Accelerated selection of a base station in a wireless communication system

• US 6,519,277 B2
• Filed: 10/16/2001
• Issued: 02/11/2003
• Est. Priority Date: 05/25/1999
• Status: Expired due to Term

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Eidson, Donald Brian
• Primary Examiner(s): CORRIELUS, JEAN B
• Application Number:
  US09/981,141
• Publication Number:
  US 20020018520A1
• Time in Patent Office: 483 Days
• Field of Search: 375/130, 375/132, 375/133, 375/136, 375/140-142, 375/147, 375/150, 375/367, 370/328, 370/331-335, 370/342, 370/503, 370/515, 370/516
• US Class Current: 375/150
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

A mobile wireless transceiver selects one of multiple nearby base stations to facilitate communication over a wireless network. Each base station transmits a pilot signal that includes a spreading signal transmitted at one of many possible phase offsets. The wireless transceiver selects an initial one of the possible phase offsets of the spreading signal and then correlates a received signal against the spreading signal at consecutive ones of the possible phase offsets. Correlation begins at the selected initial phase offset and continues until a component of the received signal and the spreading signal are aligned, indicating the detection of the pilot signal from one of the base stations. The transceiver then selects a non-consecutive one of the possible phase offsets of the spreading signal and correlates the received signal against the spreading signal at this non-consecutive phase offset to determine whether any other component of the received signal is aligned with the spreading signal at the selected non-consecutive phase offset.

Claims

1. A method for use in selecting one of multiple nearby base stations to facilitate communication over a wireless network, where each base station transmits a pilot signal that includes a spreading signal transmitted at one of many possible phase offsets, the method comprising:

(a) selecting an initial one of the possible phase offsets of the spreading signal;

(b) correlating a received signal against the spreading signal at consecutive ones of the possible phase offsets, beginning at the selected initial phase offset, until a component of the received signal and the spreading signal are aligned, indicating the detection of the pilot signal from one of the base stations;

(c) thereafter selecting a non-consecutive one of the possible phase offsets of the spreading signal; and

(d) correlating the received signal against the spreading signal at the selected non-consecutive phase offset to determine whether any other component of the received signal is aligned with the spreading signal at the selected non-consecutive phase offset.

2. The method of claim 1, further comprising, if no component of the received signal is aligned with the spreading signal at the selected non-consecutive phase offset, correlating the received signal against consecutive ones of the possible phase offsets, beginning at the selected non-consecutive phase offset, until another component of the received signal is aligned with the spreading signal, indicating the detection of the pilot signal from another of the base stations.

3. The method of claim 2, further comprising thereafter selecting another non-consecutive one of the possible phase offsets at which to correlate the spreading signal against the received signal.

4. The method of claim 3, wherein the selected initial phase offset and the selected non-consecutive phase offsets are separated from each other by a predetermined number of possible phase offsets.

5. The method of claim 1, wherein the selected initial phase offset and the selected non-consecutive phase offset are separated from each other by a predetermined number of possible phase offsets.

6. The method of claim 1, further comprising selecting the base station that produces the pilot signal having the greatest received signal strength.

7. The method of claim 1, further comprising ignoring any pilot signal with a received signal strength that is below a predetermined threshold.

8. The method of claim 1, wherein the possible phase offsets are equally spaced.

9. The method of claim 1, wherein selecting a non-consecutive one of the possible phase offsets includes:

(a) selecting a phase offset at which a pilot signal is expected to occur; and

(b) defining an aperture that begins a predetermined number of chips of the spreading signal before the selected phase offset.

10. The method of claim 9, wherein the aperture ends a predetermined number of chips of the spreading signal after the selected phase offset.

11. The method of claim 10, wherein the aperture includes equal numbers of chips before and after the selected phase offset.

12. The method of claim 10, wherein the aperture includes unequal numbers of chips before and after the selected phase offset.

13. The method of claim 9, wherein correlating the received signal against the spreading sequence of the selected non-consecutive phase offset includes correlating of consecutive phase offsets across the aperture to allow for propagation delay in the received signal.

14. A receiver circuit for use in selecting a base station to facilitate communication over a wireless network, where the base station transmits a pilot signal that includes a spreading signal transmitted at one of many possible phase offsets, the receiver circuit comprising:

(a) a spreading signal generator configured to generate a copy of the spreading signal;

(b) a phase offset selector configured to receive the copy of the spreading signal and to output the spreading signal at selected ones of the possible phase offsets;

(c) a correlator configured to receive the spreading signal and to correlate a received signal against the spreading signal at each of the selected phase offsets to determine whether any component of the received signal is aligned with the spreading signal at any of the selected phase offsets;

(d) control circuitry configured to;

(1) cause the phase offset selector to output the spreading signal at consecutive ones of the possible phase offsets, beginning at an initial phase offset, until a component of the received signal and the spreading signal are aligned, indicating the detection of the pilot signal from the base station; and

(2) thereafter cause the phase offset selector to output the spreading signal at a non-consecutive one of the possible phase offsets to determine whether any other component of the received signal is aligned with the spreading signal at the non-consecutive phase offset.

15. The receiver circuit of claim 14, wherein the control circuitry is configured to instruct the phase offset selector to output the spreading signal at consecutive ones of the possible phase offsets, beginning at the selected non-consecutive phase offset, if no component of the received signal is aligned with the spreading signal at the selected non-consecutive phase offset.

16. The receiver circuit of claim 15, wherein the control circuitry is configured to cause the phase offset selector to output the spreading signal at another non-consecutive one of the possible phase offsets upon detecting another pilot signal.

17. The receiver circuit of claim 16, wherein the selected initial phase offset and the selected non-consecutive phase offsets are separated from each other by a predetermined number of possible phase offsets.

18. The receiver circuit of claim 14, wherein the selected initial phase offset and the selected non-consecutive phase offset are separated from each other by a predetermined number of possible phase offsets.

19. The receiver circuit of claim 14, wherein the control circuitry is configured to select the base station that produces the pilot signal having the greatest received signal strength.

20. The receiver circuit of claim 14, wherein the control circuitry is configured to ignore any pilot signal with a received signal strength that is below a predetermined threshold.

21. The receiver circuit of claim 14, wherein the possible phase offsets are equally spaced.

22. The receiver circuit of claim 14, wherein the control circuitry, in instructing the phase offset selector to output the spreading signal at a selected non-consecutive one of the possible phase offsets, is configured to:

(a) select a phase offset at which a pilot signal is expected to occur; and

(b) define an aperture that begins a predetermined number of chips of the spreading signal before the selected phase offset.

23. The receiver circuit of claim 22, wherein the aperture ends a predetermined number of chips of the spreading signal after the selected phase offset.

24. The receiver circuit of claim 23, wherein the aperture includes equal numbers of chips before and after the selected phase offset.

25. The receiver circuit of claim 23, wherein the aperture includes unequal numbers of chips before and after the selected phase offset.

26. The receiver circuit of claim 22, wherein the control circuitry is configured to instruct the phase offset selector to output the spreading signal at phase offsets across the aperture to allow for propagation delay in the received signal.

27. A method for use in determining the availability of a phase offset for use in a wireless network, the method comprising:

(a) selecting an initial one of possible phase offsets of a spreading signal;

(b) correlating a received signal against the spreading signal at consecutive ones of the possible phase offsets, beginning at the selected initial phase offset, until a component of the received signal and the spreading signal are aligned, indicating the detection of a pilot signal from a base station;

(c) thereafter selecting a non-consecutive one of the possible phase offsets of the spreading signal; and

(d) determining the availability of the selected non-consecutive one of possible phase offsets by correlating the received signal against the spreading signal at the selected non-consecutive phase offset to determine whether any other component of the received signal is aligned with the spreading signal at the selected non-consecutive phase offset.

28. The method of claim 27 wherein the step of determining the availability of the selected non-consecutive phase offset comprises correlating the received signal against the spreading signal at the selected non-consecutive phase offset to determine whether any other component of the received signal is aligned with the spreading signal at the selected non-consecutive phase offset, and if said received signal is aligned with said spreading signal, outputting a signal indicative of the non-availability of the selected non-consecutive phase offset.

29. A receiver circuit for use in determining the availability of a phase offset for use in a wireless network where a base station transmits a pilot signal that includes a spreading signal transmitted at one of many possible phase offsets, the receiver circuit comprising:

(a) a spreading signal generator configured to generate a copy of the spreading signal;

(b) a phase offset selector configured to receive the copy of the spreading signal and to output the spreading signal at selected ones of the possible phase offsets;

(c) a correlator configured to receive the spreading sign and to correlate a received signal against the spreading signal at each of the selected phase offsets to determine whether any component of the received signal is aligned with the spreading signal at any of the selected phase offsets;

(d) control circuitry configured to;

(1) cause the phase offset selector to output the spreading signal at consecutive ones of the possible phase offsets, beginning at an initial phase offset, until a component of the received signal and the spreading signal are aligned, indicating the detection of the pilot signal from a base station; and

(2) thereafter cause the phase offset selector to output the spreading signal at a non-consecutive one of the possible phase offsets to determine whether the phase offset is being used by a base station.

30. The receiver circuit of claim 29 wherein said control circuitry if further configured to determine whether the phase offset is being used by a base station by determining whether any other component of the received signal is aligned with the spreading signal at the non-consecutive phase offset.