Challenging automotive applications, such as ADAS and autonomous driving, require advanced solutions for range and objects detection. Among these, a relevant role is played by the LiDAR (light detection and ranging) system. Also known as time-of-flight (ToF), laser scanner or laser radar, LiDAR is a sensing technology whose main task is to detect objects and map their distances. This is achieved by illuminating a target with an optical pulse (whose width ranges from a few nanoseconds to several microseconds) and measuring the characteristics of the reflected return signal. Key factors for extracting useful information from returned light signals are pulse power, round-trip time, phase shift, and pulse width. Even though several different types of LiDAR systems are available, they can be grouped into two categories with respect to the beam steering type: mechanical and optical LiDARs. A mechanical LiDAR relies on high-grade optics and a rotating assembly to create a wide field-of-view (FOV), up to 360°. The associated signal-to-noise ratio (SNR) is quite excellent over the FOV, but the solution is bulky and heavy. Solid-state LiDARs, on the contrary, feature no spinning mechanical parts, providing a high degree of reliability. Even though their FOV is reduced, there is a way to overcome this limitation.
This article will introduce a novel LiDAR technology developed by XenomatiX called true solid-state for ADAS, autonomous driving, and other road applications. It should be noted that, in addition to automotive applications, LiDAR technology can be exploited for 3D aerial and geographic mapping, safety systems in factories, smart ammunition and gas analysis.
Today, most of LiDAR systems are mechanical. They use spinning heads resulting in a bulky, heavy and expensive solution. To overcome these limitations, technologies such as oscillating mirrors have been adopted to downscale the size of the solution. However, it still remains a somewhat mechanical device. Since the beginning, XenomatiX philosophy has been that, in automotive applications, the only moving part is the vehicle.
During an interview with EE Times Europe , Filip Geuens, CEO of XenomatiX, said, “Automotive has completely different requirements, it’s about cost, size, and reliability. LiDAR technology has to be chosen as a function of these three key factors. That’s why we felt provisional laser diodes and mechanical moving parts are not the way forward.”
The company, founded in 2013 and headquartered in Leuven, Belgium, introduced the term ”true” to identify solid-state LiDAR systems which are built using a semiconductor-based laser source and detector and without scanning nor moving parts. This novel solution takes a fundamentally different approach with respect to conventional optical LiDARs, which use sequential measurements to send laser light in one direction, take a measurement, and then move on to the next position. They measure and acquire the surrounding scenario in a step-by-step way.
“Since the scanning mechanism is the weak point of a LiDAR system, XenomatiX approach has been to eliminate the scanning mechanism introducing the multi-beam capability, which sends out thousands of laser beams all at the same time.” said Geuens. “This is the true innovation we are proud of.”
The whole scene can be detected in “one flash” without the constraints of shorter-range or high power, with ranges beyond 200 meters and normal power consumption. Moreover, unlike scanning LiDARs, the high-resolution point clouds need no post-treatment for time-space correction, allowing a much higher frame rate and providing a better correction.
As a result, XenomatiX’s LiDAR does not have to move very fast, as conventional “point and measure” optical systems. Since all the scene is measured by sending all the beams at the same time without performing any scanning, the system has more time to process the high-resolution grid of measurement points.
“We don’t need the fastest laser, since we have a LiDAR that works in global shutter mode, meaning it looks at the entire scene in a single shot, in a single frame,” said Geuens. “This involves a few nice benefits: our system is not affected by motion blur, and we don’t need an extremely powerful laser driver that can send out nanosecond pulses.”
The approach adopted by XenomatiX is a solution for scanning while in motion since it removes the lag time caused by scanning sensors as they move through their scanning pattern. As a matter of fact, this concept is well-suited for automotive applications, since it eliminates the need to compensate for motion: all the beams are sent out at exactly the same time, acquiring all of the points at the same time via a global shutter. Figure 1 shows the XenoLidar-X, a stand-alone solution with no moving parts which can be used for both autonomous driving and industrial applications. This design proves effective in all scenarios where lighting and weather conditions can vary to a great degree. It is XenomatiX next-generation, solid-state solution, featuring 15,000 laser beams which we are projecting simultaneously. That improves resolution to a level of 0.15° horizontal and vertical, in line with today’s most demanding market requirements.
Figure 1: XenoLidar-X (solid-state)
In its solid-state LiDARs, XenomatiX uses VCSELs (vertical-cavity surface-emitting lasers), which are notoriously low power laser sources that provide very good durability and lifetime expectation, much better than traditional diode lasers.
“Since we have more time to measure, we can still put enough energy in the laser beams to also do long-range measurements,” said Geuens.
XenomatiX LiDARs are known as 6D LiDARs, meaning they provide two types of outputs with perfect overlay. The first is a point cloud, a 3D geometry which includes all the detected laser spots. The second is a visual 2D camera image. It can be seen as a LiDAR with an inherently incorporated camera, or a camera with LiDAR performance and no parallax error. The availability of redundant data enables sensor fusion, providing complementary information which strongly supports safety applications. The 6 th dimension is the reflectivity of objects, based on the amount of returned laser light.
“Our detector is a special type of CMOS, it’s a pixel we designed ourselves. It is like a CMOS camera able to operate in three-dimensional mode, giving the coordinates of every detected spot,,” said Geuens. “It can also operate in two-dimensional mode, providing a visual image. The visual image and the point cloud are sent to a central ECU, where they are processed for free space or objects detection using proprietary AI algorithms.”
XenomatiX calls it four-dimensional AI, meaning it performs pattern recognition in a four-dimensional space, where x, y, z, coordinates are combined with the intensity of the reflected laser beam. The sensor has been designed to also work as a detector in a 2D mode when the laser is off. If the laser is switched on, the system can use the same pixels to do 3D measurements and generate the three-dimensional point cloud. Solid-state LiDARs provide also excellent reliability, which is a key factor in automotive applications. Mean Time Between Failure (MTBF) is, in fact, very good due to the absence of moving parts, to the use of VCSELs (which are lasers with a long lifetime), and to the maturity of the CMOS technology.
As mentioned before, an advantage offered by LiDARs which have moving parts is the wide field-of-view, which can be extended to cover up to 360 degrees. Spinning heads allow looking in all directions. XenomatiX LiDARs can still achieve a wide FOV by combining multiple modules to get higher coverage. Multiple LiDAR units can be placed on the corners of the vehicle in order not to have blind zones.
With a flexible and modular design, XenomatiX can offer a small, light, and future-proof sensor for an easy integration. The company has ongoing partnerships with Tier I automotive suppliers, like AGC, Marelli, Kautex, and others to develop a complete, customizable, modular, and flexible LiDAR solution. These partnerships will promote the integration of LiDARs into the windshield, rear window, grill, headlight, taillight, and bumper of the vehicle.
>> This article was originally published on our sister site, EE Times Europe.
- Understanding wavelength choice in LiDAR systems
- ADAS experts ponder sensor integration in future vehicles
- What’s driving change in automotive electronics systems
- Time-of-flight technology promises enhanced accuracy
- Smart cities: the case for lidar in intelligent transport systems
For more Embedded, subscribe to Embedded’s weekly email newsletter.