Frequency nonlinearity calibration in frequency-modulated continuous wave radar

Various embodiments include methods and systems having a frequency-modulated continuous wave radar operable to compensate a return signal for nonlinearity in the associated radar signal that is transmitted. The radar signal can be mixed with a delayed version of the radar signal such that the mixed signal can be used to generate an estimate of the nonlinearity. The estimate can be used to compensate the return signal from an object that reflects the associated transmitted radar signal. Additional apparatus, systems, and methods can be implemented in a variety of applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending, commonly assigned, U.S. patent application Ser. No. 15/493,751, entitled “LEAKAGE SIGNAL CANCELLATION,” filed on Apr. 21, 2017, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present disclosure is related to sensing technologies, in particular, to radar-based sensing technologies.

BACKGROUND

A radar system transmits a signal and receives its echo. By processing the echo signal, the radar system is able to detect objects, and to estimate the distances, velocities, and directions associated with the objects. Historically, a pulsed radar is used in military applications, where targets of interest are typically far away from the radar system. The pulsed radar emits short pulses, and in the silent period receives the echo signals. The transmitter of the pulsed radar system is turned off before the measurement starts. However, in many civilian applications, such as automotive radar, wireless gesture recognition, vital sign monitoring, and other monitoring implementations, the objects of interest are usually close to the radar. Due to the short round-trip-delay (RTD) of the desired reflection signal, a pulsed radar doesn't work as well at close range. Instead of a pulsed radar, a frequency-modulated continuous wave or waveform (FMCW) radar is used for short distances.

In FMCW radar, the transmission signal is modulated in frequency (or in phase) and differences in phase or frequency between the transmitted signal and a received signal are used to measure distance to the object from which the transmitted signal is reflected. A linear frequency modulated (LFM) waveform can be used, whose instantaneous frequency linearly increases or decreases over time. With the change in frequency being linear over a wide range, then the distance can be determined by a frequency comparison, with the frequency difference being proportional to the distance. However, in practice, nonlinearity exists in the frequency sweep of the transmitted waveform. This can result in severe performance degradation.

SUMMARY

A frequency-modulated continuous wave radar system based on transmitting a radar signal having a linear instantaneous frequency includes a mechanism to estimate and compensate for a nonlinearity in the linear instantaneous frequency introduced by the waveform generator of the radar signal. Though the waveform generator is designed and constructed to operate to provide a linear sweep of frequency, such a waveform generator does not generate a perfectly ideal waveform. There is a difference in phase between the waveform generated as a radar signal to be transmitted from an antenna and an ideal waveform corresponding to the desired radar signal. This difference in phase translates to a nonlinearity in the desired linear instantaneous frequency for the generated radar signal. Determination of an estimate of this nonlinearity allows for the adjustment of a return radar signal to approach that corresponding to the ideal waveform in the processing of the return radar signal. The return signal, which corresponds to the transmitted radar signal, received at a receiver antenna is mixed with the generated radar signal from the waveform generator to provide an output signal, which is converted to a first digital signal. A delay generator is coupled to the waveform generator to receive the radar signal that is directed to the transmitter antenna of the frequency-modulated continuous wave radar system and to provide a delayed radar signal. The delayed radar signal is mixed with the generated radar signal from the waveform generator to provide an output signal, which is converted to a second digital signal. The second digital signal is processed to generate an estimate of the nonlinearity introduced to the radar signal at the waveform generator. The estimate is used to compensate the first digital signal to provide a compensated digital signal that can be used to perform functions associated with detection of an object.

According to one aspect of the present disclosure, a system having a frequency-modulated continuous wave radar, the system comprising: a waveform generator to generate a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity; a transmitting antenna to transmit the radar signal; a receiving antenna to receive a return signal from an object that reflects the transmitted radar signal; a first mixer to mix the radar signal with the return signal and to output a first mixer output signal; a first analog-to-digital converter to convert the first mixer output signal to a first digital mixer output signal; a delay generator coupled to the waveform generator to generate a delayed radar signal; a second mixer to mix the radar signal with the delayed radar signal and to output a second mixer output signal; a second analog-to-digital converter to convert the second mixer output signal to a second digital mixer output signal; and circuitry to generate an estimate of the nonlinearity based on the second digital mixer output signal and to compensate the first digital mixer output signal by use of the estimate.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the circuitry is arranged to generate the estimate as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the circuitry is arranged to record the first digital mixer output signal and to resample the first digital mixer output signal at an adjusted time using the estimate.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the circuitry to resample includes an interpolation of the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that a delay of the delay generator to generate a delayed radar signal is in the range from 100 picoseconds to 10 nanoseconds.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system includes a first low pass filter coupling the first mixer to the first analog-to-digital converter and a second low pass filter coupling the second mixer to the second analog-to-digital converter.

According to one aspect of the present disclosure, there is provided a system having a frequency-modulated continuous wave radar, the system comprising: a waveform generator to generate a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity; a transmitting antenna to transmit the radar signal; a receiving antenna to receive a return signal from an object that reflects the transmitted radar signal; a delay generator coupled to the waveform generator to generate a delayed radar signal; a mixer coupled to the waveform generator to receive the radar signal; a switch having an input coupled to the delay generator, an input coupled to a path to the receiving antenna, and an output coupled to the mixer such that with the switch operatively coupling the receiving antenna to the mixer, an output of the mixer provides a first mixer output signal from mixing the radar signal with the return signal, and with the switch operatively coupling the delay generator to the mixer, an output of the mixer provides a second mixer output signal from mixing the radar signal with the delayed radar signal; an analog-to-digital converter coupled to the mixer to convert the first mixer output signal to a first digital mixer output signal and to convert the second mixer output signal to a second digital mixer output signal; and circuitry to generate an estimate of the nonlinearity based on the second digital mixer output signal and to compensate the first digital mixer output signal by use of the estimate.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that the circuitry is arranged to generate the estimate as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the circuitry is arranged to record the first digital mixer output signal and to resample the first digital mixer output signal at an adjusted time using the estimate.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the circuitry to resample includes an interpolation of the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that a delay of the delay generator to generate a delayed radar signal is in the range from 100 picoseconds to 10 nanoseconds.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the system includes a low pass filter coupling the mixer to the analog-to-digital converter.

According to one aspect of the present disclosure, there is provided a method of operating a frequency-modulated continuous wave radar, the method comprising: generating, using a waveform generator, a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity; transmitting the radar signal from a transmitting antenna; receiving, at a receiving antenna, a return signal from an object that reflects the transmitted radar signal; mixing the radar signal with the return signal and outputting a first mixer output signal; converting the first mixer output signal to a first digital mixer output signal; generating, using a delay generator, a delayed radar signal from the radar signal; mixing the radar signal with the delayed radar signal and outputting a second mixer output signal; converting the second mixer output signal to a second digital mixer output signal; and generating an estimate of the nonlinearity based on the second digital mixer output signal and compensating the first digital mixer output signal by use of the estimate.

Optionally, in any of the preceding aspects, another implementation of the aspect provides that generating the estimate of the nonlinearity includes estimating the nonlinearity as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that compensating the first digital mixer output signal includes recording the first digital mixer output signal and resampling the first digital mixer output signal at an adjusted time using the estimate.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that resampling the first digital mixer output signal includes an interpolating the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the method includes operating a switch with a mixer that provides the first mixer output signal and the second mixer output signal in a calibration mode or in a compensation mode such that the calibration mode is executed with the switch operatively coupling the delay generator to the mixer, and the compensation mode is executed with the switch operatively coupling the mixer to the receiving antenna.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the method includes applying a fast Fourier transform to compensated first digital mixer output signal to detect the object and to estimate a delay associated with transmitting the radar signal and receiving the return signal.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the method includes using the compensated first digital mixer output signal to determining one or more from a set including distance, velocity, and direction associated with the object.

Optionally, in any of the preceding aspects, a further implementation of the aspect provides that the method includes operating the frequency-modulated continuous wave radar in an automobile or a terminal device.

DETAILED DESCRIPTION

The functions or algorithms described herein may be implemented in software in an embodiment. The software may consist of computer executable instructions stored on computer readable media or computer readable storage device such as one or more non-transitory memories or other type of hardware based storage devices, either local or networked. Further, such functions correspond to modules, which may be software, hardware, firmware or any combination thereof. Multiple functions may be performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, an application specific integrated circuit (ASIC), microprocessor, or other type of processor operating on a processing system, such as but not limited to a computer system, such as a personal signal processing device, personal computer, server, or other computer system, turning such processing system into a specifically programmed machine.

In various embodiments, an online calibration is provided to estimate and compensate frequency sweep nonlinearity in FMCW radar. Calibration is online in that the components for measurement, estimation, and compensation can be integrated with systems including the FMCW radar. Such systems can include, but are not limited to, applications for automotive radar, radar-based gesture recognition and vital sign monitoring used in smart watch and other wearable devices.

In various embodiments, a delay line (DL) technique can be used to estimate frequency sweep nonlinearity. Such techniques can include mixing a waveform that is being transmitted with a delayed version of the waveform, and estimating nonlinearity, associated with a received signal from reflection of the transmitted waveform, via processing the signal at a mixer output from mixing the waveform being transmitted and its delayed version. The delayed version of the waveform may include a delay in the range from 100 picoseconds to 10 nanoseconds or other ranges. Processing this mixed signal provides a calibration method that provides an estimate to compensate the nonlinearity in the received signal to the radar system. This approach has lower computational complexity and can deal with larger nonlinearity than conventional approaches, especially for short-range radar systems, for example, automotive radar, gesture recognition, vital side monitoring, and other monitoring systems.

An ideal waveform for transmission in an FMCW radar can be taken to be a signal, s(t):
s(t)=ej2π(fct+0.5γt2),  (1)
with fcand γ being the center frequency for the waveform and the chirp rate. A chirp, which can be referred to as a sweep signal, is a signal in which the frequency increases or decreases with time. The chirp rate is the rate of change in the chirp. The instantaneous frequency for s(t) is given as fc+γt, linearly increasing over time t.

The received signal, as a reflected signal from an object to which the transmitted signal is incident, can be modeled as x(t):
x(t)=βs(t−τ)=βej2π(fc(t−τ)+0.5γ(t−τ)2),  (2)
with β and τ being amplitude and delay, respectively. The signals s(t) and x(t) can be combined at a mixer having output, y(t):
y(t)=x*(t)s(t)=βej2π(fcτ−0.5γt2)ej2πγtτ,  (3)
which is a sinusoid over t, where x*(t) is the complex conjugate of x*(t). From applying a fast Fourier transform (FFT) to y(t), objects can be detected, and the associated delay τ can be estimated.

However, in practical systems, the frequency is not linear.FIG. 1is a comparison of an ideal frequency over time relationship for a transmitted waveform in curve103compared with a frequency over time relationship, in a non-ideal system, in curve113. A non-ideal waveform transmitted in an FMCW radar, corresponding to the ideal waveform, can be taken to be:
s(t)=ej2π(fct+0.5γt2+ε(t)),  (4)
where ε(t) is a difference in phase between the waveform generated as the radar signal to be transmitted from an antenna and a ideal waveform corresponding to the radar signal, which ε(t) may be referred to as a denoting a phase error. The instantaneous frequency for s(t) is now given as fc+γt+ε′(t), which is not perfectly linear. The term, ε′(t), is the time derivative of ε(t) and is a nonlinearity added to the linear instantaneous frequency, where this nonlinearity is an unwanted artifact from generation of the radar signal.

The received signal, as a reflected signal from an object to which the transmitted signal is incident, for the non-ideal case, can now be modeled as:
y(t)βs(t−τ)=βej2π(fc(t−τ)+0.5γ(t−τ)2+ε(t−τ)).  (5)
The signals s(t) and x(t) combined at the mixer have output, y(t):
y(t)=x*(t)s(t)=βej2π(fcτ−0.5γt2)ej2π(γtτ+ε(t)−ε(t−τ)),  (6)
which is not a perfect sinusoid over t. Applying a fast Fourier transform (FFT) to y(t) of the non-ideal case without calibration yields performance degradation.

FIG. 2is a block diagram of an embodiment of an example system200including a FMCW radar. System200includes a waveform generator202to generate a radar signal for transmission, a transmitting antenna206to transmit the radar signal, a receiving antenna216to receive a return signal that is a reflection of the transmitted radar signal from an object, which can be viewed as an echo of the transmitted signal. Waveform generator202can be implemented using a voltage controlled oscillator (VCO). The radar signal from waveform generator202can be a processed signal for transmission by transmitting antenna206. In typical implementations, the radar signal from waveform generator202can be operated on by a power amplifier (PA)204to provide a processed radar signal to transmitting antenna206. In a similar situation, the received return signal can be a processed return signal. In typical implementations, the return signal form receiving antenna216can be operated on by a low noise amplifier214to provide a processed return signal.

System200can include a mixer207having an input coupled to waveform generator202to receive the radar signal that is generated for transmission and an input coupled to a path to the receiving antenna216. Mixer207includes an output to provide a primary mixed signal that can be processed to determine distances, velocities, and directions associated with objects. Prior to processing to determine distances, velocities, and directions associated with the objects, the primary mixed signal can be applied to an analog-to-digital converter212. Analog-to-digital converter (ADC)212can be coupled to mixer207by a low pass filter (LPF)209such that the primary mixed signal is filtered, according to the settings of the LPF209, and provided to ADC212.

The output of ADC212can be coupled to a processing module220to compensate the received return signal after processing by mixer207, LPF209, and ADC212. Processing module220can include circuitry for a nonlinearity compensator224to compensate the processed received signal and a nonlinearity estimator225that provides an input to nonlinearity compensator224. For example, after generating an estimate of ε′(t), nonlinearity estimator225can provide the estimate of ε′(t) to nonlinearity compensator224. Nonlinearity compensator224can operate on the signal that is output from ADC212using the estimate of ε′(t). For the data signals {y [n]} from ADC212, nonlinearity compensator224can generate a new set of data signals {y[n]}, where each value of the new set at n is equal to a value for the output from ADC212at a time shifted based on ε′(t). Nonlinearity compensator224and nonlinearity estimator225of processing module220can be implemented in an ASIC. Such an ASIC may include a processor with a limited instruction set. Processing module220can include data storage to hold signal data being processed. Depending on the architecture of system200, processing module220may be realized with one or more processors and one or more data storage devices to store instructions and hold signal data being processed.

System200also includes a delay generator215coupled to waveform generator202to provide a delayed radar signal. The delayed radar signal can be provided as the generated radar signal, from waveform generator202to be transmitted, delayed by a delay of the delay generator215. The delay can be in the range from 100 picoseconds to 10 nanoseconds. Other delay values may be used. Delay generator215is coupled to an input of a mixer217, which also has an input coupled to waveform generator202to receive the generated radar signal from waveform generator202. Mixer217has an output to provide a mixer output signal that provides a basis for using the circuitry of processing module220to estimate a nonlinearity in the instantaneous frequency of the radar signal to compensate a received return signal received at the receiving antenna from an object that reflects the transmitted radar signal. Processing module220can be coupled to mixer217by a LPF219and an ADC222. ADC222can be arranged with LPF219to process the mixer output signal into a digital signal to be processed by processing module220.

System200can be viewed as having two parts: a nonlinearity estimation section and a nonlinearity compensation section.FIG. 3Ashows an embodiment of a nonlinearity estimation section305of example system200ofFIG. 2. In nonlinearity estimation section305is delay generator215, mixer217, LPF219, ADC222, and nonlinearity estimator225of processing module220. In operation, a radar signal generated by waveform generator202, where the radar signal is being transmitted, is also provided to DL215. The generated radar signal can have an instantaneous frequency, where the instantaneous frequency is linear plus an unwanted and unknown nonlinearity, and has a center frequency and a chirp rate. DL215operatively imparts a delay to the radar signal to generate the delayed radar signal. The delay imparted by the delay generator to generate a delayed radar signal can be in the range from 100 picoseconds to 10 nanoseconds. Other delay values may be used. DL215can be implemented using a conventional delay generator. Examples of delay generator include an arrangement of an appropriate length of coax cable, inductor-capacitor delay lines, resistor-capacitor circuits, or other delay circuit in an integrated circuit. The delay generator may be a variable delay generator that can select amounts of delay to apply different delays. Testing can be conducted to determine the appropriate amount of delay to impart to the generated signal.

The generated radar signal and the generated delay radar signal is provided to mixer217to mix the generated radar signal with the delayed radar signal and to provide a mixer output signal, which can be given by

yDL⁡(t)=⁢ej⁢⁢2⁢⁢π⁡(fc⁢τDL-0.5⁢⁢γ⁢⁢τDL2)⁢ej⁢⁢2⁢⁢π⁡(γ⁢⁢t⁢⁢τDL+ɛ⁡(t)-ɛ⁡(t-τDL))≈⁢ej⁢⁢2⁢⁢π⁡(fc⁢τDL-0.5⁢⁢γ⁢⁢τDL2)⁢ej⁢⁢2⁢⁢π⁡(γ⁢⁢t⁢⁢τDL+ɛ′⁡(t)⁢τDL)(7)
where τDLis the known small delay of DL215, and ε′(t) is the time derivative of ε(t), where ε(t) is referred to as a phase error, herein. The mixer output signal yDL(t) can be applied to LPF219, whose output is provided to ADC222. The output of ADC222is provided to nonlinearity estimator225of processing module220.

The circuitry of nonlinearity estimator225of processing module220, can estimate a derivative of a phase error of the generated radar signal based on the mixer output signal to compensate a received signal received at the receiving antenna from an object that reflects the transmitted processed signal. That is, the circuitry of nonlinearity estimator225can generate an estimate of the nonlinearity of the instantaneous frequency based on the digital mixer output signal from ADC222. Nonlinearity compensator224can be arranged to estimate the derivative of the phase error, which is the nonlinearity of the instantaneous frequency, as a function of time based on phase of the mixer output signal, the center frequency, the chirp rate, and the delay. From the above equation, ε′(t) can be estimated as

ɛ′⁡(t)=12⁢⁢π⁢⁢τDL⁡[angle⁢⁢(yDL⁡(t))-2⁢⁢π⁡(fc⁢τDL-0.5⁢⁢γ⁢⁢τDL2+γ⁢⁢t⁢⁢τDL)],(8)
where the angle (yDL(t)) is the phase of the mixer output signal yDL(t). The estimated derivative can be provided to nonlinearity compensator224of processing module220to compensate the received return signal received at the receiving antenna from an object that reflects the transmitted processed signal. The output of ADC222and the estimated derivative can be stored in processing module220according to the discrete times of the ADC222for processing by the nonlinearity compensator224. Nonlinearity estimation section305may be structured as an independent unit that can be coupled to a FMCW radar system.

FIG. 3Bshows an embodiment of a nonlinearity compensation section310of example system200ofFIG. 2. Nonlinearity compensation section310can include components of what may be termed a conventional FMCW radar. For example, a conventional FMCW radar may include components similar to LNA214, mixer207, LPF209, and ADC212. Nonlinearity compensation section310provides a novel mechanism to compensate for nonlinearity introduced into the generated radar signal from waveform generator202. The circuitry of nonlinearity compensation section310of processing module220can apply the estimated nonlinearity (estimated derivative of the phase error) to compensate the processed received return signal. The received return signal from the receiving antenna can be operated on by LNA214and processed by mixer207. Mixer207can be arranged in system200to mix the generated radar signal from waveform202with a form of the return signal received from the object that reflects the transmitted radar signal to provide a primary mixed signal. The form of the return signal may be the return signal received by receiving antenna216. Typically the form of the return signal input to mixer207is from processing by LNA214. ADC212is arranged in system200to process the primary mixed signal into a digital received signal as a processed return signal.

In a short-range radar, the delay τ associated the transmission of a generated signal and the reception of its reflection from an object is small. Hence, the primary mixed signal at the output of mixer207can be given as

The primary mixed signal can be processed by LPF209prior to conversion to a digital signal by ADC212, where output of the ADC212provides the digital return signal to the processing module220. The circuitry of nonlinearity compensator224of processing module220can be arranged to operate on the digital return signal to compensate the digital return signal by a resampling based on the estimated nonlinearity, provided by nonlinearity estimator225.

FIG. 3Cis a block diagram of an embodiment of an example resampling implementation in a nonlinearity compensator such as nonlinearity compensator224ofFIGS. 2, 3A, and 3B. In an example resampling procedure, consider original samples, as a set of raw samples {y[n]}, which can be received at nonlinearity compensator224from ADC212, and may be recorded in data storage226in nonlinearity compensator224or other section of processing module220. The original samples are given by
y[n]=y(nΔt).  (10)
From a review of the approximate signal of equation (9), it can be seen that the recorded data can be approximately resampled as follows:

to provide a compensated signal. After generating an estimate of ε′(t), nonlinearity estimator225can provide the estimate of ε′(t) to nonlinearity compensator224at a number of discrete times. Nonlinearity compensator224can provide ε′(t) at times nΔt to an interpolator228of nonlinearity compensator224to generate a new set of data signals {{tilde over (y)}[n]}, where each value of the new set at n is equal to a value for the output from ADC212at a time shifted based on ε′(t). The time shift can be provided as nΔt−ε′(nΔt)/γ as in equation (11). An example of a resampling step can be implemented using an interpolation technique, which may be a linear interpolation. Consider the following. Let y[0], y[1], . . . , y[N−1] be the raw samples, which are sampled from a continuous signal y(t) at time 0, Δt, 2*Δt, . . . , (N−1)*Δt, where * is the multiplication operator. Assume that the value of the sample at time 3.7*Δt is to be determined. Using a linear interpolation technology, this value of the samples can be computed as y[3]*0.3+y[4]*0.7 approximately. Similarly, other samples at any time between 0 and (N−1)*Δt can be computed. Other interpolation technologies, such as cubic, spline, etc., can be used. The resampling procedure can result in the nonlinear term ε′(t) effectively being cancelled such that the resampling step effectively eliminates the phase shift due to the nonlinearity.

FIGS. 4A-4Dillustrate sequencing of a compensation of a received return signal associated withFIGS. 3A-3Bfrom mixer output to a resampled sequence.FIG. 4Ashows output from a mixer, such as mixer207ofFIGS. 3A-3B, for the ideal case in curve430with respect to the non-ideal case in curve435.FIG. 4Bshows an output from an ADC, such as ADC212ofFIGS. 3A-3B, with data points440projected on the analog signal.FIG. 4Cshows resampled data points445with respect to the data points440ofFIG. 4B. For times

n⁢⁢Δ⁢⁢t-ɛ′⁡(n⁢⁢Δ⁢⁢t)γ,⁢y⁡(n⁢⁢Δ⁢⁢t-ɛ′⁡(n⁢⁢Δ⁢⁢t)γ)
can be assigned a value from the original data interpolated from the magnitudes of the data at the sampled times immediately before and immediately after

n⁢⁢Δ⁢⁢t-ɛ′⁡(n⁢⁢Δ⁢⁢t)γ.
This interpolation is shown inFIG. 4C. Other techniques may be used to provide the resampled data points.FIG. 4Dshows the resampled sequence without the original data points.

FIG. 5shows a simulation of a received return signal for an ideal case, a non-ideal case, a case with compensation. Curve550is a representation of the ideal case, which provides an ideal waveform with a narrow main lobe and low side lobes. Curve555is a representation of the non-ideal case with nonlinearity and no calibration/compensation of the received signal. Curve555shows a wider main lobe and higher side lobes than the ideal case of curve550, which indicates poor detection and estimation performance. Curve560is a representation of a resampled sequence, as taught herein, used to provide a corresponding analog curve. Curve560shows that a system implementing the compensation technique, associated withFIGS. 3A-3B, can provide a performance similar to the ideal case reflected in curve550.

FIG. 6shows an alternative embodiment of an example system600similar to system200ofFIG. 2, but using only one mixer627in combination with a switch618. In addition, the number of LPFs and ADCs used can be reduced. System600has low complexity and can provide off-line calibration. The off-line calibration is calibration that can be conducted while system600is not using its FWCW radar. This off-line calibration in this example arrangement of system600is provided by switch618.

System600can include a waveform generator602, a PA604, and a transmitting antenna606in combination with receiving antenna616, LNA614, mixer627, LPF629, and an ADC632to operate as a FMCW radar. Switch618has an input coupled to a delay generator615, an input coupled to a path to receiving antenna616, and output coupled to mixer627such that with the switch operatively coupling delay generator615to mixer627, system600is arranged to operate in a calibration mode. In calibration mode, switch618is set to provide output of DL615in line with the components to provide a signal to a nonlinearity estimator625of a processing module620to run a nonlinearity calibration. With switch618operatively coupling the path to receiving antenna616to mixer627, system600is arranged to operate in a compensation mode, which can also be referred to as an operation mode. In the compensation mode, switch618can be set to the output of LNA614, taking DL615off-line, to run nonlinearity compensation.

ADC632can be arranged in system600to process the mixer output signal into a digital received return signal as a processed received return signal in compensation mode and to provide the mixer output signal to estimate a nonlinearity for calibration. The mixer output provided to ADC632can be first processed by LPF629. ADC632can provide the mixer output signal to the nonlinearity estimator625of processing module620as a digital signal to estimate a nonlinearity for calibration. ADC632can provide the mixer output signal to the nonlinearity compensator624of processing module620as a digital signal to compensate the return signal received at receiving antenna616. Processing module620can provide the output from ADC632to nonlinearity compensator624or to nonlinearity estimator625depending on whether system600is in a compensation mode or in calibration mode, respectively. A switch in processing module620(not shown), operating in conjunction with switch618, may be used to provide the appropriate digital signals to nonlinearity compensator624and nonlinearity estimator625.

The circuitry of nonlinearity compensator624and nonlinearity estimator625can process the data from the received return signal and calibration data in a manner similar or identical to operation of nonlinearity compensator224and nonlinearity estimator225of system200ofFIG. 2. The compensated data from system600or system200can be used in a variety of systems that use FMCW radar. Such compensating systems can be used in, but are not limited to, automotive radar, gesture recognition, vital sign monitoring, and in other radar-based applications. For example, compensating systems similar to or identical to compensating systems, as taught herein, can be used in automobiles, smart phones, smart watches, and other terminal devices.

FIG. 7is a flow diagram of features of an embodiment of an example method700of operating a system having a FMCW radar. At710, a radar signal is generated using a waveform generator. The radar signal can have an instantaneous frequency that is linear plus a nonlinearity. The nonlinearity may be an artifact of a linear sweep generator, used as the waveform generator, which does not provide a perfectly linear instantaneous frequency. At720, the radar signal is transmit from a transmitting antenna. The radar signal may be an amplified radar signal. At730, a return signal from an object that reflects the transmitted radar signal is received at a receiving antenna.

At740, the radar signal is mixed with the return signal and a first mixer output signal is output. The mixing may be performed using one of a number of mixers or may be performed by a mixer in conjunction with a switch such that the mixer can mix different sets of signals. At750, the first mixer output signal is converted to a first digital mixer output signal. At760, a delayed radar signal generated from the radar signal using a delay generator. At770, the radar signal is mixed with the delayed radar signal and a second mixer output signal is output. At780, the second mixer output signal converted to a second digital mixer output signal.

At790, an estimate of the nonlinearity is generated based on the second digital mixer output signal and the first digital mixer output signal is compensated using the estimate. Generating the estimate of the nonlinearity can include estimating the nonlinearity as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal. Compensating the first digital mixer output signal can include recording the first digital mixer output signal and resampling the first digital mixer output signal at an adjusted time using the estimate. Resampling the first digital mixer output signal can include interpolating the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time.

Variations of method700or methods similar to method700can include a number of different embodiments that may or may not be combined depending on the application of such methods and/or the architecture of systems in which such methods are implemented. Such methods can include operating a switch with a mixer that provides the first mixer output signal and the second mixer output signal in a calibration mode or in a compensation mode. The calibration mode can be executed with the switch operatively coupling the delay generator to the mixer, and the compensation mode can be executed with the switch operatively coupling the mixer to the receiving antenna.

Variations of method700or methods similar to method700can include applying a fast Fourier transform to compensated first digital mixer output signal to detect the object and to estimate a delay associated with transmitting the radar signal and receiving the return signal. Such methods can include using the compensated first digital mixer output signal to determine one or more characteristics for the object from a set including distance, velocity, and direction associated with the object. Such methods can include operating the frequency-modulated continuous wave radar in an automobile or a terminal device. Method700can be implemented in different order of executing steps of method700and may be implemented in system200ofFIG. 2, system600ofFIG. 6, or similar systems.

FIG. 8is a block diagram of an embodiment of an example system800having a FMCW radar. System800includes a signal generator means810having an instantaneous frequency, where the instantaneous frequency is linear plus a nonlinearity. The nonlinearity may be an artifact of a linear frequency sweep that does not provide a perfectly linear instantaneous frequency. Signal generator means810provides the radar signal to a transmitter means820to transmit the radar signal. The radar signal provided to transmitter means820may be an amplified radar signal. The transmitted radar signal may be reflected from an object, providing a return signal. The return signal from an object that reflects the transmitted radar signal can be received at receiver means830.

The radar signal can be provided to a mixer means840from signal generator means810and the return signal can provided to mixer means840from receiver means830. The return signal may be provided to mixer840as an amplified return signal. Mixer means840can mix the radar signal from signal generator means810with the return signal from the receiver means830and output a first mixer output signal. The first mixer output signal can be provided to an analog-to-digital conversion means850to convert the first mixer output signal to a first digital mixer output signal.

The radar signal can be provided to a delay means860from signal generator means810, where delay means860generates a delayed radar signal from the radar signal. Delay means860provides the delayed radar signal to mixer means840, where mixer means840mixes the radar signal form signal generator means810with the delayed radar signal and outputs a second mixer output signal. Mixer means840may be realized as a number of mixing means or a combination of a switching means and mixing means to generate the first mixer output signal and the second mixer output signal. The second mixer output signal can be provided to analog-to-digital conversion means850to convert the second mixer output signal to a second digital mixer output signal. Analog-to-digital conversion means850may be realized as a number of analog-to-digital converting means or a single analog-to-digital converting means used with a switching means, which switching means may be associated with the mixer means or with a separate switching means. The first mixer output signal and the second mixer output signal may be provided by one or more low pass filtering means.

The first digital mixer output signal and the second digital mixer output signal can be provided from analog-to-digital conversion means850to an estimation and compensation means870. Estimation and compensation means870can estimate the nonlinearity in the generation of the radar signal by signal generator means810, based on the second digital mixer output signal, and can compensate the first digital mixer output signal using the estimate. The compensated first digital mixer output signal can be provided by estimation and compensation means870for further processing of the return radar signal.

FIG. 9is a block diagram of features of an embodiment of an example system900having a FMCW radar901with frequency nonlinearity calibration of FMCW radar901as taught herein. FMCW radar901can include components as shown inFIGS. 2 and 6may include features discussed with respect toFIGS. 1-8. System900may be integrated into an automobile, a smart phone, a smart watch, other terminal device, and other devices that have functions including short range radar applications.

System900may also include, in addition to FMCW radar901, a number of components such as a control circuitry930, memory module935, communications unit940, data processing unit945, electronic apparatus950, peripheral devices955, display unit(s)960, user interface962, and selection device(s)964. A number of these components can be realized in a common integrated circuit. These components may be structured in a set of integrated circuit.

Control circuitry930can be realized as one more ASICs. Control circuitry930may be structured to provide, among other things, adjustment to gain levels and other variable parameters of the circuitry of FMCW radar901and can be part of estimation and compensation circuitry of FMCW radar901. Depending on the architecture and designed functions of system900, control circuitry930can be realized as one or more processors, where such processors may operate as a single processor or a group of processors. Processors of the group of processors may operate independently depending on an assigned function. In controlling operation of the components of system900to execute schemes associated the functions for which system900is designed, control circuitry930can direct access of data to and from a database.

System900can include control circuitry930, memory module935, and communications unit940arranged to operate as a processing unit to control management of FMCW radar901and to perform operations on data signals collected by FMCW radar901. For example, control circuitry930, memory module935, and communications unit940can be arranged to determine one or more characteristics for an object detected by FMCW radar901from a set including distance, velocity, and direction associated with the object and provide the data to display unit(s)960, memory module935, and/or to systems external to system900via communications unit940. Depending on the application, communications unit940may use combinations of wired communication technologies and wireless technologies

Memory module935can include a database having information and other data such that system900can operate on data to perform functions of system900. Data processing unit945may be distributed among the components of system900including memory module935and/or electronic apparatus950.

System900can also include a bus937, where bus937provides electrical conductivity among the components of system900. Bus937may include conductive traces in an integrated circuit in which a number of components of system900are located. Bus937may include an address bus, a data bus, and a control bus, where each may be independently configured. Bus937may be realized using a number of different communication mediums that allows for the distribution of components of system900. Use of bus937can be regulated by control circuitry930. Bus937may be operable as part of a communications network to transmit and receive signals including data signals and command and control signals.

In various embodiments, peripheral devices955may include drivers to provide voltage and/or current input to FMCW radar901, additional storage memory and/or other control devices that may operate in conjunction with control circuitry930and/or memory module935. Display unit(s)960can be arranged with a screen display that can be used with instructions stored in memory module935to implement user interface962to manage the operation of FMCW radar901and/or components distributed within system900. Such a user interface can be operated in conjunction with communications unit940and bus937. Display unit(s)960can include a video screen or other structure to visually project data/information and images. System900can include a number of selection devices964operable with user interface962to provide user inputs to operate data processing unit945or its equivalent. Selection device(s)964can include a touch screen or a selecting device operable with user interface962to provide user inputs to operate data processing unit945or other components of system900.

In various embodiments, a system can include a set of processors and a set of associated non-transitory machine-readable storage devices to perform tasks for which the system is structured. The system may include a FMCW radar that can be operated, using the set of processors along with instructions stored in the set of non-transitory machine-readable storage devices, including compensating a processed return radar signal for nonlinearity in the generation of the radar signal by a waveform generator, as taught herein. Such set of non-transitory machine-readable storage devices can comprise instructions stored thereon, which, when performed by a machine, cause the machine to perform operations, the operations comprising one or more features similar to or identical to features of methods and techniques described with respect to method700, variations thereof, and/or features of other methods taught herein such as associated withFIGS. 1-9. The physical structures of such instructions may be operated on by one or more processors. For example, executing these physical structures can cause the machine to perform operations comprising: generating, using a waveform generator, a radar signal having an instantaneous frequency, the instantaneous frequency being linear plus a nonlinearity; transmitting the radar signal from a transmitting antenna; receiving, at a receiving antenna, a return signal from an object that reflects the transmitted radar signal; mixing the radar signal with the return signal and outputting a first mixer output signal; converting the first mixer output signal to a first digital mixer output signal; generating, using a delay generator, a delayed radar signal from the radar signal; mixing the radar signal with the delayed radar signal and outputting a second mixer output signal; converting the second mixer output signal to a second digital mixer output signal; and generating an estimate of the nonlinearity based on the second digital mixer output signal and compensating the first digital mixer output signal using the estimate.

A number of operations can be controlled via the set of processors and the set of non-transitory machine-readable storage devices. Operations can include generating the estimate of the nonlinearity to include estimating the nonlinearity as a function of time based on phase of the second digital mixer output signal, center frequency of the radar signal, chirp rate of the radar signal, and delay of the delayed radar signal. Compensating the first digital mixer output signal can include recording the first digital mixer output signal and resampling the first digital mixer output signal at an adjusted time using the estimate. Resampling the first digital mixer output signal can include interpolating the first digital mixer output signal at sampled times immediately before and immediately after the adjusted time. Operations can include operating a switch with a mixer that provides the first mixer output signal and the second mixer output signal in a calibration mode or in a compensation mode such that the calibration mode is executed with the switch operatively coupling the delay generator to the mixer, and the compensation mode is executed with the switch operatively coupling the mixer to the receiving antenna.

Operations can include applying a fast Fourier transform to compensated first digital mixer output signal to detect the object and to estimate a delay associated with transmitting the radar signal and receiving the return signal. Operations can include using the compensated first digital mixer output signal to determine one or more characteristics for the object from a set including distance, velocity, and direction associated with the object.

Further, a machine-readable storage device, herein, is a physical device that stores data represented by physical structure within the device. Such a physical device is a non-transitory device. Examples of machine-readable storage devices can include, but are not limited to, read only memory (ROM), random access memory (RAM), a magnetic disk storage device, an optical storage device, a flash memory, and other electronic, magnetic, and/or optical memory devices. The machine-readable device may be a machine-readable medium such as memory module935ofFIG. 9. While memory module935is shown as a single unit, terms such as “memory,” “memory module,” “machine-readable medium,” “machine-readable device,” and similar terms should be taken to include all forms of storage media, either in the form of a single medium (or device) or multiple media (or devices), in all forms. For example, such structures can be realized as centralized database(s), distributed database(s), associated caches, and servers; one or more storage devices, such as storage drives (including but not limited to electronic, magnetic, and optical drives and storage mechanisms), and one or more instances of memory devices or modules (whether main memory; cache storage, either internal or external to a processor; or buffers). Terms such as “memory,” “memory module,” “machine-readable medium,” and “machine-readable device,” shall be taken to include any tangible non-transitory medium which is capable of storing or encoding a sequence of instructions for execution by the machine and that cause the machine to perform any one of the methodologies taught herein. The term “non-transitory” used in reference to a “machine-readable device,” “medium,” “storage medium,” “device,” or “storage device” expressly includes all forms of storage drives (optical, magnetic, electrical, etc.) and all forms of memory devices (e.g., DRAM, Flash (of all storage designs), SRAM, MRAM, phase change, etc., as well as all other structures designed to store data of any type for later retrieval.

As noted, the machine-readable non-transitory media, such as computer-readable non-transitory media, includes all types of computer readable media, including magnetic storage media, optical storage media, flash media and solid state storage media. It should be understood that software can be installed in and sold with a device having a FMCW radar. Alternatively the software can be obtained and loaded into the device having a FMCW radar, including obtaining the software through physical medium or distribution system, including, for example, from a server owned by the software creator or from a server not owned but used by the software creator. The software can be stored on a server for distribution over the Internet, for example. Execution of various instructions may be realized by the control circuitry of the machine to execute one or more features similar to or identical to features of methods and techniques described with respect to method700, variations thereof, and/or features of other methods taught herein such as associated withFIGS. 1-8. For example, the instructions can include instructions to operate a FMCW radar as part of other systems in accordance with the teachings herein. Control circuitry for operation of the FMCW radar as part of other systems can include one or more ASICs.