Dear Joseph,
thank you for all the work you're putting into compiling the comments on the NPRM. I have a few modifications and one additional comment that you can consider putting into the document, of course at your discretion!
- Section 5.1:
- The sentence "We agree that cellular V2N connectivity in terms of (Uu) communication could complement V2V and V2I to achieve a longer range." should be modified, because V2N will not be used to increase the range of basic safety messages. Instead, I propose to rewrite this as follows:
- "We agree that cellular V2N connectivity could complement V2V and V2I to enable additional services when the vehicles are inside the coverage area of a cellular network."
- Furthermore, the link in [3] to the SCOOP project website seems to be working, why was it claimed to be broken?
- Section 5.2 (V2P):
- My argument about antennas wasn't entirely wrong but weak. Instead, I propose to rewrite the entire section as in Appendix A of this email, using a different argument: C-V2X will require an additional radio interface (which is expensive), whereas DSRC and WiFi could share the same radio.
- Section 6.1 "V2X Channel Needs"
- I believe that this section should be more tightly connected to Section 3.1 (Spectrum Needs). It is also related to the argument that the 30 MHz band should not be split. Can we move this section to follow immediately after Section 3.1?
- Section 10.1
- I propose slight rewordings to emphasize that the slow market adoption was in the past, please see the full text in Appendix B of this mail.
- New subsection on shortcomings of C-V2X
- I believe we should better highlight some of the technological advantages of DSRC over C-V2X. The missing backwards compatibility in NR C-V2X towards LTE C-V2X is one example that we already mention in the document. I have one more example: C-V2X requires accurate time synchronization through GNSS, which is problematic in tunnels. The full text is in Appendix C of this email. You can add this to the final document if you find an appropriate space for it (for example, between 8.3 and 8.4 ?), or ignore it if it doesn't fit.
Appendix A
In its waiver request, the 5GAA states that “C-V2X enables direct, peer-to-peer mode communications […] between vehicles and pedestrians, cyclists and other vulnerable persons (“V2P”) […]”. This statement is false: C-V2X would not “enable” V2P, but instead make V2P vastly more complex and expensive compared to existing DSRC technology. Mobile phones of cyclists or pedestrians are not compatible with the C-V2X PC5 sidelink interface for direct peer-to-peer communication with vehicles at 5.9 GHz. Despite strong similarities, the cellular 4G/5G interface and the C-V2X PC5 interface cannot be integrated into a single radio interface because most pedestrians would not be willing to sacrifice all cellular data connectivity in order to receive V2P messages. Therefore, a second radio interface for C-V2X PC5 will be required. We anticipate that such additional hardware will only be integrated into expensive, high-end mobile phones, which would not be affordable to many children or elderly persons, i.e., to the most vulnerable road users.
On the contrary, DSRC enables V2P communications at significantly lower cost: Most mobile phones are now equipped with IEEE 802.11ac/ax WiFi modules, which currently support channels up to 5835 MHz and could be easily expanded up to 5925 MHz. As DSRC is based on IEEE 802.11 protocols, minor changes to existing WiFi designs will enable direct communication between DSRC-capable vehicles and mobile phones of pedestrians and cyclists. Furthermore, DSRC-based V2P and regular WiFi can reside on the same radio interface, which can be switched to V2P mode on the road and to regular WiFi connectivity at home. Thus, DSRC technology will in the future allow direct V2P communications using inexpensive mobile phones without the need for additional hardware.
Appendix B
While it is true that the adoption of DSRC did not move as quickly as it was originally anticipated, we believe that the reasons for this were related neither to the technological aspects of DSRC nor to its maturity for mass deployment. On the contrary, the US-DoT pilot programs, of which many have already started their operation phases, provide increasing evidence to show that the technology is ready for mass market rollout. In fact GM, Toyota, and other automotive manufacturers [[4], [5], [6]] made prior commitments to mass deployment of DSRC based system across their respective brands. It is in our belief that the slow adoption of DSRC in the past was more related to the lack of incentive and motivation from road operators scaling up their deployments as well as a reluctance of automotive manufacturers to voluntarily invest in a technology whose benefits to customers are only now becoming more evident as a more significant level of penetration of the technology is being reached.
Furthermore, we believe that the uncertainty that would be created by the proposed switch from already tested and deployed DSRC technology to C-V2X technology without significant deployments would significantly slow down investments and market adoption of V2X technology in general.
Appendix C
Contrary to DSRC protocols, which are able to manage the access to the wireless channel in a distributed manner, the channel access management of C-V2X PC5 requires accurate time synchronization, which must be acquired by GNSS systems like GPS [NEW REFERENCE 7, see below]. Even though this requirement does not lead to any additional costs because V2X systems already require GNSS systems for positioning, GNSS signals cannot be received in deep tunnels, which could lead to a loss of time synchronization, which could in turn reduce the efficiency and reliability of C-V2X systems in tunnels.
However, it is paramount for any V2X technology to provide reliable communication of safety messages in tunnels. On several past occasions, fires that resulted from traffic collisions in tunnels have spread rapidly and led to catastrophic loss of life. DSRC systems do not require time synchronization on a microsecond level and are therefore not impaired by the lack of GNSS reception in tunnels.
We note here that the lack of GNSS reception will not entirely prevent positioning. The vehicle’s position inside the tunnel could still be estimated by combining dead-reckoning systems, RADAR, LIDAR, and camera data. We acknowledge that positioning could be further improved by installing additional road-side units, which would also provide the time synchronization that is necessary for C-V2X. Nevertheless, it remains unclear whether public authorities will have sufficient funds to install these units.
[7]
https://www.unece.org/fileadmin/DAM/trans/doc/2017/wp29grrf/S2_P2._QC-5G-ConnectedCars.pdf To unsubscribe from the STDS-802-11-TGBD list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-11-TGBD&A=1