Proximity detection using DPSK waveform

• US 5,627,526 A
• Filed: 09/30/1994
• Issued: 05/06/1997
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Belcher, Donald K., McBryde, Lamar G., Darby, Albert D. Jr.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Corrielus, Jean B.
• Application Number:
  US08/315,348
• Time in Patent Office: 949 Days
• Field of Search: 340/572, 340/573, 340/568, 340/531, 340/539, 340/825.49, 340/825.54, 340/825.31, 340/825.32, 340/825.69, 340/825.72, 340/941, 375/283, 375/258, 375/271, 342/419, 342/458
• US Class Current: 375/283
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G08B 21/02 Alarms for ensuring the safety of persons

Abstract

A method and system for determining whether a transmitting unit is proximate a receiving unit wherein the transmitting unit includes a magnetic field generator for a providing a plurality of time-sequential magnetic fields, each of the sequences being a differential phase shift key (DPSK) modulated code. The magnetic field is transmitted at a relatively interference free frequency of 72 KHz and the DPSK modulation frequency is about 1200 bits per second. Each pair of transmitting and receiving unit uses with a distinguishing code selected from a predetermined group of generally orthogonal codes.

Claims

1. A system for determining whether a first device is proximate a second device,

said first device comprising a magnetic field generator for providing a plurality of time-sequential magnetic fields, said plurality of fields comprising a differential phase shift key (DPSK) modulated code;

and

said second device comprising means for determining whether a predetermined number of repetitions of said code have been received within a predetermined period of time.

2. The system of claim 1 wherein said first device comprises a DPSK modulator for modulating said magnetic fields at a rate of about 1200 bits per second.

3. The system of claim 1 wherein said first device comprises a transmitter for transmitting said magnetic fields at a frequency of about 72 KHz.

4. The system of claim 1 wherein said second device comprises a receiver for receiving said magnetic fields at a frequency of about 72 KHz.

5. The system of claim 1 wherein said second device comprises a DPSK demodulator for demodulating said magnetic fields.

6. The system of claim 1 wherein each said code comprises a series of ten bits.

7. The system of claim 1 wherein said code is selected from a predetermined group of generally orthogonal codes.

8. The system of claim 7 wherein said group of generally orthogonal codes comprises:

space="preserve" listing-type="tabular">______________________________________ Code Number Code ______________________________________ 1 0000110111 2 0001011111 3 0001111001 4 0010101101 5 0011001101 6 0011010101 7 0011101011 8 0011111100 9 0100101101 10 0101010101. ______________________________________

9. The system of claim 8 wherein said group of generally orthogonal codes further comprises:

space="preserve" listing-type="tabular">______________________________________ Code Number Code ______________________________________ 11 0101100011 12 0110110010 13 1001110010 14 1010010011 15 1011100001 16 1101000110 17 1101010011 18 1101101111 19 1110001010 20 1111101110. ______________________________________

10. The system of claim 1 wherein said second device further comprises means for providing an alarm when less than the predetermined number of said code repetitions have been received within the predetermined period of time.

11. The system of claim 1 wherein said first device is carried by one of the members of the group consisting of an animal, person and object, so that the proximate location of the member of the group relative to the second device may be determined.

19. The method of claim 10 further comprising the step of providing an alarm when less than the predetermined number of said coded time-sequential magnetic fields have been received at the second device within the predetermined period of time.

12. A method of determining whether a first device is proximate a second device, the method comprising the steps of:

(a) generating plural time-sequential magnetic fields at the first device;

(b) differential phase shift key (DPSK) modulating the time-sequential magnetic fields in a code comprising a series of bits;

(c) transmitting said coded time-sequential magnetic fields from said first device repeatedly; and

(d) determining whether a predetermined number of the coded time-sequential magnetic fields have been received at the second device in a predetermined period of time.

13. The method of claim 12 wherein the DPSK modulation is at a rate of about 1200 bits per second.

14. The method of claim 12 wherein the magnetic fields are transmitted at a frequency of about 72 KHz.

15. The method of claim 12 wherein each code comprises a series of ten bits.

16. The method of claim 12 further comprising the step of selecting the code from a predetermined group of generally orthogonal codes.

17. The method of claim 16 wherein the group of generally orthogonal codes comprises:

space="preserve" listing-type="tabular">______________________________________ Code Number Code ______________________________________ 1 0000110111 2 0001011111 3 0001111001 4 0010101101 5 0011001101 6 0011010101 7 0011101011 8 0011111100 9 0100101101 10 0101010101. ______________________________________

18. The method of claim 15 wherein the group of generally orthogonal codes further comprises:

space="preserve" listing-type="tabular">______________________________________ Code Number Code ______________________________________ 11 0101100011 12 0110110010 13 1001110010 14 1010010011 15 1011100001 16 1101000110 17 1101010011 18 1101101111 19 1110001010 20 1111101110. ______________________________________

20. In a method of determining whether a first device is proximate to a second device, the improvement comprising the steps of:

(a) repeatedly transmitting a multi-bit code via a sequence of differential phase shift key (DPSK) modulated magnetic fields from the first device to the second device; and

(b) determining if less than a predetermined number of repetitions of the code are received at the second device in a predetermined period of time.