Spectrum Policies for Intelligent Transportation Systems
23 Pages Posted: 31 Mar 2017 Last revised: 23 Aug 2017
Date Written: September 1, 2017
The FCC has allocated 75 MHz of spectrum for Intelligent Transportation Systems (ITS). This spectrum will support connected vehicles equipped with Dedicated Short Range Communications (DSRC) technology. DSRC will enable road safety applications, as well as other applications based on IP communications when the ITS spectrum is not needed for safety. The question of whether ITS spectrum should be shared with unlicensed devices is hotly debated, and there are two competing proposals that would make some or all of this spectrum available for unlicensed devices. This paper investigates how much spectrum should be allocated to ITS, whether ITS spectrum not used for safety communications should be shared with unlicensed devices, and if so how much. To address those issues, we observe the throughputs of vehicular networks and unlicensed Wi-Fi hotspot devices while varying the amount of spectrum allocated to ITS and the portion of that spectrum that is shared with unlicensed devices on a co-equal basis. This paper quantifies three possible impacts: (i) the performance of connected vehicles and unlicensed devices as a function of spectrum allocated and the extent of sharing between ITS and unlicensed devices, (ii) the bandwidth used to achieve a given performance, and (iii) the cost savings obtained by providing Internet access over DSRC-based mesh networks in the ITS band instead of a cellular network. Our method is based on a packet-level simulation of throughputs of DSRC and unlicensed devices, for which parameters are set in part from information collected from a real DSRC-based city-wide vehicular network, and locations of Wi-Fi hotspots deployed in Portugal. We have also developed an engineering-economic model of the economic benefit of offloading Internet traffic from cellular networks to DSRC connected vehicles. We found that vehicles and hotspots on shared spectrum would use half as much bandwidth as would be used with vehicles and hotspots on separate bands, for base case conditions that represent data rates of Internet traffic and penetration of DSRC devices in vehicles for a few years into the future in densely populated areas. Under those conditions, it is highly efficient to share the portion of the ITS band not used for safety messages with unlicensed devices. Moreover, the economic benefit per MHz of allocated ITS spectrum, to carry Internet traffic over DSRC connected vehicles, is similar between shared and no shared spectrum. If there is benefit to allow unlicensed devices in ITS spectrum, then sharing results more economic benefit than allocating ITS spectrum to vehicles only.
Keywords: Spectrum allocation, spectrum sharing, connected vehicles, Intelligent Transportation Systems, ITS, Dedicated Short Range Communications, DSRC
JEL Classification: D24, D60
Suggested Citation: Suggested Citation