Claims for Patent: 9,577,864

Summary for Patent: 9,577,864

Title:	Method and apparatus for use with received electromagnetic signal at a frequency not known exactly in advance
Abstract:	In a software receiver, a received electromagnetic signal is sampled in "slices", each having a duration of some multiple of a reference frequency. The samples of each slice are correlated with values in a pair of reference signals, such as sine and cosine, at the reference frequency. This yields a two-tuple for each slice, which two-tuples may be stored. The stored two-tuples can be simply added to arrive at a correlation value of narrower bandwidth than that of any slice taken alone. The stored two-tuples can be taken in sequence, each rotated by some predetermined angle relative to its predecessor in sequence, and the rotated two-tuples summed to arrive at a correlation value with respect to a frequency that is offset from the reference frequency to an extent that relates to the predetermined angle. In this way, the receiver is able to proceed despite the transmitted frequency not being known exactly in advance and does not require prodigious storage or computational resources.
Inventor(s):	Fleming; Robert Alan (Nicasio, CA), Kushner; Cherie Elaine (Nicasio, CA), McAllister; William (Saratoga, CA), Zdeblick; Mark (Portola Valley, CA)
Assignee:	Proteus Digital Health, Inc. (Redwood City, CA)
Application Number:	14/917,834
Patent Claims:	1. A method for use with respect to a received electromagnetic signal, the method carried out with respect to a reference frequency, the method comprising: passing the received electromagnetic signal through an analog front end; passing the signal thence to an analog-to-digital converter having an output, the output defining a resolution thereof; sampling the output of the analog-to-digital converter at a sampling rate, the sampling rate being at least as frequent as twice the reference frequency, the samples thereby defining a time series of samples; for a first number of samples exceeding the duration of one cycle at the reference frequency, said first number of cycles defining a first slice, carrying out a first correlation calculation arriving at a first scalar correlation value with respect to the first slice relative to a first reference waveform at the reference frequency; for the samples defining the first slice, carrying out a second correlation calculation arriving at a second scalar correlation value with respect to the first slice relative to a second reference waveform at the reference frequency, the second reference waveform having a non-zero phase difference from the first reference frequency; the first scalar correlation value with respect to the first slice and the second scalar correlation value with respect to the first slice defining a two-tuple for the first slice; and storing the two-tuple for the first slice in a physical memory. 2. The method of claim 1 further comprising the steps of: for a second number of samples exceeding the duration of one cycle at the reference frequency, said second number of cycles defining a second slice, carrying out a first correlation calculation arriving at a first scalar correlation value with respect to the second slice relative to the first reference waveform; for the samples defining the second slice, carrying out a second correlation calculation arriving at a second scalar correlation value with respect to the second slice relative to the second reference waveform; the first scalar correlation value with respect to the second slice and the second scalar correlation value with respect to the second slice defining a two-tuple for the second slice; and storing the two-tuple for the second slice in the physical memory. 3. The method of claim 2 wherein the carrying-out of correlation calculations and the storage in the physical memory are repeated n-2 times, thereby resulting in storage of n two-tuples, one for each of n respective slices, in the physical memory. 4. The method of claim 3 comprising the further step of summing the two-tuples. 5. The method of claim 4 wherein a correlation result with respect to a single slice defines a respective bandwidth, and wherein a consequence of the summing of the two-tuples is that any correlation result with respect to the reference frequency is of narrower bandwidth as compared with the respective bandwidth for a single slice. 6. The method of claim 3 comprising the further steps of: selecting a first rotation rate associated with a first frequency offset from the reference frequency, the first rotation rate defining a first rotation angle; for each of the n two-tuples, applying the first rotation angle n times to the two-tuple thus defining a rotated two-tuple corresponding to each of the two-tuples; summing the rotated two-tuples corresponding to the each of the n two-tuples. 7. The method of claim 6 wherein the sum of the rotated two-tuples is indicative of a correlation with the first frequency. 8. The method of claim 6 comprising the further steps of: selecting a second rotation rate associated with a second frequency offset from the reference frequency, the second rotation rate defining a second rotation angle; for each of the n two-tuples, applying the second rotation angle n times to the two-tuple thus defining a rotated two-tuple corresponding to each of the two-tuples; summing the rotated two-tuples corresponding to the each of the n two-tuples. 9. The method of claim 8 wherein the sum of the rotated two-tuples is indicative of a correlation with the second frequency. 10. The method of claim 8 wherein the first frequency is higher than the reference frequency and wherein the second frequency is lower than the reference frequency. 11. The method of claim 6, further comprising analyzing the first elements of the rotated two-tuples, and the second elements of the rotated two-tuples, to identify at least first and second phases among various time intervals, thereby detecting a phase-shift-keyed signal. 12. Apparatus for use with respect to a received electromagnetic signal, and with respect to a reference frequency, the apparatus comprising: an analog front end disposed to receive the electromagnetic signal and having an output; an analog-to-digital converter receiving the output of the analog front end, the analog-to-digital converter having an output, the output defining a resolution thereof; computational means having a processor responsive to the output of the analog-to-digital converter for sampling the output of the analog-to-digital converter at a sampling rate, the sampling rate being at least as frequent as twice the reference frequency, the samples thereby defining a time series of samples; the computational means disposed, for a number of samples exceeding the duration of one cycle at the reference frequency, the number of cycles defining a first slice, to carry out a first correlation calculation arriving at a first scalar correlation value relative to a first reference waveform at the reference frequency; the computational means disposed to carry out a second correlation calculation defining the first slice, arriving at a second scalar correlation value relative to a second reference waveform at the reference frequency, the second reference waveform having a non-zero phase difference from the first reference frequency; the first scalar correlation value with respect to the slice and the second scalar correlation value with respect to the slice defining a two-tuple for the slice; the computational means disposed to store the two-tuple in a memory. 13. The apparatus of claim 12 wherein the number of samples amounts to at least two cycles at the reference frequency. 14. The apparatus of claim 13 wherein the number of samples amounts to at least four cycles at the reference frequency. 15. The apparatus of claim 14 wherein the number of samples amounts to at least eight cycles at the reference frequency. 16. The apparatus of claim 12 wherein the resolution is one-bit resolution. 17. The apparatus of claim 12 wherein the sampling rate is at least two times the reference frequency. 18. The apparatus of claim 12 wherein the first and second reference waveforms are each sinusoidal. 19. The apparatus of claim 18 wherein the first and second reference waveforms are in a phase relationship of sine and cosine. 20. The apparatus of claim 12 wherein the output of the analog-to-digital converter defines raw data, the apparatus further characterized by being disposed to discard each item of raw data after the first correlation calculation and the second correlation calculation have been carried out with respect to the item of raw data. 21. The apparatus of claim 12 wherein the analog front end comprises in sequence a first amplifier, a bandpass filter, and a second amplifier having an output, the output of the second amplifier coupled with the analog-to-digital converter.