Frame synch detection with rate adaptation
A device includes a receiver to receive a packet over a channel at a first frequency and generate a sampled stream of data at a first sample rate corresponding to the first frequency. A data resampler circuit includes a re-timer engine to determine, using a ratio between the first sample rate and a crystal oscillator (XO)-divided sample rate, re-timer values. The data resampler circuit includes 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. A correlation circuit uses the re-sampled data values, and the re-timer values to match an expected data pattern to a corresponding data pattern detected in a frame of the packet.
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 ratio between the first sample rate and a crystal oscillator (XO)-integer-divided sample rate, a plurality of re-timer values; 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 and the plurality of re-timer values to match an expected data pattern to a corresponding data pattern detected in a frame of the packet.
2 . The wireless device of claim 1 , wherein the plurality of re-timer values comprise differences between pulses of a first clock corresponding to the XO-integer-divided sample rate and closest corresponding pulses of a second clock corresponding to the first sample rate.
3 . The wireless device of claim 2 , wherein the time shifting circuit comprises a plurality of digital fractional delay filters that re-sample, using the first clock, the data values based on corresponding ones of the plurality of re-timer values.
4 . The wireless device of claim 2 , wherein the data resampler circuit further comprises a clock generator to generate the first clock, the clock generator configured to:
receive a phase-locked loop (PLL) clock that is derived based on the second clock;
remove a pulse from the PLL clock in response to each removal command from the re-timer engine; and
generate the first clock comprising the PLL clock with the removed pulses, the first clock corresponding to, on average, the XO-integer-divided sample rate.
5 . The wireless device of claim 4 , wherein the re-timer engine is configured 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 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 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 clock generator in response to the one value being added.
7 . The wireless device of claim 1 , wherein the correlation circuit is configured 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 configured to:
determine a numerical fractional value associated with a period of a clock corresponding to the XO-integer-divided sample rate;
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 configured to:
obtain, based on in-phase and quadrature values of the re-sampled data values, oversampled frequency samples; and
buffer the oversampled frequency samples into a fixed number of symbols equal to those of a data pattern of the frame; and
the correlation circuit is configured 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 ratio between the first sample rate and a crystal oscillator (XO)-integer-divided sample rate, a plurality of re-timer values;
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 and the plurality of re-timer values, an expected data pattern to a corresponding data pattern detected in a frame of the packet.
11 . The method of claim 10 , wherein the plurality of re-timer values comprise differences between pulses of a first clock corresponding to the XO-integer-divided sample rate and closest corresponding pulses of a second clock corresponding to the first sample rate.
12 . The method of claim 11 , wherein the method of operating the wireless device further comprises employing a plurality of fractional delay filters that re-sample, using the first clock, the data values based on corresponding ones of the plurality of re-timer values.
13 . The method of claim 11 , 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 second clock;
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 first clock comprising the PLL clock with the removed pulses, wherein the first 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 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 a clock corresponding to the XO-integer-divided sample rate;
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, oversampled frequency samples;
buffering the oversampled frequency samples into a fixed number of symbols equal to those of a data pattern of the frame; 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; 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 ratio between the first sample rate and a crystal oscillator (XO)-integer-divided sample rate, a plurality of re-timer values; 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 and the plurality of re-timer values to match an expected data pattern to a corresponding data pattern detected in a frame of the packet.
20 . The system of claim 19 , wherein the plurality of re-timer values comprise differences between pulses of a first clock corresponding to the XO-integer-divided sample rate and closest corresponding pulses of a second clock corresponding to the first sample rate.