for the data reduction of times of arrival of radar signals'"'"' pulse trains detected by cells where the cells are included in a system for position determination as sub units to an information centre and where the pulse trains consist of a number of pulses, wherein the method comprises the following steps:

generating and marking a time window with a finite time extent;

calculating times of arrival for pulses in the time window relative to a start of the time window thereby deriving pulse arrival times;

calculating and associating with each pulse in the time window a pulse repetition interval estimate;

sorting pulses and their pulse arrival times into groups according to their respective pulse repetition interval estimates;

calculating a pulse repetition interval value per group based on the pulses sorted into groups,;

in each group successively reducing the pulse arrival times of the pulses in the group by the pulse repetition interval value corresponding to the group until all the pulse arrival times have a value between zero and the pulse repetition interval value corresponding to the group and thereby deriving data-reduced pulse arrival times;

in each group taking the average value of the data-reduced pulse arrival times per group and thereby deriving a calculated arrival time position per group;

successively reducing the calculated arrival time positions by a reducing value that exceeds the propagation time of the pulses between two cells in a pair of cells until the calculated arrival time position assumes a value that is greater than zero and less than the reducing value and thereby deriving a reduced arrival time position per group.

2. The method according to claim 1, wherein the method also comprises the following steps:

correlating reduced arrival time positions from two cells in a pair of cells at least based on the marking of the time windows;

calculating a bearing for the transmitter of the radar signals relative to the pair of cells based on correlated reduced arrival time positions.

3. The method according to claim 2, wherein the method also comprises the following steps:

correlating bearings calculated by different pairs of cells;

calculating by the information centre from at least two bearings that are correlated the position of the radar whose radar signals have been detected by cells.

4. The method according to claim 1, wherein the reduced arrival time position is sent to the information centre, for a bearing to be calculated, via existing public communication networks or other communication networks that are part of the total defence system.

5. The method according to claim 1, wherein the reduced arrival time position calculated in one of the cells of a pair of cells is sent to the other cell in the pair of cells for a bearing to be calculated and in that the calculated bearing for the pair of cells is sent to the information centre by the other cell via existing public communication networks or other communication networks that are part of the total defence system.

6. The method according to claim 1, wherein an initial sorting of the pulses according to pulse frequency and/or amplitude is carried out before the pulses are sorted into groups.

7. The method according to claim 2, wherein the correlation is also carried out using at least one of the parameters of the radar signals such as frequency, pulse length, coding or pulse repetition frequency.

8. A method for the data reduction of times of arrival of radar signals detected by cells, wherein time windows with a finite time extent are generated whereby times of arrival for radar signals detected in a time window are calculated relative to the start of the time window after which calculated arrival times are successively reduced by a reducing value until the calculated arrival times assume a value between zero and the reducing value.

10. The method according to claim 8, wherein the reducing value is greater than the maximum time of arrival difference that can arise when a radar signal is received by two cells in a pair of cells and less than the time extent of a time window.

11. The method according to claim 8, wherein an identity marking of the time window is carried out upon the generation of a time window where the identity marking is so that time windows generated in different cells can be associated with each other so that times of arrival from different cells can be correlated.

9. A method for the data reduction of times of arrival of radar signals detected by cells, wherein at least one time window with a finite time extent is generated whereby a time of arrival for a radar signal detected in the time window is calculated relative to the start of the time window after which the calculated arrival time is successively reduced by a reducing value until the calculated arrival time assumes a value between zero and the reducing value.

25. The method according to claim 9, wherein the reducing value is greater than the maximum time of arrival difference that can arise when a radar signal is received by two cells in a pair of cells and less than the time extent of a time window.

26. The method according to claim 9, wherein an identity marking of the time window is carried out upon the generation of a time window where the identity marking is so that time windows generated in different cells can be associated with each other so that times of arrival from different cell, can be correlated.

12. A system for determining the position of particular objects, objects that generate electromagnetic signals with a geographically limited and varying with time geographical extent, in an area where these objects can be detected using the electromagnetic signals that the objects generate, wherein the system comprises

at least one information centre equipped to receive information from sub units via information transfer,

at least four cells for each information centre in the system where these cells act as sub units to an information centre and where the cells are arranged in twos as pairs of cells, where each cell includes

at least one sensor for the detection of the said electromagnetic signals where the sensor comprises an aerial with associated receiver,

a real-time clock for the generation of time windows with a limited time extent,

means of recording times of arrival of pulses in a pulse train in the detected electromagnetic signals in relation to the start of the time windows,

means of calculating a pulse train arrival time from the recorded arrival times and data reducing the calculated pulse train arrival time by modulo calculation in order thereby to derive a data-reduced arrival time,

means of synchronising time windows between cells in a pair of cells,

and where the system is able to correlate data-reduced arrival times from cells in pairs of cells from characteristics of pulse trains, to calculate bearings from differences in correlated data-reduced arrival times, to correlate bearings calculated from data-reduced arrival times from different pairs of cells from absolute time and characteristics of the pulse trains and to thereafter calculate from correlated bearings the positions of the objects whose electromagnetic signals have been detected by cells in the system.

13. The system according to claim 12, wherein the said electromagnetic signals are within the radio frequency range and including radar signals.

14. The system according to patent claim 13, wherein the characteristics of the pulse trains includes at least one parameter out of either frequency, pulse length, coding or pulse repetition frequency.

15. The system according to claim 12, wherein the information transfer utilises existing public communication networks or other communication networks that are part of the total defence system and in that the data-reduced arrival times are transferred from the cells to their respective information centre by any of the said networks.

16. The system according to claim 12, wherein certain of the cells are able to be activated and deactivated from their information centre via the transfer of information.

17. The system according to claim 12, wherein the system comprises one or more groups where one or more cells are allocated into one of the said groups in accordance with particular criteria and where the criteria in accordance with which a cell is allocated into a certain group include one or more of the following:

the function of the cell, design of the cell, type of information transfer for the cell or geographical location of the cell.

18. The system according to claim 17, wherein each cell has a unique address code and in that each cell belonging to a group has a group address that is the same for all the cells belonging to the same group.

19. The system according to claim 12, wherein the cells are able to be provided with new parameters from an information centre, where these parameters define the object and form a basis for decisions made by the cell.

20. The system according to claim 12, wherein the cells include a number of different programs for function and decision-making and in that an information centre is able to choose to activate any of these via the transfer of information.

21. The system according to claim 12, wherein the cells are able to receive and store one or more new programs from an information centre.

22. The system according to claim 16, wherein one or more of the cells include means for two-way communication between an information centre and this cell or these cells.

23. The system according to claim 22, wherein one or more of the cells include means for one-way communication between an information centre and this cell or these cells, in addition to the means for two-way communication and in that the activation and deactivation of cells takes place via the one-way communication.

24. The system according to claim 23, wherein one or more of the cells include a power supply via batteries and/or solar cells and in that each individual cell of these cells goes into standby mode with low power consumption in order to save power while the cell is not activated.