U.S. patent application number 15/492160 was filed with the patent office on 2017-10-26 for adaptive filtering for fmcw interference mitigation in pmcw radar systems.
The applicant listed for this patent is UHNDER, INC.. Invention is credited to Curtis Davis, Fred Harris, Raghunath K. Rao, David Trager.
Application Number | 20170307753 15/492160 |
Document ID | / |
Family ID | 60022606 |
Filed Date | 2017-10-26 |
United States Patent
Application |
20170307753 |
Kind Code |
A1 |
Harris; Fred ; et
al. |
October 26, 2017 |
ADAPTIVE FILTERING FOR FMCW INTERFERENCE MITIGATION IN PMCW RADAR
SYSTEMS
Abstract
A radar sensing system for a vehicle includes a transmitter
configured for installation and use on a vehicle and able to
transmit radio signals. The radar sensing system also includes a
receiver and a processor. The receiver is configured for
installation and use on the vehicle and able to receive radio
signals. The received radio signals include transmitted radio
signals that are reflected from objects in the environment. The
received radio signals further include radio signals transmitted by
at least one other radar system. The processor samples the received
radio signals to produce a sampled stream. The processor is
configured to control an adaptive filter. Responsive to the
processor, the adaptive filter is configured to filter the sampled
stream, such that the radio signals transmitted by the at least one
other radar system are removed from the received radio signals.
Inventors: |
Harris; Fred; (Lemon Grove,
CA) ; Trager; David; (Buda, TX) ; Davis;
Curtis; (St. Louis, MO) ; Rao; Raghunath K.;
(Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UHNDER, INC. |
Austin |
CA |
US |
|
|
Family ID: |
60022606 |
Appl. No.: |
15/492160 |
Filed: |
April 20, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62450184 |
Jan 25, 2017 |
|
|
|
62327005 |
Apr 25, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 13/34 20130101;
G01S 2013/93271 20200101; G01S 13/931 20130101; G01S 2013/93272
20200101; G01S 7/023 20130101; G01S 13/36 20130101; G01S 2007/356
20130101; G01S 13/325 20130101; G01S 13/93 20130101 |
International
Class: |
G01S 13/93 20060101
G01S013/93; G01S 13/93 20060101 G01S013/93; G01S 13/34 20060101
G01S013/34 |
Claims
1. A radar sensing system for a vehicle, the radar sensing system
comprising: a transmitter configured for installation and use on a
vehicle, and further configured to transmit a radio frequency (RF)
signal; a receiver configured for installation and use on the
vehicle, and further configured to receive an RF signal that
includes the transmitted RF signal reflected from objects in the
environment, as well as further including other radio signals
transmitted from at least one other radar system; a processor; an
adaptive filter; a bypass mechanism; wherein the receiver is
further configured to down-convert and sample the received RF
signal to produce a sampled stream, and wherein the sampled stream
is provided to the processor; wherein the processor, responsive to
processing of the sampled stream, controls the adaptive filter to
filter the sampled stream, such that the other radio signals
transmitted from the at least one other radar system are removed
from the received RF signal; and wherein the bypass mechanism is
configured to determine whether an output of the adaptive filter is
to be selected or an unfiltered sampled stream is to be
selected.
2. The radar sensing system of claim 1, wherein the adaptive filter
comprises a least mean square (LMS)-type of filter.
3. The radar sensing system of claim 2, wherein the LMS-type filter
includes a finite impulse response filter.
4. The radar sensing system of claim 3 comprising a plurality of
receivers, each with a finite impulse response (FIR) filter,
wherein all of the FIR filters use the same weight values for
processing the received signal.
5. The radar sensing system of claim 3, wherein a portion of the
coefficients are adapted and another portion of the coefficients
are held constant.
6. (canceled)
7. The radar sensing system of claim 1, wherein the bypass
mechanism is configured to make a selection based at least in part
on a root mean square (RMS) amplitude value of an input of the
adaptive filter and an RMS amplitude value of the output of the
adaptive filter.
8. The radar sensing system of claim 1, wherein the unwanted
interference is internal to the system.
9. The radar sensing system of claim 1, wherein the unwanted
interference is due to clock spurs.
10. The radar sensing system of claim 1, wherein the at least one
other radar system comprises at least one frequency modulated
continuous wave radar system.
11. A radar sensing system for a vehicle, the radar sensing system
comprising: a transmitter configured for installation and use on a
vehicle, and further configured to transmit radio signals; a
receiver configured for installation and use on the vehicle, and
further configured to receive radio signals that include the
transmitted radio signals reflected from objects in the
environment, as well as further including other radio signals
transmitted from at least one other radar system; a processor; an
adaptive filter; wherein the receiver is further configured to
down-convert and sample the received radio signals to produce a
sampled stream, and wherein the sampled stream is provided to the
processor; wherein the processor is configured to control the
adaptive filter, and responsive to the processor, the adaptive
filter is configured to output a filtered sampled stream, such that
the effect of radio signals transmitted from the at least one other
radar system are removed from the sampled stream; and wherein the
processor is further configured to measure an amplitude of the
sampled stream and to measure an amplitude of the filtered sampled
stream, and wherein the processor is further configured to select
the filtered sampled stream for further range and velocity
processing when a ratio of the amplitude of the filtered sampled
stream to the amplitude of the sample stream is below a first
threshold, otherwise the sampled stream is selected for the further
range and velocity processing.
12. The radar sensing system of claim 11, wherein the processor is
further configured to measure the amplitudes of the filtered
sampled stream and the sampled stream by measuring root mean square
signal levels of the filtered sampled stream and the sampled
stream.
13. The radar sensing system of claim 11, wherein the stream
selected for further processing is forwarded to a correlator and
fast Fortier transform (FFT) processing module for further
processing.
14. The radar sensing system of claim 11, wherein the adaptive
filter comprises a least mean square (LMS)-type of filter.
15. The radar sensing system of claim 14, wherein the LMS-type
filter includes a finite impulse response filter.
16. The radar sensing system of claim 11, wherein the at least one
other radar system comprises at least one frequency modulated
continuous wave radar system.
17. A method for removing interference from a radio signal received
by a vehicle radar sensing system, said method comprising:
providing a radar sensing system comprising a transmitter
configured for installation and use on a vehicle and configured to
transmit radio signals, and a receiver configured for installation
and use on the vehicle and configured to receive radio signals that
are the transmitted radio signals reflected from objects in the
environment, and wherein the received radio signals further include
other radio signals transmitted from at least one other radar
system; providing an adaptive filter; down-converting and
digitizing the received radio signals to produce a baseband sampled
stream; providing the baseband sampled stream to the adaptive
filter, wherein the adaptive filter is configured to output a
filtered baseband sampled stream, such that the effect of the radio
signals transmitted from the at least one other radar system are
removed from the baseband sampled stream; measuring an amplitude of
the baseband sampled stream and measuring an amplitude of the
filtered baseband sampled stream; and selecting the filtered
baseband sampled stream for further range and velocity processing
when a ratio of the amplitude of the filtered baseband sampled
stream to the amplitude of the baseband sampled stream is below a
first threshold, otherwise, selecting the baseband sampled steam
for the further range and velocity processing.
18. The method of claim 17, wherein measuring the amplitudes of the
filtered baseband sampled stream and the baseband sampled stream
comprise measuring root mean square signal levels of the filtered
baseband sampled stream and the baseband sampled stream.
19. The method of claim 17, wherein the further range and velocity
processing comprises correlation and fast Fortier transform (FFT)
processing, respectively.
20. The method of claim 17, wherein providing an adaptive filter
comprises providing a least mean square (LMS)-type of filter.
21. The method of claim 20, wherein the LMS-type filter includes a
finite impulse response filter.
22. The method of claim 17, wherein the at least one other radar
system comprises at least one frequency modulated continuous wave
radar system.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the filing benefits of U.S.
provisional applications, Ser. No. 62/450,184, filed Jan. 25, 2017,
and Ser. No. 62/327,005, filed Apr. 25, 2016, which are both hereby
incorporated by reference herein in their entireties.
FIELD OF THE INVENTION
[0002] The present invention is directed to radar systems, and more
particularly to radar systems for vehicles.
BACKGROUND OF THE INVENTION
[0003] The use of radar to determine range and velocity of objects
in an environment is important in a number of applications
including automotive radar and gesture detection. A radar system
typically transmits radio signals and listens for the reflection of
the radio signals from objects in the environment. By comparing the
transmitted radio signals with the received radio signals, a radar
system can determine the distance to an object. Using multiple
transmissions, the velocity of an object can be determined. Using
multiple transmitters and receivers, the location (angle) of an
object can also be determined.
[0004] There are several types of signals used in different types
of radar systems. One type of radar signal is known as a
frequency-modulated continuous waveform (FMCW). In an FMCW radar
system, the transmitter of the radar system sends a continuous
signal in which the frequency of the signal varies. This is
sometimes called a chirp radar system. Mixing (multiplying) the
reflected wave from an object with a replica of the transmitted
signal results in a CW signal with a frequency that represents the
distance between the radar transmitter/receiver and the object. By
sweeping up in frequency and then down in frequency, the Doppler
frequency can also be determined.
[0005] Another type of radar signal is known as a phase-modulated
continuous waveform (PMCW). For this type of radio signal, the
phase of the transmitted signal is modulated according to a certain
pattern or code, sometimes called the spreading code, known at the
PMCW radar receiver. The transmitted signal is phase modulated by
mixing a baseband signal (e.g., with two values +1 and -1) with a
local oscillator to generate a transmitted signal with a phase that
is changing corresponding to the baseband signal (e.g., +1
corresponding to a phase of 0 radians and -1 corresponding to a
phase of .pi. radians). For a single transmitter, a sequence of
phase values that form the code or spreading code that has good
autocorrelation properties is required so that ghost objects are
minimized. The rate at which the phase is modulated determines the
bandwidth of the transmitted signal and is called the chip
rate.
[0006] In a PMCW radar system, the receiver performs correlations
of the received signal with time-delayed versions of the
transmitted signal and looks for peaks in the correlation. The
time-delay of the transmitted signal that yields peaks in the
correlation corresponds to the delay of the transmitted signal when
reflected off an object. The distance to the object is found from
that delay and the speed of light.
[0007] A PMCW radar will receive not only the reflected signals
from the transmitter of the PMCW radar. A PMCW radar operating in
the presence of an FMCW radar will also receive the signals from
the FMCW radar. The signal from the FMCW radar can significantly
affect the performance of a conventional PMCW radar system.
Potentially, these FMCW signals can be much stronger than the
reflected signals from the PMCW radar. This may cause the radar
system's estimated range, velocity and direction to be
significantly in error.
SUMMARY OF THE INVENTION
[0008] The present invention provides methods and a system for
achieving better performance in a radar system using
phase-modulated continuous wave (PMCW) radar when there are one or
more other radar systems using a frequency-modulated continuous
wave (FMCW) type of radar transmission and operating
simultaneously. The invention accomplishes better detectability of
a PMCW radar object by applying a filtering technique to the
received radio signal that mitigates the effect of an interfering
FMCW radar on the PMCW radar. Another source of potential
interference is clock harmonics. The same techniques that are
described below for FMCW interference mitigation will also work on
clock harmonics.
[0009] A radar sensing system for a vehicle in accordance with an
embodiment of the present invention includes at least one
transmitter, at least one receiver, a memory, and a processor. The
at least one transmitter is configured for installation and use on
a vehicle and further operable or configured to transmit a radio
frequency (RF) signal. The at least one transmitter is further
operable or configured to transmit an RF signal using a phase
modulated signal. The transmitted RF signal is generated by
up-converting a baseband signal. The at least one receiver is
configured for installation and use on the vehicle and further
operable or configured to receive an RF signal. The received RF
signal includes the transmitted RF signal reflected from multiple
objects in the environment and potentially radio signals from other
radars such as a frequency modulated continuous wave (FMCW) radar
transmitter. The received RF signal is down-converted and sampled.
The sampled result is provided to a processor. The processor
selectively applies an adaptive filter to the received RF signal to
mitigate the effect of an interfering waveform from a radar
transmitting an FMCW radio signal. After adaptively filtering the
received RF signal, the radar performs correlations with various
delayed versions of the baseband transmitted signal. The
correlations are used to determine an improved range, velocity and
angle of objects in the environment.
[0010] A radar sensing system for a vehicle in accordance with an
embodiment of the present invention includes at least one
transmitter, at least one receiver, a memory, and a processor. The
at least one transmitter is configured for installation and use on
a vehicle and transmits a radio frequency (RF) signal. The at least
one transmitter phase modulates the transmitted RF signal using
codes generated by at least one of a pseudo-random sequence
generator and a truly random number generator. The at least one
receiver is configured for installation and use on the vehicle and
further operable or configured to receive an RF signal. The
received RF signal includes the transmitted RF signal reflected
from an object. In addition, the received RF signal may also
include radio signals transmitted from one or more other radar
systems, for example an FMCW radar. A down-converted received RF
signal is sampled and provided to a processor. The processor
selectively and adaptively filters the sampled signal to mitigate
the effect of the FMCW radar on the PMCW radar system and then
estimates the range, velocity and angle of objects in the
environment.
[0011] A radar sensing system for a vehicle in accordance with an
embodiment of the present invention includes at least one
transmitter, at least one receiver, a memory, and a processor. The
at least one transmitter is configured for installation and use on
a vehicle and transmits a radio frequency (RF) signal. The at least
one receiver is configured for installation and use on the vehicle
and further operable or configured to receive an RF signal
containing signals reflected from the transmitted signal as well as
signals from one or more other radar systems. The reflected RF
signal is the transmitted RF signal reflected from objects in the
environment of the radar system. The radio signals from one or more
other radar systems may be from an FMCW type of radar. A
down-converted received RF signal is sampled and provided to a
processor. The processor selectively filters out the interference
from the FMCW radar system in an adaptive manner.
[0012] The radar system may include in the receiver a mechanism for
deciding when to employ the cancellation (filtering) processing.
The decision could be based on measuring the root mean square value
(i.e., magnitude) of both the input and the output of the adaptive
filter. The decision to filter could also be based on additional
information such as obtained from other receivers in the radar
system.
[0013] These and other objects, advantages, purposes and features
of the present invention will become apparent upon review of the
following specification in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a plan view of an automobile equipped with one or
more radar systems in accordance with the present invention;
[0015] FIG. 2 is a block diagram illustrating a radar system with a
plurality of receivers and a plurality of transmitters in
accordance with the present invention;
[0016] FIGS. 3 and 4 illustrate aspects of how PMCW digital radar
works;
[0017] FIG. 5 is a block diagram illustrating the basic processing
blocks of a transmitter and receiver in a radar system in
accordance with the present invention;
[0018] FIG. 6 is a block diagram illustrating an exemplary baseband
signal processor in accordance with the present invention;
[0019] FIG. 7 is a block diagram illustrating an interference
mitigation processor in accordance with the present invention;
[0020] FIG. 8 is a block diagram illustrating the adaptive filter
of FIG. 7 in accordance with the present invention;
[0021] FIG. 9 is an exemplary plot of an output of a correlator
without any external interference in the case of two objects in the
environment in accordance with the present invention;
[0022] FIG. 10 is an exemplary plot of an output of a correlator
with a fixed frequency external interferer without the adaptive
mitigation processing in accordance with the present invention.
[0023] FIG. 11 is an exemplary plot of an output of a correlator
with a fixed frequency external interferer with adaptive mitigation
processing in accordance with the present invention.
[0024] FIG. 12 is an exemplary plot of an output of a correlator
without any external interference in the case of two objects in the
environment and spreading codes of length 1023 in accordance with
the present invention;
[0025] FIG. 13 is an exemplary plot of an output of a correlator
with a chirp type external interferer without the adaptive
mitigation processing in accordance with the present invention;
and
[0026] FIG. 14 is an exemplary plot of an output of a correlator
with a chirp type external interferer with adaptive mitigation
processing in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The present invention will now be described with reference
to the accompanying figures, wherein numbered elements in the
following written description correspond to like-numbered elements
in the figures. Methods and systems of the present invention may
achieve better performance from a radar system in the presence of a
simultaneously operating FMCW radar by applying an adaptive filter
to the down-converted and sampled received RF signal at one or more
of the receivers in a radar system. The adaptive filtering may be
selectively applied based on a measurement of the interference as
well by considering other factors or conditions.
[0028] A radar system utilizes one or more transmitters to transmit
signals. These signals are reflected from objects (also known as
targets) in the environment and received by one or more receivers
of the radar system. A transmitter-receiver pair is called a
virtual radar (or sometimes a virtual receiver).
[0029] The transmitted radio signal from each radar transmitter
consists of a baseband transmitted signal, which is up-converted to
an RF signal by an RF upconverter. The up-converted RF signal may
be obtained by mixing the baseband transmitted signal with a local
oscillator signal at a carrier frequency. The baseband transmitted
signal used for transmission by one transmitter of the radar system
might be phase modulated using a series of codes. These codes, for
example, consist of repeated sequences of random or pseudo-random
binary values for one transmitter, e.g., (-1, -1, -1, -1, 1, 1, 1,
-1, 1, 1, -1, -1, 1, -1, 1), although any sequence, including
non-binary sequences and non-periodic sequences could be used and
different sequences could be used for phase modulating the outputs
of different transmitters. Each value of the phase modulation code
sequence is often called a chip. A chip would last a certain
duration called the chip time. The inverse of the chip time is the
chip rate. That is, the chip rate is the number of chips per
second. In an exemplary aspect of the present invention, the
sequences of random binary values may be provided by a truly random
number generator. A truly random number generator is explained in
more detail in U.S. Pat. No. 9,575,160, which is hereby
incorporated by reference herein in its entirety. The random bit
stream (with values +1 or -1) from the truly random number
generator may be multiplied with an output of pseudorandom binary
values from a pseudorandom number generator (PRNG).
[0030] The transmitted radio signals are reflected from objects in
the environment and are received back at the radar receivers (or
virtual receivers). Each object in the environment may reflect the
transmitted radio signal. The received radio signal at the radar
system would consist of the sum of the radio signals reflected from
various objects (targets) in the environment. In addition, a second
radar system operating in the vicinity of the first radar system
will generate a transmitted radio signal that may be received by
the first radar system and interfere with the reflected radio
signals from the first radar system. In other words, the first
radar system would receive radio signals that include radio signals
from transmitters of the first radar system that are reflected from
objects in the environment, as well as radio signals transmitted by
one or more other radar systems.
[0031] At the receiver (receive pipeline) of the radar system, the
received radio signal is down-converted by typical amplification,
filtering, and mixing with in-phase and quadrature-phase components
of an oscillator. The output after down-conversion and sampling is
a sequence of complex value digitized samples comprising a
mathematical real component and a mathematical imaginary component
that are provided to a processor. The baseband signals used at the
transmitter and the reflected radio signals after down-conversion
in the receiver are provided to correlators. The complex valued
digitized samples at the output of the down-converter are
correlated with various time-delayed replicas of the baseband
transmitted signals for different receivers to produce complex
correlation values over a certain duration. That is, a sequence of
digitized samples that correspond to a certain time duration of the
received signal are correlated with a time-delayed replica of the
baseband transmitted signal. The process is repeated for subsequent
samples, thus producing a sequence of complex correlation values
for a given time-delay. This process is also performed for
different transmitter/receiver pairs (virtual receivers).
[0032] A selected correlator that has a replica that is matched in
delay to the time delay of the reflected radio signal from an
object will produce a large magnitude complex correlator output. A
single correlator will produce a sequence of correlator outputs
that are large if the reflected signal has a delay that matches the
delay of the replica of the baseband transmitted signal. If the
velocity of the radar system is different from the velocity of the
object causing the reflection, there will be a Doppler shift in the
frequency of the reflected signal relative to the transmitted
signal. A sequence of correlator outputs for one particular delay
corresponding to an object moving in the environment will have
complex values that rotate at a rate related to the Doppler shift.
Using a sequence of correlator outputs (also referred to as a
scan), the Doppler shift may be estimated, and thus the velocity of
the object in the environment determined. The longer the sequence
of correlator outputs used to estimate the Doppler frequency, the
greater the accuracy and resolution of the estimation of the
Doppler frequency, and thus the greater the accuracy in estimating
the velocity of the object.
[0033] The correlation values for various time delays and various
virtual radars are arranged in two-dimensional arrays known as time
slices. A time slice is a two-dimensional array with one dimension
corresponding to delay or range bin and the other dimension
corresponding to the virtual radar (transmitter-receiver pair). The
samples are placed into respective range bins of the
two-dimensional array (as used herein, a range bin refers to a
distance range corresponding to a particular time delay
corresponding to the round-trip time of the radar signal from a
transmitter, to the target/object, and back to the receiver). The
virtual receivers of the radar system define one axis of the
two-dimensional time slice and the range bins define the second
axis of the two-dimensional time slice. Another new time slice
comprising complex correlation values is generated every 2-30
microseconds. Over a longer time interval, herein referred to as a
"scan" (typically, in a duration of 1-60 milliseconds or longer),
multiple time slices are accumulated to form a three-dimensional
radar data cube. One axis or dimension of the three-dimensional
radar data cube is defined by time (of each respective time slice
requiring 2-30 microseconds), while the receivers (or virtual
radar) define a second axis of the three-dimensional radar data
cube, and the range bins and their corresponding time delays define
a third axis of the three-dimensional radar data cube. A radar data
cube may have a preselected or dynamically defined quantity of time
slices. For example, a radar data cube may include 100 time slices
or 1000 time slices of data. Similarly, a radar data cube may
include different numbers of range bins. The optimized use of radar
data cubes is described in detail in U.S. Pat. No. 9,599,702, which
is hereby incorporated by reference herein in its entirety.
[0034] A single correlator output corresponding to a particular
range bin (or delay) is a complex value that corresponds to the sum
of products between a time-delayed replica of the baseband
transmitted signal--with a time-delayed replica corresponding to
each range bin--and the received down-converted complex samples.
When a particular time-delayed replica in a particular range bin
correlates highly with the received signal, it is an indication of
the time delay (i.e., range of the object) for the transmitted
radio signal that is received after the transmitted radio signal
reflects from an object. Multiple correlators produce multiple
complex correlation values corresponding to different range bins or
delays. As discussed herein, each time slice contains one
correlation value in a time series of correlation values upon which
Doppler processing is performed (e.g., Fast Fourier Transform). In
other words, a time series of complex correlation values for a
given range bin is used to determine the Doppler frequency and thus
the velocity of an object in the range bin. The larger the number
of correlation values in the time series, the higher the Doppler
resolution. A matched filter may also be used to produce a set of
outputs that correspond to the correlator outputs for different
delays.
[0035] There may be scans for different correlators that use
replicas of the transmitted signal with different delays. Because
there are multiple transmitters and multiple receivers, there may
be correlators that process a received radio signal at each
receiver that are matched to a particular transmitted radio signal
by a particular transmitter. Each transmitter-receiver pair is
called a "virtual radar" (a radar system preferably has 4 virtual
radars, or more preferably 32 virtual radars, and most preferably
256 or more virtual radars). The receive pipeline of the radar
system will thus generate a sequence of correlator outputs (time
slices) for each possible delay and for each transmitter-receiver
pair. This set of data is called a radar data cube (RDC). The
delays are also called range bins. The part of the radar data cube
for one point in the sequence of correlator outputs is called a
time slice, and it contains one correlator output for each range
bin and transmitter-receiver pair combination.
[0036] The complex-valued correlation values contained in a
three-dimensional radar data cube may be processed, preferably by a
processor established as a CMOS processor and coprocessor on a
semiconductor substrate, which is typically a silicon substrate. In
one embodiment, the processor comprises fixed function and
programmable CPUs and/or programmable logic controls (PLCs).
Preferably, the system will be established with a radar system
architecture (including, for example, analog RF circuitry for the
radar, processor(s) for radar processing, memory module(s), and
other associated components of the radar system) all on a common
semiconductor substrate. The system may preferably incorporate
additional processing capabilities (such as, for example, image
processing of image data captured by one or more vehicle cameras
such as by utilizing aspects of the systems described in U.S. Pat.
Nos. 5,877,897; 5,796,094; 6,396,397; 6,690,268 and 5,550,677,
which are hereby incorporated herein by reference in their
entireties) within the same semiconductor substrate as well.
[0037] The ability of a continuous wave radar system to distinguish
multiple targets is dependent upon the radar system's range, angle,
and Doppler resolutions. Range resolution is limited by a radar's
bandwidth (i.e., the chip rate in a phase modulated continuous wave
radar), while angle resolution is limited by the size of the
antenna array aperture. Meanwhile, increasing Doppler resolution
only requires a longer scan. A high Doppler resolution is very
valuable because no matter how close two objects or targets are to
each other, as long as they have slightly differing radial velocity
(their velocity towards or away from the radar system), they can be
distinguished by a radar system with a sufficiently high enough
Doppler resolution. As discussed herein, the detection of objects
with a PMCW radar system may be adversely effected by the nearby
operation of one or more frequency modulated continuous wave (FMCW)
radar systems.
[0038] FIG. 1 illustrates an exemplary radar system 100 configured
for use in a vehicle 150. In an aspect of the present invention, a
vehicle 150 may be an automobile, truck, or bus, etc. As
illustrated in FIG. 1, the radar system 100 may comprise one or
more transmitters and one or more receivers 104a-104d for a
plurality of virtual radars. Other configurations are also
possible. As illustrated in FIG. 1, the radar system 100 may
comprise one or more receivers/transmitters 104a-104d, control and
processing module 102 and indicator 106. Other configurations are
also possible. FIG. 1 illustrates the receivers/transmitters
104a-104d placed to acquire and provide data for object detection
and adaptive cruise control. The radar system 100 (providing such
object detection and adaptive cruise control or the like) may be
part of an Advanced Driver Assistance System (ADAS) for the
automobile 150.
[0039] FIG. 2 illustrates the structure of an exemplary radar
system 200 containing one or more transmitting antennas 201, one or
more receiving antennas 202, one or more transmitters 203, one or
more receivers 204, memory modules 205, 206, as well as interfaces
to other parts of a vehicle system via various types of networks
207, such as Ethernet, CAN-FD, or FlexRay. There may also be
processing capability contained in the ASIC 208 apart from the
transmitters 203 and receivers 204.
[0040] The radar sensing system of the present invention may
utilize aspects of the radar systems described in U.S. Pat. Nos.
9,575,160 and/or 9,599,702, and/or U.S. patent application Ser. No.
15/416,219, filed Jan. 26, 2017, and/or Ser. No. 15/292,755, filed
Oct. 13, 2016, and/or U.S. provisional applications, Ser. No.
62/382,857, filed Sep. 2, 2016, Ser. No. 62/381,808, filed Aug. 31,
2016, Ser. No. 62/327,003, filed Apr. 25, 2016, Ser. No.
62/327,004, filed Apr. 25, 2016, Ser. No. 62/327,006, filed Apr.
25, 2016, Ser. No. 62/327,015, filed Apr. 25, 2016, Ser. No.
62/327,016, filed Apr. 25, 2016, Ser. No. 62/327,017, filed Apr.
25, 2016, Ser. No. 62/327,018, filed Apr. 25, 2016, and/or Ser. No.
62/319,613, filed Apr. 7, 2016, which are all hereby incorporated
by reference herein in their entireties.
[0041] FIG. 3 illustrates the basic waveforms of a PMCW radar.
Depending on the baseband signal, one of two phases of a sinusoidal
signal are generated. In a binary system, one of two phases of a
sinusoidal signal are generated, typically 0 degrees and 180
degrees. This also corresponds to transmitting a signal or the
opposite of that signal when the binary baseband chip is a 0 or a
1. More than two phases could be used if the baseband signal is not
binary.
[0042] The transmitted radio signal is then a sequence of
sinusoidal signals with different phases as illustrated in FIG. 4.
Each phase lasts T.sub.c seconds, which is called the chip time.
The inverse of the chip time is the chip rate, which is measured in
chips per second. The chip rate might be on the order of 500
Mbps.
[0043] Also illustrated in FIG. 4 is the received radio signal that
is due to a reflection of the transmitted radio signal from an
object. The received radio signal (that includes the transmitted
radio signal reflected from an object in the environment) will have
the same basic shape as the transmitted radio signal but will be
delayed by an amount corresponding to the round-trip time for the
radio signal to propagate from the transmitter, to reflect from the
object, and then back to be received by the receiver.
[0044] FIG. 5 illustrates an exemplary block diagram of a
transmitter 500 in a radar system and an exemplary block diagram of
a receiver 550 in the radar system. There may be more than one
transmitter 500 and more than one receiver 550 in the radar system.
A baseband signal is generated by a base band signal generator 510
which outputs digital signal samples that are used to form a
baseband signal. These samples could be complex samples,
representing the in-phase (I) and quadrature-phase (Q) baseband
signals. These samples are used as the input to a digital-to-analog
converter (DAC), represented as block 520. The baseband analog
signal at the output of the DAC is used as the input to the
up-converter 530 which generates the RF signal for transmission
through the transmit antenna 540. The received radio signal from
the receiver antenna 560 is down-converted in an exemplary
down-converter module 570, and sampled and quantized in an
exemplary analog-to-digital converter (ADC) 580. The down-converted
signals might be complex (or a pair of real signals) representing
the in-phase (I) and quadrature-phase (Q) of the RF signal. The
output of the ADC 580 is processed by the baseband processing unit
590. The baseband processing unit 590 will be aware of the baseband
transmitted signal output from the baseband signal generator 510.
Optionally, the baseband signal generator 510 and the baseband
signal processor 590 may be combined into a single processor
510/590. There may be multiple baseband processing units 590 for a
given ADC output that correspond to different transmitters (e.g.,
in a MIMO radar system, with multiple transmitters and multiple
receivers). That is, for one receiver there may be a baseband
processing unit that uses the baseband signal of a first
transmitter and another baseband processing unit that uses the
baseband signal of a second transmitter.
[0045] Aspects of the present invention are concerned with the
baseband signal processing unit 590 of the receiver 550. Because
there may be signal interference from one or more radar systems of
the FMCW-type, the output of the ADC 580 at the receiver 550 may
include an interfering frequency-modulated radio signal in addition
to the desired radio signal that has been generated by the PMCW
radar system transmitter, reflected off of objects in the
environment, and then received for processing by the receiver 550.
Mitigating interference from FMCW-type radar systems is the subject
of this invention. In one aspect of the present invention, an
adaptive filter is used to remove the interfering FMCW
interference. However, it is possible that there are no waveforms
from FMCW-type radar systems present (or that those waveform(s) are
present, but below a threshold level), in which case there is no
need to adaptively filter the received radio signal. As illustrated
in FIG. 6, exemplary baseband signal processor 590 includes an FMCW
mitigation module 610, followed by a correlation and FFT processing
module 620 that provides further processing, such as a correlation
to determine the range bin (distance) of an object, and an FFT to
determine the velocity (or Doppler shift) of the object. An input
to the FMCW mitigation module 610 is the output of the ADC 580. The
results of the baseband processing for one receiver are combined
with other similar receivers to perform an angle-of-arrival
estimation of an object. The baseband processing unit 590 of one
receiver 550 may be combined with the baseband processing of other
receivers 550.
[0046] Baseband signal processor (590) will first adaptively filter
the complex digitized sample with a least mean square (LMS) type of
adaptive filter. An LMS filter is a well-known example of an
adaptive filter that finds a difference between an input and an
output, and using an error function and previous filter
coefficients, determines updated filter coefficients. Exemplary LMS
adaptation equations are illustrated below. The notation uses bold
values for vectors. The vector w.sub.n=represents the vector of L
tap weights. The vector x.sub.n represents the last L inputs
x.sub.n=(x.sub.n, x.sub.n-1, . . . , x.sub.n-L+1). The step size
parameter is denoted as .mu.. A leakage coefficient a is chosen
between 0 and 1.
w.sub.n+1=Aw.sub.n+.mu.e.sub.nx.sub.n
e.sub.n=x.sub.n-y.sub.n
y.sub.n=w.sub.n.sup.Tx.sub.n
[0047] FIG. 8 illustrates an exemplary block diagram of an adaptive
filter 710. The adaptive filter of FIG. 8 includes a finite impulse
response (FIR) filter 810 with L taps, an error calculator 820, and
a weight update calculator 830. The FIR filter output is a
correlation of the contents of a shift register with a weight
vector w. The difference between the filter output and the input is
an error signal. This is also the output of the mitigation filter.
The error signal, the current input of complex samples, and the
current set of weights used for the FIR filter, are used to update
the set of weights of the FIR filter. In other words, the error
signal is the output of the adaptive filter process. The eventual
goal of the adaptive filter process will be to have removed much of
the FMCW interference from the input of the filter.
[0048] The complex signal at the output of the interference
mitigation filter will have reduced effect due to the interfering
FMCW signal. As illustrated in FIG. 6, this mitigation filter
output is correlated with the spreading code corresponding to one
or more desired transmitters. After adaptively filtering the
received radio signal, correlations with various delayed versions
of the transmitted baseband signal are performed in the
correlation, FFT processing module 620.
[0049] FIG. 9 illustrates an output of a matched filter when there
are two objects in the environment but no other radar system
operating. The exemplary transmitted radio signal is transmitting 8
periods of an m-sequence of length 255 with a chip rate of 500M
chips/second. The received radio signal is down-converted, sampled,
and used as the input to a matched filter where the filter is
matched to one period of the m-sequence of length 255. A matched
filter is a method of correlating the received signal with all
possible delays of the transmitted sequence. The output has 8 large
spikes corresponding to a near object for each period of the
m-sequence transmitted. FIG. 9 also illustrates that there are also
8 smaller amplitude spikes corresponding to a more distant
target/object.
[0050] FIG. 10 illustrates an output of the same matched filter
when, in addition to the two objects in the environment, there is a
tone jammer with fixed frequency (which is similar to an FMCW radar
system) that interferences with the reflected radio signals
reflecting off of the objects. The output of the tone jammer,
illustrated in FIG. 10 is used to simulate an interfering FMCW
radar system. While the large spikes due to the radio signal
reflecting off of the near object are still visible and detectable,
the spikes due to the more distant object are sometimes lower than
the signal due to the interference. Here, the interference is
assumed to be 4 times (12 dB) larger than the desired signal from
the nearer object.
[0051] FIG. 11 illustrates an output of the same matched filter
when prior to performing the matched filtering, adaptive
interference cancelling is done as described above. As illustrated
in FIG. 11, the adaptive filter effectively removes the undesired
signal(s) and now signals reflected from both the nearby object and
from the more distant object are clearly visible.
[0052] As another example, consider a radar system that transmits 4
periods of a spreading code of length 1023 with a chip rate of 500
Mchips/s. There are two objects in the environment. FIG. 12
illustrates an exemplary filter output when there is no signal
interference (e.g., from an FMCW radar or equivalent) in the signal
input and no adaptive filtering performed by the adaptive filter
710. FIG. 13 illustrates an exemplary filter output when there is
interference from another radar system, such as an FMCW radar that
acts as a jammer. This FMCW radar transmits a chirp signal, which
is a tone which varies in frequency. FIG. 13 further illustrates
the effect of interference from an FMCW radar in the absence of any
adaptive filtering. FIG. 13 also illustrates the output of a
matched filter when the tone or chirp signal from the interfering
FMCW radar has 20 dB larger amplitude than the desired return
signals from the objects. As illustrated in FIG. 13, the second
object (the more distant object) becomes buried in the interfering
FMCW radar signal. When an adaptive filter is employed, as
described herein, the interference from the FMCW radar may be
significantly reduced so that the radio signal reflected from the
second, weaker object is visible. This is illustrated in FIG. 14,
where even when an input signal includes interference from an
FMCW-type radar system, adaptive filtering has removed the majority
of the interference so that the radio signal reflected from the
second, weaker object is not buried in the interference.
[0053] In some cases, there is not another radar transmitting an
FMCW-type of signal or the signal from an interfering FMCW-type
radar is small in amplitude. In such a case, it is not useful to
try to remove the nonexistent interference. As illustrated in FIG.
7, a selection mechanism 730 and controller 720 may be used to
bypass the adaptive filtering (as performed by the adaptive filter
710). The selection mechanism 730 and controller 720 may also be
referred to as a bypass mechanism. By default, the received radio
signal bypasses the adaptive filter 710 without any
cancelation/filtering. As illustrated in FIG. 7, the input radio
signal to the adaptive filter 710 is also received by the selection
mechanism 730 and a controller 720. To determine when to use the
adaptive filter output and when to use the unfiltered input signal,
a measurement of the root mean square (RMS) signal amplitude before
and after cancelation/filtering may be performed by the controller
720 and a ratio of the RMS amplitude of the filter output to the
RMS amplitude of the filter input is calculated. If the ratio is
smaller than a selected threshold value, the adaptive filter's
output, with the signal interference removed, is used. If the ratio
is larger than the selected threshold value, the output of the
adaptive filter is not selected for use, instead, the unfiltered
input signal is used.
[0054] By default, the switch 730 that determines whether to employ
the adaptive filtering can be set by the controller 720 to pass the
received complex samples without any filtering. While a filter
output is generated by the adaptive filter 710, the unfiltered
signal is selected by the switch 730, as controlled by the
controller 720.
[0055] An alternative to this automatic determination of whether to
employ or bypass the interference canceller, software can be used
to decide whether to use the adaptive filter, where the decision is
based not only on the RMS values or amplitude of the input and
output but upon other information as well. The other information
could include information provided by other receivers in the radar
system.
[0056] The preferred embodiments work with a value of mu between
2.sup.-6 and 2.sup.-13. The preferred leakage includes values from
2.sup.-8 to 2.sup.-15. The number of taps may be changed depending
on the situation. The values of the taps may be read and written
from a processor executing software. Optionally, the taps may be
frozen (unchanged) for some period of time.
[0057] In a preferred embodiment, only a single adaption filter is
needed, even for multiple receivers. For example, there may be
separate complex FIRs for each receiver that use a same set of
coefficients. This is possible because the correction or filtering
is phase-independent. The notch filtering of the FMCW tone works
for all RX paths even though they may be phase-shifted relative to
each other. This may save quite a bit of area in the
implementation.
[0058] Changes and modifications in the specifically described
embodiments can be carried out without departing from the
principles of the present invention, which is intended to be
limited only by the scope of the appended claims, as interpreted
according to the principles of patent law including the doctrine of
equivalents.
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