By: Onn Haran
We’ve just released a new whitepaper measuring C-V2X communication range for different antenna installations. The results were so surprising that it costed me a beer. Who would imagine that two vehicles with a single antenna would hear each other more than 1.8km apart? Not me, but I was happy to lose that bet.
We were also surprised to see that removing the cable compensator connecting the front antenna, and instead connecting the front antenna directly to the ECU, using 8dB cable, had barely any impact on the communication range. We predicted that the HARQ gain, achieved when ECU implements TX antenna diversity and each recipient vehicle receives two copies of the original message, would be meaningful. But not to that extent.
The results show that communication range is long enough even with a single antenna for most vehicles, or without a cable compensator, when the ECU is located next to the rear antenna. The Automotive market is extremely cost sensitive. If the cost of the front antenna can be saved, then it should be. If the cost of the compensator can be saved, then it should be. The OEMs are optimizing costs, and that cost reduction may cross the target feature price threshold, allowing some OEMs to approve C-V2X mass-deployment. Every road-user will benefit from that, getting closer to more effective V2X penetration.
The answer to the question of the title is yes: communication range can be too long. US Department of Transportation (USDOT) determined the minimal range as 300 meters to provide early alert before initiating a takeover (Do Not Pass Warning – DNPW). The 300 meters range should be measured in open air, yet for the DNPW use-case, it is very likely that a big truck will block the airwaves between the two vehicles, effectively decreasing the range. To compensate for that, and to allow safety margins, 700 meters range in open-air seems like a good target. Any communication system capable of longer ranges, will end up receiving messages for distant vehicles without contributing to better safety.
The irrelevant received messages are verified for security authenticity, software stack is running in the processor, and the message is forwarded to another processors or ECU. Meaning, resources are unnecessarily used. Thermal design and system cost might be impacted.
Longer range isn’t better. There is no need to excel. If system cost can be decreased by using single antenna or by removing cable compensator, there is no reason to hesitate to doing so.