Vehicular communication systems are a type of network in which vehicles and roadside units are the communicating nodes, providing each other with information, such as safety warnings and traffic information. As a cooperative approach, vehicular communication systems can be more effective in avoiding accidents and traffic congestions than if each vehicle tries to solve these problems individually.
Generally, vehicular networks are considered to contain two types of nodes: vehicles and roadside stations. Both are dedicated short-range communications (DSRC) devices. DSRC works in 5.9 GHz band with bandwidth of 75 MHz and approximate range of 1000 m.The network should support both private data communications and public (mainly safety) communications but higher priority is given to public communications. Vehicular communications is usually developed as a part of intelligent transportation systems (ITS). ITS seeks to achieve safety and productivity through intelligent transportation which integrates communication between mobile and fixed nodes. To this end, ITS heavily relies on wired and wireless communications.
The main motivation for vehicular communication systems is safety and eliminating the excessive cost of traffic collisions. According to World Health Organizations (WHO), road accidents annually cause approximately 1.2 million deaths worldwide; one fourth of all deaths caused by injury. Also about 50 million persons are injured in traffic accidents. If preventive measures are not taken road death is likely to become the third-leading cause of death in 2020 from ninth place in 1990. A study from the American Automobile Association (AAA) concluded that car crashes cost the United States $300 billion per year.
However the deaths caused by car crashes are in principle avoidable. US Department of Transport states that 21,000 of the annual 43,000 road accident deaths in the US are caused by roadway departures and intersection-related incidents. This number can be significantly lowered by deploying local warning systems through vehicular communications. Departing vehicles can inform other vehicles that they intend to depart the highway and arriving cars at intersections can send warning messages to other cars traversing that intersection. Studies show that in Western Europe a mere 5 km/h decrease in average vehicle speeds could result in 25% decrease in deaths. Policing speed limits will be notably easier and more efficient using communication technologies.
Although the main advantage of vehicular networks is safety improvements, there are several other benefits. Vehicular networks can help in avoiding congestion and finding better routes by processing real time data. This in return saves both time and fuel and has significant economic advantages.
Vehicular communications is mainly motivated by the desire to implement Intelligent Transport Systems (ITS) because of their key benefits in safety and traveling ease. Several ITS institutions operate around the world to bring ITS concepts to real world. In the United States one of the main players is U.S. Department of Transportation (USDoT) . The federal DoT promotes ITS through investment in potentially high payoff initiatives. One of these major initiatives, Vehicle Infrastructure Integration (VII), seeks to increase safety by providing vehicle to vehicle and vehicle to roadside units communications through Dedicated Short Range Communications (DSRC).
Intelligent Transportation Society of America (ITSA), which has members from many diverse areas including private companies, universities, and governmental agencies, aims to improve cooperation among public and private sector organizations. ITSA summarizes its mission statement as “vision zero” meaning its goal is to reduce the fatal accidents and delays as much as possible.
Many universities are pursuing research and development of vehicular ad hoc networks. For example, University of California, Berkeley is participating in California Partners for Advanced Transit and Highways (PATH), along with several other universities in California and elsewhere such as Stanford, UCLA, MIT, Texas A&M etc.
Car manufacturers and communication corporations are also investing in vehicular communications; among them are Kapsch, General Motors, Daimler Chrysler, Ford Motor Company, Siemens, Honda, Toyota, BMW, Mercedes-Benz and Mark IV.
Integrated automobile devices like OnStar have begun to make a presence on U.S. markets, with automobile manufacturers like GM offering them as options on their vehicles. Third party companies use these devices to offer services such as directions and emergency assistance to their customers. Although these devices may add an extra level of safety and peace of mind, they do not offer drivers the freedom to communicate with each other.
V2V (short for vehicle to vehicle) is an automobile technology designed to allow automobiles to “talk” to each other. The systems will use a region of the 5.9 GHz band set aside by the United States Congress in 1999, the unlicensed frequency also used by WiFi.
V2V is currently in active development by General Motors, which demonstrated the system in 2006 using Cadillac vehicles. Other automakers working on V2V include BMW, Daimler, Honda, Audi, Volvo and the Car-to-Car communication consortium.
V2V is also known as VANETs (Vehicular Ad Hoc Networks). It is a variation of MANETs (Mobile Ad Hoc Networks), with the emphasis being now the node is the vehicular. In 2001, it was mentioned in a publication that ad hoc networks can be formed by cars and such networks can help overcome blind spots, avoid accidents, etc. Over the years, there have been considerable research and projects in this area, applying VANETs for a variety of applications, ranging from safety to navigation and law enforcement.
In April 2014 it was reported that U.S. regulators were close to approving V2V standards for the U.S. market, and that officials were planning for the technology to become mandatory by 2017.
Two categories of draft standards provide outlines for vehicular networks. These standards constitute a category of IEEE standards for a special mode of operation of IEEE 802.11 for vehicular networks called Wireless Access in Vehicular Environments (WAVE). 802.11p is an extension to 802.11 Wireless LAN medium access layer (MAC) and physical layer (PHY) specification. As of November 2006 Draft 1.3 of this standard is approved . 802.11p aims to provide specifications needed for MAC and PHY layers for specific needs of vehicular networks. IEEE 1609 is a family of standards which deals with issues such as management and security of the network:
- 1609.1 -Resource Manager: This standard provides a resource manager for WAVE, allowing communication between remote applications and vehicles.
- 1609.2 -Security Services for Applications and Management Messages
- 1609.3 -Networking Services: This standard addresses network layer issues in WAVE.
- 1609.4 -Multi-channel Operation: This standard deals with communications through multiple channels.
The current state of these standards is trial-use. A vehicular communication networks which complies with the above standards supports both vehicular on-board units (OBU) and roadside units (RSU). RSU acts similar to a wireless LAN access point and can provide communications with infrastructure. Also, if required, RSU must be able to allocate channels to OBUs. There is a third type of communicating nodes called Public Safety OBU (PSOBU) which is a vehicle with capabilities of providing services normally offered by RSU. These units are mainly utilized in police cars, fire trucks, and ambulances in emergency situations.
As mentioned before DSRC provides several channels (seven 10 MHz channels in North America) for communications. Standards divide the channels into two categories: a control channel and service channels. Control channel is reserved for broadcasting and coordinating communications which generally takes place in other channels. Although DSRC devices are allowed to switch to a service channel, they must continuously monitor the control channel. There is no scanning and association as there is in normal 802.11. All such operations are done via a beacon sent by RSUs in the control channel. While OBUs and RSUs are allowed to broadcast messages in the control channels, only RSUs can send beacon messages.
In North America DSRC devices operate over seven 10 MHz channels. Two of the channels are used solely for public safety applications which means that they can only be used for communications of message with a certain priority or higher.
Although 802.11p and 1609 drafts specify baselines for developing vehicular networks, many issues are not addressed yet and more research is required.
Vehicular communication networks will provide a wide range of applications with different characteristics. As these networks have not yet been implemented, a list of such applications is speculative and apt to change in the future (However safety, which is the main purpose of these networks, will most probably remain the most important applications). Furthermore some of these applications require technologies that are not available now. Ultimately we would like to delegate the full handling control of our cars to the vehicles themselves; somewhat similar to autopilot. The classifications of applications is not unique and many institutions involved in intelligent transportation systems propose their own set of applications and classifications. We classify the possible applications in the following categories:
Providing safety is the primary objective of vehicular communication networks. Vehicles who discover an imminent danger such as an obstacle inform others. Electronic sensors in each car can detect abrupt changes in path or speed and send an appropriate message to neighbors. Vehicles can notify close vehicles of the direction they are taking so the drivers can make better decisions; a more advanced version of turn signals. In more advanced systems, at intersections the system can decide which vehicle has the right to pass first and alert all the drivers. Some of the immediate applications are:
- Warnings on entering intersections.
- Warnings on departing the highways
- Obstacle discovery
- Sudden halts warnings
- Reporting accidents
- Lane change warnings
Traffic management is utilized by authorities to ease traffic flow and provide a real time response to congestions. Authorities may change traffic rules according to a specific situation such as hot pursuits and bad weather. Applications include:
- Variable speed limits
- Adaptable traffic lights
- Automated traffic intersection control
- Accommodating ambulances, fire trucks, and police cars
Driver assistance systems
Roadside units can provide drivers with information which help them in controlling the vehicle. These may be conventional vehicles driven by humans or they could even be autonomous vehicles. Even in the absence of RSUs, small transmitters may be able to issue warnings such as bridge or tunnel height or gate width:
- Parking a vehicle
- Cruise control
- Lane keeping assistance
- Roadsign recognition
Policing and enforcement
Police, governments, and private entities can use vehicular communications in several ways:
- Speed limit warnings
- Restricted entries
- Pull-over commands
Pricing and payments
Electronic payment results in convenient payments and avoiding congestions caused by toll collection and makes pricing more manageable. For instance tolls can be variable for weekdays and weekends and during rush hours:
- Toll collecting
- Parking payments
Direction and route optimization
For reaching a destination there are usually many different routes. By collecting relevant information system can find the best paths in terms of travel time, expenses (such as toll and fuel), … Cars can talk to each other to inform you about traffic jams before you reach them so that you can take less congested road.
Advertising, Travel-related information
In an unfamiliar town drivers may be assisted to find relevant information about available services: Businesses could use information about passing vehicles and their movements to target advertising, or to select outlet locations. Vehicle identification and communications could be correlated with individuals identity and with handheld devices to extend the range of tracking and information gathering.
- Business locations
- Car services
- Gas stations
- Location-based service
General information services
As with many other communication networks, vehicular networks can be used to obtain various content and services (not directly related to traveling). In this respect there are numerous applications. In the case that wireless vehicular networks are integrated to the Internet, which is very likely, virtually every application that is currently used in the Internet will find its way to vehicular networks as well. However applications with lower bandwidth requirements are likely to become widespread sooner. Some applications can be:
- Web surfing
- File downloads
Automated highway is not yet realizable but nevertheless is an important application. In these highways the vehicles are able to cruise without help of their drivers. This is done by cooperation between vehicles. For example each vehicle knows the speed and direction of travel of its neighboring vehicles through communication with them. The status is updated frequently; therefore each vehicle can predict the future up to some necessary time.
Summary of vehicular communication systems
Recognition of collision scenarios and obstacles
- Front to rear and front to front collisions are identified on straight and curved roads.
- Algorithm runs and calculates the expected trajectory of the vehicle and relative distances and velocities of surrounding vehicles.
- Based on the analysed information, it sends information to driver about the safest path that can be taken.
Automatic deactivation of system
The system will be ineffective when there is a large snowfall, high precipitation, as there is a possibility of faulty interpretation of data especially while using laser or ultrasonic sources for sensing. So, in these cases the system will be automatically turned off.
Use of radar, laser, ultrasonic sensors have certain limitations and will not offer communication between large number of vehicles, such as vehicles at a junction, etc. So, GPS and wifi are the two methods by which any type of communication can be achieved in all types of conditions. Automatically analyzing the traffic signs and signals is also possible by incorporation of cameras onto the vehicles or emission of warning signals directly from the traffic boards which can be read by the receivers in the vehicles.