Identifying a code for signal decoding
In some aspects, techniques for wireless signal decoding are described. In some instances, a number of superposition codes are computed based on a set of orthogonal binary codes. The set of orthogonal binary codes includes multiple subsets; each superposition code corresponds to one of the subsets and includes a combination of the binary codes in the corresponding subset. One of the subsets is selected based on a correlation between a wireless signal and the superposition code that corresponds to the subset. One of the binary codes is then selected from the selected subset based on a correlation between the wireless signal and the binary code. The wireless signal is decoded based on the selected binary code.
1. A method of decoding a wireless signal, the method comprising:
identifying superposition codes based on a set of orthogonal binary codes, the set comprising a plurality of subsets, each superposition code corresponding to one of the subsets and comprising a combination of the binary codes in the corresponding subset;
selecting a first subset of the plurality of subsets based on a correlation between a wireless signal and a first superposition code, the first superposition code corresponding to the first subset;
selecting a first binary code from the first subset based on a correlation between the wireless signal and the first binary code; and
decoding the wireless signal by operation of a data processor based on the first binary code.
2. The method of claim 1 , comprising:
computing superposition code correlations between the wireless signal and the superposition codes, the superposition code correlations including the correlation between the wireless signal and the first superposition code;
selecting the first subset based on a peak in the correlation between the wireless signal and the first superposition code;
computing individual code correlations between the wireless signal and at least two of the binary codes in the first subset, the individual code correlations including the correlation between the wireless signal and the first binary code; and
selecting the first binary code based on a peak in the correlation between the wireless signal and the first binary code.
3. The method of claim 1 , comprising performing an iterative, binary search after selecting the first subset, wherein each iteration of the iterative, binary search comprises:
identifying, for the current iteration, a current subset of the binary codes;
dividing the current subset into two inspection subsets for the current iteration;
identifying superposition codes based on the two inspection subsets for the current iteration; and
based on correlations between the wireless signal and the superposition codes for the two inspection subsets, selecting one of the two inspection subsets as the current subset for the next iteration.
4. The method of claim 1 , comprising computing the superposition codes.
5. The method of claim 4 , wherein computing the superposition code corresponding to a subset comprises:
generating phased codes by applying a distinct phase to each binary code in the subset; and
summing the phased codes.
6. The method of claim 5 , wherein the phased codes are generated by applying a distinct phase and distinct amplitude to each binary code in the subset.
7. The method of claim 1 , comprising wirelessly receiving the wireless signal by operation of a radio interface.
8. The method of claim 1 , wherein the wireless signal comprises a WCDMA transmission from a mobile device, and selecting the first binary code comprises identifying the first binary code as a scrambling code associated with the mobile device.
9. A wireless signal processing system comprising:
a radio system configured to detect a wireless signal; and
a data processing system configured to perform operations comprising:
receiving the wireless signal from the radio system;
obtaining superposition codes based on a set of orthogonal binary codes, the set comprising a plurality of subsets, each superposition code corresponding to one of the subsets and comprising a combination of the binary codes in the corresponding subset;
selecting a first subset from the plurality of subsets based on a correlation between the wireless signal and a first superposition code, the first superposition code corresponding to the first subset;
selecting a first binary code from the first subset based on a correlation between the wireless signal and the first binary code; and
decoding the wireless signal based on the first binary code.
10. The wireless signal processing system of claim 9 , the operations comprising:
computing superposition code correlations between the wireless signal and the superposition codes, the superposition code correlations including the correlation between the wireless signal and the first superposition code;
selecting the first subset based on a peak in the correlation between the wireless signal and the first superposition code;
computing individual code correlations between the wireless signal and at least two of the binary codes in the first subset, the individual code correlations including the correlation between the wireless signal and the first binary code; and
selecting the first binary code based on a peak in the correlation between the wireless signal and the first binary code.
11. The wireless signal processing system of claim 9 , the operations comprising performing an iterative, binary search after selecting the first subset, wherein each iteration of the iterative, binary search comprises:
identifying, for the current iteration, a current subset of the binary codes;
dividing the current subset into two inspection subsets for the current iteration;
identifying superposition codes based on the two inspection subsets for the current iteration; and
based on correlations between the wireless signal and the superposition codes for the two inspection subsets, selecting one of the two inspection subsets as the current subset for the next iteration.
12. The wireless signal processing system of claim 9 , the operations comprising computing the superposition codes.
13. The wireless signal processing system of claim 12 , wherein computing the superposition code corresponding to a subset comprises:
generating phased codes by applying a distinct phase to each binary code in the subset; and
summing the phased codes.
14. The wireless signal processing system of claim 13 , wherein the phased codes are generated by applying a distinct phase and distinct amplitude to each binary code in the subset.
15. The wireless signal processing system of claim 9 , wherein the wireless signal comprises a WCDMA transmission from a mobile device, and selecting the first binary code comprises identifying the first binary code as a scrambling code associated with the mobile device.