Vehicle radar system with blind spot detection

A vehicle radar system for monitoring a blind spot of a vehicle includes a radar transmitter mounted on the vehicle and a transmitting antenna coupled to the radar transmitter. The transmitting antenna transmits radiation in a pattern into a region adjacent to the vehicle, the pattern comprising a first radiation lobe and a second radiation lobe. A null region of the pattern between the first lobe and the second lobe is directed into the region approximately perpendicular to a longitudinal axis of the vehicle, the longitudinal axis running between a rear end of the vehicle and a front end of the vehicle and running along a line of travel of the vehicle.

BACKGROUND

1. Technical Field

This application is related to vehicle radar systems, and, more particularly, to vehicle radar systems with blind spot detection.

2. Discussion of Related Art

Some automotive radar systems monitor the immediate surroundings of a host vehicle and can enable safety or comfort features such as blind spot detection and lateral collision avoidance. Blind spot detection radar sensors must cover a very wide area and must have the ability to classify the obstacles in the radar field of view. In particular, for example, the radar sensor must be able to distinguish a flat wall or guardrail from a stagnant vehicle at low speed, i.e., a vehicle travelling in the same direction and at approximately the same speed as the host vehicle.

Conventional vehicle blind spot detection/monitoring systems typically implement one broad radar transmit pattern and an array of receivers. The receiver beam is either steered or formed digitally. For example, in some systems, switchable relatively narrow beams scan the area of interest. This approach has the disadvantage of requiring multiple analog receiver circuits, which can be relatively high-cost. In other systems, a single broad transmit antenna is used for short range, and several, e.g., four, separate receivers are used to enable digital beam forming. These approaches to digital beam forming can also add substantially to the cost of the system.

SUMMARY

The present invention is directed to a vehicle radar system with blind spot detection which overcomes these drawbacks of the prior art. The vehicle to which the invention is directed can be any type of moving vehicle, including an automobile, bus, truck, motorcycle, bicycle, etc. The invention is described herein referring to the vehicle as an automobile. However, it will be understood that the invention is applicable to other types of vehicles.

According to the present invention, a fixed transmission (Tx) pattern with specific characteristics is used. The Tx pattern is fixed, i.e., not steerable, and has a null in the direction perpendicular to the direction of travel of the vehicle. According to the invention, such a pattern can be realized by a network feeding two rows of patches with a fixed phase shift, i.e., a fixed phase difference between rows, which can be, for example, 120 degrees. If the radar transceiver, which is also interchangeably referred to herein as a “radar sensor” or simply “sensor,” is mounted at +20 degrees directed toward the rear of the vehicle, then the null in the Tx pattern is formed at −20 degrees relative to the sensor bore sight, such that the null is created perpendicular to the direction of travel of the vehicle.

As a result of this feature of the Tx pattern, the return from a stationary object, e.g., wall or guardrail, having zero range rate, i.e., no Doppler, is minimized, while the return from the guardrail in the forward and rearward directions has a measurable Doppler shift. This facilitates classification of the guardrail. Another road vehicle stagnating in the blind spot detection zone provides a return from the side lobe and the main backward beam with no Doppler shift as the vehicle is stagnating, i.e., has no range rate.

According to one aspect, a vehicle radar system for monitoring a blind spot of a vehicle is provided. The vehicle has a longitudinal axis running between a rear end of the vehicle and a front end of the vehicle and runs along a line of travel of the vehicle. The vehicle radar system includes a radar transmitter mounted on the vehicle and a transmitting antenna array coupled to the radar transmitter. The radar transmitter and transmitting antenna array transmit radiation in a pattern into a region adjacent to the vehicle. The pattern includes a first radiation lobe and a second radiation lobe. A null region of the pattern between the first lobe and the second lobe is directed into the region approximately perpendicular to the longitudinal axis of the vehicle.

In some exemplary embodiments, a bore sight of the antenna is directed away from the vehicle at an angle of approximately 20 degrees from the null region toward the rear end of the vehicle.

In some exemplary embodiments, the transmitting antenna array comprises at least one planar antenna cell.

In some exemplary embodiments, the transmitting antenna array comprises a first antenna cell and a second antenna cell for transmitting the radiation into the region. A phase shifter between the first and second antenna cells adjusts phase of at least one of the first and second antenna cells to steer the radiation.

In some exemplary embodiments, the phase shifter introduces approximately 120 degrees of phase difference between the first and second antenna cells.

In some exemplary embodiments, the system further comprises at least one receiving antenna array for receiving radiation return signals from objects in the region adjacent to the vehicle.

In some exemplary embodiments, the at least one receiving antenna array comprises first and second receiving antennas.

In some exemplary embodiments, the at least one receiving antenna array comprises at least one planar antenna cell.

In some exemplary embodiments, the system further comprises a processor for processing the radiation return signals to determine at least one of speed and range of the objects in the region adjacent to the vehicle.

In some exemplary embodiments, the region adjacent to the vehicle in which the objects are detected includes a blind spot of the vehicle.

In some exemplary embodiments, the radar system is a pulsed Doppler radar system.

In some exemplary embodiments, the radar system operates at a radar frequency of 24 GHz.

DETAILED DESCRIPTION

FIG. 1includes a schematic diagram which illustrates a vehicle10equipped with a radar system for blind spot detection/monitoring, according to some exemplary embodiments. InFIG. 1, vehicle10is illustrated such that the front end12of vehicle10is facing in the direction indicated by directional arrow14, which indicates the direction of travel of vehicle10. The rear end18of vehicle10includes a rear bumper16to which the radar transceiver20according to exemplary embodiments is attached. It should be noted that radar transceiver20is also interchangeably referred to herein as a “radar sensor” or simply as a “sensor.” In some particular embodiments, in accordance with Blind Spot Information System (BSIS) and Rear Cross Traffic Alert system requirements, radar sensor20provides a minimum total 100-degree field of view, including a minimum +50 degree field of view to provide timely detection of a vehicle approaching from the rear and a minimum −50 degree field of view for detection of an approaching vehicle from the front. A region adjacent to vehicle10includes a must-alert zone22and a may-alert zone24. The radar system is required to provide an alert when any portion of another vehicle26occupies any portion of must-alert zone22, which may also be referred to as the “blind spot” of vehicle10. The radar system is permitted to and may provide an alert when another vehicle26occupies any portion of may-alert zone24.

FIG. 2includes a detailed schematic diagram of vehicle10and the region adjacent to vehicle10, according to some exemplary embodiments. As described above, vehicle10includes front end12and rear end18, which define a direction of forward travel indicated by arrow14. In some exemplary embodiments, must-alert zone22, i.e., blind spot of vehicle10, is defined to extend vertically from reference B to reference C and horizontally from reference G to reference F. As noted above, if any portion of another vehicle enters any portion of must-alert zone22, an alert will be generated. May-alert zone24extends outside of must-alert zone22vertically from reference A to reference D and horizontally from reference H to reference E. No alerts are issued if another vehicle is located completely outside of may-alert zone24, i.e., in must-not-alert zoned25.

It should be noted thatFIG. 2includes specific exemplary dimensions related to must-alert zone22, may-alert zone24and vehicle10. It will be understood that these dimensions are exemplary only and that the various zones and vehicle10can have other dimensions.

According to the inventive concept, the radar system monitors the region immediately adjacent to vehicle10in order to provide alerts when other vehicles enter the blind spot of vehicle10.FIGS. 3A and 3Binclude schematic diagrams illustrating vehicle10and the region adjacent to vehicle10, which is monitored by blind spot detection radar, according to some exemplary embodiments. Vehicle10is illustrated to be moving in a forward direction at a velocity, i.e., direction and speed, indicated by vector14.FIGS. 3A and 3Balso include schematic representations of potential objects30,31,32,33,34,35, which may be stationary with respect to vehicle10or may be moving laterally or in parallel, i.e., forward or backward, with respect to vehicle10, as indicated schematically by a velocity vector at each object.FIG. 3Aillustrates examples of detected object which will cause alerts to be generated, andFIG. 3Billustrates example of detected objects which will not cause alerts to be generated.

Referring toFIG. 3A, objects30and32are moving primarily backward, but also have a lateral motion component directed toward vehicle10. These could be other merging vehicles entering the blind spot of vehicle10from the front and side of vehicle10, and, therefore, will cause alerts to be generated. Object31is located in the blind spot of vehicle10and is moving in the same direction as vehicle10. It is moving at approximately the same speed as, i.e., stagnating with, or slightly faster than, i.e., overtaking, vehicle10. Object31will also cause an alert to be generated.

Referring toFIG. 3B, detected objects33,34and35are detected as moving backwards with respect to vehicle10, and in a direction parallel to vehicle10, at approximately the same speed as the speed at which vehicle10is moving. These objects33,34and35are concluded to be stationary with respect to the roadway, and may be stationary objects such as guardrails, walls, or the like. Such objects do not cause alerts to be generated.

FIG. 4includes a schematic diagram of rear bumper16of vehicle10, according to some exemplary embodiments. Referring toFIG. 4, radar transceivers or sensors20are attached to the inside of rear bumper16. In some exemplary embodiments, two radar sensors20are attached to respective left and right sides of bumper16. In some embodiments, radar sensors20are oriented to be pointed an angle ω from the longitudinal axis11. In some particular exemplary embodiments, the angle ω is approximately 20 degrees. Other angles can be selected; ω=20 degrees will be used in this description as an exemplary illustration. With the orientation angle co, the bore sights17of radar sensors20are oriented the angle ω toward the rear of vehicle10from the side-to-side axis13that is perpendicular to longitudinal axis11.

FIG. 5includes a schematic diagram illustrating radar transmit patterns used to monitor the blind spot of vehicle10, according to some exemplary embodiments. Referring toFIG. 5, two transmit pattern curves40and42are illustrated. According to the inventive concept, the transmit pattern can be achieved by using an array of two transmit antenna cells. A phase shifter is used to adjust the phase of each cell to steer the beam into the antenna bore sight or squint.FIG. 5includes a first transmit pattern40in a bold line and a second transmit pattern42in a fine line. The pattern40in the bold line is generated by introducing approximately 120 degrees of phase difference between the two antenna cell feeds. The pattern42in the fine line is generated by introducing approximately 65 degrees of phase difference between the two antenna cell feeds. The amount of phase difference and, hence, the shape of the transmit pattern used, can be selected based upon the desired performance characteristics and features of the application in which the system is to be used.

Referring toFIG. 5, and referring specifically to the transmit pattern40in the bold line as an exemplary illustration, transmit pattern40includes a first main lobe44and a second front side lobe46. First main lobe44provides high gain in the backward direction for detection of vehicles entering the blind spot from the rear. Ground stationary target returns, i.e., returns from ground stationary targets such as guardrails, walls, etc., include a Doppler shift, since such ground stationary targets are in motion relative to vehicle10. Second front side lobe46enables detection of a front-entry stagnant or merging vehicle.

Pattern40also includes a null48between lobe44and lobe46. Null48in the direction perpendicular to longitudinal axis11of vehicle10(FIG. 4) enables target classification. Specifically, null48allows for the discrimination between ground stationary objects, e.g., guardrails, and other vehicles traveling in the blind spot zone. With null48perpendicular to the direction of travel, the return from a ground stationary object having zero range rate, i.e., no Doppler, is minimized. The return from the ground stationary object in the forward and backward directions has a measurable Doppler shift, which facilitates classification of the ground stationary object. On the other hand, a vehicle stagnating in the blind spot zone provides a return from second front side lobe46and the first main lobe44with no Doppler shift, i.e., no range rate.

Continuing to refer toFIG. 5, the axis between 0 and 180 degrees is parallel to longitudinal axis11of vehicle10. The axis between 90 and 270 degrees is parallel to side-to-side axis13. Bore sight17of radar sensor20is directed +20 degrees rearward from side-to-side axis13. Thus, null48in pattern40is generated at −20 forward of bore sight17, which places null48on side-to-side axis13, projecting perpendicular to longitudinal axis11of vehicle10.

FIG. 6includes a schematic plan view diagram of transmit antenna circuitry50used to generate the radar transmit pattern for blind spot detection/monitoring, according to some exemplary embodiments. Referring toFIG. 6, transmit antenna circuitry50includes two antenna cells52and54used to transmit radar signals into the region adjacent to vehicle10. A phase shifter circuit56adjusts the phase of the feed60of each antenna cell52,54to steer the beam into the antenna bore sight or squint. In some exemplary embodiments, phase shifter circuit56includes diodes58.

In some exemplary embodiments, phase shifter circuit56introduces a predetermined amount of phase difference between the two antenna cells52and54, depending on the desired shape of the transmit pattern. In some particular exemplary embodiments, phase shifter circuit56generates a phase difference between antenna cells52and54of approximately 120 degrees, which results in transmit pattern40illustrated inFIG. 5. In other particular exemplary embodiments, phase shifter circuit56generates phase difference between antenna cells52and54of approximately 65 degrees, which results in transmit pattern42inFIG. 5. Other phase differences for generating other transmit patterns are possible, within the scope of the present inventive concept.

FIG. 7includes a detailed schematic diagram of a measured antenna transmission pattern40A generated in accordance with some exemplary embodiments. Referring toFIG. 7, the horizontal axis refers to the angle of transmission from the antenna, with 0 degrees being located at bore sight17of the antenna. The vertical axis is signal strength, in dBm. As illustrated in the curve ofFIG. 7, transmission pattern40A includes a first main lobe44A and a second front side lobe46A. First main lobe44A provides the maximum gain in the direction toward the rear. Pattern40A also includes a null48A between lobe44A and lobe46A. Null48A is located at approximately −20 degrees from bore sight17toward the front. With bore sight17directed +20 degrees toward the rear, null48A is directed perpendicular to longitudinal axis11of vehicle10.

FIG. 8includes an image of a printed circuit board (PCB)70, which is part of the radar transceiver20, according to some exemplary embodiments. Referring toFIG. 8, PCB70includes a receiver section, which includes receive antenna circuitry64and a transmitter section, which includes transmit antenna circuitry50. As described above, transmit antenna circuitry50includes two antenna cells52and54used to transmit radar signals into the region adjacent to vehicle10. Phase shifter circuit56adjusts the phase of the feed of each antenna cell52,54to steer the beam into the antenna bore sight or squint, as described above in detail. Receive antenna circuitry64can include two wide-pattern antenna rows66and68. In some exemplary embodiments, antenna rows66and68are separated by one-half wavelength in order to enable bearing measurement by phase-comparison/phase monopulse techniques. PCB70also includes the electronic circuitry62used to carry out the required processing and other functions to provide radar signal transmission, reception and processing used to implement the various features of the various embodiments as described herein in detail.

FIG. 9includes a schematic diagram illustrating an approach to applying a phase comparison technique to the signals received by two receive antenna rows66and68to determine bearing angle θ to a target, according to some exemplary embodiments.FIG. 9also includes mathematical equations used in calculating the bearing angle θ, according to some exemplary embodiments.

According to some embodiments, the radar detection system uses a 24 GHz narrow-band pulsed radar waveform.FIG. 10includes a schematic diagram of the timing of the transmit pulse waveform, according to some exemplary embodiments. Referring toFIG. 10, the waveform is a pulsed waveform with a long, i.e., greater than 100 ns, rectangular transmit pulse. In the particular exemplary illustration ofFIG. 10, the time duration tPULSEof the rectangular transmit pulse is approximately 150 ns. According to exemplary embodiments, the pulse repetition frequency (PRF) is greater than 1.0 MHz. Hence, the pulse repetition period tPRFis less than 1.0 μs, since only detection at near range is relevant to the blind spot radar detection system. In the particular exemplary illustration ofFIG. 10, tPRF=500 ns.

According to some exemplary embodiments, the receiver gate is set to be very narrow, i.e., less than 10 ns.FIG. 11includes a schematic timing diagram which illustrates the timing of the transmit pulse waveform and the receiver gate pulse waveform, according to some exemplary embodiments. Referring toFIG. 11, again, the transmit pulse width is illustrated to be approximately 150 ns. The receiver gate pulse is illustrated to be 10 ns wide. Thus the receiver gate is set to be very narrow and the range step/bin increment is a fraction of the receiver gate size. This arrangement causes a significant mismatch and a loss of sensitivity in favor of an accurate localization of targets. For example, in some exemplary embodiments, the receiver gate is activated after a delay which allows for range detection increments in 10 cm steps. Also, very near range detection is realized. In some particular exemplary embodiments, a range limit of 0.2 m was achieved.

FIG. 12includes a schematic block diagram of transmit and receive circuitry in a radar transceiver or sensor, such as transceiver or sensor20described above, according to some exemplary embodiments. Referring toFIG. 12, a transmit trigger signal Tx Trig is received by pulse shaping circuitry74to generate the transmit timing pulse having the timing described above in detail. An RF oscillator76generates the RF signal, e.g., the 24 GHz radar signal, to be transmitted into the region adjacent to vehicle10. The transmit timing pulse generated by pulse shaping circuitry74is used to gate the RF signal to transmit antenna50by enabling RF switch to selectively pass the pulsed radar signal with the timing of the transmit timing pulse. Transmit antenna50transmits the pulsed radar signal into the region adjacent to vehicle10, including the blind spot.

Continuing to refer toFIG. 12, receive antennas64receive radar signals returning from objects illuminated by the transmitted radar signals. An antenna select circuit is used to selectively enable the return radar signals from the antennas such that the return signal from only one of the receive antennas at a time is processed. The selected received signal is amplified by low-noise amplifier (LNA)88. The received radar signals are phase shifted as required by phase shifter88and are routed to I and Q mixers82and84. A receive trigger signal Rx Trig is received by pulse shaping circuitry80to generate a receive enabling pulse signal, which is applied to RF switch78. The RF signal generated by RF oscillator76is gated to the I and Q mixers82and84through RF switch78, which is selectively enabled to pass the pulsed RF signal by the pulse signal generated by pulse shaping circuitry80. This pulsed RF signal mixes with the received amplified and phase-shifted radar signals to generate I and Q IF signals for the returning received radar signals for further processing.

FIG. 13Aincludes a schematic block diagram illustrating the sample-and-hold processing of one of the I and Q IF signals, according to some exemplary embodiments.FIG. 13Bincludes a timing diagram illustrating the timing of the sample-and-hold processing of one of the I and Q IF signals, according to some exemplary embodiments. Referring toFIGS. 13A and 13B, the I or Q IF signal is received from I or Q mixer82or84, respectively, at a sample switch92. The closing of sample switch92and, therefore, the sampling of the I or Q IF signal, is controlled according to the timing of the sample switch pulse waveform indicated in the timing diagram ofFIG. 13B. The sample switch is closed at a time which corresponds to a certain range, according to time of flight (TOF). If there is a target-reflected signal at this time, then it will be sampled. An exemplary illustrative sampled I or Q waveform illustrated in the timing diagram is filtered or “held” using capacitor96, and the sampled and held I or Q IF signal is filtered to a baseband I or Q signal by low-pass filter98. An exemplary illustrative baseband I or Q signal is illustrated in the timing diagram ofFIG. 13B. The sampled-and-held baseband I or Q signal is routed to analog-to-digital converter (A/D)100, where it is converted to digital data for further processing.

FIG. 14includes a schematic block diagram and timing diagram of RF, i.e., radar, pulses in flight, according to some exemplary embodiments. Referring toFIG. 14, the transmit pulse is illustrated to extend approximately 333 ns in time. For a single point target at range R, a signal is available to the receiver processor at time t=2R/c, after the rising edge of the transmit pulse, where c is the speed of light. If there is another target at R+ΔR, the signal energy due to the second target may also be admitted to the receiver processor if ΔR<c*X PulseWidth/2=2 m, in this illustrative exemplary embodiment in which the receive gate is 13.3 ns in duration.

FIG. 15includes a schematic timing diagram which illustrates the relative timing between transmit pulses and receiver gate pulses, used to detect targets in the blind spot of vehicle10, according to some exemplary embodiments. Referring toFIG. 15, the top timing curve is the transmit pulse curve. It illustrates the timing of a series of radar pulses transmitted into the region adjacent to vehicle10. The second timing curve represents the receive gate pulse waveform for one of the receive antennas. It will be understood that the same waveform is used with both receive antennas. As illustrated inFIG. 15, for a first series of k transmit pulses and receiver gate pulses, the rising edge of the receiver gate pulse is timed to occur a predetermined time X after the rising edge of the transmit pulse, i.e., after the pulsed radar signal is transmitted into the region adjacent to vehicle10. The value of the delay X is determined by the range currently being analysed. That is, the receiver gate is open, i.e., active, for the time period during which returns from objects at the desired range would arrive back at radar transceiver20. For each range, k pulses are transmitted. After the kth pulse, the next pulse, i.e., the first receive gate pulse of the next range being analysed, is generated at a delay of X+ΔX after the rising edge of the transmit pulse. The additional delay ΔX is determined based on the range resolution or sensitivity of the system. In the illustrated exemplary embodiments, the selected ΔX is based on a range resolution of approximately 10 cm. It will be understood that other range resolutions are possible. The next series of k pulses can be initiated at a time of X+2ΔX following the rising edge of the associated transmit pulse. This pattern continues for both receive antennas and for the entire region being scanned by the system.

In some conventional blind spot monitoring and detection systems, a frequency-modulated waveform is employed. These waveforms suffer from feed-through/coupling between receiver and transmitter circuits, which limits very-near-range detection capability. These conventional systems overcome this issue at the cost of increased complexity or hardware in order to increase the dynamic range of the receiver. According to the present inventive concept, implementation of the pulsed waveform described in detail above mitigates these issues, thus providing a simpler and more cost effective solution. Also, the pulsed waveform of the inventive concept has the advantage of being less demanding of processor (CPU) time than frequency-modulated approaches. Also, the pulsed waveform of the inventive concept provides an unambiguous measurement of range and velocity on a sweep-by-sweep basis, thus reducing the latency of the system and enabling the classification of the obstacle by an analysis of the Doppler signature associated with each target.

According to the present inventive concept, the radar return signal is captured by a receiver antenna and down-converted by a homodyne mixer to baseband typically below 20 kHz before being digitalized by an A/D converter. Typically, the useful bandwidth of the baseband signal, which is set according to the Doppler/velocity of the relevant target, is less than 40 kHz for a 24 GHz radar system. The radar waveform includes 128 to 1024 points sampled with eight to sixteen bits resolution. The digital signal is processed by radar signal processing algorithms providing the localization, i.e., range, relative velocity, bearing, of potential relevant targets. An application layer, also referred to as a feature algorithm, can assess the list of reported obstacles and makes the final decision, e.g., warning, desired speed, etc.