V2X communications – LTE versus DSRC: Page 4 of 4

April 09, 2018 // By Mark Patrick, Mouser Electronics
V2X communications – LTE versus DSRC
With all the hype surrounding self-driving vehicles based on artificial intelligence (AI), image recognition and sophisticated sensors, it is easy to forget about another important interrelated technology that also promises to help revolutionise driving. It is, in fact, destined to be a critical factor in making autonomous vehicles a reality. Known by the acronym V2X, it covers both vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications.

C-V2X versus the Incumbents

Supporters of DSRC and C-ITS will argue that they are far more suitable for V2X applications than C-V2X because they have been carefully constructed from first principles for one clearly-defined purpose, rather than being bolted on to an existing standard. For example, DSRC and C-ITS are designed to offer low networking overheads and low latency, they claim. Latency is a key issue for V2X. Functions like collision avoidance will require round trip latencies below 50ms. The NHTSA believes that “...at this time, DSRC is the only mature communication option that meets the latency requirements to support vehicle communication based crash avoidance...” – although it has clearly kept the door open for other technology platforms. In addition, proponents point out that DSRC and C-ITS have been in development for almost twenty years and this means they are stable and assured. Large-scale tests are underway in various locations. Meanwhile, the 5G Automotive Association (5GAA), main industry body promoting C-V2X, promises that it “can be commercially ready by 2018.”

Opponents of DSRC and C-ITS will say that the very fact that these technologies have been under development for close to two decades without reaching the mass market in any meaningful form clearly suggests that they may never be market-ready. Also that they are grounded in old technology that lacks a viable upgrade path. It may also be pointed out that although LTE and 5G technology might not have originally been designed with V2X in mind, C-V2X can leverage the economies of scale that the huge global mobile telecommunications market present in order to reduce hardware, software and development costs.


Can old and new Standards co-exist?

The 5GAA states that C-V2X technology does not have to be a complete replacement for C-ITS and DSRC. C-V2X is designed to be able to share the available spectrum with 802.11p-based V2X systems by switching to vacant channels within the 5.9 GHz band. In addition, it can support the upper protocol layers of C-ITS and DSRC – effectively replacing only the IEEE 802.11 MAC and PHY radio layer with 3GPP-specified equivalents, while allowing the specialised higher-level DSRC and C-ITS V2X messaging standards to run as normal. With these capabilities, C-V2X appears to meet the NHTSA’s requirements for mandatory V2X devices.

Perhaps the question of which technology is better is not actually as critical as it seems. Automobile OEMs could choose the underlying technology they prefer, or even hedge their bets and provision for supporting both – IC vendor Qualcomm has, for instance, recently announced its 9150 C-V2X chipset which does just this.


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