20 PART | I ITS technology enablers
traffic variations as seen by the different network tenants (Koutlia, Umbert, Gar-
cia, & Casadevall, 2017). Other projects have handled the traffic of different net-
work slices at the LTE-scheduler level (or its equivalent in other technologies).
Moreover, the successful deployment and optimization of V2X networks
enabled by existing 4G/5G network infrastructures require a solid understand-
ing of the radio-propagation conditions in high-mobility scenarios, which allows
for validating the suitability of the networks for CCAM solutions, especially in
terms of throughput, latency, and reliability. Drive testing using off-the-shelf
tools based on data gathered from commercial user equipment terminals such as
smartphones is a common approach to the problem. However, such testing solu-
tions all too often limit the evaluation to high-level figures of merit and depend
on closed hardware and software tools, which are hardly customizable to incor-
porate new functionalities. Additionally, data collected from MNO infrastruc-
tures using mobile smartphones and/or on-board devices must be also validated
by means of independent measurements, especially in specific-vehicular sce-
narios such as dense urban environments, viaducts, or tunnels.
The main advantage of testbeds is that they are not developed for a specific
experiment or waveform and, at the same time, they only transmit and send the
signals over-the-air in real-time, whereas the signal processing tasks are car-
ried out in real-time and/or offline from the recorded signals. Since the advent
of hardware solutions for a software-defined radio, testbeds became flexible,
powerful, and affordable tools for assessing wireless communication systems
(Caban, Naya, & Rupp, 2011), including channel characterization (Domínguez-
Bolaño, Rodríguez-Piñeiro, García-Naya, & Castedo, 2017). Additionally, they
can incorporate sophisticated synchronization mechanisms or geo-reference the
acquired data, making them suitable for high-mobility scenarios.
2.4 Wireless access for vehicular environments (WAVE) and
its migration toward IEEE 802.11p
The history of V2V and V2I communication goes back in 1992 when the United
States started research on the Dedicated Short Range Communication (DSRC) pro-
tocol. With the United States, Japan, and Europe working on DSRC it soon evolved
to a standard of the IEEE 802.11 family of standards in 2004. Initially it was based
on IEEE 802.11a standard and the wi-fi architecture and used the 5.9 GHz band.
In an effort to support high-speed moving objects (such as vehicles in highways)
the IEEE working group improved the protocol and simplified the communication
mechanisms, thus leading to Wireless Access for Vehicular Environments (WAVE)
amendment of the IEEE 802.11 standard, which was intended to be used by intel-
ligent transport systems for short-range communication (Eichler, 2007).
The WAVE standard focused on the immediate, stable, and secure transmis-
sion of traffic information collected by vehicles and sensors in the road network
infrastructure. It is now used both by onboard equipment and road infrastruc-
ture when they exchange real-time traffic information. The benefits from the
use of wirelessly transmitted information are multiple and include increased
road safety, fewer congestions, and faster and energy-efficient transport. WAVE