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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?

IEEE 802.11p is ready for deployment and is gaining momentum. There have been four ITS "Plug-test" events, organised by the ETSI, with the most recent taking place in Helmond, the Netherlands, in March 2015 [3] and the first in November 2011. There have been extensive field trials as well, in projects like Safety Pilot in the USA [4], Drive C2X in Europe [5], Score@F [6] in France, and simTD in Germany [7], the ITS corridor [6] in which the Dutch, German and Austrian infrastructure organisations assessed the maturity of 802.11p for V2I and the C-ITS central systems technologies. These field trials reflect the significant investments for the last 10 years to validate the 802.11p technology. Any other technology addressing the same application would require all of this to be re-done.

The United States have decided, based on collected evidence, that IEEE 802.11p technology can significantly reduce the number of collisions on the road, and is expected to mandate the use of 802.11p for safety-related use-cases in the second quarter of 2016 [2]. The DoT signalled its intention in 2015 with an Advanced Notice [8]. One American carmaker has already decided to include 802.11p in their production, in advance of the mandate [10].

The market for 802.11p is expected to pick up significantly in 2016, following the U.S. mandate. Adding to the momentum is the increasingly strong evidence for the safety benefits of V2x, and the gradual realisation that alternative solutions, including cellular, are far from market-introduction C or even specification.

Cellular for V2V is still far out
C-ITS systems are typically defined by their application requirements and don't specify a particular technology. There are, at present, several technologies, in addition to 802.11p, that aim to support V2x use-case requirements. Among these are cellular-based technologies, including 3G, LTE, and LTE-A [11-13].

Figure 3: Mobile subscriptions worldwide. Source: Ericsson Mobility Report, Nov 2011

Used by billions of people around the world every day (figure 3), cellular technology is, far and away, the most successful wireless standard of our time. The technical specifications for cellular are defined by the 3 rd Generation Partnership Project (3GPP). What today is thought of as broadband cellular, and referred to as 4G or LTE, dates back to 2009, and Release 8 of the 3GPP standard. Because the cellular infrastructure is extensive, it takes time to upgrade. In all, it's taken roughly six years for Release 8 to obtain large-scale deployment.

Given the worldwide success, and global availability, of cellular, the possibility of exploiting the cellular infrastructure and cellular user equipment (UE) for V2x is extremely appealing. However, current versions of cellular can only address basic V2x use-cases, but lacks support for low latency and high mobility use cases. These are the items most closely associated with safety-related use cases.

Underscoring the need for further development of cellular to support V2x and the relevance of the benefits brought by C-ITS, the 3GPP has established a V2x study group to advance C-ITS technology. Once the 3GPP has assessed and agreed upon the new capabilities needed to support all V2x use cases, there will be a period of development, and significant investment, to implement these capabilities. Then, once new 3GPP standards are available for deployment, there will be a further delay as the infrastructure is upgraded to support the new capabilities. Realistically speaking, it will be many years before cellular technology is fully capable of meeting all the requirements of V2x communication (figure 5).

Cellular for non-safety-related use-cases: V2I/I2V
Cellular technology, as it stands today, is well suited for non-safety-related uses-cases like those listed in Table II of the Appendix. On the whole, these are use-cases that involve the infrastructure, in V2I and I2V communication, where content originates or is processed in the cloud.

LTE Release 8 can cover most of these use cases with little or no modification, since it offers the required performance and bandwidth. It's unclear, though, how LTE networks will perform in very congested scenarios, and under certain operator roaming conditions. For example, messages for traffic management are particularly relevant to highly congested urban scenarios. As an option for managing high levels of congestion, one might consider a point-to-multi-point interface, such as the evolved Multimedia Broadcast/Multicast Service (eMBMS) as defined in the upcoming LTE-A Release 9. However, eMBMS is designed to support static scenarios, such as the crowd watching a football match in a stadium. That is, the interface can effectively manage communications for a crowd of people, as long as they remain fairly stationary, but won't provide the necessary efficiency when dealing with a high number of incoming and outgoing vehicles.

Similarly, it's unclear how handovers between mobile network operators (MNOs) and cooperation between application service providers will be managed, or how the presence of data traffic from other applications might affect I2V applications. There is also the question whether I2V applications present a compelling enough business-case to justify the investments needed to deploy eMBMS for such a purpose. There are very few multi-cast/broadcast solutions in place today, due to the high cost of infrastructure investment and UE upgrades.

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