Patent Application
20180159647
This invention generally relates to vehicular radar systems, and in particular to the use of a controller area network to synchronize vehicle radar devices.
A new class of safety systems, referred to as advanced driver assistance systems (ADAS), has been introduced into automobiles to reduce human operation error. The proliferation of such assistance systems, which may provide functionality such as rear-view facing cameras, electronic stability control, and vision-based pedestrian detection systems, has been enabled in part by improvements in microcontroller and sensor technologies. These systems may be enabled by smart sensors based on millimeter-wave automotive radars. Enhanced embedded radar-based solutions are enabling complementary safety features for ADAS designers. See, for example, “Making Cars Safer Through Technology Innovation,” October 2013.
In an automotive radar system, one or more radar sensors may be used to detect obstacles around the vehicle and the speeds of the detected objects relative to the vehicle. A processing unit in the radar system may determine the appropriate action needed, e.g., to avoid a collision or to reduce collateral damage, based on signals generated by the radar sensors. Current automotive radar systems are capable of detecting objects and obstacles around a vehicle, the position of any detected objects and obstacles relative to the vehicle, and the speed of any detected objects and obstacles relative to the vehicle. Via the processing unit, the radar system may, for example, alert the vehicle driver about potential danger, prevent a collision by controlling the vehicle in a dangerous situation, take over partial control of the vehicle, or assist the driver with parking the vehicle.
Currently, an integrated circuit (IC) containing a radar transceiver may be placed at each location in a vehicle where a radar signal is needed. For example, three ICs may be located on the front of a vehicle (middle and both corners) to provide forward looking coverage. Additional ICs may be deployed on the sides and rear of the vehicle.
The Controller Area Network (CAN) is an International Standardization Organization (ISO) defined serial communications bus originally developed for the automotive industry to replace the complex wiring harness with a two-wire bus. As an alternative to conventional multi-wire looms, CAN Bus allows various electronic components such as electronic control units, microcontrollers, devices, sensors, actuators and other electronic components throughout the vehicle to communicate on a single or dual-wire network data bus at data rates up to 1 Mb/s.
Particular embodiments in accordance with the invention will now be described, by way of example only, and with reference to the accompanying drawings:
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.
Specific embodiments of the invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. In the following detailed description of embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.
With the advancement in radar technology more and more high end automotive applications are being created; surround view is one of them. The automotive surround view camera system is an emerging automotive ADAS (Advanced Driver Assistance System) technology that assists the driver in parking the vehicle safely by allowing him/her to see a top-down view of the 360 degree surroundings of the vehicle. Such a system normally consists of four to six wide-angle (fish-eye lens) cameras mounted around the vehicle, each facing a different direction. From these camera inputs, a composite view of the surroundings of the vehicle is synthesized and shown to the driver in real-time during parking. Surround view is described in detail in “Surround view camera system for ADAS on TI's TDAx SoCs,” October 2015, Vikram Appla et al, which is incorporated by reference herein.
Object detection by radar may be used to determine distance from the vehicle to various nearby objects. This information may be merged with the surround view camera images to further improve the accuracy and safety of ADAS. To take advantage of high end data blending algorithms and better interference mitigation techniques, the operation of the radar sensors fitted around the vehicle may need to be synchronized within a couple of micro-seconds.
Synchronizing the radar sensors fitted across the vehicle body could be done with additional cable and an IO (input/output) interface on each radar device; however, adding a special purpose wiring harness to a vehicle may add significant expense.
A system will now be disclosed that uses an existing CAN interface to synchronize the radar sensors. The CAN bus is a typical car communication interface that may be used to share an object list determined by each radar module with a centralized CPU (central processing unit). With a minor update in the interface design on a radar sensor module, the existing CAN Car communication interface may be used to synchronize the surround view radar sensors.
In this example, high speed SerDes (serializer-deserializer) links such as links 111, 112 may be used to couple each radar module 101-106 to CPU 110 in order to transfer image data to CPU 110 from each radar module 101-106.
In this example, a single CAN bus 120 is routed throughout vehicle 100. Various stubs, such as 123, 124 may be dropped from bus 120 to connected to individual modules, such as radar units 101-106, controller 121, and CPU 110. Controller 121 may be part of the vehicle engine and/or body control system, for example. Many other control modules of various sorts that control the engine, suspension, climate control system, etc of vehicle 100 may be similarly connected to CAN 110. CPU 110 may send control commands to radar modules 101-106 using CAN 110, for example.
The CAN bus was developed by BOSCH as a multi-master, message broadcast system that specifies a maximum signaling rate of 1 megabit per second (bps). Unlike a traditional network such as USB (universal serial bus) or Ethernet, CAN does not send large blocks of data point-to-point from node A to node B under the supervision of a central bus master. In a CAN network, many short messages like temperature or RPM are broadcast to the entire network, which provides for data consistency in every node of the system.
The CAN bus was developed to replace the complex wiring harness with a two-wire bus. The specification calls for high immunity to electrical interference and the ability to self-diagnose and repair data errors. These features have led to CAN's popularity in a variety of industries including building automation, medical, and manufacturing.
The CAN communications protocol, ISO-11898: 2003, describes how information is passed between devices on a network and conforms to the Open Systems Interconnection (OSI) model that is defined in terms of layers. Actual communication between devices connected by the physical medium is defined by the physical layer of the model. The ISO 11898 architecture defines the lowest two layers of the seven layer OSI/ISO model as the data-link layer and physical layer arbitration on message priority (CSMA/CD+AMP). CSMA means that each node on a bus must wait for a prescribed period of inactivity before attempting to send a message. CD+AMP means that collisions are resolved through a bit-wise arbitration, based on a preprogrammed priority of each message in the identifier field of a message. The higher priority identifier always wins bus access. That is, the last logic-high in the identifier keeps on transmitting because it is the highest priority. Since every node on a bus takes part in writing every bit “as it is being written,” an arbitrating node knows if it placed the logic-high bit on the bus.
The ISO-11898:2003 Standard, with the standard 11-bit identifier, provides for signaling rates from 125 kbps to 1 Mbps. The standard was later amended with the “extended” 29-bit identifier. The standard 11-bit identifier field provides for 211, or 2048 different message identifiers, whereas the extended 29-bit identifier provides for 229, or 537 million identifiers. The CAN is well known and currently implemented in millions of vehicles. A more detailed overview is provided in “Introduction to the Controller Area Network (CAN), Steve Corrigan, revised July 2008, which is incorporated by reference herein. A complete set of the latest version of the ISO-11898 standard is available from the ISO (International Organization for Standards).
Processing system 110 may be based on SoC (system on a chip) devices such as those available from Texas Instruments Incorporated (TI), such as the TDA3x and TDA3x family of devices that may be augmented to include embodiments of the techniques disclosed herein. TI has fully integrated a set of peripherals into the TDAxx solution to simplify design and minimize space, thus facilitating sensor fusion. Communication interfaces, especially for camera and radar based systems like surround view and back-up camera, may benefit from TI's latest generation FPD-Link III SerDes family, which helps reduce the effort to connect remote ADAS satellites to central processing modules using a single coaxial cable. Reduced wiring effort and smaller modules due to smaller connectors and highly integrated components help ensure that the ever growing number of sensor modules for ADAS is not burdening new cars with high extra cost and weight. See, for example, “Paving the way to self-driving cars with advanced driver assistance systems,” Hannes Estl, August, 2015.
While an automobile 100 is illustrated herein, other embodiments may be placed in other types of vehicles, such as trucks, trains, planes, drones, etc. and used to assist or fully control operation of the vehicle.
A reflected signal 222 from an obstacle 210 may be received by a low noise amplifier 204 via receiver antenna 209. The received signal may be mixed with the transmitted signal by mixer 204 to generate an intermediate frequency (IF) which is proportional to a distance d between the object and the radar module.
A maximum IF bandwidth for IF amplifier 205 is dictated by the ramp slope and maximum range required to be detected by radar. The amplified IF may then be converted to the digital domain by analog to digital converter (ADC) 206. A first dimension FFT (Fast Fourier Transform), referred to as the range FFT, may be performed by digital signal processor (DSP) 207 across one chirp 323 (
Similarly, a second and a third dimension FFTs may be computed across all the chirps within a frame and across all the receiver (RX) and transmitter (Tx) antennas to get velocity/Doppler and angle. While only a single TX antenna 208 and a single RX antenna 209 are illustrated here for simplicity, there are typically multiple TX and RX antennae in each radar module.
As mentioned above, with advancements in radar technology, more and more high end automotive applications are being developed, such as a “Surround View Radar System.” A surround view system enhances the performance (better accuracy, detection) of the system by taking advantage of data blending from multiple sensors, such as cameras and radar. High end data blending algorithms require the radar sensors fitted around car to be synchronized with a minimum skew as possible.
In the example illustrated in
As will be described in more detail below, radar modules 101 and 102 are synchronized to have a defined time offset 532 between the start of each of the chirps transmitted by radar modules 101 and 102. In this manner, a reflected signal 4023 from radar module that is received by radar module 401 may be filtered out. Due to a small amount of uncertainty “u” 531 in the exact timing between radar modules 101, 102, the exact time that an interfering signal 4023 may be received by radar module 101 may vary by “u” microseconds 531, where u may be in the range of less than 1 microsecond, for example. “U” represents an uncertainty in synchronization which can be an artifact of different cable lengths to different radar nodes, asynchronous nature of the clock in each node, etc. In addition, since relatively low cost oscillators may be used in each of the radar modules 101, 102, their timing may drift over time. Therefore, by periodically resynchronizing the drift may be limited to an allowable delay amount of time “ad” 530. In order to maintain synchronization, the global synchronization may be retransmitted approximately every 100 milliseconds in this example. In this example, radar modules 101, 102 may be initially synchronized to have an offset time 532 of approximately 5 microseconds, for example.
Each radar module 101-106 of
As is well known, each message on the CAN bus is treated as a broadcast message and is received by all modules that are connected to the CAN bus. For each message, any module that has a message ID that matches the message ID of the current message will accept the message; all other modules will ignore the message. Therefore, a controller for the radar system, such as CPU 110 in
During operation, timing engine 642 may be configured to start transmission of a radar frame at a time that is offset from receipt of interrupt 644 by the offset time amount. Thus, one radar module, such as radar module 101 in
Referring back to
No additional cabling or interface logic on the device is required to achieve the synchronization across multiple Radar sensor nodes 101-106 and CPU 110. This is a big advantage considering the length of the cable to reach all of the radar modules may be significant. For example, a typical vehicle may require a cable that has a length that is in the order of 10s of meters to reach all of the radar modules.
A transmit channel may include a suitable transmitter and antenna. A receive channel includes a suitable receiver and antenna. Further, each of the receive channels 720 may be identical and include a low-noise amplifier (LNA) 721 with one or more stages to amplify the received signal, a mixer 722 to mix the signal generated by the transmission generation circuitry with the received signal to generate an IF (intermediate frequency) signal, a baseband bandpass filter 723 for filtering the IF signal, a variable gain amplifier (VGA) 724 for amplifying the filtered IF signal, and an analog-to-digital converter (ADC) 725 for converting the analog IF signal to a digital IF signal. The mixer serves as a down converter that generates an output signal with a frequency equal to the difference between the frequency of the inputs received from the low-noise amplifier and the transmission generation circuitry, both of which are radio frequency (RF) signals. The bandpass filter, VGA, and ADC of a receive channel may be collectively referred to as a baseband chain or baseband filter chain. Further, the bandpass filter and VGA may be collectively referred to as an IF amplifier (IFA).
The receive channels 720 are coupled to a digital front end (DFE) and Digital Signal Processor (DSP) system module 750. The DFE 750 includes functionality to perform decimation filtering on the digital IF signals to reduce the data transfer rate. A processor and/or a signal processor in control module 750 may also perform other operations on the digital IF signals, e.g., DC offset removal, digital compensation of non-idealities in the receive channels, such as inter-RX gain imbalance non-ideality, inter-RX phase imbalance non-ideality and the like. The DFE and DSP module 750 may be coupled to a high speed serial interface (I/F) 754 to transfer decimated digital IF signals to a processing unit that may be located in another IC, for example, when the radar SoC 700 is in normal mode. The DFE and DSP system module may also be coupled to the control (CNTL) module 740 to complete the function of the radar module in both functional and test modes and external data communication.
A CAN interface 741 may provide an interface for communication with a processing unit located in another module, such as CPU 110 in
The control module 740 and DFE and DSP System module 750 may include functionality to control the operation of the radar SoC 700 in normal mode and in test mode. The CNTL circuitry 740 may include one or more temperature sensors and various RF/analog measurement components.
A 10 GHz or higher frequency modulation synthesizer (FM-Synth) module 730 generates the RF signals that are then multiplied by four and provided to the transmitter channels. The programmable timing engine 731 includes functionality to receive chirp parameter values for a sequence of chirps in a radar frame from the control module 740 and to generate chirp control signals that control the transmission and reception of the chirps in a frame based on the parameter values. The chirp parameters are defined by the radar system architecture and may include, for example, a transmitter enable parameter for indicating which transmitters to enable, a chirp frequency start value, a chirp frequency slope, a chirp duration, indicators of when the transmit channels should transmit and when the DFE output digital should be collected for further radar processing, etc. One or more of these parameters may be programmable.
Programmable timing engine 731 may also be programmed to insert an offset time value to delay the start of a radar frame in response to a global synchronization message received on the CAN interface 741, as described above with regard to
The radio frequency synthesizer (SYNTH) 732 includes functionality to generate FMCW (frequency modulated continuous wave) signals for transmission based on chirp control signals from the timing engine 731. In some embodiments, the SYNTH 732 may include a phase locked loop (APLL) with a voltage controlled oscillator (XO).
The clock multiplier 733 increases the frequency of the transmission signal (LO signal) to the LO frequency of the mixers 722. The clean-up PLL (phase locked loop) operates to increase the frequency of the signal of an external low frequency reference clock (not shown) to the frequency of the SYNTH 732 and to filter the reference clock phase noise out of the clock signal.
The clock multiplier 733, synthesizer 732, timing generator 731, and clean up PLL are an example of transmission generation circuitry. The transmission generation circuitry generates a radio frequency (RF) signal as input to the transmit channels and as input to the mixers in the receive channels via the clock multiplier. The output of the transmission generation circuitry may be referred to as the LO (local oscillator) signal or the FMCW signal.
A bus interface of each of the two or more devices may be coupled to a communication bus within a vehicle and configured at step 802 to accept a same message broadcast via the communication bus. For example, in the CAN embodiment described above, the message may have a specific message identification (ID) header.
A message that has the specific message ID may be received from the communication bus in step 804 simultaneously by each of the two or more devices. The message may be transmitted by a control module that is coupled to the communication bus.
Operation of the two or more devices may be synchronized in step 806 by triggering a task on each of the two or more devices in response to receiving the message having the specific message ID.
Periodically a drift interval may be exceeded in step 808. The drift interval may be defined based on a drift rate of a local oscillator in the two or more devices, for example. The drift interval may be selected so that the two or more devices remain synchronized within a defined range. When the drift interval is exceeded in step 808, step 804 and 806 may be repeated to bring the two or more devices back into close synchronization.
While the invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various other embodiments of the invention will be apparent to persons skilled in the art upon reference to this description. For example, while a CAN communication bus was described herein, other embodiments may use other types of known or later developed communication buses that allow a broadcast message to be selectively received by specified modules that are coupled to the communication bus.
While synchronization of radar modules was described herein, other embodiments may use the techniques described herein to synchronize the operation of various types of modules, such as actuators, illumination, etc.
While a synchronization of modules within a vehicle was described herein, embodiments of the techniques disclosed herein may be applied to systems such as agricultural equipment, nautical machinery, medical apparatus, semiconductor manufacturing equipment, avionics, machine tools, etc.
While embodiments have been described herein in reference to ADAS, one of ordinary skill in the art will understand embodiments for synchronization of multiple radar modules for applications other than ADAS may benefit from embodiments of the present disclosure, such as, for example, industrial applications, robotics, drones, etc.
While automobiles were discussed above, embodiments of the disclosure are not limited to autos and trucks. Any type of vehicle that may benefit from awareness of nearby objects may benefit from an embodiment of the disclosure. For example, robots, manufacturing and assembly devices, motorcycles, bicycles, etc. may all be regarded as “vehicles” and make use of an embodiment of the disclosure. Similarly, vehicles for movement of a mobility impaired person, such as a wheel chair or scooter, may benefit from an embodiment of the disclosure. Similarly, a “vehicle” to be used by a blind person for walking assistance may also benefit from an embodiment of the disclosure.
Certain terms are used throughout the description and the claims to refer to particular system components. As one skilled in the art will appreciate, components in digital systems may be referred to by different names and/or may be combined in ways not shown herein without departing from the described functionality. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” and derivatives thereof are intended to mean an indirect, direct, optical, and/or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, and/or through a wireless electrical connection.
Although method steps may be presented and described herein in a sequential fashion, one or more of the steps shown and described may be omitted, repeated, performed concurrently, and/or performed in a different order than the order shown in the figures and/or described herein. Accordingly, embodiments of the invention should not be considered limited to the specific ordering of steps shown in the figures and/or described herein.
It is therefore contemplated that the appended claims will cover any such modifications of the embodiments as fall within the true scope and spirit of the invention.
