Direct detection LiDAR system and method with synthetic doppler processing
A detection system includes a signal transmitter for transmitting transmitted signals into a region and a receiver for receiving reflected signals generated by reflection of the transmitted signals and for generating receive signals indicative of the reflected signals. A processor coupled to the receiver receives the receive signals and processes the receive signals to generate detections of one or more objects in the region. The processing includes altering phase shift to generate phase-modulated signals from the receive signals and generating the detections from the phase-modulated signals.
1. A detection system, comprising:
a signal transmitter for transmitting frequency-modulated continuous-wave (FMCW) transmitted signals into a region, the transmitted signals comprising a series of signal pulses, each signal pulse comprising a signal having a varying frequency, variation of the frequency within each signal pulse following a ramp over time between a first frequency and a second frequency;
a receiver for receiving reflected signals generated by reflection of the transmitted signals and generating receive signals indicative of the reflected signals; and
a processor coupled to the receiver for receiving the receive signals and processing the receive signals to generate detections of one or more objects in the region, the processing including:
generating a first two-dimensional data matrix comprising n rows of N complex data values, wherein n is a quantity of signal pulses of the transmitted signals, each row of the two-dimensional data matrix corresponding to one of the signal pulses of the transmitted signals, and wherein N is a quantity of complex data values generated for each signal pulse, and each column of the two-dimensional data matrix corresponds to n complex data values for all of the signal pulses of the transmitted signals,
performing a complex fast Fourier Transform (FFT) of length N on each row of the two-dimensional data matrix,
generating a second repopulated two-dimensional data matrix comprising n rows of N complex FFT elements, each row of the two-dimensional data matrix corresponding to one of the signal pulses of the transmitted signals, each row comprising complex FFT elements resulting from the complex FFT performed on each row of the first two-dimensional data matrix, each column of the second repopulated two-dimensional data matrix representing range bin data from signal pulses of the transmitted signals, and
generating a third repopulated two-dimensional data matrix comprising n rows of N complex data values, each row of the two-dimensional data matrix corresponding to one of the signal pulses of the transmitted signals, each column of the second repopulated two-dimensional data matrix representing range bin data from signal pulses of the transmitted signals, each column of the third repopulated matrix being augmented with an adjusted phase term, such that a synthetic Doppler frequency is implemented in each column range bin, the adjusted phase terms being used in generating the detections.
2. The detection system of claim 1 , wherein the adjusted phase term is generated using a phase modulator, the phase modulator altering phase shift in a local oscillator (LO) signal.
3. The detection system of claim 1 , wherein the adjusted phase term is generated by altering an output of a direct digital synthesizer (DDS) utilized in generating the transmitted signals and the receive signals.
4. The detection system of claim 1 , wherein the adjusted phase term is generated by adding a phase shift value to in-phase and quadrature-phase detector signals generated from the receive signals.
5. The detection system of claim 1 , wherein the phase shift value is numerically indexed.
6. The detection system of claim 1 , wherein the ramp is a linear ramp.
7. The detection system of claim 1 , wherein the first frequency is lower than the second frequency.
8. The detection system of claim 1 , wherein the first frequency is higher than the second frequency.
9. The detection system of claim 1 , wherein the signal transmitter angularly scans the transmitted signals into the region at varying angles.
10. The detection system of claim 1 , wherein the signal transmitter comprises a scanning mirror for scanning the transmitted signals at varying angles into the region.
11. The detection system of claim 10 , wherein the scanning mirror is a micro-electromechanical (MEMS) scanning mirror.
12. The detection system of claim 1 , wherein the detection system is an automotive detection system.
13. The detection system of claim 1 , wherein:
the detection system is a radar system;
the signal transmitter is a radar signal transmitter;
the transmitted signals are transmitted radar signals; and
the reflected signals are reflected radar signals.
14. The detection system of claim 1 , wherein:
the detection system is a LiDAR system;
the signal transmitter is a LiDAR signal transmitter;
the transmitted signals are transmitted LiDAR signals; and
the reflected signals are reflected LiDAR signals.