With uncertainty surrounding both the technology and timeframe that enable short-range wireless communications in the transportation environment, many potential deployers are naturally considering what might be accomplished by leveraging cellular connectivity in place of dedicated short-range communications (DSRC) or LTE-Cellular vehicle-to-everything (LTE-CV2X).

The short answer is that cellular communications can be used for connected and automated vehicles (CAVs) in the right context. Some applications that were originally envisioned for short-range wireless communications can be accomplished using cellular network technology. On the other hand, information exchanges with low latency requirements, or requirements related to data proximate to the roadside, will be challenging to deliver using cellular networks reliably.

A Little Context

When we think about intelligent transportation system (ITS) communications, we are usually talking about more than just the physical media. Every ITS device can be considered to have four basic blocks of functionality:
 

• Communications – by which devices exchange data; this includes a transmitter, receiver, and hardware and software to control those devices and perform network management.
• Security – which handles authentication of incoming messages, encryption/decryption, and protection of on-board assets.
• Management – by which all of the functions of the device are controlled.
• Application functions – which are what we typically think of: for a traffic signal controller, all of the logic of controlling the traffic signal and making decisions based on inputs (e.g., from sensors) in an application function.

Discussions about cellular communications – whether 3G/4G/5G, LTE, New Radio, LTE-CV2X or DSRC – are all about access technology, a subset of communications functionality. An ITS device then needs a lot more to be properly specified: higher layer communications technologies (e.g., TCP/IP, HTTP, TLS, and other transport, networking and facility technologies), security and management for those communications functions, not to mention the application (and its management and security support) that accomplishes the ITS mission.

So, all that aside, what kinds of applications initially considered for DSRC could now be considered for LTE-CV2X? And what about 5G? To answer these questions, we first need to understand the difference in the technologies and labels. Briefly summarized, 5G includes a host of technologies, some of which have applicability to ITS use cases, just as some 4G technologies had applicability to some ITS use cases.

Understanding the 4G/5G Labels

The terms 4G and 5G refer to the specifications written by the 3rd Generation Partnership Project (3GPP) that form the basis for cellular networks. Specifications are collected in releases, which are the formal requirements that define how network devices interoperate.

Marketing terms like 5G refer to a span of releases; for example, 4G nominally includes releases 10 through 14, while 5G refers to 15, 16 and beyond. Given that each release provides new capabilities, and since the 4G/5G term can include more than one release, the marketing term can lead to confusion over available capabilities. For example, is a 4G network running release 10 or release 14? There are substantial differences.

Within ITS, 3GPP specifications are typically considered for two of the fundamental links used for ITS communications:
 

• Wide-area wireless, where one or both communicating parties are communicating from a mobile entity (e.g., a smartphone or vehicle)
• Short-range wireless, where one or both communicating parties are mobile and both parties are within a short range (e.g., visual, less than a few hundred meters) of one another
   

The situation is quite different for both. We need to know what is included in each release to understand when we might apply cellular in these two cases.

For information exchanges that can operate over wide-area wireless, any deployment with available 4G capacity is likely sufficient, though network congestion is a concern, particularly on older networks.

For information exchanges that must occur locally over short-range wireless, we need to understand a bit more about the specifications. Specifically:
 

• 3GPP Release 14 (4G) allows direct device-to-device communication (no cellular base stations involved). This is commonly termed LTE-CV2X and may be used for many of the applications for which DSRC was initially selected, assuming the other relevant specifications (e.g., application specifications, etc.) are updated.
• 3GPP Release 15 (5G) defines the beginning of 5G, introduces a new radio concept, and adds management power and flexibility from the telecom operator’s perspective. It does not change device-to-device communications from R14.
• GPP Release 16 (5G) leverages the new radio and allows the use of unlicensed spectrum. Device-to-device communication with the new radio is defined but does not interoperate directly with R14. Devices using R16 will need R14 radios to communicate with LTE-CV2X devices.

5G: Marketing vs. Reality

What about all the 5G advertising that talks about high speeds and implies low latencies? These are all about wide-area communications using cellular base stations. The 5G specifications open a host of new spectrum blocks to cellular use. Some of these blocks offer an extended range, some of them offer higher speeds.

Wireless communications are bound by physics, however: as the frequency increases, the range decreases. The highest speeds available in 5G that have attracted so much attention are commonly called “millimeter-wave”, which operates in wide frequency bands around 26, 28 or 39 GHz. These offer very high data rates but extremely short range.

The short range also causes deployment challenges, as significant coverage can only be achieved if the carrier installs many base stations. What may be of more use to the ITS space is the availability of the mid-range spectrum in 5G, which allows higher data rates with only a modest loss in range compared with existing 4G LTE connections.

When assessing the applicability of available wireless–to-ITS applications, one place to start is the Architecture Reference for Cooperative and Intelligent Transportation (ARC-IT). As a reference architecture, ARC-IT includes a variety of application concepts. While it references standards to provide users with as much information as possible, it also includes many concepts that have yet to be standardized; thus, it tends to be a little more forward looking and may aid in planning for deployment.

Any service package within ARC-IT that includes a short-range wireless information exchange likely requires a complete communications, management and security stack that uses either DSRC or LTE-CV2X. Many service packages include wide-area wireless flows that can be satisfied with 4G or 5G cellular communications using base stations in areas where coverage is sufficient. Where a service might use either wide-area or short-range communications for the same information exchange, ARC-IT notes this explicitly.

The Bottom Line

The communications world is constantly changing, albeit at the pace of standards development and deployment, but it is continually evolving nonetheless. Deployers and operators will need to pay attention to communications providers’ offerings in their regions, and explore the trade-offs between networks they own and control versus services provided by others. Future technologies, including additional upgrades to 5G and potential new offerings in the satellite communications market, make this an exciting space to watch.

Do you have questions about ITS communications or how to prepare for connected and automated vehicles? Contact us to learn more about Iteris’ connected and automated vehicle solutions.

About the Author:

Tom Lusco is a senior systems engineer at Iteris.

Connect with Tom on LinkedIn.