Coherent combining/noncoherent detection (CCND) method and apparatus for detecting a pilot signal in a wireless communication system

• US 8,379,692 B2
• Filed: 11/07/2002
• Issued: 02/19/2013
• Est. Priority Date: 11/09/1998
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems LLC (Broadcom, Inc.)
• Inventors: Wang, Xiao-an
• Primary Examiner(s): Payne, David C.
• Assistant Examiner(s): Dsouza, Adolf
• Application Number:
  US10/289,699
• Publication Number:
  US 20030053528A1
• Time in Patent Office: 3,757 Days
• Field of Search: 370/203, 370/320, 370/335, 370/342, 375/130, 375/140, 375/142, 375/147, 375/148, 375/367
• US Class Current: 375/147
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• 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: Y02D 30/70 in wireless communication networks

Abstract

A method and apparatus are disclosed for detecting a pilot signal in a wireless receiver using coherent combining/noncoherent detection techniques. Coherent combining/noncoherent detection techniques are used to detect the pilot signal whenever the receiver is already frequency locked, or otherwise known to have a small frequency offset Conventional noncoherent combining/noncoherent detection techniques are utilized to initially acquire the timing of the forward channel. Once the receiver is frequency locked, coherent combining/noncoherent detection techniques may be used to continuously detect the pilot signals. After the receiver is frequency locked, the residue frequency error is small over several consecutive correlator outputs The correlator outputs can thus be combined coherently (since the frequency error is known to be small), and the phase dependency is then eliminated by noncoherent detection.

Claims

1. A method for detecting a pilot signal in a wireless receiver, said method comprising the steps of:

detecting said pilot signal using a noncoherent combining technique and a noncoherent detection technique when a frequency offset is above a predefined threshold;

reducing said frequency offset between said receiver and an incoming signal to at least said predefined threshold; and

detecting said pilot signal using a coherent combining technique and a noncoherent detection technique while said frequency offset remains below said predefined threshold.

2. The method according to claim 1, wherein said noncoherent detection technique further comprises the step of determining whether a signal path to said pilot signal is present based on the value of D₁, where

3. The method according to claim 1, further comprising the step of determining the number of time periods for which said receiver will be substantially frequency locked based on said frequency offset.

4. The method according to claim 1, wherein said receiver is a CDMA receiver.

5. The method according to claim 1, wherein said coherent combining technique and said noncoherent detection technique is for M groups of L correlator outputs;

and

said M groups are noncoherently combined in order to detect said pilot signal.

6. The method according to claim 5, wherein said steps of detecting said pilot signal and noncoherently combining said M groups are performed by the following computation:

7. The method according to claim 5, wherein said method is performed when the accumulation length is too large for coherent combining over L correlator outputs.

8. The method according to claim 5, wherein said receiver is a CDMA receiver.

9. A wireless receiver comprising:

a noncoherent combiner and a noncoherent detector for locking the frequency of said receiver to an incoming data signal when a frequency offset does not satisfy a predefined threshold; and

a coherent combiner and a noncoherent detector for detecting said pilot signal when said frequency offset satisfies the predefined threshold.

10. The wireless receiver according to claim 9, wherein said noncoherent detection technique determines whether a signal path to said pilot signal is present based on the value of D₁, where

11. The wireless receiver according to claim 9, further comprising a processor for determining the number of time periods for which said receiver will be substantially frequency locked based on a frequency offset between said receiver and an incoming data signal.

12. The wireless receiver according to claim 9, wherein said receiver is a CDMA receiver.