Method and apparatus for identifying the source of a digital signal

• US 6,526,035 B1
• Filed: 06/09/1998
• Issued: 02/25/2003
• Est. Priority Date: 06/09/1998
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Östberg, Christer, Henningsson, Håkan, Atarius, Roozbeh, Eriksson, Håkan B.
• Primary Examiner(s): Kizou, Hassan
• Assistant Examiner(s): Elallam, Ahmed
• Application Number:
  US09/093,315
• Time in Patent Office: 1,722 Days
• Field of Search: 370/310, 370/313, 370/328, 370/331, 370/334, 370/342, 370/345, 370/350, 370/563, 370/569, 370/441
• US Class Current: 370/342
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence

Abstract

A receiver can identify the source of a signal from an unsynchronized source. The receiver has an antenna for receiving two signals. The receiver correlates the first signal with a code to find a first location in time, and correlates the second signal with the same code to find a second location in time. The receiver calculates a time difference between the first location in time and the second location in time and uses the time difference to identify the source of the two signals. A group of base stations or directional antennas use the same long code and synchronization codes. However, each source shifts the long code by a different amount so that for any two sources there is a unique difference between the shifts in the long code. Each source shifts a set of synchronization codes the same amount as the long code. The synchronization codes can be any short code that is relatively easy for the mobile station to detect. When the receiver receives the two signals, the receiver calculates the difference in the shifts. Because there is a unique difference for each pair of sources, the receiver can identify the source of a signal from an unsynchronized source without having to connect to the source to use a broadcast channel or control channel. The receiver can distinguish between different synchronized sources without any prior synchronization.

Claims

1. A receiver that can directly identify a source of a digital signal from an unsynchronized source, the receiver comprising:

an antenna, the antenna receiving a first signal and a second signal;

a first correlator, the first correlator correlating a code with the first signal to identify a first location in time of the code in the first signal;

a second correlator, the second correlator correlating the code with the second signal to identify a second location in time of the code in the second signal; and

,

a difference generator, the difference generator calculating a time difference between the first location in time of the code in the first signal and the second location in time of the code in the second signal, wherein the time difference identifies a pair of sources of the digital signal.

2. A receiver as described in claim 1, further comprising a memory unit, the memory unit storing a plurality of time differences associated with pairs of sources.

3. A receiver as described in claim 2, wherein there is a unique time difference for each pair of sources.

4. A receiver as described in claim 3, wherein the code is a portion of a long code.

5. A receiver as described in claim 3, wherein the first location is the beginning of a long code.

6. A receiver as described in claim 3, wherein the first location is the beginning of a portion of a long code.

7. A receiver as described in claim 3, wherein the first location is the beginning of a synchronization code.

8. A receiver as described in claim 7, wherein the synchronization code is repeated in time.

32. A receiver as described in claim 1, wherein the code is the same code used for the first signal and the second signal, and wherein the code has a first time shift for the first signal and a second time shift for the second signal.

9. A receiver that can directly identify a source of a digital signal from an unsynchronized source, the receiver comprising:

means for receiving a first signal;

means for receiving a second signal;

means for determining a first location in time of a code in the first signal;

means for determining a second location in time of the code in the second signal; and

,

means for calculating a time difference between the first location in time of the code in the first signal and the second location in time of the code in the second signal, wherein the time difference identifies a pair of sources of the digital signal.

10. A receiver as described in claim 9, further comprising means for storing a plurality of time differences associated with pairs of sources.

11. A receiver as described in claim 10, wherein there is a unique time difference for each pair of sources.

12. A receiver as described in claim 11, wherein the code is a long code.

13. A receiver as described in claim 11, wherein the code is a portion of a long code.

14. A receiver as described in claim 11, wherein the code is a synchronization code.

15. A receiver as described in claim 14, wherein the synchronization code is repeated in time.

33. A receiver as described in claim 9, wherein the code is the same code used for the first signal and the second signal, and wherein the code has a first time shift for the first signal and a second time shift for the second signal.

16. A radio communication system having source identifiable transmissions that can be identified by an unsynchronized receiver, the system comprising:

a first source, the first source transmitting a first signal using a code with a first shift; and

,

a second source, the second source transmitting a second signal using the code with a second shift;

wherein the difference between the first and the second shift is an unique difference, and wherein the unique difference identifies a pair of sources of the transmissions.

17. A radio communication system having source identifiable transmissions that can be identified by an unsynchronized receiver, the system comprising:

a first source, the first source transmitting a first signal using a code with a first shift;

a second source, the second source transmitting a second signal using the code with a second shift; and

,

a third source, the third source transmitting a third signal using a code with a third shift, wherein the second shift minus the first shift and the third shift minus the first shift are unique differences, wherein each unique difference identifies a pair of sources of the transmissions.

18. A system as described in claim 17, wherein the code is a long code.

19. A system as described in claim 17, wherein the code is a synchronization code.

20. A system as described in claim 19, wherein the synchronization code is repeated in time.

21. A method for identifying a source of a signal, the method comprising the steps of:

receiving a first signal;

receiving a second signal;

determining a first location in time of a code in the first signal;

determining a second location in time of the code in the second signal; and

calculating a time difference between the first location in time of the code in the first signal and the second location in time of the code in the second signal, wherein the time difference identifies a pair of sources of the signals.

22. A method as described in claim 21, the method further comprising the step of:

searching a list of time differences associated with pairs of sources.

23. A method as described in claim 22, wherein the code is a long code.

24. A method as described in claim 22, wherein the code is a portion of a long code.

25. A method as described in claim 22, wherein the code is a synchronization code.

26. A method as described in claim 25, wherein the synchronization code is repeated in time.

34. A method as described in claim 21, wherein the code is the same code used for the first signal and the second signal, and wherein the code has a first time shift for the first signal and a second time shift for the second signal.

27. A method for transmitting a source identifiable signal, the method comprising the steps of:

transmitting a first signal using a code with a first shift; and

,

transmitting a second signal using the code with a second shift;

wherein the difference between the first and the second shift is an unique difference, and wherein the unique difference identifies a pair of sources of the signals.

28. A method of transmitting a source identifiable signal, the method comprising the steps of:

transmitting a first signal using a code with a first shift;

transmitting a second signal using the code with a second shift; and

,

transmitting a third signal using the code with a third shift, wherein the second shift minus the first shift and the third shift minus the first shift are unique differences, wherein each unique difference identifies a pair of sources of the signal.

29. A method as described in claim 28, wherein the code is a long code.

30. A method as described in claim 28, wherein the code is a synchronization code.

31. A method as described in claim 30, wherein the code is repeated in time.