#383 Bringing Connected Vehicle Communications to Unlicensed Spectrum

Principal Investigator
Jon Peha
Start Date
July 1, 2022
End Date
June 30, 2023
Research Type
Grant Type
Grant Program
FAST Act - Mobility National (2016 - 2022)
Grant Cycle
2022 Mobility21 UTC


Connected vehicles can never reach their potential without adequate access to spectrum. This project explores methods of supplementing spectrum already allocated for “intelligent transportation systems” with unlicensed spectrum. It will propose and assess novel techniques for spectrum sharing between connected vehicles and infrastructure that use C-V2X technology and the next generation of Wi-Fi.  No device in the band would be allowed to cause or experience excessive harmful interference.    
Until recently, there was 75 MHz of spectrum allocated for intelligent transportation systems (ITS), but the Federal Communications Commission (FCC) took 45 MHz away from ITS and reallocated it to unlicensed devices.  The stated goal was to make possible the deployment of the next generation of Wi-Fi known as Wi-Fi 6.  Without this change, no spectrum band had all of the properties desired for Wi-Fi 6. However, this left designers of connected vehicle systems with the challenge of putting all the same communications in 30 MHz instead of 75 MHz.  At the same time, the FCC changed the technology that can be used for connected vehicles from DSRC to C-V2X.

This project explores how connected vehicles can continue to use some or all of the 45 MHz that has been taken from the ITS band while peacefully coexisting with Wi-Fi 6.  As currently defined, C-V2X and Wi-Fi 6 would not coexist well together, because the Wi-Fi 6 media access control (MAC) algorithm uses LBT, and C-V2X does not.  Researchers (including the PI of this proposal) have previously made advances in spectrum sharing between Wi-FI and DSRC, but DSRC did use LBT, and those those approaches are not applicable with C-V2X.  Researchers also faced a similar problem when trying to find a way for LTE-based microcells to operate in unlicensed spectrum along with Wi-Fi.  The resulting solution, which is now known as LTE-LAA, was to develop a form of LTE that did use LBT.  Unfortunately, if this approach were adopted with C-V2X and Wi-Fi 6, it would make sharing work better for Wi-Fi 6, but it is our hypothesis that this would seriously degrade performance for certain connected vehicles messages that are critical to roadway safety.  

We believe that there are ways to make modest modifications to the C-V2X MAC which will allow C-V2X and Wi-Fi 6 to coexist without causing excessive and harmful interference to each other, and without degrading performance for safety-critical connected vehicle communications.  That is the basis of this proposal.

First, we will define a family of modified MAC algorithms for C-V2X that have the potential to support coexistence with Wi-Fi 6 effectively, with input constants that can be adjusted based on preferences of standards bodies and spectrum regulators.  Second, we will develop simulation software to assess these algorithms.  Simulation software already exists for C-V2X, but none of that software allows Wi-Fi devices to share the band, so this will require software development.  Third, we will construct a number of realistic scenarios in which Wi-Fi 6 devices, vehicles with C-V2X on-board units and roadside infrastructure with C-V2X must share spectrum.  Fourth, we will use our simulation software to determine performance of both C-V2X and Wi-Fi 6 in our scenarios of interest.  We will consider both C-V2X as currently designed, and C-V2X with the novel modifications to the MAC algorithm that we wish to evaluate.  We will compare these algorithms with more conventional approaches, including separate allocations for C-V2X and Wi-Fi 6 with no spectrum sharing.  In each scenario, we will compare the various algorithms and spectrum management approaches with respect to their ability to provide good performance for both connected vehicles and Wi-Fi 6.  The results will reveal whether our approach would allow both connected vehicles and Wi-Fi 6 to succeed, if spectrum policymakers ever adopt the approach.    
By end of month 2, define the range of MAC algorithms that we will compare.
By end of month 6, create software that can realistically mimic the behavior of Wi-Fi 6 and C-V2X devices in various scenarios, where scenarios are defined by factors such as vehicle density, infrastructure device density, vehicle movement, Wi-Fi device density, Wi-Fi placement, and other factors.
By end of month 9, quantitatively compare the performance that can be achieved in a given amount of spectrum using the various different approaches under consideration, in a variety of scenarios.
By the end of month 12, produce a report describing our findings, and share those findings with policymakers, stakeholders, and other researchers.    
Deployment Plan
In this project, deployment means that government policymakers will make decisions using our results.  To the extent possible given COVID-related restrictions, the PI expects to bring information to spectrum policymakers at the Federal Communications Commission, the Department of Transportation, and possibly elsewhere as appropriate.

One important element of this will be a white paper on meeting spectrum needs of connected vehicles in the wake of last year’s FCC decision.  We will publicly release this white paper no later than June 2023.  We will also share it directly with policymakers at the Federal Communications Commission and the Department of Transportation, and offer to supplement the public document with private off-the-record consultations.  Finally, we will share this document with stakeholders.

Another important element is our direct interaction with stakeholder groups.  The industry group ITS America remains a critical partner in this regard.  We will continue to interact with ITS America,. One goal for these interactions is to learn from them about the needs and plans of many of the companies working in this space so that our work can be more relevant. Another goal is to educate them on our ideas and findings so that they can make better decisions regarding their spectrum strategies.  This includes strategies for spectrum use by the wireless devices that they deploy, and their spectrum policy recommendations to  government agencies.  In addition to ITS America, we are also in communications with some of the individual companies in this coalition on their spectrum needs for vehicles, notably Panasonic and Toyota.
Expected Accomplishments and Metrics
We expect to advance knowledge on how to meet the spectrum needs of connected vehicles, especially in the new policy environment in which C-V2X rather than DSRC is the technology allowed to operate in the ITS band, and spectrum dedicated to ITS is limited to 30 MHz.  We also expect to advance knowledge on how spectrum can be shared fairly and effectively between dissimilar protocols, one based on LBT and one not.

Spectrum policymakers can apply this knowledge in ways that could change the industry.  One way to do so is by considering new rules for the spectrum that was shifted from ITS to unlicensed.  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.  We hope to show that this is not the case, to provide alternatives, to quantitatively and qualitatively assess the pros and cons these alternatives, and to present these results to policymakers who can make decisions on spectrum policy for intelligent transportation systems.    

Individuals Involved

Email Name Affiliation Role Position
pluetkeh@andrew.cmu.edu Luetkehans, Peter Carnegie Mellon University Other Staff - Business Manager
peha@cmu.edu Peha, Jon Carnegie Mellon University PI Faculty - Tenured
bdshang@cmu.edu Shang, Bodong Carnegie Mellon University Other Student - PhD


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


Type Name Uploaded
Data Management Plan data_management_plan_Bringing_Connected_Vehicle_Communications_to_Unlicensed_Spectrum.docx March 4, 2022, 10:13 a.m.
Publication A New FCC Policy that Forces Consideration of the Harm Claim Threshold Sept. 23, 2022, 1:48 p.m.
Progress Report 383_Progress_Report_2022-09-30 Sept. 24, 2022, 11:17 a.m.
Presentation Spectrum Sharing for C-V2X and Wi-Fi March 26, 2023, 10:39 a.m.
Progress Report 383_Progress_Report_2023-03-30 March 27, 2023, 10:41 a.m.
Publication Feasibility of Using Beam Steering to Mitigate Ku-Band LEO-to-GEO Interference March 30, 2023, 6:49 a.m.
Publication Rethinking Connected Vehicles for Spectrum Scarcity March 30, 2023, 6:49 a.m.
Publication Multi-Network Access in 5G: Economies of Scale, without the Scale March 30, 2023, 6:50 a.m.
Publication Spectrum for Connected Vehicles March 30, 2023, 6:51 a.m.
Publication Cost-Effective Designs of Smart City Technologies for Vehicular Communications March 30, 2023, 6:51 a.m.

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Name Type
Panasonic Deployment Partner Deployment Partner
ITS America Deployment Partner Deployment Partner