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Saturday, September 9 • 9:34am - 10:07am
Spectrum Policies for Intelligent Transportation Systems

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The FCC has allocated 75 MHz of spectrum for Intelligent Transportation Systems (ITS). This spectrum will support connected vehicles by allowing automobiles to communicate with each other and with roadside infrastructure using a technology called Dedicated Short-Range Communications (DSRC). The question of whether ITS should have an exclusive allocation of 75 MHz is hotly debated, and there are two competing proposals that would make some or all of this spectrum available for unlicensed devices through either primary-secondary sharing or sharing on a co-equal basis. This paper investigates how much spectrum should be allocated to ITS, whether ITS spectrum should be shared with unlicensed devices, and if so under what rules.

One motivation for allocating spectrum to ITS is to support highway safety applications. While safety communications have priority, ITS spectrum can be used for other purposes when it is not needed for safety. As a result, much of the spectrum may be used for non-safety purposes. Previous work has shown that once spectrum is allocated to ITS and DSRC technology is widely deployed, it can be more cost-effective to providing Internet access using mesh networks of these devices than using today’s cellular networks. Thus, allocating more spectrum for ITS can reduce Internet costs. There are also disadvantages, because spectrum allocated for ITS is unavailable for other purposes.

This paper will assess various spectrum policies. We vary the amount of spectrum allocated to ITS. We also consider four possible policies regarding sharing the portions of ITS spectrum that do not contain safety-critical communications: (i) spectrum is allocated only for connected vehicles, (ii) spectrum is shared with unlicensed devices on a primary-secondary basis, such that unlicensed-devices can operate only if they are sufficiently far from any DSRC device, (iii) spectrum is shared with unlicensed devices on a co-equal basis, where DSRC and unlicensed devices must coexist but are not expected to cooperate, and (iv) spectrum is shared with unlicensed devices on a co-equal basis, where regulations require DSRC and unlicensed devices to cooperate.  

For each spectrum policy, this paper quantifies three possible impacts: (i) the cost savings obtained by providing Internet access over DSRC-based mesh networks in the ITS band instead of a cellular network, thereby reducing the number of cell towers needed, (ii) the value of spectrum allocated to ITS and therefore made unavailable for other purposes, and (iii) the extent to which ITS spectrum can be used by unlicensed devices that are sharing the band.  

Our method involves multiple inter-related models, and data collected from a citywide connected vehicle deployment. We estimate costs and cost savings by developing a detailed and realistic engineering-economic model of the networks used to provide Internet access. Some costs and savings depend on the throughput achieved in the DSRC-based mesh network, and the throughput achieved by unlicensed devices. To estimate throughputs, we have built a packet-level simulation of both DSRC and unlicensed devices. Finally, to make this simulation realistic, we have obtained information about vehicle location and movement, signal propagation, and other characteristics from a citywide deployment in Portugal.

avatar for Alexandre Ligo

Alexandre Ligo

PhD Candidate, Carnegie Mellon University

avatar for Jon Peha

Jon Peha

Carnegie Mellon University

Saturday September 9, 2017 9:34am - 10:07am EDT
ASLS Hazel Hall - Room 221