Multichannel demodulator

• US 6,639,906 B1
• Filed: 12/09/1997
• Issued: 10/28/2003
• Est. Priority Date: 12/09/1997
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Levin, Jeffrey A.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US08/987,172
• Time in Patent Office: 2,149 Days
• Field of Search: 370/209, 370/328, 370/332, 370/335, 370/342, 370/350, 370/441, 370/519, 375/200, 375/206, 375/208, 375/356, 375/367, 455/126, 455/127, 455/456
• US Class Current: 370/342
• CPC Class Codes: H04B 1/70735 Code identification H04B1/7083 takes precedence
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/70753 Partial phase search
• CPC Class Codes: H04B 1/70756 Jumping within the code, i.e. masking or slewing H04B1/70758 takes precedence
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/7113 Determination of path profile
• CPC Class Codes: H04B 2001/70935 using a bank of matched fileters, e.g. Fast Hadamard Transform

Abstract

A system and method for performing the digital receive processing for multiple signals received over the same RF band is described. In a preferred embodiment of the invention, digital RF samples are stored in a queue which is accessed by a searcher and demodulator. The searcher and demodulator are preferably located on the same integrated circuit along with the queue. The demodulator demodulates a set of reverse link signals stored within the queue where each reverse link signal is received with at a particular time offset and processed using a particular channel code. The searcher periodically searches for reverse link signals not being processed by the demodulator, and for access requests transmitted via the access channel. The searcher preferably searches during the worthy power control groups of each reverse link signal, which corresponds to the two of sixteen power control groups transmitted during, an eighth rate frame.

Claims

1. A system for demodulating a set of CDMA signals, each signal having one or more multipath instances comprising:

antenna input memory for storing digital samples of radio frequency energy;

searcher for demodulating said digital samples at a first set of time offsets;

demodulator for demodulating said digital samples at a second set of offsets;

a control system for specifying said first set of time offsets and said second set of time offsets, wherein said demodulator is further for retrieving a first set of samples from said antenna input memory; and

demodulating said first set of samples with a first PN code applied at an offset from said first set of offsets.

2. The system as set forth in claim 1 wherein said searcher is further for:

retrieving a second set of samples from said antenna input memory; and

demodulating said second set of samples with a second PN code applied at an offset from said second set of offsets.

3. The system as set forth in claim 1 wherein:

said demodulator is further for demodulating at offsets for which signals have already been detected; and

said searcher is further for demodulating at offsets for which it is unknown if a signal is being received.

4. The system as set forth in claim 1 wherein said second set of offsets changes more rapidly than said first set of offsets.

5. The system as set forth in claim 1 wherein said first set of offsets has fewer members than said second set of offsets.

6. The system of claim 1 further comprising:

demod PN code generator for generating a first set of PN codes for demodulating said digital samples at said first set of offsets; and

search PN code generator for generating a second set of PN codes for demodulating at said digital samples at said second set of offsets.

7. The system of claim 1 wherein said antenna input memory stores said digital samples in a circular queue arrangnment.

8. The system of claim 1 wherein said antenna input memory stores approximately four Walsh symbols worth of digital samples.

9. The system as set forth in claim 1 further comprising a time tracking unit for indicating whether a time offset in said first set of offsets should be advanced or retarded.

16. The method of claim 1 wherein said digital samples are stored in a circular queue arrangnment.

17. The method of claim 1 wherein approximately four Walsh symbols worth of digital samples are stored.

10. A method for demodulating a set of CDMA signals, each signal having one or more multipath instances comprising the steps of:

storing digital samples of radio frequency energy in antenna input memory;

retrieving a first set of samples from said antenna input memory;

demodulating said digital samples at a first set of time offsets;

demodulating said digital samples at a second set of offsets; and

demodulating said first set of samples with a first PN code applied at an offset from said first set of offsets.

11. The method as set forth in claim 10 further comprising the steps of:

retrieving a second set of samples from said antenna input memory; and

demodulating said second set of samples with a second PN code applied at an offset from said second set of offsets.

12. The method as set forth in claim 10 wherein said first set of offsets are for signals have already been detected;

and said second set of offsets is for which signals have not been detected.

13. The method as set forth in claim 10 wherein said second set of offsets changes more rapidly than said first set of offsets.

14. The method as set forth in claim 10 wherein said first set of offsets has fewer members than said second set of offsets.

15. The method of claim 10 further comprising the steps of:

generating a first set of PN codes for demodulating said digital samples at said first set of time offsets; and

generating a second set of PN codes for demodulating at said digital samples at said second set of time offsets.

18. The method as set forth in claim 10 further comprising the step of indicating whether a time offset in said first set of offsets should be advanced or retarded.