Frame synch detection with rate adaptation

1. A wireless device comprising:

a receiver to wirelessly receive a packet over a channel at a first frequency and generate a sampled stream of data from the packet at a first sample rate corresponding to the first frequency;

a data resampler circuit coupled to the receiver, the data resampler circuit comprising:

a re-timer engine to determine, using a fractional conversion ratio between the first sample rate and a crystal oscillator (XO)-integer-divided sample rate, a plurality of re-timer values comprising differences between pulses of a pseudo clock corresponding to the XO-integer-divided sample rate and closest corresponding pulses of a clock corresponding to the first sample rate; and

a time shifting circuit to re-sample data values of the sampled stream of data associated with locations of the plurality of re-timer values; and

a correlation circuit coupled to the data resampler circuit, the correlation circuit to use the re-sampled data values, the pseudo clock, and the plurality of re-timer values to match an expected data pattern to a corresponding data pattern detected in a frame delimiter of the packet.

2. The wireless device of claim 1 , wherein the XO-integer-divided sample rate averages a fraction of a frequency of an integer-divided XO sample rate and the first sample rate is a non-integer sample rate specific to the channel.

3. The wireless device of claim 1 , wherein the time shifting circuit comprises a plurality of digital fractional delay filters that re-sample, using the pseudo clock, the data values based on corresponding ones of the plurality of re-timer values.

4. The wireless device of claim 1 , wherein the data resampler circuit further comprises a pseudo clock generator to generate the pseudo clock, the pseudo clock generator to:

receive a phase-locked loop (PLL) clock that is derived based on the clock corresponding to the first sample rate;

remove a pulse from the PLL clock in response to each removal command from the re-timer engine; and

generate the pseudo clock comprising the PLL clock with the removed pulses, the pseudo clock corresponding to, on average, the XO-integer-divided sample rate.

5. The wireless device of claim 4 , wherein the re-timer engine is further to:

detect a re-timer value of the plurality of re-timer values that satisfies a threshold value; and

in response to the detection, trigger a removal command to the pseudo clock generator.

6. The wireless device of claim 4 , wherein the re-timer engine comprises:

a register to store a re-timer value of the plurality of re-timer values;

a summer to add the fractional conversion ratio to the re-timer value to determine a fractional re-timer value;

a comparator to compare the fractional re-timer value to a predetermined negative decimal value; and

a switch to cause a one value to be added to the fractional re-timer value to generate a positive re-timer value in response to the fractional re-timer value becoming less than or equal to the predetermined negative decimal value; and

wherein the comparator is to trigger a removal command to the pseudo clock generator in response to the one value being added.

7. The wireless device of claim 1 , wherein the correlation circuit is further to:

detect a peak within the re-sampled data values that is within a threshold value of a corresponding peak of the expected data pattern;

determine a re-timer value of the plurality of re-timer values most closely corresponding in time to the detected peak;

correct a location of the peak using at least the re-timer value; and

correlate the peak at the corrected location with the corresponding peak.

8. The wireless device of claim 7 , wherein, to correct the location of the peak, the correlation circuit is to:

determine a numerical fractional value associated with a period of the pseudo clock;

determine a re-timer fractional value corresponding to an edge of the detected peak using the clock and based on the re-timer value; and

combine the numerical fractional value and the re-timer fractional value with the location to generate the corrected location of the peak.

9. The wireless device of claim 1 , wherein

the data resampler circuit is further to:

obtain, based on in-phase and quadrature values of the re-sampled data values, soft frequency samples;

estimate oversampled frequency samples of the soft frequency samples at a multiple of a symbol rate of the pseudo clock; and

buffer the oversampled frequency samples into a fixed number of symbols equal to those of a frame synch pattern of the frame delimiter; and

the correlation circuit is further to correlate the buffered oversampled frequency samples with expected frequency symbols of the expected data pattern to detect a correlation peak.

10. A method of operating a wireless device that comprises a receiver, a data resampler circuit coupled to the receiver, and a correlation circuit coupled to the data resampler circuit, wherein the method of operating the wireless device comprises:

receiving wirelessly, by the receiver, a packet over a channel at a first frequency;

generating, by the receiver, a sampled stream of data from the packet at a first sample rate corresponding to the first frequency;

determining, by the data resampler circuit using a fractional conversion ratio between the first sample rate and a crystal oscillator (XO)-integer-divided sample rate, a plurality of re-timer values comprising differences between pulses of a pseudo clock corresponding to the XO-integer-divided sample rate and closest corresponding pulses of a clock corresponding to the first sample rate;

re-sampling, by the data resampler circuit, data values of the sampled stream of data associated with locations of the plurality of re-timer values; and

matching, by the correlation circuit using the re-sampled data values, the pseudo clock, and the plurality of re-timer values, an expected data pattern to a corresponding data pattern detected in a frame delimiter of the packet.

11. The method of claim 10 , wherein the XO-integer-divided sample rate averages a fraction of a frequency of an integer-divided XO sample rate and the first sample rate is a non-integer sample rate specific to the channel.

12. The method of claim 10 , wherein the method of operating the wireless device further comprises employing a plurality of fractional delay filters that re-sample, using the pseudo clock, the data values based on corresponding ones of the plurality of re-timer values.

13. The method of claim 10 , wherein the method of operating the wireless device further comprises:

receiving, by the data resampler circuit, a phase-locked loop (PLL) clock that is derived based on the clock corresponding to the first sample rate;

removing a pulse from the PLL clock in response to each removal command received from a re-timer engine; and

generating, by the data resampler circuit, the pseudo clock comprising the PLL clock with the removed pulses, wherein the pseudo clock corresponds to, on average, the XO-integer-divided sample rate.

14. The method of claim 13 , wherein the method of operating the wireless device further comprises:

detecting a re-timer value of the plurality of re-timer values that satisfies a threshold value; and

triggering, by the re-timer engine, a removal command in response to the detecting.

15. The method of claim 13 , wherein the method of operating the wireless device further comprises:

storing a re-timer value of the plural of re-timer values in a register;

adding, with a summer, to determine a fractional re-timer value, the fractional conversion ratio to the re-timer value;

comparing, with a comparator, the fractional re-timer value to a predetermined negative decimal value;

causing, using a switch, a one value to be added to the fractional re-timer value to generate a positive re-timer value in response to the fractional re-timer value becoming less than or equal to the predetermined negative decimal value; and

triggering, by the comparator, a removal command in response to the one value being added.

16. The method of claim 10 , wherein the method of operating the wireless device further comprises:

detecting, by the correlation circuit, a peak within the re-sampled data values that is within a threshold value of a corresponding peak of the expected data pattern;

determining a re-timer value of the plurality of re-timer values most closely corresponding in time to the detected peak;

correcting a location of the peak using at least the re-timer value; and

correlating, by the correlation circuit, the peak at the corrected location with the corresponding peak.

17. The method of claim 16 , wherein correcting the location of the peak comprises:

determining a numerical fractional value associated with a period of the pseudo clock;

determining a re-timer fractional value corresponding to an edge of the detected peak using the clock and based on the re-timer value; and

combining the numerical fractional value and the re-timer fractional value with the location to generate the corrected location of the peak.

18. The method of claim 10 , wherein the method of operating the wireless device further comprises:

obtaining, based on in-phase and quadrature values of the re-sampled data values, soft frequency samples;

estimating oversampled frequency samples of the soft frequency samples at a multiple of a symbol rate of the pseudo clock;

buffering the oversampled frequency samples into a fixed number of symbols equal to those of a frame synch pattern of the frame delimiter; and

correlating the buffered oversampled frequency samples with expected frequency symbols of the expected data pattern to detect a correlation peak.

19. A system comprising:

a first wireless device adapted to gain access to a secured enclosure by transmitting data comprising a frame delimiter; and

a second wireless device located within the secured enclosure, the second wireless device comprising:

a receiver to wirelessly receive a packet over a channel at a first frequency and generate a sampled stream of data from the packet at a first sample rate corresponding to the first frequency;

a data resampler circuit coupled to the receiver, the data resampler circuit comprising:

a re-timer engine to determine, using a fractional rate between the first sample rate and a crystal oscillator (XO)-integer-divided sample rate, a plurality of re-timer values comprising differences between pulses of a pseudo clock corresponding to the XO-integer-divided sample rate and closest corresponding pulses of a clock corresponding to the first sample rate; and

a time shifting circuit to re-sample data values of the sampled stream of data associated with locations of the plurality of re-timer values; and

a correlation circuit coupled to the data resampler circuit, the correlation circuit to use the re-sampled data values, the pseudo clock, and the plurality of re-timer values to match an expected data pattern to a corresponding data pattern detected in a frame delimiter of the packet.

20. The system of claim 19 , wherein the XO-integer-divided sample rate averages a fraction of a frequency of an integer-divided XO sample rate and the first sample rate is a non-integer sample rate specific to the channel.