V2X in 5G – But How Will it Work?

We are back with a ‘talk’ about V2X in 5G!
It now seems to be a well-established opinion that humans are actually not very good at driving cars. We occasionally get tired or distracted. Our brains may not even have the required processing power to analyze all the information which it is fed, resulting in slow or bad decisions and – in the worst case – accidents.

V2X and V2V

Vehicle-to-Everything (V2X) and not least Vehicle-to-Vehicle (V2V) communication are expected important use cases for 5G, under the umbrella term URLLC (Ultra-Reliable and Low Latency Communication). In fact, it started already in 4G/LTE with the introduction of Proximity Services (ProSe). These are services that are based on the fact that two UEs (terminals used by humans or integrated in things) are close to each other and can communicate in direct mode, as opposed to communicating with or via the 4G base station (eNB). The 4G radio specifications from 3GPP define sidelink radio channels for this direct mode communication, over a UE-to-UE interface called PC5.

This is a good start! In order for vehicles to “talk” to each other, they need some type of radio resources. However, not necessarily 4G or 5G radio resources. DSRC (Direct Short-Range Communication) is a WLAN flavor (802.11p) and was standardized by IEEE for V2V already in 2009.

But focusing on 3GPP radio, the PC5 interface allows vehicles to communicate with other vehicles. The next question is: what will they communicate? What messages will be sent? What will cars actually “say” to each other? There is an application level interface called V5 in the 3GPP specifications, but it is highly unlikely that 3GPP themselves will define any messages on application level. And in fact, there are other players that are already doing this; the Society of Automotive Engineers (SAE) has specified V2V messages, and ETSI is also doing work in this area.

One type of basic message is, to make it simple: “I am here, I am moving in direction x with speed y”. Now the obvious question is: what will a car actually do with the information received from another car in such a message? As interesting as this may be with some type of artificial intelligence in more or less self-driving cars, this is clearly outside the scope of 3GPP, 4G and 5G and consequently outside the scope of this short text.

Going back to the 4G and 5G radio channels for V2V, there are some surprising findings in the current 3GPP specs. As of now (June 2018), there is no mentioning of sidelink radio channels in the New Radio or NG-RAN specs. TS 38.300 (……) neither contains the word “sidelink”, nor “V2X”, “V2V” or “ProSe”. The explanation for this is that these things will be included later (in Release 16). But it’s at least a bit strange that the overall descriptions don’t mention anything about 5G and V2V given all the buzz about it in white papers and marketing material from the industry.

And another little thing… we don’t want cars to collide just because they belong to different mobile operators, do we? So a common frequency spectrum needs to be used for direct mode communication over PC5, probably the 5,9 GHz band that was allocated for V2V – or actually Intelligent Transport Systems (ITS) – already some 10 years ago.

Radio Resource Management has always been of utmost importance since 2G was designed, a long time ago. Keeping interference at acceptable levels using advanced power control requires intelligence and lots of clever engineering in the base station. So how is interference control done when cars are transmitting messages in direct mode, without involvement from the eNB/gNB? Imagine hundreds of cars in some downtown traffic jam – that could create a rather noisy radio environment.

What has surprised us while researching V2V in 4G/5G is how little there is written about interference and how to handle it. We are pretty convinced that we are not the only ones who thought about it, so there are probably good ideas about interference control for V2V. But to the best of our knowledge, 3GPP specs don’t cover this (yet) and there are surprisingly few white papers or PowerPoint presentations that mention this.


So how will cars talk to each other? How will we avoid drowning the cars in interference? How will V2V in 5G work? Keep reading our articles to stay updated. As soon as we learn the answers to these questions, we’ll tell you!

Until next time,

The Apis IP-Solutions Team

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