Synchronization strategy and architecture for spread-spectrum receivers

1. A method for synchronizing the reception of a periodic synchronization signal in a spread spectrum system, the method comprising:

receiving a spread-spectrum signal having a period comprising a plurality of indexable samples;

maintaining a mean array comprising a running mean value for each of the indexable samples over a variable number of periods;

detecting a peak value of the maintained mean array;

calculating an average value of the maintained mean array;

computing a peak-to-average ratio in accordance with the detected peak value and the calculated average value;

comparing the peak-to-average ratio against a time-varying threshold; and

synchronizing the received signal when the peak-to-average ratio exceeds a current value of the time-varying threshold.

2. A method as defined in claim 1 , further comprising:

indexing the detected peak of the maintained mean array; and

providing the index of the detected peak upon synchronization.

3. A method as defined in claim 1 wherein:

each period of the variable number of periods comprises a slot; and

each of the samples of the period comprising a chip or a fraction thereof.

4. A method as defined in claim 3 wherein the spread-spectrum signal is a Wideband Code Division Multiple Access signal.

5. A method as defined in claim 1 , further comprising:

computing a chip-to-noise ratio; and

maintaining the mean array over a greater number of periods prior to synchronization for correspondingly lower computed chip-to-noise ratios.

6. A method as defined in claim 1 wherein said calculating an average value of the maintained mean array comprises down-sampling the maintained mean array such that said peak-to-average ratio is based on a periodic sub-sampling at an integer rate greater than one.

7. A method as defined in claim 1 , further comprising filtering the received spread-spectrum signal in accordance with a code to obtain the periodic synchronization signal.

8. A method as defined in claim 1 , further comprising decreasing the value of said time-varying threshold until it reaches a lower limit.

9. A method as defined in claim 8 wherein said lower limit is user-defined and greater than zero.

10. An apparatus for synchronizing the reception of a spread-spectrum signal, the apparatus comprising:

means for receiving the spread-spectrum signal having a period comprising a plurality of indexable samples;

means for maintaining a mean array comprising a running mean value for each of the indexable samples over a variable number of periods;

means for detecting a peak value of the maintained mean array;

means for calculating an average value of the maintained mean array;

means for computing a peak-to-average ratio in accordance with the detected peak value and the calculated average value;

means for comparing the peak-to-average ratio against a time-varying threshold; and

means for synchronizing the received signal when the peak-to-average ratio exceeds a current value of the time-varying threshold.

11. An apparatus as defined in claim 10 , further comprising:

means for indexing the detected peak of the maintained mean array; and

means for providing the index of the detected peak upon synchronization.

12. A program storage device readable by computer, tangibly embodying a program of instructions executable by computer to perform method steps for synchronizing the reception of a spread-spectrum signal, the method steps comprising:

receiving the spread-spectrum signal having a period comprising a plurality of indexable samples;

maintaining a mean array comprising a running mean value for each of the indexable samples over a variable number of periods;

detecting a peak value of the maintained mean array;

calculating an average value of the maintained mean array;

computing a peak-to-average ratio in accordance with the detected peak value and the calculated average value;

comparing the peak-to-average ratio against a time-varying threshold; and

synchronizing the received signal when the peak-to-average ratio exceeds a current value of the time-varying threshold.

13. A program storage device as defined in claim 12 , the method steps further comprising:

indexing the detected peak of the maintained mean array; and

providing the index of the detected peak upon synchronization.

14. A system ( 100 ) for synchronizing the reception of a spread-spectrum signal, the system comprising:

a communications network ( 114 );

a plurality of communications devices ( 110 , 200 ) in signal communication with the communications network, wherein at least one of said communications devices comprises a synchronization apparatus ( 200 , 400 );

means for receiving a spread-spectrum signal having a period comprising a plurality of indexable samples;

means for maintaining a mean array comprising a running mean value for each of the indexable samples over a variable number of periods;

means for detecting a peak value of the maintained mean array;

means for calculating an average value of the maintained mean array;

means for computing a peak-to-average ratio in accordance with the detected peak value and the calculated average value;

means for comparing the peak-to-average ratio against a time-varying threshold; and

means for synchronizing the received signal when the peak-to-average ratio exceeds a current value of the time-varying threshold.

15. A system as defined in claim 14 wherein the synchronization apparatus ( 400 ) comprises:

acode-matched filter ( 410 );

a running average unit ( 413 ) in signal communication with the code-matched filter;

a peak detector ( 422 ) in signal communication with the running average unit; and

a synchronizer ( 424 ) in signal communication with the peak detector for providing an index of a peak.

16. A system as defined in claim 15 , the synchronization apparatus ( 400 ) further comprising a period averaging unit ( 427 ) in signal communication with the running average unit ( 413 ) for providing a period average to the synchronizer ( 424 ).

17. A system as defined in claim 14 , the synchronization apparatus ( 400 ) further comprising:

means for indexing the detected peak of the maintained mean array; and

means for providing the index of the detected peak upon synchronization.