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V2x: 802.11p trumps LTE and 5G

Posted: 09 May 2016 ?? ?Print Version ?Bookmark and Share

Keywords:C-ITS? vehicle-to-infrastructure? V2I? V2V? V2x?

The concept of vehicles sharing information and working together to make transportation safer, greener, and more enjoyable, is truly compelling. The technologies associated with this concept, collectively known as Cooperative Intelligent Transportation Systems (C-ITS), promise to reduce traffic congestion, lessen the environmental impact of transportation, and significantly reduce the number of lethal traffic accidents. The impact on safety alone makes C-ITS worth considering, since, according to the World Health Organisation (WHO), roughly 1.25 million people died in 2015 due to traffic accidents, and with an associated governmental cost of about 3% of GDP [1].

Figure 1: Comparison between IEEE 802.11p and cellular connectivity pipes to the car. The key difference is the direct communications among 802.11p equipped devices. Cellular based services rely on the presence of the network.

A key enabling technology of C-ITS is wireless communication, covering vehicle-to-vehicle (V2V) communication, vehicle-to-infrastructure (V2I) communication, and infrastructure-to-vehicle (I2V) communication (figure 2). Collectively, these wireless transactions are referred to as V2x communication.

V2x has to support the many safety-related and non-safety-related use-cases of ITS systems. Tables I and II, in the Appendix, list the primary use-cases. Table I gives safety-related use-cases, such as the ability to transmit and receive the message "emergency electronic brake lights," a message that is transmitted by a vehicle in broadcast mode every tenth of a second to signal the event of emergency breaking. Table II gives non-safety-related use-cases, such as the message "traffic light optimal speed advisory," which is designed to improve traffic flow by using periodic broadcasts to recommend the best speed.

Figure 2: Artist's view of communicating vehicles and infrastructure. Vehicles can be cars, airplanes, trains and ships. The Central traffic Management System (CMS) manages the multiple aspects of the Cooperative Intelligent Transport System (C-ITS).

To support safety-related and non-safety-related messages, the wireless technologies used in V2x communication need to do several things. They need to operate in a very dynamic environment with high relative speeds between transmitters and receivers, and they need to support extremely low latency in the safety-related applications (50 ms for the "pre-crash sensing warning message", see Table I). They also need to tolerate the high load generated by the periodic transmission of multiple messages by multiple actors, and the high vehicle density typical of congested traffic scenarios. Another consideration is that V2x messages are local in nature, meaning they are most important to nearby receivers. For example, a "pre-crash sensing warning message" is extremely relevant for the vehicles in the surrounding of the crash, but irrelevant to far-away vehicles.

802.11p is here today
The de-facto standard for V2x is Dedicated Short Range Communication (DSRC) wireless technology, which is based on the IEEE 802.11p standard, the 1609 Wireless Access in Vehicular Environment (WAVE) protocol in the U.S., and the European Telecommunications Standards Institute (ETSI) TC-ITS European standards. This is confirmed by the publication of the report to congress written by the U.S. Department of Transportation (DoT) [2], which clearly explains the benefits of IEEE 802.11p for V2x.

IEEE 802.11p was designed, from the beginning, to meet every V2x application requirement with the most stringent performance specifications. In 1999, the U.S. Federal Communications Commission (FCC) set aside 75MHz of bandwidth, in the 5.9GHz region, for V2x, and the IEEE 802.11p standard operates within this range. The standard was approved in 2009, and since then, there have been a number of field trials. Several semiconductor companies, including Autotalks, NXP Semiconductors, and Renesas, have also designed and tested 802.11p-compliant products.

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