A Radar in Every Bumper

As the auto industry aggressively marches toward huge advances in vehicle safety and ultimately to autonomous vehicles, major enablers will be RF and microwave technology, and millimeter-wave radars in particular.

Not long ago, autonomous vehicles were the stuff of science fiction. Today, they’re being tested throughout the world. Google’s autonomous vehicles alone have racked up more than 1.8 million miles (with a human on board for now) and logged only 12 incidents. There’s little doubt that in the not-too-distant future, autonomous vehicles will become a commercial reality in some form. When that day comes, it will be thanks in no small measure to the versatility of radar, which is increasingly auto manufacturers’ choice for use in blind spot and side-impact detection systems and for adaptive cruise control.

Of course, radar is not alone in enabling today’s rapidly-advancing vehicle safety systems. Infrared and visible-light cameras augment radar’s capabilities and have their own unique benefits, acoustic sensors are used in parking-assist systems, and radar’s optical counterpart (LIDAR) is also used in some vehicles. (LIDAR stands for Light Detection and Ranging.) However, even Google’s LIDAR-centric Prius test cars have two radars in the front bumper and two in the back.

In less than a decade, radar has become available even in lower-cost compact cars either as an option or increasingly as standard equipment. Radar accounts for more than 35% of the collision avoidance sensor market according to Grandview Research, and its market penetration is increasing (Figure 1), surpassed only by cameras.

Figure 1: Estimates (in billions) from Grandview Research clearly show the steady upward march of radar in vehicles.

Radar for the Road

One major characteristic that differentiates vehicle safety radars (from radars used for more traditional applications) is their much higher operating frequencies (76 to 80 GHz), which were allocated internationally for this purpose. They were chosen because of their signal propagation characteristics and are defined as “millimeter wave” for their very small wavelengths. The millimeter-wave region is generally considered to begin above 30 GHz and until now frequencies above about 40 GHz have been devoid of activity other than by some scientific and military systems.

There are several reasons for this. Foremost is that millimeter-wave signal propagation severely limits range and decreases in range as frequency increases. Tiny millimeter-wave signals are susceptible to attenuation by virtually anything in front of them, from rain and snow and even fog, to foliage and any solid structure. Even with a clear line of sight, range is much less than at the lower frequencies used by applications such as wireless communication and radio and television broadcast.

Millimeter-wave systems have traditionally been very expensive to manufacture, as their mechanical components such as antennas are very small and require precision machining. There are also only a few semiconductors that provide acceptable performance (or work at all) at such high frequencies. All of these drawbacks could have been surmounted if there was a huge commercial market to drive down costs and fund innovation, but as none existed, the millimeter-wave region remained a frontier waiting to be conquered. Auto safety is that conquering hero.

Although the aforementioned characteristics make millimeter-wavelengths unappealing for most applications, they’re actually beneficial for use by auto safety systems. For example, the range-limiting characteristics of millimeter wavelengths in general do not apply to every millimeter-wave frequency because atmospheric absorption at some frequencies is less than at others (Figure 2). Reduced absorption increases usable range -- but not so much as to cause widespread interference, and as these spectral snippets are narrow in bandwidth. Consequently, frequencies between 71 and 81 GHz are excellent “places” for auto radar to operate.

Figure 2: Attenuation dips between about 70 and 100 GHz, increasing achievable communication range. (Source: https://commons.wikimedia.org/wiki/ File:Micrwavattrp.png)

Earlier, some applications operated at 24 GHz where system cost was lower (although system size was larger) but the higher frequencies are now almost universally accepted as shown in Table 1. Another benefit of millimeter wavelengths is that only very low RF output power is required for radar systems, which for the auto cost-sensitive industry is essential and high power levels are very difficult to generate as well.

Table 1 Vehicular radar applications and operating frequencies

A Radar in Chips

Low power levels plus advances in semiconductor fabrication now allow a complete radar transceiver to be formed with only a few devices. A typical radar module consists of a transmitter, voltage-controlled oscillator (VCO), and receiver ICs, along with a microcontroller unit (MCU). The chips are connected via a local oscillator operating at about 38 GHz. Together these devices can provide a complete radar solution for adaptive cruise control, emergency braking, lane departure warning and blind-spot detection systems that consume power efficiently.

Getting to Autonomy

The list of specific auto safety functions, each with its own acronym, that require some type of sensor or sensors is long and growing, which makes sorting them out confusing at best. Collectively they’re grouped under the term Advanced Driver Assistance System (ADAS) that includes everything from collision avoidance to lane departure and blind spot warning, and backup cameras to systems designed to detect the awareness of the driver (or lack thereof), to name only a few. Some types merely detect “impending doom” but others are designed to prevent it, much like some systems used in commercial aviation. Ironically, as auto safety systems increasingly rely on radar, the next generation of aviation safety systems will not, using satellite navigation instead.

One by one, many auto safety functions will become mandatory in vehicles as their performance and value is demonstrated. For example, the National Highway Traffic Safety Administration (NHTSA) recently ruled that all vehicles weighing less than 5 tons and built after May 2018 must have backup cameras. Progress in this area will be simultaneous with development of autonomous vehicles that will rely on all sorts of sensor-based systems to provide situational awareness, collision avoidance, and many other functions.

Table 1 A simple demonstration on how LIDAR works. By Mike1024 (Drawn and animated by Mike1024) [Public domain], via Wikimedia Commons.

One of the least developed but critical elements necessary to make autonomous vehicles a reality is their ability to communicate with other vehicles and to networks such as Wi-Fi and cellular systems. No type of sensor, RF or optical, has the range or field of view needed to locate the car you’re riding in from ten cars ahead or behind, so vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) systems will be essential to achieving true autonomy.

In a V2V system, two or more vehicles that are within acceptable communication range automatically establish a connection to form an ad-hoc network. They can then transmit and receive data about their location, speed, and direction. As this type of network allows all participants to act as routers, they can connect with other vehicles further away. The overall system must be able to make rapid decisions automatically so that timely warnings can be created and sent.

V2I expands the range and type of data that can be included to decision-making purposes by incorporating a broad array of infrastructure into the mix, gathering data about traffic and road conditions and “recommending” specific actions that vehicles in specifics areas should take. This can presumably also reduce emissions and fuel consumption. These recommendations could be offered to drivers via their information panels or by external signs or both. In an “ideal” scenario, these suggestions would turn into actions taken not by the driver but by the car, up to a point defined by the Vienna Convention on Road Traffic.

V2V systems have been designated to operate between 5.85 and 5.925 GHz, which was set aside by Congress for this purpose and has been harmonized with the EU and elsewhere. Although various communication standards have been proposed, the most likely will be an IEEE 802.11 variant called IEEE 802.11p that is designed to meet the criteria of Intelligent Transportation Systems (ITS). In particular, since a moving vehicle and “roadside infrastructure” may be able to communicate for a very short time, IEEE 802.11p makes it possible to exchange data without first being authenticated. Rather, transmission and reception can begin as soon as they are detected. As this varies from standard IEEE 802.11 protocol, the new “p” variant was required. The variant is part of IEEE 1609 Family of Standards for Wireless Access in Vehicular Environments (WAVE), which defines the architecture, communications model, management structure, security mechanisms, and physical access for low-latency communication up to 27Mb/s over ranges up to 1000m.

Every vehicle manufacturer is actively working to bring V2V to fruition and numerous consortia have been created to ensure progress in a more or less coherent way. Toyota, for one, has committed to having some of its models V2I-enabled as an option this year in Japan, compatible with advanced vehicle-infrastructure cooperative systems that operate at the Intelligent Transportation System (ITS) frequency. While industry-wide compatible systems may seem a long way away, the intensive development taking place in this industry along with efforts by NHTSA, the Department of Transportation, and similar agencies throughout the world to create a set of standards are shrinking this timeline. In fact, it is possible that manufacturers may be required to deploy V2V systems in the U.S. by 2017. NHTSA has stated that it believes this technology could reduce accidents by as much as 80%.

Data from Everywhere

The scope of the ITS is ambitious, considering all of the data, cars, infrastructure, and new technology involved. However, the technological sophistication of modern vehicles is somewhat astonishing considering that the carburetor was invented in 1876 and wasn’t widely phased out until the late 1990s. Jerry Maldonado, vice president of automation, customer lifecycle solutions at CA Technologies, put this in perspective in a company blog. According to Maldonado, a luxury car today has about 100 individual microprocessors and even a relatively modest one has 25 to 30, including the dreaded event recorder that verifies how you were operating your vehicle when it crashed.

He also compiled an estimate of the lines of code they employ, comparing this with other data-intensive platforms. An F-22 fighter by his estimates has 12 million lines of code, the flight software in a Boeing 7878 Dreamliner has 15 million lines, and the Android operating system has 12 million. A Chevrolet Volt has 12 million. In short, today’s most complex vehicles are formidable mobile computing platforms whose computational assets will increase as the number of parameters gathered by V2V and V2I are added in coming years.

A considerable portion of this information will come from disparate sources ranging from on-board and external cameras, to sensors in the pavement, and other sources that have not been developed yet. Everything from traffic lights to railroad crossings and pedestrians will be discernable to these systems. Within this information will be data gathered by radar sensors whose number will likely increase, thanks to a radar’s ability to provide precision information about the host vehicle as well as those to its front, side, and back.

Ubiquitous though radar systems may be, they are not the only RF and microwave systems that will be essential in and out of the autonomous vehicle; massive amounts of data captured by the connected car will arrive by means of Wi-Fi or cellular systems. The autonomous vehicle and all the external systems that enable it to function not only provide information about a vehicle, they allow connection to other vehicles, roadside infrastructure, and the Web. The possibilities of what can be done with such data on a massive scale are enticing with respect not only to traffic management and law enforcement, but on a grander scale of economics as someday vehicular traffic will be precisely quantifiable enough to forecast consumption, population behavior, and other presently intangible attributes of society on a near real-time basis.

Future Perfect?

As the world reels from a string of breaches and massive data collection by intelligence agencies, security is getting increased attention in automotive circles. It is becoming increasingly obvious that no matter how secure companies and government agencies attempt to be, someone will ultimately find a way in.

Once autonomous vehicles are plying the streets everywhere, more information about where we go, what we do, what we buy, and whether we travel within the scope of what is deemed to be “sensible” will be available for analysis. And it will likely be available to hackers, as well. Alongside this issue is whether or not most people will like having some unseen entity guiding how they drive and where.

All the same, the economic result of much safer and autonomous vehicles will save many lives and billions of dollars in prevented accidents. It is also a massive new market for some sectors of the RF and microwave industry. Every vehicle will have multiple radars, become its own Wi-Fi hotspot perhaps along with cellular capability, and huge numbers of radar and optical sensors will be mounted on so-called “street furniture” such as benches and the like; all connected without wires. This together with the ubiquity of “IoT” devices will ensure the health of the RF wireless industry as far into the future as anyone is likely to guess.

Barry Manz is a contributing writer for Mouser Electronics and president of Manz Communications, Inc., a technical media relations agency he founded in 1987. He has since worked with more than 100 companies in the RF and microwave, defense, test and measurement, semiconductor, embedded systems, lightwave, and other markets. Barry writes articles for print and online trade publications, as well as white papers, application notes, symposium papers, technical references guides, and Web content. He is also a contributing editor for the Journal of Electronic Defense, editor of Military Microwave Digest, co-founder of MilCOTS Digest magazine, and was editor in chief of Microwaves & RF magazine.

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