Method and apparatus for use with received electromagnetic signal at a frequency not known exactly in advance

摘要

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.

主权项

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.