TCU Testing at the Heart of Vehicle Connectivity
Adding a telematics control unit to the vehicle and keeping it operational demands a focused approach towards testing this vital component.
The wireless connectivity between the modern vehicle and the outside world is possible thanks to a constantly evolving component called the telematics control unit (TCU). The TCU is at the center of all connectivity-related use cases, so its operation must be flawless. Closely related to the TCU are over-the-air tests (OTA), electromagnetic compatibility (EMC), electromagnetic interference (EMI), and automotive Ethernet. All should be kept in mind when designing the strategy to test TCUs.
The TCU is loaded with multiple wireless technologies that enable the vehicle to exchange information with its surroundings. It is also connected to multiple components inside the vehicle, including other electronic control units and domain controls, via wired connections using automotive Ethernet and controller area network (CAN) bus. Connecting the vehicle to the cloud, roadside infrastructure and other road users enables new business models for vehicle OEMs and promise new safety and convenience features for the drivers and passengers.
Autonomous fleets can benefit from the wireless link between the vehicle and the cloud infrastructure. Remote debugging, remote assistance and teleoperation are a few possibilities that are possible over the cellular link. Constant monitoring of the health of an autonomous vehicle (AV) and updating high-definition maps in real time are a few other examples that are made possible via connectivity. These applications do come with their own set of challenges such as latency, throughput, cellular network coverage, etc., but LTE and 5G cellular technologies provide adequate tools to deploy them.
Engineering teams working on training and testing autonomous fleets can benefit from the addition of advanced Wi-Fi versions like 802.11ax to the TCU. Engineers are constantly updating large fleets of AVs with newer versions of software and taking these AVs for the drive tests. It is a challenge to bring back large amounts of data from the field and upload for analysis before the next version of the software is installed on the AV fleet. Using a wired connection is inefficient and using an LTE connection for this use case is very expensive.
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 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.
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 like Wi-Fi/Bluetooth. GNSS simulators, by comparison, can emulate satellite constellations with GPS, GLONASS, GALILEO, BEIDOU, and QZSS/SBAS configurations conveniently in a lab environment. These two types of emulators give users the ease of testing complex scenarios conveniently in a lab environment. They also provide them with the toolset to create repeatable tests – often next to impossible in drive tests where engineers are dependent on live cellular networks and GNSS signals. The focus is on protocol stack verification, end-to-end throughput, user experience, coexistence and interference testing.
Engineers can configure the network emulators to test user applications with various modulation schemes and scheduling configurations. Infotainment apps running on the head unit also use the connectivity path provided by the TCU to the cloud services. From a user experience perspective, it is critical to test end-to-end connectivity between the apps hosted in the cloud and application clients installed on the head unit.
Protecting from attack
Security analysis is another key area that must be addressed during the testing phase. Endpoint geolocation, domain name lookup, traffic analysis of encrypted and unencrypted data, digital certificate analysis, keyword search and port scanning are some topics that must be considered while designing the strategy to test TCUs.
While the TCU provides the much-needed connectivity to the vehicle, it can also be the prime target for an external security attack. PEN, or penetration testing, is often used to stress test connected systems to look for possible security breaches and expose the points that are vulnerable to a cybersecurity attack. This is critical for connected as well as autonomous vehicles.
It is vital to create stressful conditions for the TCU during the testing phase. This makes it essential to test not only in ideal conditions but also test the TCU in RF faded environments and in presence of interference from other radio frequencies. The coexistence of multiple wireless technologies inside the TCU as well as inside the vehicle is something that must be considered during design and validation.
The vehicle can drive in various weather environments, subjecting the TCU to extreme temperatures. It is not uncommon to see test engineers considering the temperature range of -40C to 85C, to test automotive parts. TCU is no exception; the unit can be placed inside a temperature-controlled chamber to verify that it works as expected across a wide range of temperatures.
Production tests, TCU future
The focus in the production environment is quite different than that of feature verification and integration testing. Automated production line testing is essential, with the goal to achieve close to zero downtime. Testing both multiple devices and multiple technologies simultaneously is desirable. The devices are set in factory test mode (FTM) and testing is geared towards improving the efficiency on the production line. Automated setups control multiple RF testers; it is quite common to consider integrating robotic arms in production settings.
TCU design is evolving at a rapid pace. As cellular networks across the world move from LTE to 5G New Radio networks, the TCU needs to be 5G ready. Development teams should consider software-defined radios along with appropriate RF front end and antennas that support the 5G frequency range that the local regulators and cellular operators plan to deploy. Using this approach allows OEMs to upgrade the TCU from 4G to 5G simply via software upgrades.
OEMs might consider charging the end customer for swapping the old 4G TCU with the 5G NR TCU hardware. Alternatively, this could be done for free if the OEM sees possibilities of discovering alternative revenue streams. Such decisions need to align with the overarching business strategy.
Nikhil Kumar recently joined Lucid Motors as senior technical program manager. He wrote this article in late 2020 while technical program manager for automotive connectivity at Rohde & Schwarz.