Fast fourier transform signal processing method for doppler radar speed sensor
First Claim
1. A signal processing method for a vehicle speed sensing system having an RF transceiver coupled to an antenna for transmitting an RF signal towards the terrain over which the vehicle moves and for receiving a reflected Doppler signal therefrom, the transceiver generating a time-domain in-phase reference signal I and a time-domain quadrature signal Q which is offset in phase by 90 degrees from the reference signal I, and a digital signal processor which receives the I and Q signals, the signal processing method comprising:
- executing a complex fast Fourier transform routine to convert the time domain I and Q signals to frequency domain values I(f) and Q(f);
converting the frequency domain values I(f) and Q(f) to a vehicle speed signal;
identifying vibration domain frequency values resulting from vehicle vibration; and
preventing such vibration frequency domain values from effecting the conversion of the frequency domain values I(f) and Q(f) to the vehicle speed signal.
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Abstract
A vehicle speed sensing system includes an RF transceiver coupled to an antenna for transmitting an RF signal towards the terrain over which the vehicle moves and for receiving a reflected Doppler signal therefrom. The transceiver generates a time-domain in-phase reference signal I and a time-domain quadrature signal Q which is offset in phase by 90 degrees from the reference signal I. A digital signal processor which receives the I and Q signals, and uses a complex fast Fourier transform routine to convert the time domain I and Q signals to frequency domain values I(f) and Q(f). The digital signal processor further processes the I(f) and Q(f) values and generates a speed a direction signal which is unaffected by vehicle vibrations.
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Citations
3 Claims
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1. A signal processing method for a vehicle speed sensing system having an RF transceiver coupled to an antenna for transmitting an RF signal towards the terrain over which the vehicle moves and for receiving a reflected Doppler signal therefrom, the transceiver generating a time-domain in-phase reference signal I and a time-domain quadrature signal Q which is offset in phase by 90 degrees from the reference signal I, and a digital signal processor which receives the I and Q signals, the signal processing method comprising:
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executing a complex fast Fourier transform routine to convert the time domain I and Q signals to frequency domain values I(f) and Q(f);
converting the frequency domain values I(f) and Q(f) to a vehicle speed signal;
identifying vibration domain frequency values resulting from vehicle vibration; and
preventing such vibration frequency domain values from effecting the conversion of the frequency domain values I(f) and Q(f) to the vehicle speed signal. - View Dependent Claims (2, 3)
obtaining and storing reverse and forward frequency domain values with corresponding amplitude values, each forward frequency domain value representing a forward vehicle speed, each reverse frequency domain value representing a reverse vehicle speed, and each reverse domain frequency value having a corresponding mirror image forward frequency domain value representing an equal and opposite vehicle speed; and
calculating the ratio of an amplitude of a frequency domain value to an amplitude of a corresponding mirror image frequency domain value; and
if said ratio is less than a threshold, preventing such frequency domain value from being converted to the vehicle speed value.
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3. The signal processing method of claim 2, wherein:
each reverse frequency domain value represents a speed equal to and opposite from its corresponding mirror image forward frequency domain value.
Specification