Interference associated with analog radars needs to be mitigated now, not later.
When our cars brake automatically to avoid an accident, or tuck themselves neatly into a tight parking space without our hands touching the steering wheel, we don’t experience it as a technological miracle as much as the fulfillment of a consumer expectation. This fact is a testament to just how far we have come in the push toward autonomous mobility, that the installation of advanced driver-assistance systems (ADAS) has quietly become an industry standard in the production of new vehicles.
But the technology that makes ADAS work, and that will ultimately carry us into the next, more advanced phase of commercial AVs, still has serious limitations. In order to achieve continued progress and bring about the next generation of mobility, OEMs and system developers will need to make hard decisions about where to focus. In the end, some of the technologies that have been instrumental in bringing us to this point may need to be reimagined—or even replaced—if we hope to reach that next phase in the foreseeable future.
Among the immediate challenges for developers is the use of radar in ADAS, which has recently emerged as a cause of concern as the technology becomes more widespread. Radar is an essential component for achieving accurate sensing in a variety of systems. It is critical to detecting distance objects as well as the speed at which pedestrians or another vehicle may be travelling.
Distance and speed may arguably be the most important aspects of any ADAS. As the volume of radars on roadways increases, many experts worry about potential signal interference—a real liability, and one that would be unconscionable to overlook.
We must first frame and understand the problem: What exactly is radar interference, and what is the extent of the difficulty it represents for AV developers?
Radar interference has been described as the “Achilles’ heel” of automated and driver-assisted vehicles. Radar interference in the context of AVs is surprisingly easy to understand. An emitter transmits a signal that reflects off an object and is collected and processed by the radar’s receiver. But when two or more signals from separate radars cross paths, they can interfere with each other, causing any number of complications.
Interference raises safety issues given that radar is often an indispensable component of ADAS sensing capabilities. Essential functions such as parking-assist, blind-spot detection, adaptive cruise control, forward collision warnings and automatic emergency brakes are all made possible through the use of radar.
The issue gets even trickier when you consider that the latter function is becoming mandatory in as many as 40 countries, as adopted by the United Nations Economic Commission for Europe (UNECE), China, and most recently the U.S.
The worst-case scenario is that the interference problem won’t be sufficiently mitigated before our roads are filled with radar-equipped vehicles in support of more ADAS deployments, potentially resulting in avoidable accidents and fatalities due to signal interference. The phenomenon is referred to as “radar congestion,” occurring when too many radar signals degrade sensor performance.
Radar interference can occur between radars on the same vehicle as well as among radars on adjacent vehicles. If it weren’t quite literally a matter of life and death, we might be able to appreciate the irony of something like this happening as the result of a global mandate. The irony is, of course, lives would be endangered by a technology meant to protect us.
The possibility of widespread radar interference diminishing the integrity of safety features constitutes a very real challenge for ADAS designers. Still, no industry consensus exists for solving the interference problem.
The automotive sector has been aware of potential issues related to interference for nearly a decade, informed by a report released by a Europe-based project known as MOSARIM (More Safety for All by Radar Interference Mitigation). The problem has also been studied by various agencies, and the common conclusion is that radar interference poses little to no threat in environments with few competing radars.
When congestion occurs, however, the possibility of an error vastly increases.
As stated in a report by the National Highway Traffic Safety Administration, “systems that operate well in environments with few other radars may suffer significant degradation of performance in radar congested environments… in scenarios with many vehicles operating radars in the 76-81GHz band, the power from other radars will likely exceed the power of echoes from targets needed for specific performance, by several order of magnitude.”
To the present, the auto industry has done little more than rely on an allocated frequency spectrum for vehicles (the 76- to 81-GHz range noted above) while leaving the details to individual automotive radar developers. That despite the fact that all must operate together within this limited bandwidth. Unfortunately, regulating radar developers would be difficult, and even the best results would likely only emerge over time after overcoming industry resistance.
The truth is that radar interference needs to be mitigated now, not later. The most logical path forward might be re-evaluating current radar technologies, determining how those technologies might be improved or whether they should be replaced by technologies better equipped to cope with interference.
Many ADAS-equipped vehicles today use frequency modulated continuous wave (FMCW) technologies, or “analog radar”. FMCW-based systems lack the adaptability to function properly in certain environments, including those congested with radar signals. Current FMCW radars rely on techniques such as frequency hopping and timing jitter on the transmit side, as well as time-domain excision on the receive end to mitigate mutual interference from nearby radars.
Those techniques, however, are not without their limitations, and many analog radars still run the risk of detecting a “ghost” target, resulting in “false alarms” that trigger unnecessary activation of automatic braking.
By contrast, digital radar technologies are natively better at mitigating interference compared with their analog counterparts.
Digital radars differ from analog systems in many ways, most notably its unique code for each transmit signal. This is a key element of digital code modulation (DCM), allowing radars to distinguish their own signal from multiple other signals in congested environments.
That feature is absolutely crucial for the widespread adoption of AVs and ADAS technologies. While frequency-hopping techniques used by analog radars remain problematic due to bandwidth availability and lack of standardization, digital radar is comparatively unbounded through its use of 1018 different unique identifier codes. In fact, DCM makes it inherently more immune to mutual interference, reducing ghost targets that can trigger a false activation of automated braking systems.
In the absence of regulations, radar interference will at best be a major obstacle to the expansion of autonomous mobility. Worst case, it creates extreme liability and public safety concerns. With regulatory intervention far from certain, OEMs and developers will need to reevaluate radar technologies installed in their vehicles. At the very least, digital radar’s potential role in mitigating interference deserves serious consideration.
This article was originally published on EE Times.
Max Liberman is a vice president at digital automotive radar vendor Uhnder Inc.