Method and apparatus for beacon discovery in a spread spectrum cellular radio communication system

• US 7,019,691 B1
• Filed: 04/07/2005
• Issued: 03/28/2006
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: PCTEL, Inc. (Amphenol Corporation)
• Original Assignee: Pctel Maryland Incorporated (Amphenol Corporation)
• Inventors: Soltanian, Amir, Srivastava, Vikash, Peric, Mirjana
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US11/100,937
• Time in Patent Office: 355 Days
• Field of Search: 342/357.06, 342/368, 342/372, 342/374, 701/207, 701/213
• US Class Current: 342/368
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 41/5009 Determining service level performance parameters or violations of service level contracts, e.g. violations of agreed response time or mean time between failures [MTBF]
• CPC Class Codes: H04L 43/0852 Delays

Abstract

An apparatus (and corresponding methodology) for discovering beacon signals in a spread spectrum radio communication system is selectively operable in one of two modes. The first mode employs a local reference timing signal, while the second mode employs a GPS-derived reference timing signal. Preferably, the first mode identifies a baseline beacon signal that satisfies a constraint based upon time delays for detected beacon signals which are indicative of the relative distance of the transmitting base stations, thus providing selection of a baseline beacon signal that originates from a relatively close base station. The index of the baseline beacon signal is recovered and then used together with relative timing derived from the local reference timing signal to assign indices to other detected beacon signals. In another aspect, control means is provided for selectively switching between the first and second modes in accordance with a plurality of user-selectable modes, which preferably include a GPS-priority mode (whereby the control means automatically switches between the first and second modes based upon GPS signal receive status) and an Indoor mode (whereby the control means operates in the first mode irrespective of GPS signal receive status).

Claims

1. An apparatus for discovering beacon signals communicated from base stations to mobile units in a spread spectrum radio communication system, wherein the beacon signals comprise a common code sequence that is transmitted at predetermined phase delays relative to one another, each predetermined phase delay having an index value associated therewith, and wherein the beacon signals are part of corresponding channels between the base stations and the mobile units, the apparatus comprising:

a radio subsystem that downconverts a received RF signal to a baseband signal and samples the baseband signal to derive baseband samples in digital form that represent at least one received beacon signal;

buffer means, operably coupled to said radio subsystem, for storing said baseband samples;

means for generating a local reference timing signal; and

beacon discovery means, operably coupled to said buffer means and said means for generating a local reference timing signal, for

i) correlating said baseband samples with said common code sequence over different phase delays to identify a set of correlation peaks that correspond to a plurality of detected beacon signals,

ii) for each correlation peak in the set of i), deriving and storing a time offset based upon said local reference timing signal,

iii) for each correlation peak in the set of i), deriving and storing a time delay relative to said time offset, said time delay based upon said time offset for the correlation peak in ii) and said predetermined phase delays, wherein said time delay is indicative of a distance between said apparatus and a base station that transmits a detected beacon signal corresponding to the correlation peak,

iv) identifying a particular detected beacon signal within said plurality of detected beacon signals, said particular detected beacon signal satisfying a constraint based upon said time delay of each correlation peak derived in iii),

v) recovering the index value for said particular detected beacon signal from a channel corresponding to said particular detected beacon signal, and

vi) for each given detected beacon signal within a subset of said plurality of detected beacon signals that does not include said particular detected beacon signal, assigning and storing an index value to said given detected beacon signal based upon the recovered index value for said particular detected beacon signal and relative timing between said particular detected beacon signal and said given detected beacon signal.

2. An apparatus according to claim 1, wherein:

said beacon discovery means derives and stores signal quality data pertaining to said set of correlation peaks, and associates the stored index values assigned to the detected beacon signals to said signal quality data for subsequent processing operations.

3. An apparatus according to claim 1, wherein:

said beacon discovery means derives said relative timing between said particular detected beacon signal and said given detected beacon signal by normalizing said time offset for said given detected beacon signal in accordance with said time delay for said particular detected beacon signal.

4. An apparatus according to claim 3, wherein:

said beacon discovery means normalizes said time delay for said given detected beacon signal in accordance with said time delay for said particular detected beacon signal.

5. An apparatus according to claim 1, wherein:

said constraint is further based upon a received power level of said correlation peaks.

6. An apparatus according to claim 1, wherein:

said constraint is realized by, for each given detected beacon signal in said plurality of detected beacon signals, summing differences between said time delay for a given detected beacon signal and for each other detected beacon signal to derive a score for the given detected beacon signal, and identifying the detected beacon signal with the lowest score as said particular detected beacon signal.

7. An apparatus according to claim 6, wherein:

in the event that a set of detected beacon signals share the lowest score, identifying one of said set with highest power as said particular detected beacon signal.

8. An apparatus according to claim 1, further comprising:

a GPS receiver for receiving and recovering a GPS signal; and

means for generating a second timing reference signal based upon said GPS signal;

wherein said beacon discovery means is operably coupled to said means for generating a second timing reference signal.

9. An apparatus according to claim 1, wherein:

said beacon discovery means operates in a first predetermined operational mode to perform i) through vii), and operates in a second predetermined operational mode to;

viii) for each correlation peak, derive and store a time offset based upon said second timing reference signal, and

ix) for each given detected beacon signal, assign and store an index value to said given detected beacon signal based upon said time offset and said predetermined phase delays.

10. An apparatus according to claim 9, wherein:

operations of said beacon discovery means in said second predetermined operation mode further include;

x) for each correlation peak, deriving and storing a time delay relative to said time offset, said time delay based upon said time offset for the correlation peak.

11. An apparatus according to claim 1, wherein:

said spread spectrum radio communication system comprises a CDMA network.

12. An apparatus according to claim 11, wherein:

said beacon signals are pilot signals with an index value ranging from 0 to 511 corresponding to phase offsets that are 64 chips apart.

13. An apparatus according to claim 1, wherein:

at least one of said buffer means, said means for generating a local reference timing signal, and said beacon discovery means is realized as part of a processing platform.

14. An apparatus according to claim 13, wherein:

said processing platform comprises at least one of an digital signal processor, an FPGA, and an ASIC.

15. An apparatus for discovering beacon signals communicated from base stations to mobile units in a spread spectrum radio communication system, wherein the beacon signals comprise a common code sequence that is transmitted at predetermined phase delays relative to one another, each predetermined phase delay having an index value associated therewith, and wherein the beacon signals are part of corresponding channels between the base stations and the mobile units, the apparatus comprising:

a radio subsystem that downconverts a received RF signal to a baseband signal and samples the baseband signal to derive baseband samples in digital form that represent at least one received beacon signal;

buffer means, operably coupled to said radio subsystem, for storing said baseband samples;

means for generating a local reference timing signal;

a GPS receiver for receiving and recovering a GPS signal;

means for generating a second timing reference signal based upon said GPS signal;

beacon discovery means, operably coupled to said buffer means, said means for generating a local reference timing signal, and means for generating a second timing signal that is operable in a first operational mode and a second operational mode,

wherein in said first operational mode, said beacon discovery means employs said local reference timing signal as a first time reference for operations that assign indices to detected beacon signals; and

wherein in said second operational mode, said beacon discovery means employs said second timing signal as a second time reference for operations that assign indices to detected beacon signals; and

control means for selectively switching between said first operational mode and said second operation mode in accordance with a plurality of user-selectable modes dictated by user input.

16. An apparatus according to claim 15, wherein:

said plurality of user-selectable modes comprises a GPS-priority mode whereby said control means automatically switches to said second operation mode when said GPS receiver is receiving said GPS signal and automatically switches to said first operational mode when said GPS receiver is not receiving said GPS signal.

17. An apparatus according to claim 15, wherein:

said plurality of user-selectable modes comprises an Indoor mode whereby said control means automatically operates in said first operational mode irrespective of whether said GPS receiver is receiving said GPS signal.

18. An apparatus according to claim 15, wherein:

said spread spectrum radio communication system comprises a CDMA network, and said beacon signals are pilot signals with an index value ranging from 0 to 511 corresponding to phase offsets that are 64 chips apart.

19. A method for discovering beacon signals communicated from base stations to mobile units in a spread spectrum radio communication system, wherein the beacon signals comprise a common code sequence that is transmitted at predetermined phase delays relative to one another, each predetermined phase delay having an index value associated therewith, and wherein the beacon signals are part of corresponding channels between the base stations and the mobile units, the method comprising:

downconverting a received RF signal to a baseband signal and sampling the baseband signal to derive baseband samples in digital form that represent at least one received beacon signal;

storing said baseband samples;

generating a local reference timing signal; and

discovering beacon signals by;

i) correlating said baseband samples with said common code sequence over different phase delays to identify a set of correlation peaks that correspond to a plurality of detected beacon signals,

ii) for each correlation peak in the set of i), deriving and storing a time offset based upon said local reference timing signal,

iii) for each correlation peak in the set of i), deriving and storing a time delay relative to said time offset, said time delay based upon said time offset for the correlation peak in ii) and said predetermined phase delays, wherein said time delay is indicative of a distance between said apparatus and a base station that transmits a detected beacon signal corresponding to the correlation peak,

iv) identifying a particular detected beacon signal within said plurality of detected beacon signals, said particular detected beacon signal satisfying a constraint based upon said time delay of each correlation peak derived in iii),

v) recovering the index value for said particular detected beacon signal from a channel corresponding to said particular detected beacon signal, and

vi) for each given detected beacon signal within a subset of said plurality of detected beacon signals that does not include said particular detected beacon signal, assigning and storing an index value to said given detected beacon signal based upon the recovered index value for said particular detected beacon signal and relative timing between said particular detected beacon signal and said given detected beacon signal.

20. A method according to claim 19, further comprising:

deriving and storing signal quality data pertaining to said set of correlation peaks; and

associating the stored index values assigned to the detected beacon signals to said signal quality data for subsequent processing operations.

21. A method according to claim 19, wherein:

said relative timing between said particular detected beacon signal and said given detected beacon signal is derived by normalizing said time offset for said given detected beacon signal in accordance with said time delay for said particular detected beacon signal.

22. A method according to claim 21, further comprising:

normalizing said time delay for said given detected beacon signal in accordance with said time delay for said particular detected beacon signal.

23. A method according to claim 19, wherein:

said constraint is further based upon a received power level of said correlation peaks.

24. A method according to claim 19, wherein:

said constraint is realized by, for each given detected beacon signal in said plurality of detected beacon signals, summing differences between said time delay for a given detected beacon signal and for each other detected beacon signal to derive a score for the given detected beacon signal, and identifying the detected beacon signal with the lowest score as said particular detected beacon signal.

25. A method according to claim 24, further comprising:

in the event that a set of detected beacon signals share the lowest score, identifying one of said set with highest power as said particular detected beacon signal.

26. A method according to claim 19, further comprising:

receiving and recovering a GPS signal; and

generating a second timing reference signal based upon said GPS signal.

27. A method according to claim 19, further comprising:

operating in a first predetermined operational mode to perform i) through vii), and operating in a second predetermined operational mode to discover beacon signals by;

viii) for each correlation peak in the set of i), deriving and storing a time offset based upon said second timing reference signal, and

ix) for each given detected beacon signal, assigning and storing an index value to said given detected beacon signal based upon said time offset and said predetermined phase delays.

28. A method according to claim 27, wherein:

said second predetermined operation mode further includes;

x) for each correlation peak in the set of i), deriving and storing a time delay relative to said time offset, said time delay based upon said time offset for the correlation peak.

29. A method according to claim 19, wherein:

said spread spectrum radio communication system comprises a CDMA network.

30. A method according to claim 29, wherein:

said beacon signals are pilot signals with an index value ranging from 0 to 511 corresponding to phase offsets that are 64 chips apart.