Method & apparatus for step two W-CDMA searching

• US 20030063656A1
• Filed: 09/19/2001
• Published: 04/03/2003
• Est. Priority Date: 09/19/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Rao, Subramanya P., Gho, Gwang-Hyun, Venkatesan, Sivarama, Agrawal, Avneesh, Terasawa, Daisuke
• Granted Patent: US 6,768,768 B2
• Time in Patent Office: Days
• US Class Current: 375/142
• CPC Class Codes: H04B 1/70735 Code identification H04B1/7083 takes precedence
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70707 Efficiency-related aspects

Abstract

Techniques for searching in asynchronous systems are disclosed. In one aspect, a plurality of codes, such as SSCs, are correlated with a received signal at a plurality of offsets to produce a code/slot energy corresponding to each code/slot boundary pair. Unique subsets of the code/slot energies are summed to produce code sequence energies, the maximum of which indicates a located code sequence and slot boundary. In another aspect, the correlation is performed by sub-correlating the received signal with a common sequence, and performing a Fast Hadamard Transform (FHT) on the results. In yet another aspect, one sub-correlator can be used to search a plurality of peaks simultaneously. Various other aspects of the invention are also presented. These aspects collectively have the benefit of circuit area and search-time efficiency which translate into reduced costs, increased standby time, increased acquisition speed, higher quality signal transmission, increased data throughput, decreased power, and improved overall system capacity.

Claims

1. A method for searching comprising:

correlating a received signal with a plurality of codes at a plurality of slot boundaries, to produce a code/slot energy corresponding to each code/slot boundary pair; and

summing unique subsets of the code/slot energies to produce a plurality of code sequence energies.

2. The method of claim 1, further comprising detecting the maximum code sequence energy to indicate a located code sequence and slot boundary.

3. The method of claim 1, wherein the correlating step further comprises:

sub-correlating the received signal with a common sequence to produce a sub-correlation sequence, the common sequence being a component common to each of the plurality of codes; and

performing a Fast Hadamard Transform (FHT) on the sub-correlation sequence to produce code/slot correlations.

4. The method of claim 3, wherein the sub-correlation step further comprises:

multiplying a subset of samples of the received signal with a first component of the common sequence to produce a plurality of results; and

summing the plurality of results to produce a partial result.

5. The method of claim 4, wherein the sub-correlation step further comprises:

storing a sequence of the partial results; and

multiplying the sequence of partial results with a second component of the common sequence to produce the sub-correlation sequence.

6. The method of claim 3, further comprising calculating energies from the code/slot correlations.

7. A method for generating correlations for a plurality of codes comprising:

correlating a subset of received samples with a common sequence to produce a sub-correlation sequence, the common sequence being a component common to each of the plurality of codes; and

performing a Fast Hadamard Transform (FHT) on the sub-correlation sequence to produce the correlations.

8. The method of claim 7, further comprising:

squaring the in-phase and quadrature components of each of the correlations; and

summing the respective squares to produce a plurality of energies.

9. The method of claim 7, wherein the correlating step further comprises:

multiplying a subset of the received samples with a first component of the common sequence to produce a plurality of results; and

adding the plurality of results to produce a partial result.

10. The method of claim 9, wherein the correlating step further comprises:

storing a sequence of the partial results; and

multiplying the sequence of partial results with a second component of the common sequence to produce the sub-correlation sequence.

11. A searcher comprising:

means for correlating a received signal with a plurality of codes at a plurality of slot boundaries to produce a code/slot energy corresponding to each code/slot boundary pair; and

means for summing unique subsets of the code/slot energies to produce a plurality of code sequence energies.

12. The searcher of claim 11, further comprising means for detecting the maximum code sequence energy to indicate a located code sequence and slot boundary.

13. A searcher comprising:

a correlator for correlating a received signal with a plurality of codes at a plurality of slot boundaries to produce a code/slot energy corresponding to each code/slot boundary pair;

a memory for storing the code/slot energies; and

a summer for summing unique subsets of the code/slot energies to produce a plurality of code sequence energies.

14. The searcher of claim 13, further comprising a detector for receiving the code sequence energies and detecting the maximum code sequence energy.

15. The searcher of claim 13, wherein the correlator comprises:

a sub-correlator for correlating the received signal with a common sequence to produce a sub-correlation sequence;

an FHT for receiving the sub-correlation sequence and producing code/slot correlations; and

an energy calculator for generating code/slot energies from the code/slot correlations.

16. The searcher of claim 15, wherein the sub-correlator comprises:

a shift register for receiving samples of the received signal;

a plurality of multipliers for multiplying samples from the shift register with a first component of the common sequence;

an adder for adding the plurality of multiplier results;

a memory for receiving and storing the output of the adder at periodic intervals to produce a stored partial sub-correlation sequence; and

an XOR for receiving a partial sub-correlation sequence from the memory and bit-wise XORing the partial sub-correlation sequence with a second component of the common sequence to produce a sub-correlation sequence.

17. A correlator comprising:

a sub-correlator for correlating a received signal with a common sequence to produce a sub-correlation sequence;

an FHT for receiving the sub-correlation sequence and producing code/slot correlations; and

an energy calculator for generating code/slot energies from the code/slot correlations.

18. A sub-correlator comprising:

a shift register for receiving samples of a received signal;

a plurality of multipliers for multiplying samples from the shift register with a first component of a common sequence;

an adder for adding the plurality of multiplier results;

a memory for receiving and storing the output of the adder at periodic intervals to produce a stored partial sub-correlation sequence; and

an XOR for receiving a partial sub-correlation sequence from the memory and bit-wise XORing the partial sub-correlation sequence with a second component of the common sequence to produce a sub-correlation sequence.

19. The sub-correlator of claim 18, wherein the memory receives and stores the output of the adder at a plurality of periodic intervals to produce a plurality of partial sub-correlation sequences.

20. The sub-correlator of claim 19, wherein the memory contains a plurality of random access memories (RAMs), each RAM selectable such that a first partial sub-correlation sequence can be written to a first RAM simultaneously with a read access of a second partial sub-correlation sequence from a second RAM.

21. A searcher for searching a plurality of peaks, comprising a sub-correlator for correlating a received signal with a common sequence to produce a sub-correlation sequence for each of the plurality of peaks.

22. The searcher of claim 21, further comprising:

one or more FHTs for receiving the sub-correlation sequences and producing code/slot correlations for each of the plurality of peaks;

one or more energy calculators for generating code/slot energies from the code/slot correlations for each of the plurality of peaks;

one or more summers for summing unique subsets of the code/slot energies to produce a plurality of code sequence energies for each of the plurality of peaks; and

one or more detectors for receiving the code sequence energies and detecting the maximum code sequence energy for each of the plurality of peaks.

23. A subscriber unit including a searcher comprising:

means for correlating a received signal with a plurality of codes at a plurality of slot boundaries to produce a code/slot energy corresponding to each code/slot boundary pair; and

means for summing unique subsets of the code/slot energies to produce a plurality of code sequence energies.

24. A W-CDMA system including a searcher comprising:

means for correlating a received signal with a plurality of codes at a plurality of slot boundaries to produce a code/slot energy corresponding to each code/slot boundary pair; and

means for summing unique subsets of the code/slot energies to produce a plurality of code sequence energies.