Decoding the Continental ARS540 – The Millimeter Wave Radar Designed for L5 Autonomous Driving

Introduction:

This article is authorized for publication by Zuo Si Automotive Research, authored by Zhou Yanwu.

The product iteration of millimeter wave radar is fiercely competitive in the market, just like laser radar. What advantages does Continental’s ARS540 have that the author of this article claims it to be the most advanced in the world (without exception)?

Continental’s ARS540 is the most advanced millimeter wave radar in the world, without exception. Why is it called the most advanced? Because the ARS540 has nine world-first or unique features. BMW’s next-generation autonomous vehicle, the iNext, will be the first to use it, and North American GM will also use it in its high-end vehicles. This is a millimeter wave radar designed for L5 level autonomous driving.

Firstly, the ARS540 has the highest resolution millimeter wave radar, with a horizontal azimuth resolution of 1° (the original design in 2017 was 1.2°), which is 7-12 times higher than most millimeter wave radar horizontal resolutions, where most millimeter wave radar horizontal resolutions are only 7-12°.

Secondly, the ARS540 is the only millimeter wave radar that can truly measure target height, meaning its elevation resolution is high, reaching 2.3°. Why measure height? Because manhole covers, speed bumps, overpasses, pedestrian bridges, and roadside metal signs can cause radar malfunctions, so traditional radars filter out static targets. If height can be measured, the confidence in target detection can be improved, and static targets will no longer be filtered out.

Height Measurement of ARS540

Thirdly, the ARS540 has an effective range of up to 300 meters at a horizontal FOV of 120°, far exceeding other millimeter wave radars. Other millimeter wave radars have an effective range of up to 250 meters, but their FOV shrinks to only 8-10°, far lower than the ARS540’s 120° (the first generation design was 100°, and the final specification is 120°).

Fourthly, the ARS540 is the only millimeter wave radar capable of outputting images, which Continental refers to as Radar Detection Image Output (RDI), or point cloud output. The effect approaches that of an 8-line laser radar.

Fifthly, the ARS540 uses micro-Doppler technology, making it the only millimeter wave radar that can detect vulnerable road users (VRUs) such as the elderly and children.

Sixthly, the ARS540 is the only millimeter wave radar that uses SAR synthetic aperture technology to improve near-distance resolution; within a range of 10 meters, the ARS540 will use SAR technology to enhance angular resolution.

Seventh, the ARS540 is the only millimeter wave radar that does not filter out static targets. Most millimeter wave radars filter out static targets due to concerns about false positives, but the ARS540 has ultra-high resolution and can detect object height, which eliminates concerns about false positives, thus retaining static targets.

Eighth, the ARS540 is the only millimeter wave radar capable of trajectory tracking and prediction in complex traffic scenarios. Ninth, the ARS540 can detect hidden vehicles. The previous generation product from Continental, the ARS430, had a 40% chance of detecting hidden vehicles, while the ARS540 can achieve 80%. Most millimeter wave radars can only achieve 20%, thus filtering out such data.

The ARS540 adopts a cascading form, combining four NXP 77GHz millimeter wave radar transceivers (MMIC) MR3003, where each MR3003 has 3 transmitters and 4 receivers. With four chips, it totals 12 transmit and 16 receive channels. Currently, most millimeter wave radars use a single-chip transceiver, typically with only 3 transmitters and 4 receivers, resulting in only 12 virtual channels, while the ARS540 has 192 virtual channels, greatly enhancing resolution. It can be referred to as an image radar.

In practice, height measurement or pitch angle measurement of millimeter wave radar is not a new concept; Bosch proposed this feature on its MRR radar in 2012, and domestic companies such as Huayu Automotive, Wuhu Sensetek, Muniu Technology, and Aoku also have similar solutions. Why does Continental dare to claim it as the world’s only “truly” height measurement?

As we know, traditional radars output information in three dimensions: azimuth, speed, and distance. The latter two are obtained through FFT, while the former is derived from the phase difference information of multiple antennas. Traditional radars do not have pitch angle antenna channels, only azimuth angle antenna channels, so naturally, there is no pitch angle information. There are several solutions to this problem, usually by increasing the pitch channels. However, under the condition of constant total channel numbers, this means a decrease in horizontal azimuth angle accuracy, as the horizontal azimuth angle is the primary information. Increasing the total channel number raises costs significantly, and the computational load may increase several times or even dozens of times. Currently, 77GHz radar processing chips are mainly monopolized by Infineon and NXP, leaving few suitable chips available. Therefore, most manufacturers’ pitch channels are only barely adequate, with very low accuracy. Bosch’s MRR uses the amplitude ratio of the pitch antenna pattern to calculate pitch angles, a method that does not increase channel numbers or costs but increases the main beam width of the pitch antenna. This method requires prior knowledge and cannot distinguish whether non-horizontal targets are high or low.

Continental may have adopted Monopluse’s design, which is equivalent to using a physical antenna for pitch angle testing and then increasing accuracy through MIMO virtual channels. The AR540 employs dual-beam forming, with one beam being 48 (Az.) x 1 (El.) = 48 channels, converted to azimuth design, significantly improving azimuth measurement accuracy. The other is 24 (Az.) x 6 (El.) = 144 channels, which includes pitch angle measurement.

The ARS540 was designed in 2016, initially using two NXP S32R274 chips, but this led to some issues, as two S32R274 chips resulted in a PCB area that was too large, while automotive radar aims for a compact size. Additionally, the front-end sensor fusion requires a relatively high bandwidth; Continental’s original design used MIPI CSI3, which has a bandwidth of 14.88Gbps, better than the commonly used MIPI CSI2, whereas the S32R274 uses MIPI CSI2. However, there are very few chips that support MIPI CSI3. Furthermore, Continental sought higher ADC precision to ensure the height resolution is practical, and synchronizing the clocks of two chips is also quite troublesome. Ultimately, Continental decided to use Xilinx’s Zynq UltraScale+ RFSoC series FPGA.

Xilinx’s Zynq UltraScale+ RFSoC series FPGA is designed specifically for the RF field, internally containing ultra-high precision ADCs and DACs, with options for 12 and 14 bits, and up to 16 ADCs or DACs. Typically, ASICs consider cost, and ADC and DAC configurations are not this extravagant; the S32R274 only has four 12-bit ADCs with a sampling rate of only 10Msps.

Framework diagram of Xilinx’s Zynq UltraScale+ RFSoC

Xilinx’s Zynq UltraScale+ RFSoC contains powerful DSP computational resources, with 3145-4272 selectable 48-bit DSP elements, which means FFT accuracy can be increased.

The first FFT operation resolves the distance value; for vehicle-mounted millimeter wave radar, a 256-point FFT is sufficient, while military applications can go up to 8192 points. The second FFT operation resolves the speed value, as speed is less critical than distance; a 128-point FFT is sufficient. The maximum FFT for the S32R274 is 512 points. Xilinx’s Zynq UltraScale+ RFSoC can easily achieve 4096 points. With a 4-core A53 and Cortex R5, the ARS540 can run embedded Linux, RTEMS, or QNX, meeting functional safety certification requirements.

Of course, FPGAs are still a bit more expensive than ASICs, and there are few people who can proficiently use HDL languages. Calibrating the antennas of 4D radar is also a challenge. The ARS540 has once again established Continental’s dominance in the millimeter wave radar field and widened the moat.

Not only in the field of millimeter wave radar, but also LiDAR, binocular, Infotainment, monocular vision, and domain controllers are vast territories for FPGAs.

END

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