Timing estimation in communication systems

1. A method of symbol timing estimation, the method including:

despreading samples of a received direct-sequence spread-spectrum signal to obtain despread symbol samples;

performing non-coherent integration on at least a subset of the despread symbol samples to obtain integrated values;

applying a threshold to the integrated values to obtain peak integration values;

selecting a set of peaks from the peak integration values;

applying curve fitting to the set of peaks;

projecting results of the curve fitting backwards and forwards in time to obtain a group of sampling instants;

using the set of peaks to select from the despread symbol samples a group of the despread symbol samples, wherein using the set of peaks comprises using the group of sampling instants to select the group of despread symbol samples; and

further processing the group of despread symbol samples.

2. The method of claim 1 , wherein the curve fitting is polynomial curve fitting.

3. The method of claim 1 , further including computing the threshold based on at least a subset of the integrated values.

4. The method of claim 3 , wherein computing the threshold comprises obtaining a mean of the at least a subset of the integrated values.

5. The method of claim 4 , wherein computing the threshold further comprises obtaining the threshold by performing a process selected from the group consisting of:

obtaining a standard deviation of the at least a subset of the integrated values and adding to the mean a multiple of the standard deviation; and

multiplying the mean by a predetermined factor.

6. The method of claim 1 , wherein the threshold is a predetermined value.

7. The method of claim 1 , wherein selecting the set of peaks comprises:

finding a maximum of the peak integration values; and

searching for further peaks within predetermined time windows in backward and forward directions in time.

8. A non-transitory computer readable medium having stored thereon executable instructions configured to result in the implementation of operations including:

despreading samples of a received direct-sequence spread-spectrum signal to obtain despread symbol samples;

performing non-coherent integration on at least a subset of the despread symbol samples to obtain integrated values;

applying a threshold to the integrated values to obtain peak integration values;

selecting a set of peaks from the peak integration values;

applying curve fitting to the set of peaks;

projecting results of the curve fitting backwards and forwards in time to obtain a group of sampling instants;

using the set of peaks to select from the despread symbol samples a group of the despread symbol samples, wherein using the set of peaks comprises using the group of sampling instants to select the group of despread symbol samples; and

further processing the group of despread symbol samples.

9. The non-transitory computer readable medium of claim 8 , wherein the curve fitting is polynomial curve fitting.

10. The non-transitory computer readable medium of claim 8 , wherein the operations further include computing the threshold based on at least a subset of the integrated values.

11. The non-transitory computer readable medium of claim 10 , wherein computing the threshold comprises obtaining a mean of the at least a subset of the integrated values.

12. The non-transitory computer readable medium of claim 11 , wherein computing the threshold further comprises obtaining the threshold by performing a process selected from the group consisting of:

obtaining a standard deviation of the at least a subset of the integrated values and adding to the mean a multiple of the standard deviation; and

multiplying the mean by a predetermined factor.

13. The non-transitory computer readable medium of claim 8 , wherein the threshold is a predetermined value.

14. The non-transitory computer readable medium of claim 8 , wherein selecting the set of peaks comprises:

finding a maximum of the peak integration values; and

searching for further peaks within predetermined time windows in backward and forward directions in time.

15. An apparatus to perform symbol timing synchronization, the apparatus including:

at least one processor; and

the non-transitory computer readable medium according to claim 8 .

16. A symbol timing synchronization apparatus, including:

a despreader configured to despread samples of a received direct-sequence spread-spectrum signal to obtain despread symbol samples;

a non-coherent integrator coupled to receive the despread symbol samples and configured to output integrated values based on the despread symbol samples;

a thresholding device configured to apply a threshold to the integrated values to obtain peak integration values;

a peak selector configured to select a set of peaks from the peak integration values;

a curve fitter configured to apply curve fitting to the set of peaks;

a sample selector configured to receive the despread symbol samples and configured to select, based on timing instants derived from the set of peaks, a group of the despread symbol samples for further processing; and

a projection module configured to project results of the curve fitting backwards and forwards in time to obtain a group of sampling instants and to provide the group of sampling instants to the sample selector.

17. The apparatus of claim 16 , wherein the thresholding device is configured to compute the threshold based on at least a subset of the integrated values.

18. The apparatus of claim 16 , wherein the threshold is a predetermined value.

19. The apparatus of claim 16 , wherein the peak selector is configured to:

find a maximum of the peak integration values; and

search for further peaks within predetermined time windows in backward and forward directions in time.