Method and apparatus for cell search for W-CDMA with effect of clock offset
The invention discloses a cell search method for a CDMA system for a three-stage cell search procedure. The cell search method have the steps of matching incoming signals; over-sampling the incoming signals N times against a chip rate; down-sampling the incoming signals and outputting N over-samples (Y 1 (k), Y 2 (k), Y N (k)) to N parallel signal paths; choosing randomly a sample of the N over-samples; and transmitting the sample chosen randomly from the N over-samples into a first stage process, a second stage process and a third stage process to accomplish a trial. The invention significantly reduces the effect of clock offset so as to accomplish fast cell search.
1. A cell search method for a CDMA system for a three-stage cell search procedure, comprising the steps of:
matching incoming signals;
over-sampling the incoming signals N times against a chip rate;
down-sampling the incoming signals and outputting N over-samples (Y 1 (k), Y 2 (k), Y N (k)) to N parallel signal paths;
choosing randomly a sample of the N over-samples;
transmitting the sample chosen randomly from the N over-samples into a first stage process,
a second stage process and a third stage process to accomplish a trial;
achieving a slot synchronization of the incoming signal in the first stage process;
achieving a code group and frame synchronization of the incoming signal in the second stage process;
selecting a scrambling code of the incoming signal in the third stage process; and
testing the scrambling code against a threshold η 0 by a first verification;
wherein if the threshold is not exceeded, then the trial is considered to be failure and a new trial will be restarted without penalty; or
the selected scrambling code goes for a second verification unit;
wherein if the scrambling code passes the second verification, then the trial succeeds, otherwise the a new trial will be restarted with a penalty time T P (ms) and an initial sampling point at a matched filter output is assumed to be random.
2. A cell search method as claimed in claim 1 , wherein the sample of the N over-samples (Y 1 (K), Y 2 (K), Y N (K)) is chosen randomly to go through the three-stage search processes in each trial.
3. A cell search method as claimed in claim 1 , wherein the sample of the N over-samples (Y 1 (k), Y 2 (k), Y N (k)) is chosen randomly and independently to be proceeded in each stage of each trial.
4. A cell search method as claimed in claim 1 , wherein achieving the slot synchronization further comprises the step of:
using a generalized hierarchical Golay sequence as a primary synchronization code (PSC) in a primary synchronization channel (PSCH).
5. A cell search method as claimed in claim 1 , wherein achieving a code group and frame synchronization further comprises the step of:
a second stage detector using 16 secondary synchronization codes (SSCs) orthogonal to the PSC in a secondary synchronization channel (SSCH).
6. A cell search method as claimed in claim 5 , wherein the secondary synchronization channel (SSCH) is further encoded into a set of 64 code words by using a (15,3) comma-freed Reed Solomon code (CFRS), with each code word in the set representing a code group, to identify a frame boundary and code group.
7. A cell search method as claimed in claim 1 , wherein the scrambling code is determined by selecting one of the 8 codes by in a common pilot channel (CPICH) after the code group and frame boundary is identified.
8. A cell search method as claimed in claim 1 , wherein a first stage detector uses a non-coherent combined matched filter for slot synchronization in the first stage.
9. A cell search method as claimed in claim 4 , wherein a first stage detector selects more than one slot boundary candidate of the primary synchronization code (PSC) for the slot synchronization, although only one candidate will be considered.
10. A cell search method as claimed in claim 5 , wherein the second stage detector uses 16 matched filters for the detection of the secondary synchronization codes (SSCs) for the code group and frame synchronization.
11. A cell search method as claimed in claim 7 , wherein the code group and frame boundary use the code group and cyclic shift position associated with a maximum value of correlation values resulted from the code words in the second stage, respectively.
12. A cell search method as claimed in claim 1 , wherein the threshold η 0 is preset according to a constant false alarm rate.
13. A cell search method as claimed in claim 1 , wherein the cell search method is used for wideband code division multiple access, frequency division duplex system (W-CDMA/FDD).
14. A cell search method as claimed in claim 1 , wherein the cell search method is used for the mobile equipment and wireless PDA system.
15. A cell search apparatus for a CDMA system for a three-stage cell search procedure, comprising:
a chip matched filter, used for matching incoming signals;
a sampling device connected to the chip matched filter, used for over-sampling the incoming signals by N times against a chip rate;
a down-sample device connected to the sampling device, used for down-sampling the incoming signals and outputting N over-samples (Y 1 (k), Y 2 (k), Y N (k)) N parallel signal paths;
an incoming signal selector connected to the down-sample device, used for choosing randomly one of the N over-samples; and to go through the succeeding stages;
a first stage detector connected to the incoming signal selector, used for achieving slot synchronization;
a second stage detector connected to the incoming signal selector, used for achieving frame boundary and code group synchronization;
a third stage detector connected to the incoming signal selector, used for achieving a scrambling code; and
an identification unit connected to the third stage detector, used for determining a trial succeed or not, wherein the identification unit further comprises:
a comparator connected to the third stage detector, used for testing the output of the third stage detector against a thresholdη 0 ;
a first decision device connected to the comparator, used for determining the scrambling code;
wherein if the threshold is exceeded, then the selected scrambling code goes for a synchronization verification unit, otherwise the trial is considered to be failure, and a new trial will be restarted without penalty; and
the synchronization verification unit connected to the first decision device, used for verifying the scrambling code; and
a second decision device connected to the synchronization verification unit, used for determining the acceptance of the scrambling code;
wherein if the scrambling code passes the second decision device, then the trial succeeds, otherwise the a new trial will be restarted with a penalty time T P (ms) and;
an initial sampling point at the matched filter is assumed uniformly distributed.
16. A cell search apparatus as claimed in claim 15 , wherein one of the N over-samples (Y 1 (k), Y 2 (k), Y N (k)) is chosen randomly to go through a three-stage search processes in each trial.
17. A cell search apparatus as claimed in claim 15 , wherein one of the N over-samples (Y 1 (k), Y 2 (k), Y N (k)) is chosen randomly and independently to be proceeded in each stage of each trial.
18. A cell search apparatus as claimed in claim 15 , wherein the first stage detector uses a generalized hierarchical Golay sequence as a primary synchronization code (PSC) in a primary synchronization channel (PSCH).
19. A cell search apparatus as claimed in claim 15 , wherein the second stage detector uses 16 secondary synchronization codes (SSCs) orthogonal to the PSC in a secondary synchronization channel (SSCH).
20. A cell search apparatus as claimed in claim 19 , wherein the SSCH is further encoded into a set of 64 code words by using a (15,3) comma-free Reed Solomon (CFRS) code, with each code word in the set representing a code group, to identify frame boundary/code group.
21. A cell search apparatus as claimed in claim 20 , wherein the scrambling code can be determined by selecting one of the 8 codes by in a common pilot channel (CPICH) after the code group and frame boundary is identified.
22. A cell search apparatus as claimed in claim 15 , wherein the first stage detector uses a non-coherent combined matched filter for slot synchronization in the first stage.
23. A cell search apparatus as claimed in claim 15 , wherein the first stage detector selects more than one slot boundary candidate of a primary synchronization code (PSC) for the slot synchronization, although only one candidate will be considered.
24. A cell search apparatus as claimed in claim 19 , wherein the second stage detector uses 16 matched filters for the detection of the secondary synchronization codes (SSCs).
25. A cell search apparatus as claimed in claim 20 , wherein the code group and frame boundary use the code group and cyclic shift position associated with a maximum value of correlation values resulted from the code words in the second stage, respectively.
26. A cell search apparatus as claimed in claim 15 , wherein the thresholdη 0 is preset according to a constant false alarm rate.
27. A cell search apparatus as claimed in claim 15 , wherein a cell search method is used for wideband code division multiple access, frequency division duplex system (W-CDMA/FDD).
28. A cell search apparatus as claimed in claim 15 , wherein the cell search apparatus is used for the mobile equipment and wireless PDA system.