  Future Connected and Autonomous Vehicles (CAVs) will be equipped with a large
set of sensors. The large amount of generated sensor data is expected to be
exchanged with other CAVs and the road-side infrastructure. Both in Europe and
the US, Dedicated Short Range Communications (DSRC) systems, based on the IEEE
802.11p Physical Layer, are key enabler for the communication among vehicles.
Given the expected market penetration of connected vehicles, the licensed band
of 75 MHz, dedicated to DSRC communications, is expected to become increasingly
congested. In this paper, we investigate the performance of a vehicular
communication system, operated over the unlicensed bands 2.4 GHz - 2.5 GHz and
5.725 GHz - 5.875 GHz. Our experimental evaluation was carried out in a testing
track in the centre of Bristol, UK and our system is a full-stack ETSI ITS-G5
implementation. Our performance investigation compares key communication
metrics (e.g., packet delivery rate, received signal strength indicator)
measured by operating our system over the licensed DSRC and the considered
unlicensed bands. In particular, when operated over the 2.4 GHz - 2.5 GHz band,
our system achieves comparable performance to the case when the DSRC band is
used. On the other hand, as soon as the system, is operated over the 5.725 GHz
- 5.875 GHz band, the packet delivery rate is 30% smaller compared to the case
when the DSRC band is employed. These findings prove that operating our system
over unlicensed ISM bands is a viable option. During our experimental
evaluation, we recorded all the generated network interactions and the complete
data set has been publicly available.
