As part of their WILLWARN project, DaimlerChrysler researchers have demonstrated that spontaneous and flexible WLAN radio networks make it possible for vehicles to warn each other about sudden road hazards - even over great distances.
The exchange of data can also be used to provide up-to-date traffic information over complete areas - a feature that will be necessary if future traffic guidance systems are to reduce the time drivers waste in traffic jams - and thus help cut emissions.
It’s truly amazing to discover just how much a car can “perceive.” For example, a vehicle knows when it’s raining heavily because its rain sensors “tell” it so. It also knows when it’s dark and foggy on a winter evening because the clock says it’s 7:24 p.m. and the driver has not only turned on the normal headlights but also the front and rear fog lights.
The outside thermometer can also provide useful information - for example, when the temperature is approaching freezing point and the road could get icy at any minute. If the car is on a secondary highway, it’s quite possible that salt vehicles haven’t been there yet, as they generally give priority to the main routes.
If conditions begin to worsen in such a situation, the car will “notice” this just as quickly as the driver does - for example, when the yaw rate sensors in the Electronic Stability Program (ESP) register a torque around the vertical axis, meaning that the vehicle is in danger of skidding. All this information is important not only to the driver of the vehicle but also to the drivers behind him or her. It’s also of use to drivers who won’t even approach the dangerous stretch of icy road for another two or three minutes - not to mention the driver of a truck filled with gasoline that will pass the site in half an hour. In other words, the data - in the form of a timely warning - is worth its weight in gold to any driver who will be passing through before conditions improve.
The Mercedes-Benz E 500 being tested by a DaimlerChrysler research team headed by Matthias Schulze can receive such warnings. A screen integrated into the vehicle’s center console suddenly displays the following warning: “Attention: Black ice on road K 1022 between the towns of Aidlingen and Gültlingen.” As it turns out, this is an area that the car will arrive at in approximately five minutes. No radio traffic update can provide drivers with such specific information on extremely localized conditions that quickly - if at all. What’s more, the traffic data offered by radio broadcasters is usually limited to conditions on major highways; only rarely will you hear a report concerning a minor road such as the one between Aidlingen and Gültlingen.
WILLWARN - the name of the system installed in the automobile used by Schulze’s team - doesn’t discriminate against small roads like the K 1022.
In fact, it has been designed to receive and transmit information throughout the entire road network in Germany. WILLWARN is the product of research work carried out by DaimlerChrysler engineers in the fields of C2C (car-to-car) communications and C2X communications (in other words, communication between vehicles and transmitters and receivers positioned along roads). The WILLWARN (“Wireless Local Danger Warning”) project is part of an EU research initiative known as PREVENT, in which various automakers and suppliers examined and tested new technological solutions for preventing accidents. Schulze’s team served as the project leader for WILLWARN.
The basic idea is simple enough: Each car on the road identifies dangerous situations on the basis of the various sensor data it already collects. Once the threat has been identified, the only thing left to do is to warn other vehicles. However, the term “only” is something of an understatement. For one thing, giving cars the ability to pass on information while the traffic continues to move is the biggest challenge the experts face. Schulze’s team had to think in terms of completely new communication structures - in this case, ad hoc networks. Such spontaneous flexible networks are required for C2C communication because vehicles on the road are continually in motion, which means the participants in the network who need to communicate with one another change constantly within seconds, with some exiting the network as others link up with it.
> Radio-based WLAN technology is the solution
Such a network obviously needs to be able to transmit information wirelessly - and the ideal technology for this is WLAN, which computer users are probably familiar with. WLAN technology offers clear benefits. For example, it can transfer large amounts of data rapidly, without generating connection costs. An IEEE 802.11 standard created especially for safety-related communication applications in motor vehicles ensures that all devices equipped with a transmitter and receiver module thus certified will be able to communicate with one another. It was in fact WLAN that created the basis on which the communication system used by WILLWARN is built. With this system, it is possible for each vehicle fitted with a transmitter and receiver to send or receive data to or from another car with the same equipment. Moreover, any vehicle in the network can act as a mobile router, meaning it can “forward” data from one vehicle to another that is too far away from the first vehicle to receive direct WLAN signals.
And that brings us to one of the biggest drawbacks of WLAN technology: its limited range. Anyone who has tried to operate a WLAN system over several floors in his or her home is well aware of this problem.
In terms of WLAN road applications, a range of 500 meters is seldom achieved, even under ideal conditions; the limit in practice is generally around 200 meters.
Schulze’s team therefore precisely analyzed how reliably the data packages are transferred from vehicle to vehicle and also tested procedures designed to ensure that the data transmission chain remains intact even when two appropriately equipped vehicles are not present in the area covered by the network. Their approach here was to create a system in which every message is sent over a specific period of time so that it can be passed on a like a baton in a relay race.
The resulting network can therefore include vehicles that do nothing more than relay messages, without themselves benefiting from the content of the warnings - for example, because they are already moving away from the danger area. If such a vehicle continues to send the message it picks up for a certain period of time, it could end up warning the driver of the truck loaded with gasoline from the aforementioned scenario, informing him of the icy road he’s approaching.
This in turn creates a new problem, however: “Just imagine hearing peeping noises and seeing blinking lights in your car every ten seconds because the vehicle is receiving warnings about an intersection in a town you’re actually circumventing on a bypass road,” says Schulze.
No doubt, such a device would quickly get on a driver’s nerves and be turned off, never to be used again. This is perhaps why “warning management,” as Schulze describes it, was the real challenge. The project team addressed this challenge by developing intelligent software for WILLWARN in the form of a program that filters all warning messages received. Only in cases where the information is relevant to the driver is it passed on (see box “Intelligent filters”).
Using the WILLWARN concept, Schulze’s team were able to impressively demonstrate how warnings can be passed along over distances much greater than the actual range of the radio technology employed.
The team was also able to show it is possible to develop warning management software solutions that prevent displays from becoming nothing more than an annoying distraction.
For Schulze, the successful development of the C2C and C2X concepts means the time has now come to test the technology on a broader and more practical scale. “There are many systems similar to the WILLWARN program we operate,” says Schulze, “and the associated projects show that the technology works. Nevertheless, so far the developers have only tested their systems under artificial laboratory conditions. Now we need to take a further step toward practical everyday applications by conducting major tests under real conditions on the road.”
> The time is right for major practical tests
The chances for conducting such tests are good, according to Schulze. All of the industrial partners involved in the projects agree that the time is now right for a major series of tests (see box “Initiatives for greater safety”). They are therefore working together on project proposals for which they hope to receive funding from various government ministries. “We need that funding because a test series on the scale we envision requires a huge amount of money,” says Schulze. Under consideration as testing sites are the greater Berlin metropolitan area and the Rhine-Main region around Frankfurt. Schulze estimates that carrying out an accurate test of the system will require equipping around 250 vehicles with the appropriate WLAN technology and installing roughly the same number of communication beacons on the streets and roads in the testing area.
He says that C2C communication systems suffer from a kind of chicken/egg problem. As long as there are only a few vehicles equipped with WLAN technology on the road, the utility of the information they send and receive will remain limited. Many people will thus ask themselves why they should spend money on such a system, as it will only become effective when a large enough number of vehicles have joined the ad hoc networks to ensure an unbroken chain of information.
For this reason, Schulze believes that C2X concepts will have to be implemented if C2C systems are to be successful on the market. “Transmission and receiver units on streets provide traffic guidance centers and private service companies with valuable up-to-date information on traffic flows,” Schulze says. Such applications could therefore be used to recoup the investment in C2X infrastructure technology. At the same time, C2X road hotspots would offer drivers immediate value by updating the software in their navigation system, for example, or providing additional information about specified routes.
Moreover, the infrastructure wouldn’t even have to be built from the ground up: “Traffic lights in cities are already networked, and there are also induction loops installed in highway blacktop that measure traffic flows. In other words, the foundation is already in place,” Schulze adds.
> Intelligent filters
If the technically limited range of an ad hoc WLAN is to be extended, the vehicles in the data network must be able to receive and pass on information independent of its relevance. However, such vehicles also need to be equipped with intelligent warning management systems that can filter the data according to its relevance. Otherwise, electronic traffic messages will become a curse rather than a blessing.
In their WILLWARN project, DaimlerChrysler researchers tested various approaches to using software filters for such applications. The relevance of a local warning concerning black ice on a particular bridge, for example, can be determined relatively easily on the basis of positioning data. A vehicle crossing the bridge records its position via GPS and transmits this information along with the warning. A system such as WILLWARN can compare this data with the likely route the driver of its own vehicle is planning to take, and then determine if the car will even be passing that spot.
Another type of filter system that bases its calculations on driving speeds would be useful for warning drivers about a red light they are in danger of overlooking. It would only trigger such a warning, however, if the driver continues to approach the light without reducing speed.
A difficult issue is the reliability of a warning message. In the case of fog, for example, it would be advisable to send out a fog warning over the ad hoc network only after several vehicles have turned on their fog lights. In other words, a trust value needs to be defined for such a warning.
> Initiatives for greater safety - worldwide
As part of its activities in the areas of car-to-car (C2C) and car-to-infrastructure (C2X) communication, DaimlerChrysler participates in several important projects and organizations.
One example is Germany’s nationwide NOW (Network on Wheels) research project, which is funded by the German Ministry of Education and Research. DaimlerChrysler’s project partners here are the automakers BMW and Volkswagen, the electronics companies NEC Deutschland and Siemens, and the Fraunhofer Institute for Open Communication Systems Focus.
This research alliance will end in the summer of 2008. Its two most important goals are to define the technical standards for a communication system that can be implemented quickly in vehicles manufactured by all automakers, and to attain exclusive access to a frequency range in the 5.9-GHz band with sufficient bandwidth to ensure the smooth operation of the safety applications without any disturbances.
The partners in the German NOW initiative are also part of the Europe-wide Car-to-Car-Communication Consortium (C2C-CC), whose members include other respected automakers operating in Europe (Audi, Fiat, Honda, Opel, Renault, VW), as well as automotive suppliers and manufacturers of electronic equipment for communication systems. The consortium is dedicated to establishing uniform standards and communication protocols, as well as obtaining a Europe-wide frequency for C2C applications.
The complex process for obtaining a frequency has already reached an advanced stage. For example, the required compatibility studies have now shown that the utilization of the desired frequency bands would not disrupt other radio communication applications operating on neighboring frequencies. A decision on the allocation of a frequency in Europe might therefore be made before the year is out.
Ad hoc networks in the U.S.
DaimlerChrysler researchers and developers are also participating in a broad-based initiative in the U.S. for testing C2C and C2X concepts: the “Vehicle Infrastructure Integration” initiative (VII). DaimlerChrysler recently worked with the Transportation Department of the state of Michigan to test the performance of transmitter and receiver modules in some 100 vehicles within the framework of a DSRC (dedicated short-range communication) testing program. Among the parameters measured were the system latency period, the volume of data transmitted, transmission quality and radio connection stability, even at high driving speeds.
As part of the VII initiative, a roadside infrastructure for DSRC transceivers and other communication equipment will be ready for operation in a test area totaling approximately 35 square kilometers near Detroit by the middle of this year. Once it is up and running, it will be used to put 20 prototype applications developed by VII partners through their paces in field operational tests under near-real conditions.
The state of California also recently equipped several intersections with DSRC technology for applications such as transmitting traffic light signal phases to approaching vehicles in order to warn them of imminent red lights. All the pilot programs will together serve as a litmus test to determine the future of the associated technologies in the U.S., because the Department of Transportation has said it will base its decision regarding widespread implementation of DSRC technology across the U.S. on the results of the projects.