Will spar over RF standards endanger V2X roll-out?

October 03, 2017 // By Christoph Hammerschmidt
Which technology is best suited for Vehicle-to-X communications? This question continues to occupy the industry. The ITS-G5 technology, which is based on the modified IEEE 802.11p WiFi standard, is opposed to the C-V2X, which is based on the 3GPP standards. Although BMW, one of the “inventors” of the V2X technology, has already moved to the C-V2X camp and industry heavyweight Qualcomm recently launched a reference design that can be regarded as a clear commitment to C-V2X, the dispute has not yet been resolved. There are still good reasons for ITS-G5, as shows our interview with Onn Haran, co-founder and CTO of chip company Autotalks. The company is regarded as one of the pioneers of V2X technology.

eeNews Europe: Is a peaceful coexistence between C-V2X and ITS-G5 possible? If not: Why not?

Onn Haran: Simply not. C-V2X will create harmful interference to ITS-G5, and probably vice versa. C-V2X is proposing to use a frequency in close proximity to ITS-G5, only 20MHz apart. The ETSI harmonized standard (EN 302 571) defines the operation requirements for both transmit and receive operation. If a C-V2X device transmits using the mask as defined by the harmonized standard (and it is yet to be proven that C-V2X can meet the mask), next to ITS-G5 device, with adjacent channel rejection as defined by the harmonized standard, the ITS-G5 device will suffer reduced reception range by at least 20%. This effect is not limited to a single C-V2X device, but to any C-V2X transmitter within the interference radius which spans more than 40 meters. Furthermore, since C-V2X and ITS-G5 are not synchronized and C-V2X messages are longer, each C-V2X transmission may interfere to up to 3 ITS-G5 messages.

ITS-G5 messages are used for safety. Those interferences can risk missing critical messages.

Another related aspect is the effective usage of spectrum. C-V2X is planning to send the exact same messages as ITS-G5. That would imply that a bandwidth of 20MHz would be needed to carry the same content that ITS-G5 can carry today using up just 10MHz. This is inefficient usage of spectrum. Frequencies are a scarce resource that should be preserved.