The second half of autonomous driving: How does DCM technology break through the radar perception bottleneck?

As the "eye" of the autonomous driving system, radar emits and receives electromagnetic waves at target objects, thereby obtaining information such as the distance from the target to the electromagnetic wave emission point, Doppler frequency, azimuth angle, elevation angle and other information. Compared with other sensors such as cameras , radar is almost unaffected by weather and light and can achieve all-day and all-weather detection. Therefore, it is also a key sensor for realizing high-level autonomous driving technology.
 
Over the past 30 years, most automotive radars have used frequency modulated continuous wave (FMCW) technology, and radar signal processing is done in analog circuits. In recent years, as autonomous driving technology transitions to higher levels, higher requirements have been placed on the resolution and accuracy of automotive radars, and more advanced digital coded modulation ( DCM ) technology has attracted attention. In DCM, signal processing is mainly done digitally. This article will explore the technical advantages of DCM radar from multiple dimensions.
 

FMCW vs. DCM  radar technology

The basic difference between FMCW and DCM radars is the signal they transmit. FMCW transmits short pulses of a signal that increases in frequency during its transmission period. In current automotive radars, FMCW signals typically occupy a 50MHz bandwidth. DCM radar transmits longer pulse signals containing special coding sequences, occupying a bandwidth of 1GHz to 2GHz.
 
Contrast

Contrast refers to the radar's ability to distinguish between two close targets. That is, the radar is able to detect and resolve differences in reflected signals between two closely spaced targets. A typical example is detecting children standing next to cars. Compared with cars (strong reflectors), children are weak reflectors. The antennas
 
used by radars to transmit and receive signals are constructed using multiple radiating elements. Radars with fewer antenna elements have wider main lobes and relatively higher side lobes, resulting in lower contrast and the inability to distinguish children and children at very close distances. car. Radars with more antenna elements, such as Uhnder's DCM radar, produce narrower antenna beams and relatively low side lobes (relative to the main lobe), thus providing higher contrast. In addition, the contrast advantage of DCM radar also comes from the DCM waveform. DCM uses spreading sequences that are modulated into the phase of an RF carrier and these spreading sequences have what is called "processing gain." That is, when the received signal is correlated with the outgoing signal, the received signal is amplified. Therefore, the echo is also amplified along with the transmitted spread spectrum waveform. This effectively improves the radar's ability to detect small targets, such as children. Anti-interference As more and more radars are installed on new vehicles, the problem of signal interference between radars has attracted increasing attention. Imagine two cars traveling in opposite directions on two lanes. When they get close, the signals from the radars on the cars interfere with each other, affecting the ability to detect targets. Radar based on DCM technology can solve the interference problem in the following three ways.
 

 



 

Sensing and monitoring interference: DCM radar can sense whether the source of interference is a signal from FMCW or DCM radar, and monitor the interference to mitigate or avoid it.

Mitigating interference: If the interfering signal is in the same frequency band and coincides with the time slot when the radar receives the echo, the DCM radar can suppress or reduce the impact of this interference. For example, a DCM radar equipped with a version of Uhnder's current chip can mitigate up to eight FMCW interferences simultaneously. In addition, since the signals emitted by each DCM radar have a unique spread spectrum sequence, signals with the same sequence will be amplified, while signals with different sequence numbers will be suppressed, thus helping the DCM radar mitigate signal interference.

Avoid interference: On the basis of sensing and monitoring, DCM radar can change its operating frequency band or transmission time slot to avoid conflict with another radar operating in the same time slot and frequency band.

 
Size

Radar size depends largely on the size of the antenna (number of transmitting and receiving components), the number of components on the printed circuit board ( PCB ) and thermal requirements. If the radar consumes more power, a larger heat sink (surface area) is required and the radar size will be larger.
 
We know that large radars are difficult to install on vehicles. To reduce radar size, some designers consider using sparse arrays to reduce the size of the antenna. A sparse array has fewer elements, but it also means that the elements need to handle a denser density of signals. Most FMCW radars cannot support this processing capability and require external digital processor support, which increases power consumption, size and cost to a certain extent.
 
DCM radars equipped with Uhnder chips are compact, providing OEMs and radar suppliers with greater flexibility when designing sensing solutions. For example, an automaker could use three ultra-thin DCM radars side by side: one for short-range detection, two combined for mid-range detection, and three combined for long-range detection.
 
Modularity

Modularity will help reduce engineering development costs and streamline supply chain and manufacturing processes. Through modularity, manufacturers can build short-range (SRR), medium-range (MRR), long-range (LRR) and very long-range (SLRR) radars using basic radar chips and achieve different resolutions through software programming
 
. There are two ways to achieve modularity. One is to cascade basic radar chips with additional digital processing chips to build more complex radars. Using this approach optimizes the simplest and cheapest radar solution, but at the same time the overall cost and power will be higher. Many FMCW radars use this approach.
 
The second approach is to build more powerful radar chips that can be programmed. Using this approach, the chip cost will increase slightly, but the total cost of ownership (TCO) of the product is still very attractive. This is also the approach followed by Uhnder's DCM radar chips. Uhnder's DCM radar chips can be programmed to select the number of transmitters and receivers. In addition, the programmable software stack that comes with the chip can help manufacturers reduce related engineering development costs.
 
Power

Currently commercially available FMCW chips support 3 or 4 transmitters and 4 receivers (3x4 or 4x4), while Uhnder's DCM radar chip supports 12 transmitters and 16 receivers (12x16). The beam width of a radar wave is inversely proportional to the product of the number of transmitting elements and receiving elements. The narrower the beam, the higher the resolution, so Uhnder's DCM radar can provide higher resolution.
 
Although, 3x4 or 4x4 FMCW radar chips can increase the resolution by cascading (3 or 4 chips). But in this case, the radar requires 3-4 radar chips and a separate digital processor chip to effectively combine the outputs of the individual FMCW radar chips. This means that this solution requires a total of 4 or 5 chips, which also require a more elaborate power subsystem, so that the overall configuration consumes more power than a single DCM radar chip and its power supply.
 
Regarding power, there is also a misconception that DCM radar requires a complex, high-power A/D converter due to its wide bandwidth. This is true for typical A/D converter designs, but Uhnder uses a unique interleaved A/D converter design that provides high dynamic range at low power and can be tuned for different bandwidths.
 
Cost

To achieve high resolution, FMCW systems tend to require more chips (3-4 radar chips, a digital processor chip and a more expensive power management chip). In addition, these chips require more complex printed circuit board (PCB) layouts and larger PCB area. PCBs for 76-81 GHz require special materials and are expensive.
 
More chips means more surrounding components, such as decoupling capacitors . And because high-resolution FMCW systems consume more power, they require more sophisticated thermal management systems. That is, the heat generated by the chip must be dissipated in an efficient manner. This increases the overall design complexity, size and cost.
 
Sensor fusion

In addition to radar, cameras are also  important sensors in current vehicle AD AS systems. Cameras are good at identifying the shape and color of objects, but do not perform well in bad weather or dark environments, while radar can provide distance and speed information of targets in a scene at all times and around the clock. By using algorithms such as deep neural networks (DNN) to fuse radar + camera information, the safety performance of autonomous driving can be further improved. According to information theory , more information can help improve decision-making. The amount of new information acquired by the radar (H(Y)) depends on the resolution of the radar, which in turn depends on the number of antenna elements. In a radar, the number of transmitting and receiving antenna elements are its eyes. If a radar has more transmitting and receiving antenna elements (virtual channels), it can see further and detect more objects at different angles in the field of view. Uhnder's single DCM radar chip provides 192 virtual channels, while common FMCW radars on the market provide 12 to 16 virtual channels. A few newer FMCW radars have 288 virtual receivers, but they are not widespread. FMCW radar chips can provide more virtual channels through cascade, and some suppliers use cascade to provide 192 to 2300 channels. However, DCM radar can also provide 3072 channels by cascading four chips. But when chips are connected, the complexity, cost and power consumption of the radar system will increase significantly. To sum up, radar based on DCM technology has advantages in contrast, anti-interference, size, power and cost. In addition, because DCM radar design supports software programming and its modular nature, it can provide more flexible solutions for today's automotive design. Founded in 2015, Uhnder was the first to introduce DCM technology into automotive radar, and successfully developed the first car-grade 4D digital imaging radar chip and related software to provide more accurate digital perception for autonomous driving technology. In 2018, Magna launched the ICON digital radar using Uhnder's radar chip, and announced in 2021 that electric vehicle manufacturer Fisker's Ocean SUV will be equipped with this digital radar. In addition, Uhnder has also established cooperative relationships with many leading companies such as Black Sesame Intelligence , Ofilon, and Forui to jointly promote the application of radar products based on DCM technology to promote autonomous driving safety.