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U Alabama study finds LTE C-V2N and DSRC connected vehicle latency approximately equivalent for infrastructure messages

A side-by-side comparison of connected vehicle technology at 85 traffic signals in the Tuscaloosa, AL area showed that latency in delivering safety messages from roadside units (RSUs) to vehicles via dedicated short range radios (DSRC) and LTE cellular (C-V2N) was “approximately equivalent,” according to a study by the University of Alabama. Researchers presented the study at the ITS America Annual Meeting in Washington, DC.

The research, conducted by Alex Hainen, Ph.D., Assistant Professor at the Department of Civil, Construction and Environmental Engineering at The University of Alabama, looked at installation, maintenance, latency of transmissions from RSUs and scalability for in-vehicle deployment. The research was conducted in conjunction with the Alabama Department of Transportation.

As connected vehicle communication methodologies, such as DSRC or cellular, continue to be debated, we wanted to look at the practical aspects of these technologies such as which can be quickly deployed by roadway operators and quickly adopted by the motoring public, and what role latency played in delivering RSU safety messages. We continue to look at additional applications for vehicle to infrastructure communications and how they can play a role in improving safety and efficiency.

—Dr. Hainen

According to the study, the main justification for choosing DSRC technology over cellular is that DSRC communications have much lower latency than cellular communications. However, the project showed the 4G LTE communications had a latency period of less than 300 milliseconds. While this period is longer than the DSRC communications, this time difference in latency periods have very little difference in the applications tested with this platform.

In the future, higher levels of automated driving may require low-latency V2V communication, but this current technology has already shown much potential as a connected traveler platform that can be easily used by today’s technology.

—Hainen et al.

The study also concluded that:

  • Cellular technology was much easier to configure and install than the DSRC equipment.

  • In terms of configuration, the cellular units have the ability to have their firmware updated via “Over-the-air” updates.

  • The most reliable way to update the DSRC units is through direct ethernet connection and one must be physically at the pole to update the unit.

  • Aftermarket OBUs cost upwards of $1,000 and usually require modification of the vehicle. This makes distribution of DSRC technology beyond pilot programs expensive and impractical.

The cellular equipment used was an AI-500-085 Processor unit provided by Applied Information. The units were installed in the traffic signal cabinets to monitor and communicate with both the cellular OBU and the TravelSafely smartphone app. The 500-085 processor also served as the Signal Phase and Timing (SPaT) translator from the traffic signal controller to the DSRC radio. DSRC radios were the ConnexUS Locomate Roadstar. Siemens M60 advanced traffic controllers were used. The TravelSafely system worked through both cellular and DSRC radio communication and processed whichever packet (either DSRC or cellular) arrived first.

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