System and method for obtaining accurate symbol rate and carrier phase, frequency, and timing acquisition for minimum shift keyed waveform
View Patent ↗The present invention relates generally to communication systems, both wired and wireless, employing a continuous phase modulation (“CPM”) waveform with a minimum shift keying (“MSK”) preamble. The present inventive system and method uses information from contiguous Fourier Transforms taken on contiguous data blocks to determine baud rate, phase, frequency offset, and bit timing of the CPM waveform or can be used to determine the frequency of continuous wave waveform. More particularly, the inventive system and method is applicable to the military satellite communications UHF frequency band for deciding whether a signal of interest is.
1. In a method for determining a carrier frequency of a continuous phase modulation (“CPM”) waveform containing a binary data sequence comprising a pattern of a predetermined number (N) of first binary tones followed by N second binary tones, the pattern repeating a predetermined number of times, said method using a Fourier Transform (“FT”), the improvement comprising the steps of:
performing a first FT of said CPM waveform to generate a first set of FT bins and a second FT of said CPM waveform to generate a second set of FT bins, wherein said second FT is contiguous with said first FT;
determining a phase difference between phase values from a first FT bin of said first set of FT bins and a second FT bin of said second set of FT bins wherein said first FT bin and said second FT bin have the largest amplitudes in the first set and second set of FT bins, respectively;
dividing said phase difference by the time duration of either said first FT or said second FT to determine a frequency offset; and
determining the carrier frequency of said CPM waveform at least in part from said first FT and said second FT by adding said frequency offset to a frequency of the first or second FT bin having the largest amplitude.
2. The method of claim 1 wherein the CPM waveform is a minimum shift keyed waveform.
3. The method of claim 1 wherein the Fourier Transform is a Discrete Fourier Transform (“DFT”).
4. The method of claim 1 wherein the Fourier Transform is a Fast Fourier Transform (“FFT”).
5. The method of claim 1 wherein said predetermined number of tones is two.
6. The method of claim 1 wherein said predetermined number of tones is greater than two.