#355 Rethinking Connected Vehicles for Spectrum Scarcity

Principal Investigator
Jon Peha
Start Date
July 1, 2021
End Date
June 30, 2022
Research Type
Grant Type
Grant Program
FAST Act - Mobility National (2016 - 2022)
Grant Cycle
2021 Mobility UTC


In Nov. 2020, the Federal Communications Commission reduced the spectrum available for Intelligent Transportation Systems by 60% in order to enable next-generation Wi-Fi. The Dept. of Transportation concluded that there will no longer be enough spectrum for connected vehicles. This research will identify and assess alternative ways to meet the spectrum needs of connected vehicles despite this scarcity, while also providing spectrum for Wi-Fi. These approaches are based on spectrum sharing.    
On November 18, 2020, the Federal Communications Commission (FCC) reduced the amount of spectrum allocated for Intelligent Transportation Systems (ITS) [FCC20], despite the strenuous objections of the Department of Transportation (DOT) [DOT20], and entreaties from the Chair of the Senate Commerce Committee (which oversees the FCC) and others to leave this matter to the next Administration.  This November 2020 decision is the culmination of extensive and often public disagreement between these two federal agencies on this matter, in part because no process was in place to jointly address the concerns of both agencies (such as the one we have proposed [PEHA20b]).  The FCC claimed that 30 MHz of ITS spectrum is sufficient to carry vehicle to everything (V2X) communications, while DOT claimed that 75 MHz is needed.  They have also disagreed over which technology should be used, how different types of V2X transmissions should be prioritized, and other aspects of ITS spectrum policy.  

The stakes of this decision are high, for both agencies and for the nation.  It is DOT’s job to make our roadways safe and efficient, and this decision matters for that mission.  DOT has estimated that two of the many safety applications that depend on ITS spectrum would by themselves prevent hundreds of thousands of crashes every year [DOT16].  Other applications that use ITS spectrum would improve roadway congestion, commute times, vehicle fuel consumption, and emission of air pollution and greenhouse gasses.  Future forms of autonomous vehicles such as platooning and maneuver coordination are likely to use and benefit from ITS spectrum as well.  All of this could be in jeopardy if there isn’t enough spectrum for V2X communications, as the DOT has concluded [DOT20].  38 Members of Congress connected with the House Committee on Transportation and Infrastructure went on record to concur with this conclusion, arguing that “the FCC's proposal undercuts the potential to prevent many of the 37,000 traffic fatalities each year by impeding the development and deployment of safety-critical technologies” [HOUSE20]. This ITS spectrum could be important for many communities, especially in smart cities [PEHA17c, PEHA18d].

In contrast, it is the FCC’s job to make sure spectrum is used efficiently and effectively to serve the public interest, and this decision matters for that mission as well [FCC19, FCC20].  The ITS band has been lightly used for over twenty years.  A new generation of Wi-Fi has emerged that could bring tremendous benefits, but this technology requires a 160 MHz channel.  No 160 MHz channel is available to unlicensed devices today at frequencies with favorable propagation characteristics for Wi-Fi.  The FCC could (and very recently did) create such a 160 MHz channel by taking 45 MHz away from the ITS band, combining it with an adjacent unlicensed U-NII band, and opening the newly combined band up to 160-MHz Wi-Fi transmissions.  It is reasonable to expect that this 45 MHz will now see heavy use in the future, and bring considerable value to users and producers of Wi-Fi, and thus the nation.

The proposed research will investigate ways to meet the objectives of DOT for the ITS band despite the FCC’s decision to reduce its size by 60%, potentially creating serious spectrum scarcity for connected vehicles.  Whereas the FCC apparently focused mostly or entirely on the goal of making sure spectrum is available for new communications technologies, and DOT apparently focused mostly or entirely on the goal of improving the safety and efficiency of automotive transportation, we will instead investigate schemes that have the potential to achieve both objectives.  In particular, we will assume that these 45 MHz of spectrum are available for 160 MHz Wi-Fi transmissions, although perhaps with some limitations that the FCC did not envision in its recent decision.  We will then consider ways that connected vehicles could use the remaining 30 MHz of the ITS band, and supplement those 30 MHz by using other bands on a shared rather than exclusive basis.  

The simplest approach may be to allow V2X communications to continue in the 45 MHz that were removed from the ITS band, which would violate the FCC’s recent decision, but on a shared basis with 160 MHz Wi-Fi rather than on an exclusive basis as was the case before Nov. 2020.  Some new limits on Wi-Fi may be needed to make that work well, such as new power spectral density limits, or a prohibition against placing these Wi-Fi devices outdoors.  Indeed, we have already looked at something similar [PEHA18c, PEHA19].  We have shown in previous work that it would be highly efficient for some (but not all) of V2X traffic to share spectrum with Wi-FI, assuming that the V2X used DSRC technology and the Wi-Fi used older technology and channels much narrower than 160 MHz.  Based on that, we urged the FCC to consider allowing V2X communications in the unlicensed bands [PEHA18c, PEHA19, PEHA20a].  We have since been invited to present these policy options and related issues to the United Nations’ International Telecommunications Union for consideration in other nations, and for possible global harmonization [PEHA20d].  However, the more important case to analyze in the wake of the FCC’s November 2020 decision employs C-V2X rather than DSRC technology for V2X, and wideband rather than narrowband technology for Wi-Fi. That case has not yet been studied by us or anyone else.  

Alternatively, V2X communications could occur in an entirely different band.  This was not allowed by the recent FCC decision, but it is also not inconsistent with the recent FCC decision.  Indeed, the FCC points out in the same document that there have been proposals from various stakeholders to give connected vehicles the ability to use 3.5 GHz or 4.9 GHz spectrum for V2X communications instead of the ITS band [FCC20], and the FCC seeks input on this idea in the future [FCC20].  In addition, in his comments at the public meeting on Nov. 18, FCC Chairman Ajit Pai pointed out that systems for vehicular safety already use spectrum at 0.9 GHz, 2.4 GHz and 80 GHz [PAI20], so the ITS band need not be everything, as was once expected.  

We will investigate different bands to assess their ability to meet the needs of various connected vehicle applications, ranging from today’s collision avoidance applications to tomorrow’s autonomous vehicle applications.  We will consider both safety-critical applications and non-safety-critical applications.  Non-safety critical applications are also important, and despite the efforts of FCC Commissioner O’Reilly, the FCC deliberately chose not to limit the ITS band to safety-critical traffic in its November 2020 decision [ORIE20].  

Different bands have different propagation characteristics, and different types of wireless systems already using the band.  For example, at 4.9 GHz, which is one of the bands that was proposed by commenters, V2X communications would have to coexist with various public safety communications systems, such as those used to connected police video cameras.  There is spectrum in the millimeter wave bands with fewer incumbent wireless systems to contend with, but attenuation in those frequencies is challenging, especially in heavy rain.  It is not obvious which is best.

It may be that the best option is to allow connected vehicles to use multiple bands on a shared basis.  Some applications require V2X communications that need only travel a short distance. This includes a number of safety applications, since there is no risk of crashing into a car that is over half a kilometer away.  Transmitting such a message over longer distance has no benefit for such applications, but long-range transmissions do harm, because they cause interference over a large area. Other applications would benefit greatly from much larger distances.  Perhaps the former should occur in higher frequencies, and the latter in lower frequencies.  The choice of band may also depend on the quality of service requirements for the application associated with V2X traffic.  For example, latency-sensitive traffic might do worse in bands that are shared with incumbent wireless systems that sporadically use the band extensively, whereas non-latency-sensitive traffic might do well in such bands.  Another advantage of using multiple bands is that utilization by legacy systems is likely to be uncorrelated, i.e. it is far less likely that two bands will both be busy at the same time if these bands are shared with dissimilar incumbent systems.

Our results will help both the FCC and the DOT find spectrum policies for Intelligent Transportation Systems spectrum that advance their respective goals, including preventing crashes, facilitating the introduction of autonomous vehicles, making room for next-generation Wi-Fi, and using valuable spectrum efficiently and effectively.  It will also shed light on the technology that municipalities across the country should use on their signal lights and in other roadside infrastructure, and the technology that automobile companies should use in their vehicles.

One step in our method is to review important applications that will generate V2X applications.  We will characterize the traffic that these applications generate, including the distribution of message size, the arrival process, and the types of events that trigger increases in transmission rates.  We will also characterize quality of service at both the network layer and at the application layer.  (Most researchers have considered only the former, but we have argued in research recently presented at a Telecommunications Research Board Conference that it is the latter that matters most [PEHA20c].)  We will start with the more established safety-critical applications for vehicles, such as those identified by the DOT and others [NHTS14, DOT16, AREN19, MIUC18, WANG17], as well as safety applications for pedestrians [DOT15].  For example, applications warn drivers when a bridge is frozen, when a signal light is about to change, or when it is unsafe to turn left at an intersection due to oncoming traffic.  We will then consider applications that may not exist yet, but are anticipated, including applications for autonomous vehicles.  For example, one important future use of V2X is platooning.  It has been demonstrated that platooning can be achieved using sensors and no V2X communications, but the distances between vehicles can be decreased with V2V communications [MIKA19]. Decreasing the distance between vehicles means longer platoons, better fuel efficiency, and ultimately lower costs, but this requires low latencies for V2X communications.  Some in the auto industry describe the following phases of applications, and we will review applications from all phases: phase 1 awareness driving, phase 2 sensing driving, and phase 3 cooperative automated driving.

Another step in our method, and the step that will require the most time and effort, is the development and use of data-driven simulations.  As we have done before for other V2X protocols (DSRC) and other applications [PEHA15, PEHA16a, PEHA16b, PEHA17a, PEHA17b, PEHA18a, PEHA18b, PEHA18c, PEHA19, PEHA20c], we will develop simulation software that mimics the behavior of communications systems, applications that generate V2X communications, and vehicular movement, so we can observe performance under different spectrum policies. 

This software will mimic vehicle mobility.  In past research, we have collected data on the mobility of many hundreds of DSRC-equipped cars, which includes location and velocity readings every 1 to 5 seconds over a period of months to years, and used that to simulate mobility.  We will supplement that with data obtained from the Department of Transportation of other trials [DOT19a], such as the one in Ann Arbor [DOT19b].    From this data, we can construct realistic models of how the geographic concentration of vehicles changes over time, since network congestion and interference come from such concentration, and how vehicles accelerate and decelerate as they approach intersections of hazards.

This software will operate at multiple layers, i.e. it will realistically characterize signal propagation and interference at the physical layer that reflects the physical characteristics of the frequencies under consideration.  It will also realistically characterize the V2X technologies, which could be C-V2X mode 3 (centralized), C-V2X mode 4 (decentralized), and DSRC.  (Our baseline will be C-V2X mode 4.)  It will realistically mimic IP, TCP, and other protocols. It will realistically mimic the applications that generate V2X traffic, and the behavior of Wi-Fi, public safety communications systems, and other wireless systems with which V2X might share spectrum.  We will do so under different population densities from dense urban to sparse rural, and different scenarios.  To do that, we need realistic models of vehicle mobility behavior, of signal propagation, of network protocols, and of applications.  

In yet another step, we will review the spectrum regulations to determine precisely how these regulations would change to enable the various spectrum policies that we are simulating, and especially those that are found to achieve good results in our simulation study.   This includes regulations for the ITS band, and the adjacent unlicensed band, both of which are expected to change in 2021 as a result of the FCC’s vote on Nov. 18, 2020, and are likely to change more after that.  It will include regulations in other bands where V2X might be supported as well, such as the 4.9 GHz public safety band.

Using the methods described above, we will consider a variety of approaches for managing spectrum for V2X, and a variety of portfolios of supported applications, to assess their pros and cons.  For the former, we will consider the case where V2X communications is limited to a 30 MHz ITS band and nothing else, the case where V2X communications occurs on this 30 MHz band and the adjacent 45 MHz which is shared with the next generation of Wi-Fi under new rules that we will propose, the case where the ITS band is supplemented with one or more other frequency bands on a shared basis.  This could be low-band, mid-band, or high-band spectrum.  For all of the above, we will also explore the possibility of using Wi-Fi rather than C-V2X or DSRC.  This will not work for most V2X traffic, but it will work for some applications that work when the car is stationary, and thus could reduce pressure on the ITS band (or perhaps someday ITS bands).  

For the latter, we will consider the possibility of supporting some kinds of V2X communications, and not others, which was suggested in the recent FCC decision [FCC20].  For example, perhaps we support the exchange of basic safety messages, but not using sensors on multiple cars to achieve cooperative awareness.  The goal here is not to suggest that any class of applications should be excluded, as this requires an understanding of the benefits of these applications which is outside the scope of our research.  The goal is to see how spectrum policy could be adjusted if some types of applications are included and other are excluded.

We will produce results that show achievable performance of both V2X communications and performance of any wireless system that must share spectrum with V2X, but whatever measure of quality of service is most appropriate for the applications and technologies under consideration.

We will consider a wide range of regions and scenarios.  National spectrum policy should ensure good performance most of the time in most places, but it cannot possibly guarantee good performance all of the time in all places without tremendous inefficiencies.  We must determine where under what circumstances a given spectrum policy works well, and when and where it doesn’t.  One approach might work poorly in a busy hour in New York City’s Time Square, because there are so many cars and so many Wi-Fi hotspots trying to transmit at once in a small area.  Another approach might work fine in Time Square, but work poorly in rural Idaho where communications must occur over large distances, and where the types of systems sharing the spectrum are quite different.

Finally, our results will provide guidance to regulators on what specific changes would be needed in spectrum regulations to make the more promising approaches a reality.

[AREN19]	Arena, F., & Pau, G. (2019). An overview of vehicular communications. Future Internet, 11(2), 27.
[DOT15]	U.S. Department of Transportation, “U.S Department of Transportation Releases Vehicle to Pedestrian Technical Scan Summary” (2015). https://www.its.dot.gov/press/2015/v2p_tech.htm
[DOT16]	U.S. Department of Transportation, “Federal Motor Vehicle Safety Standards; V2V Communications - Notice of Proposed Rulemaking (NPRM)” (2016).
[DOT19a]	US Department of Transportation, Public Data Portal, Automobile Data and Resources, https://data.transportation.gov/browse?category=Automobiles
[DOT19b]	US Department of Transportation, Safety Pilot Model Deployment Data, https://data.transportation.gov/Automobiles/Safety-Pilot-Model-Deployment-Data/a7qq-9vfe 
[DOT20]	National Telecommunications and Information Administration, Letter in the Matter of Use of the 5.850-5.925 GHz Band, Federal Communications Commission ET Docket No. 19-138, March 2020.
[FCC19]	Federal Communications Commission, Notice of Proposed Rulemaking, in the Matter of Use of the 5.850-5.925 GHz Band, ET Docket No. 19-138, December 17, 2019.
[FCC20]	Federal Communications Commission, DRAFT of First Report and Order, Further Notice of Proposed Rulemaking, and Order of Proposed Modification, in the Matter of Use of the 5.850-5.925 GHz Band, ET Docket No. 19-138, October 28, 2020.
[HOUSE20]	DeFazio, P. A. et al, House Committee on Transportation and Infrastructure. (2020). Letter to Chairman Pai and Commissioners O’Rielly, Carr, Rosenworcel, and Starks, Jan. 22, 2020.  
[MIKA19]	Mikami, M., & Yoshino, H. (2019). Field Trial on 5G Low Latency Radio Communication System towards Application to Truck Platooning. IEICE Transactions on Communications
[MIUC18]	Miucic, R. (Ed.). (2018). Connected Vehicles: Intelligent Transportation Systems. Springer.
[NHTS14]	U.S. National Highway Traffic Safety Administration, Vehicle-to-Vehicle Communications: Readiness of V2V Technology for Application, August 2014.
[ORIE20]	Michael O’Rielly, Comments at Federal Communications Commission Open Meeting, November 18, 2020.
[PAI20]	Ajit Pai, Comments at Federal Communications Commission Open Meeting, November 18, 2020.
[PEHA15]	Alexandre Ligo, Jon M. Peha, Pedro Ferreira and Joao Barros, "Comparison between Benefits and Costs of Offload of Mobile Internet Traffic Via Vehicular Networks," Proceedings of 43rd Telecommunications Policy Research Conference (TPRC), Arlington, VA, September 2015.
[PEHA16a]	A. Ligo, J. M. Peha and Joao Barros, "Throughput and Cost-Effectiveness of Vehicular Mesh Networks for Internet Access," IEEE 84th Vehicular Technology Conference (VTC), Sept. 2016.
[PEHA16b] A. Ligo and J. M. Peha, “Cost-Effectiveness of Using Connected Vehicles Infrastructure for Internet Access,” MASITE/ITSPA Annual Conference, 2016.
[PEHA17a]	A. Ligo and J. M. Peha, "Is It Cost-Effective to Share Roadside Infrastructure for Non-Safety Use?," IEEE 85th Vehicular Technology Conference (VTC), June 2017. 
[PEHA17b] A. Ligo and J. M. Peha, "Spectrum Policies for Intelligent Transportation Systems," 45th Telecommunications Policy Research Conference (TPRC), Sept. 2017. 
[PEHA17c] J. M. Peha, KEYNOTE: “Wireless Communication and Municipal Governments – Looking Forward,” Association of Boroughs, August 2017.
[PEHA18a]	A. Ligo, J. M. Peha, Pedro Ferreira and Joao Barros, "Throughput and Economics of DSRC-Based Internet of Vehicles," IEEE Access, vol. 6, pp. 7276–90, 2018. 
[PEHA18b] A. Ligo and J. M. Peha, "Cost-Effectiveness of Sharing Roadside Infrastructure for Internet of Vehicles," IEEE Transactions on Intelligent Transportation Systems, Volume 19, Issue 7, July 2018, pp. 2362-2372. 
[PEHA18c]	A. Ligo and J. M. Peha, "Spectrum for Intelligent Transportation Systems: Allocation and Sharing," IEEE International Symposium on Dynamic Spectrum Access Networks (DySPAN), Oct. 2018. 
[PEHA18d] J. M. Peha, “Smart City Technologies for Local Governments,” Fall Conference of Townships, Boroughs & Authorities, August 2017.
[PEHA19]	Alexandre Ligo and Jon M. Peha, "Spectrum for V2X: Allocation and Sharing," accepted to appear in IEEE Transactions on Cognitive Communications and Networking.
[PEHA20a]	Jon M. Peha, "Technical Standards and Spectrum Sharing for Intelligent Transportation Systems," Comments in the Matter of Use of the 5.850-5.925 GHz Band, Federal Communications Commission ET Docket No. 19-138, March 7, 2020.
[PEHA20b]	Jon M. Peha, Leading the Way: A National Task Force on Connected Vehicles, Day One Project, Federation of American Scientists, 2020.
[PEHA20c]	A. M. Ligo and J. M. Peha, “Comparison of Vehicle-to-Everything (V2X) technologies for road safety,” Transportation Research Board (TRB) Transit Safety and Security Conference, November 2020.
[PEHA20d]	Jon M. Peha, “Spectrum for Intelligent Transportation Systems (ITS),” United Nations’ International Telecommunications Union Workshop on Radio Spectrum for IMT-2020 and beyond:  Fostering Commercial and Innovative Use, December 2020.
[WANG17]	Wang, X., Mao, S., & Gong, M. X. (2017). An overview of 3GPP cellular vehicle-to-everything standards. GetMobile: Mobile Computing and Communications, 21(3), 19-25.
We have five major tasks.  They will sometimes occur in parallel, and even iteratively, but will occur roughly on the following timeline.
•	In the first 1.5 months, we will review current and proposed future applications that generate V2X traffic, and characterize the load each application can impose on a communications system, and the quality of service objectives.
•	In the following 5.5 months we will develop data-driven simulation systems that allow us to look at a wide range of spectrum policies, technologies, infrastructure strategies, and scenarios.
•	We will then spend 3 months using this simulation system to assess different spectrum policies, and show their pros and cons.
•	We will spend 1 month investigating how regulations must change to accommodate the spectrum policies that were found to be promising in the previous step.
•	In the last month, we will write up results, and travel to DC to present them to policymakers.
Deployment Plan
In this project, deployment means that government policymakers will make decisions using our results.  Thus, an important part of the work involves interacting directly with government agencies that make these decisions.  To the extent possible given COVID-related restrictions, the PI expects to brief policymakers at the FCC and elsewhere as appropriate.  (This will require multiple trips to Washington DC, as reflected in the budget.)  

The Federal Communications Commission (FCC) has already announced that it will undertake a Further Notice of Proposed Rulemaking on this matter [FCC20], and the Department of Transportation is likely to do this in 2021 as well. The PI has repeatedly responded to these requests in 2020 and previous years with formal comments, and is likely to do so again when these opportunities arise in 2021. Other activities will also be possible after the new Administration begins in 2021.  

In addition to working directly with government, the PI will also work with partners, which are companies and associations that are developing their own spectrum policy proposals that they hope government decision-makers will consider.  In 2020, the PI was invited to present his results directly to the Board of Directors of the Alliance for Automotive Innovation (AAI) and a V2X task force of the ITS America, as a way to improve spectrum policy.  The AAI consists of over three dozen companies that, according to its website “represents the manufacturers producing nearly 99 percent of cars and light trucks sold in the U.S.”  According to its website, ITS America advances “the research and deployment of intelligent transportation technologies,” drawing from members which “include state and city departments of transportation, regional and local transportation and planning agencies, private companies providing ITS products and services, auto manufacturers and suppliers, research organizations, academic institutions and industry associations.” Although researchers on this project do not represent or take the position of any stakeholder in any policy debate, and AAI and ITS America cannot endorse the future results of any researcher since those results may or may not support AAI’s case, we hope and expect to continue working with these organizations and their members in 2021 on improving government spectrum policy for intelligent transportation systems.    
Expected Accomplishments and Metrics
For several years, the FCC and DOT have proposed conflicting views of spectrum policy for intelligent transportation systems, and many people involved in this issue have unfortunately viewed this as a zero-sum game.  In this research, we will identify multiple spectrum policy options that have the potential to advance to goals of both agencies, and therefore deserve consideration.  This by itself is an accomplishment, as it may broaden the policy discussion.  We will go further by providing objective evidence that sheds light on the pros and cons of each of these options for transportation systems, for Wi-Fi, and for other wireless systems that could end up sharing spectrum with V2X communications.     

Individuals Involved

Email Name Affiliation Role Position
peha@cmu.edu Peha, Jon Carnegie Mellon University PI Faculty - Tenured
jpesner@andrew.cmu.edu Pesner, Jeremy Carnegie Mellon University Other Student - PhD


Amount of UTC Funds Awarded
Total Project Budget (from all funding sources)


Type Name Uploaded
Data Management Plan DMP_Rethinking_Connected_Vehicles_for_Spectrum_Scarcity.pdf Feb. 3, 2021, 2:46 p.m.
Presentation Peha_-_Rethinking_Connected_Vehicles_for_Spectrum_Scarcity_-_Project_355_v2_wW6iPL1.pptx Feb. 4, 2021, 1:18 p.m.
Progress Report 355_Progress_Report_2021-09-30 Sept. 21, 2021, 5:28 p.m.
Progress Report 355_Progress_Report_2022-03-30 March 30, 2022, 10:35 a.m.
Publication Spectrum for V2X: Allocation and sharing April 6, 2022, 5:34 a.m.
Publication Connected Vehicle Infrastructure for a Smart City April 6, 2022, 5:34 a.m.
Publication Capacity/cost trade-off for 5G small cell networks in the UHF and SHF bands April 6, 2022, 5:35 a.m.
Publication Cost Benefit Analysis: Evaluation among the Millimetre Wavebands and SHF Bands of Small Cell 5G Networks April 6, 2022, 5:36 a.m.
Publication Leading the Way: A National Task Force on Connected Vehicles April 6, 2022, 5:36 a.m.
Publication Cost-Effective Designs of Smart City Technologies for Vehicular Communications April 6, 2022, 5:37 a.m.
Publication Multi-Network Access in 5G: Economies of Scale, without the Scale April 6, 2022, 5:38 a.m.
Final Report 355_-_Final_Report.pdf July 8, 2022, 4:09 a.m.

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Name Type
Alliance for Automotive Innovation Deployment Partner Deployment Partner
Panasonic Deployment Partner Deployment Partner
ITS America Deployment Partner Deployment Partner