Method and system for frequency offset modulation range division MIMO automotive radar
A radar system, apparatus, architecture, and method are provided for generating a transmit reference or chirp signal to produce a plurality of transmit signals having different frequency offsets from the transmit reference signal for encoding and transmission as N radio frequency encoded transmit signals which are reflected from a target and received at a receive antenna as a target return signal that is down-converted to an intermediate frequency signal and converted by a high-speed analog-to-digital converter to a digital signal that is processed by a radar control processing unit which performs fast time processing steps to generate a range spectrum comprising N segments which correspond, respectively, to the N radio frequency encoded transmit signals transmitted over the N transmit antennas.
1. A radar system comprising:
a reference signal generator configured to produce a transmit reference signal comprising a sequence of waveforms;
a waveform generator comprising a plurality of fast-time phase shifters which are each connected to receive the transmit reference signal and which are configured to produce a plurality of transmit signals, each having a different frequency offset from the transmit reference signal;
a signal encoder to encode the plurality of transmit signals using a signal conditioning and power amplification to produce and transmit N radio frequency encoded transmit signals over N transmit antennas;
at least a first receive antenna for receiving a target return signal reflected from the N radio frequency encoded transmit signals by a target;
a downconverter configured to mix the target return signal with the transmit reference signal, thereby producing an intermediate frequency signal;
an analog-to-digital converter connected to convert the intermediate frequency signal to a digital signal; and
a radar control processing unit configured to process the digital signal with fast time processing steps to generate a range spectrum comprising N segments which correspond, respectively, to the N radio frequency encoded transmit signals transmitted over the N transmit antennas.
2. The radar system of claim 1 , where the radar control processing unit is further configured to construct a MIMO virtual array by extracting information corresponding to the N radio frequency encoded transmit signals from the N consecutive segments in the range spectrum.
3. The radar system of claim 1 , where the analog-to-digital converter has a sampling rate of at least N times of the minimally required sampling rate of a single-transmitter system that detects targets unambiguously in range.
4. The radar system of claim 1 , where each of the plurality of fast-time phase shifters is connected to receive the transmit reference signal and to generate a frequency offset modulated encoded transmit signals.
5. The radar system of claim 1 , where the plurality of fast-time phase shifters comprises a bank of K-bit phase shifters for introducing a regular progressive phase shift to the transmit reference signal at fast-time sampling intervals.
6. The radar system of claim 1 , where the signal encoder is configured to encode the plurality of transmit signals using time division multiplexing to produce a first set of N/2 radio frequency encoded transmit signals for transmission over a first set of N/2 transmit antennas during a first time slot, and to produce a second set of N/2 radio frequency encoded transmit signals for transmission over a second set of N/2 transmit antennas during a second time slot.
7. The radar system of claim 6 , where the signal encoder is configured to encode the plurality of transmit signals using time division multiplexing by activating even-numbered transmit antennas for transmitting the first set of N/2 radio frequency encoded transmit signals during the first time slot, and by activating odd-numbered transmit antennas for transmitting the second set of N/2 radio frequency encoded transmit signals during the second time slot.
8. The radar system of claim 1 , further comprising a notch filter bank connected between the downconverter and the analog-to-digital converter for filtering the intermediate frequency signal to remove zero-range interference in a fast-time spectrum of each transmitter.
9. The radar system of claim 1 , where the downconverter comprises an I/Q mixer which is connected to first and second analog-to-digital converters which respectively convert the intermediate frequency signal to an I-channel digital signal and Q-channel digital signal.
10. A method for operating a radar system, comprising:
generating a transmit reference signal comprising a sequence of chirp waveforms at a transmitter module;
generating a plurality of transmit signals from the transmit reference signal at the transmitter module using a plurality of fast-time phase shifters which are connected to receive the transmit reference signal and configured to produce a plurality of transmit signals, each having a different frequency offset from the transmit reference signal;
encoding the plurality of transmit signals using a signal conditioning and power amplification at the transmitter module to produce N radio frequency encoded transmit signals;
transmitting the N radio frequency encoded transmit signals over N transmit antennas at the transmitter module;
receiving, at least a first receive antenna of a receiver module, a target return signal reflected from the N radio frequency encoded transmit signals by a target;
mixing the target return signal with the transmit reference signal at the receiver module to produce an intermediate frequency signal;
converting the intermediate frequency signal to a digital signal with an analog-to-digital converter at the receiver module; and
processing the digital signal with fast time processing steps to generate a range spectrum comprising N segments which correspond, respectively, to the N radio frequency encoded transmit signals transmitted over the N transmit antennas.
11. The method of claim 10 , further comprising constructing a MIMO virtual array by extracting information corresponding to the N radio frequency encoded transmit signals from the N consecutive segments in the range spectrum.
12. The method of claim 10 , where generating the plurality of transmit signals comprises:
generating a plurality of different frequency offset tones; and
mixing the transmit reference signal with each of the plurality of frequency offset tones to generate the plurality of transmit signals.
13. The method of claim 12 , where a frequency offset generator generates the plurality of different frequency offset tones, and where a plurality of frequency offset modulation mixers are connected to mix the transmit reference signal with one of the plurality of different frequency offset tones.
14. The method of claim 10 , where generating the plurality of transmit signals comprises phase-shifting the transmit reference signal with the plurality of fast-time phase shifters in response to a plurality of phase shift control signals to generate the plurality of transmit signals.
15. The method of claim 14 , where phase-shifting the transmit reference signal comprises applying the transmit reference signal to a bank of K-bit phase shifters to phase-shift the transmit reference signal by introducing a regular progressive phase shift to the transmit reference signal at fast-time sampling intervals.
16. The method of claim 10 , where encoding the plurality of transmit signals comprises encoding the plurality of transmit signals using time division multiplexing to produce a first set of N/2 radio frequency encoded transmit signals for transmission over a first set of N/2 transmit antennas during a first time slot, and to produce a second set of N/2 radio frequency encoded transmit signals for transmission over a second set of N/2 transmit antennas during a second time slot.
17. The method of claim 16 , where encoding the plurality of transmit signals using time division multiplexing comprises activating even-numbered transmit antennas for transmitting the first set of N/2 radio frequency encoded transmit signals during the first time slot, and activating odd-numbered transmit antennas for transmitting the second set of N/2 radio frequency encoded transmit signals during the second time slot.
18. A radar system comprising:
a reference signal generator configured to produce a transmit reference signal comprising a sequence of chirp waveforms;
a waveform generator comprising a plurality of fast-time phase shifters which are each connected to receive the transmit reference signal and which are configured to produce a plurality of transmit signals, each having a different frequency offset that is an integer multiple of an offset frequency Af from the transmit reference signal;
a signal encoder to encode the plurality of transmit signals using a signal conditioning and power amplification to produce N radio frequency encoded transmit signals for transmission over N transmit antennas, where the signal encoder is configured to encode the plurality of transmit signals using time division multiplexing to produce a first set of N radio frequency encoded transmit signals for transmission over a first set of N transmit antennas during a first time slot, and to produce a second set of N radio frequency encoded transmit signals for transmission over a second set of N transmit antennas during a second time slot;
at least a first receive antenna for receiving a target return signal reflected from the first and second sets of N radio frequency encoded transmit signals by a target;
a downconverter configured to mix the target return signal with the transmit reference signal, thereby producing an intermediate frequency signal;
an analog-to-digital converter connected to convert the intermediate frequency signal to a digital signal; and
a radar control processing unit configured to process the digital signal with fast time processing steps to generate a range spectrum comprising N segments which correspond, respectively, to the N radio frequency encoded transmit signals transmitted in the first and second sets of N radio frequency encoded transmit signals.
19. The radar system of claim 18 , where the analog-to-digital converter has a sampling rate f s of at least 2N times the offset frequency Δf.