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Original Authors: Joram Fillol-Carlini, Continental Automotive France, Wireless Tests
Edited by Cyth Systems
The Challenge
Continental Automotive required the upgraded validation of a tire sensor with wireless communication capabilities at a lower cost compared to existing test systems.
The Solution
Developing a configurable RF communication test solution using an NI RF generator and receiver card for the ISM band (315 MHz/915 MHz). This was achieved using an NI USRP-2900 card to send and receive RF signals and LabVIEW software to create a configurable and software-defined test approach.
Testing Communication to Tire Sensors
Continental Automotive, a premium supplier of automotive solutions, manufactures various connected sensors, keys, and other equipment that operates according to different RF protocols.
Amongst these communication-capable sensors are some dedicated to monitoring continuous tire pressure so that it is always possible to know what the tire pressure is and receive an alert in the event of abnormal pressure loss. As such, the Continental tire pressure monitoring system prevents frequent cause of accidents and ensures optimal safety for the driver. It also helps to reduce CO2 emissions and fuel consumption (a tire that is under-inflated by 0.3 bar leads to an over-consumption of 1.5% on average).
Left: NI USRP‑2900 is a tunable RF transceiver with full-duplex operation used to test the tire sensor's RF capabilities,
Right: Cross-sectional diagram of tire sensor position and functionality.
The company’s quality requirements call for products to undergo many tests, which are now carried out with dedicated cards using hardware and software designed specifically for this purpose.
As a result, in the event that there are changes in customer requirements or the technologies used, it is sometimes necessary to update the dedicated card’s software or begin a new hardware design. Among the most common developments are the size of the frame, the type of modulation, the throughput, data coding, or the frequency used. Such an approach is costly in terms of resources for development as well as maintenance and prohibits a standardized approach. The company, therefore, needs to find a more practical and less expensive alternative.
The Constraints of a Test Card
In a context where hundreds of thousands of products are produced every day and where the tolerated error rate is extremely low, an application that tests equipment such as tire pressure sensors or car keys must be hardy, reliable, and fast.
It is therefore necessary to develop a hardy and flexible solution that ultimately has the same reliability as the solution currently being used. This solution needs to be easy to use while remaining complete so as to be able to adapt to future changes in technologies and protocols.
The advantage of SDR technology is that it usually requires only two components:
A card for transmitting/receiving signal.
A computer with software that can process this signal.
Combining USRP-2900 and LabVIEW Equipment
We have therefore used USRP-2900 from NI. It is an RF transceiver that covers the range from 70 MHz to 6 GHz with a maximum instantaneous bandwidth of 20 MHz with characteristics that are relatively well suited to our application’s requirements. With this USRP (Universal Software Radio Peripheral) device, we can not only capture RF product messages under test but also transmit them through two channels, Tx/Rx and Rx.
The USRP is driven by LabVIEW software on which the main operations for processing the signal for demodulating and decoding the frames coming from the sensors are carried out. We can also use LabVIEW to create an intuitive graphical user interface.
Top: LabVIEW Programming for Receiving Signal, Bottom: LabVIEW Block Diagram of Transmitted Signal
Sending and Receiving Frames With the Continental Solution
LabVIEW UI of RF Vector Signal Generation and Receiver Transmission during live test of the wireless tire sensor.
With the LabVIEW program, frames contained in the ISM frequency band can be sent and received. We can set the frequency, the baud rate, the modulation (ASK or FSK), and the number of bytes to be received as well as code/decode Manchester code. The content of the frames to be sent is customizable. We can send a sequence containing a wake-up frame followed by a defined number of frames containing useful information. (Figure 5)
Most of the variables are configurable, which requires a configuration and initialization step when first used. After completion, the program works automatically and doesn’t require any further changes. In the event of changes in the transmission and receiving protocol, we simply have to restart the software and amend the parameters during the configuration and initialization step. Then we can use the new protocol.
Conclusion
The use of the USRP-2900 card and LabVIEW software has validated the SDR approach for transmitting and receiving RF frames for vehicle access or tire pressure monitoring systems.
Original Authors:
Joram Fillol-Carlini, Continental Automotive France, Wireless Tests
Edited by Cyth Systems