Auto elocution: Vehicle-to-vehicle communication mitigates driving hazards

Fri, 04/18/2014 - 11:55am
Joshua Israelsohn, Director, JAS Technical Media

It’s not often that in-vehicle technologies take a sudden step. The automotive industry is, historically, quite conservative. However, in February, the US Department of Transportation’s (DOT) National Highway Traffic Safety Administration, (NHTSA) announced its vehicle-to-vehicle (V2V) communication initiative for light vehicles is moving forward. The technology, which DOT Secretary Anthony Foxx described as "the next generation of auto safety improvements, building on the life-saving achievements we've already seen with safety belts and air bags," could present a wide range of opportunities for the automotive-electronics sector.

At the core of V2V implementations is a so-called heartbeat message issued by each equipped vehicle every 100 ms, according to the Bureau of Transportation Statistics. A vehicle’s heartbeat message anonymously reports its position and speed, which nearby vehicles compare to their position and speed data to identify hazardous conditions beyond the driver’s line of sight (Figure 1). The anonymous data is also publicly available to roadside nodes, potentially useful for a variety of safety, mobility, and environmental purposes, according to the DOT. The fixed roadside nodes make up the vehicle-to-infrastructure (V2I) component of a V2V system, which can, for example, detect the presence of vehicles for smart traffic-light controls or inform vehicles’ V2V systems of upcoming roadwork or speed-limit changes.

V2V specifications do not stipulate the method of determining vehicle speed and position but systems deployed in support of proof-of-concept (POC) trials use GPSs as core geo-positioning technology. Unfortunately, low cost GPS receivers cannot provide the positional accuracy V2V communication systems require. The target position error is < 1 m at 95 percent circular error probable (CEP). Data collected from POC trials with compensated devices show best performance was roughly 4.5m at 95 percent CEP—significantly better than the typical uncompensated receiver’s 15m but still more than four times the goal.

The position accuracy issue can be significant to this application given that, at highway speeds the forward position of a vehicle changes about 2.7 m per 100 ms heartbeat interval. A number of methods are available to reduce position error. Two, differential GPS (DGPS) and wide-area augmentation system (WAAS), are already being used in some available commercial GPS navigation systems. Both use fixed land-based radio beacons to compensate GPS-position errors due to issues such as tropospheric and ionospheric propagation effects and satellite-position uncertainty. Unfortunately, current implementations still don’t deliver position accuracies that meet V2V communication system requirements. Other methods—nationwide differential GPS (NDGPS) and high-accuracy nationwide differential GPS (HA-NDGPS)—produced position-data accuracy results within a 2 m and 10 cm (95 percent) error band, respectively, in US DOT sponsored dynamic tests.

As developers have been advancing, testing, and proving the practicality of V2V communication systems, providers of consumer-grade GPS-based personal navigation devices (PND) have seen their market share eroded despite growing use of position data, largely due to encroachment from smartphones. For example, in 2013 US PND shipments approached 5 M units just four years after their 2009 high of 16 M units, according to ABIresearch. These very same OEMs—companies such as Garmin, Magellan, TomTom and their competitors—may well be among those in the best position to provide position capture and velocity computation technologies to the nascent V2V market, particularly if they can embed HA-NDGPS or other V2V-compliant correction methods. With the US DOT discussing V2V in terms of a potential mandate for new vehicles, the initiative represents a market opportunity on the order of PNDs at their peak, with less likelihood of rapid displacement by competing devices such as mobiles (Figure 2).

Another area in which the V2V initiative will require engineering is in antenna design. POC test results indicate that communication systems installed in tall vehicles such as SUVs performed adequately: Under best-case antenna conditions PERs (packet-error rates remained < 10 percent for ranges > 800 m. By contrast, low-height vehicles, such as sedans, suffered 90 percent PER at < 100 m. Among the findings is that “antenna pattern and orientation has a significant impact on range, and appears to be quite sensitive to the vehicle installation and body configuration; this indicates that antenna design will need to be vehicle specific,” according to the Bureau of Transportation Statistics.

Finally, there appear to be opportunities for user-interface designs that minimize the time necessary for an operator to recognize a hazard while minimizing operator distraction. If you’ve ever had a passenger yell “LOOK OUT!” without mentioning pertinent information such as for what you are to look, you understand the problem. Message displays must communicate to the operator in minimum time while properly differentiating among hazard types.

V2V communication systems have a long way to go from successful PoC trials to commercialization and are not, therefore, available for testing by people or organizations not affiliated with the DOT’s initiative. However, to get a sense of what it might be like driving with a system that issues warnings I tested a GPS-based speedometer with an over-speed warning feature (specifically the Speedometer version Warnings are both visual—a message that flashes on a smartphone screen—and audible via either the mobile’s speaker or a Bluetooth enabled earpiece.

After several days driving with the GPS speedometer, my impression was that the audible warnings were more effective and less distracting than the visual. Two to four word messages seemed to communicate with less distraction than did screen-based messages. A comfortable interface might combine visual and audible messaging in ways similar to familiar GPS navigation systems in which most information communicates through the audio channel and the screen provides special orientation.


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