Communication on the Road

April 1, 2009 By: Chaminda Basnayake GPS World

Positioning for Driver Assistance

Vehicle-to-vehicle (V2V) communication-based advanced driver assistance systems (ADAS) enable or enhance a suite of safety features by combining GPS and short-range wireless communication. The allocation of the 5.9 MHz radio spectrum for highway safety and traffic efficiency applications using Dedicated Short Range Communications (DSRC) has given automotive manufacturers the ability to go beyond traditional sensor-based safety features to provide drivers with another sense. DSRC enables vehicles to talk to surrounding vehicles and maintain a comprehensive situational awareness of roadway traffic.

General Motors first publicly demonstrated a fleet of communicating vehicles with driver warnings and automatic vehicle braking in 2005. Recently, General Motors has further developed the system with its OnStar and StabiliTrak technologies. The latest GM V2V fleet is fully integrated with production technologies with the exception of DSRC. Its built-in communication system can also interface with roadway infrastructure and support a range of new vehicle-to-infrastructure (V2I) features as they become available.

An accurate, reliable, and affordable positioning system, flexible enough to evolve with emerging V2V and V2I application requirements, obviously constitutes a prerequisite for these systems to work. This system is based on an efficient over-the-air (OTA) messaging scheme and an onboard system design that can be scaled to fit the needs of a range of in-vehicle safety features. As demonstrated in field tests, the system could support Which-Road, Which-Lane, or even Where-in-Lane applications using the same basic architecture.

Why V2V? Location and situation awareness are key enablers for almost all modern-day vehicle safety and convenience systems. These include GM OnStar, adaptive cruise-control (ACC) systems, side blind-zone alert systems, and many more. Most of these applications require specific knowledge about vehicles in close proximity, typically their speed, acceleration, and heading.

In an ACC implementation, radar, lidar, or other technologies track target vehicles in the field of view. However, this requires multiple sensors to cover different regions around the vehicle and to address the range requirements of different applications. For instance, forward- or backward-looking safety applications typically require the pairing of short- and long-range radar sensors and separate sensors to provide coverage of side blind zones as illustrated in FIGURE 1 (left panel), showing tracked and untracked vehicles using dark and light shades respectively.

FIGURE 1 Sensing with traditional sensors (left) and V2V 360-degree awareness (right)

These traditional sensors do not provide coverage beyond immediate line-of-sight, which may limit the effectiveness of these applications. For instance, in a hard-brake event that occurs far ahead, following drivers may not see the event until the vehicle directly ahead takes a responsive action. V2V systems can provide instantaneous communication between vehicles, even in situations where an event is obscured by a sharp turn, a large vehicle, or some other obstruction.

If vehicles carry location awareness technology such as GPS and the ability to talk to each other, all vehicles and even the infrastructure elements such as traffic-control devices could communicate and incorporate situation awareness onboard. In Figure 1's right panel, each vehicle can build an awareness zone (AZ) using data received from everyone within its communication range, and provide feedback to the driver. This concept is central to V2V communication.

V2V technologies eliminate two critical limitations of traditional sensor-based technologies. First, a single communication sensor can communicate with enabled vehicles within its communication range, making 360-degree situational awareness possible with only a single sensor. Second, communications range is not limited by line-of-sight, but only by the transceiver's range. A single sensor enables the formation of an AZ around the vehicle, and all equipped vehicles in the AZ can be tracked (shown in darker shade in Figure 1's right panel).

Further, communications between vehicles serve as a medium for exchange of a host of other information. For example, traditional sensors rely on analog sensing to indicate the presence of a vehicle and to estimate certain limited target data such as instantaneous speed, acceleration, and heading. V2V systems rely on digital communication packets that could send this and other specific data relating to future actions, such as turn-signal status and subsystem data such as stability status.

Why V2I? This medium also enables information exchange with communication-enabled infrastructure entities such as traffic-control devices or traffic signs. Thus V2V can extend to include V2I using the same technologies. In essence, once a vehicle is within the communication range of an equipped intersection, it becomes aware of all the information sent by all the vehicles around itself and the infrastructure elements. V2X collectively identifies the common underlying system components of V2V and V2I.

Of the two critical enabling technologies — GPS and DSRC — GPS is closer to becoming a standard technology in most vehicles today. GM OnStar, which includes GPS capability, is already available in more than 50 GM models. The Federal Communications Commission's allocation of the 5.9 MHz band for highway safety and efficiency applications using DSRC is a commitment to establishing the second key enabler. Tests show that vehicle communication using DSRC is reliable up to a range of around 300 meters in typical roadways, sufficient to meet the requirements of ADAS applications.