Autonomous Vehicle Engineering - March 2021 - 25

Connected Vehicle

Rohde & Schwarz

Internal architecture of a telematics control unit.

Deciding the scope of testing

Having a TCU loaded with the right combination of
cellular and wireless technologies is a critical design
decision. Adding a TCU to the vehicle and keeping
it operational demands a focused approach towards
designing and testing the unit.
The scope of testing a TCU is vast. It can vary from
benchmarking the RF components to product validation.
There are also other areas to focus on such as non-signaling tests, signaling tests, conducted tests, over-the-air
tests, lab tests, field tests, production tests, etc. There is
also a wide variety of testing that will depend on the
target market where the vehicle will be launched.
Cellular operator certification, local regulator
mandated features (like eCall, ERA-GLONASS), or
the preferred V2X (vehicle-to-everything) technology,
including cellular vehicle-to-everything (C-V2X),
dedicated short-range communications (DSRC), or
both, are some points that play a role in deciding the
scope of testing. It is required that product development and verification teams carefully investigate these
topics and decide the scope of testing accordingly.

Direct Test Mode

Once the TCU design is in place and the suppliers of
individual wireless technology modems are decided,
it is time to benchmark the RF characteristics of the
modems. This type of testing can be performed in the
non-signaling mode, which requires putting the device
under test in direct test mode. At this stage, the point
of interest is to verify if the individual components
perform at the RF level as advertised by the suppliers.
The non-signaling mode is used to verify the
transmitter and receiver properties of the wireless

AUTONOMOUS VEHICLE ENGINEERING

device. At this stage, the application software is still
not integrated in the TCU, so feature testing is not
possible. Instead, the focus is on benchmarking and
calibration. Adding radio frequency (RF) transceivers,
power amplifiers, filters, and antennas to the modem
demands that the TCU is calibrated.
Taking measurements in direct test mode (DTM)
comes in handy at this stage. Key RF parameters like
spectrum emission mask (SEM), adjacent channel
leakage ratio (ACLR), transmit power, error vector
magnitude (EVM), etc. are some of the key parameters
that must be measured. Chipset manufacturers provide
a customized interface that can put the device in test
mode, and users can trigger the individual modules
using APIs. Well-established chipset makers often
provide software tools that can control their chips.
Engineers can take advantage of these tools which
can easily be integrated with the RF testers designed
to make transmitter (TX) and receiver (RX) measurements. Time to test is of the essence. Consequently,
validation teams can take an efficient approach by
connecting multiple antennas on the TCU to multiple
RF connectors on the RF tester and test multiple technologies at the same time.

Connected Mode

Testing the TCU in connected mode is an effective way
to ensure that individual hardware and software components are working properly when brought together.
Such type of tests are often referred to as end-to-end
signaling tests. Network emulators are key a component
of the testbeds used for connected mode tests.
Users can not only emulate cellular networks like
5G NR/LTE but also emulate wireless access points

March 2021 25

Autonomous Vehicle Engineering - March 2021

Table of Contents for the Digital Edition of Autonomous Vehicle Engineering - March 2021