Digitally implemented fast frequency estimator/demodulator for low bit rate maritime and mobile data communications without the use of an acquisition preamble

A digital preambleless demodulator comprising:

• an input buffer for receiving an input signal which includes a carrier wave and providing a baseband output;
• an extra coarse frequency estimator for receiving said baseband output and providing a first estimation of a frequency of said carrier wave, said first estimation being within a first frequency band, said extra coarse frequency estimator comprising a first Fourier transform module for receiving said baseband output and performing a first fast Fourier transform (FFT) or a first discrete Fourier transform (DFT) on said baseband output to provide said first estimation;
• a coarse frequency estimator, connected to said extra coarse frequency estimator, for providing a second estimation of a frequency of said carrier wave, said second estimation being within a second frequency band that is narrower than said first frequency band, said coarse frequency estimator comprising a second Fourier transform module for performing either a second FFT or a second DFT on said first estimation to provide said second estimation;
• and
• a fine frequency estimator, receiving said second estimation and providing a third estimation of said frequency of said carrier wave, said third estimation being within a third frequency band that is narrower than said second frequency band, said fine frequency estimator comprising a third Fourier transform module for performing either a third FFT or a third DFT on said second estimation to provide said third estimation;
• the foregoing arrangement being such that said frequency of said carrier wave can be acquired within a predetermined resolution without necessitating a preamble in said input signal.

A method of performing digital preambleless demodulation of an input signal, said method comprising:

• receiving an input signal which includes a carrier wave;
• performing a first fast Fourier transform (FFT) or a first discrete Fourier transform (DFT) on said input signal to provide a first estimation of said frequency of said carrier wave, said first estimation being within a first frequency band;
• and
• performing a second FFT or a second DFT on said first estimation to provide a second estimation of said frequency of said carrier wave, said second estimation being within a second frequency band that is narrower than said first frequency band.