By Ute Philipp, Product Manager at Rohde & Schwarz
One new feature upcoming in the next Bluetooth release is the Unified Test Protocol (UTP) Test Mode for Bluetooth Low Energy, as an additional alternative to conventional testing with a cable, which can simplify over-the-air (OTA) controlled device testing. This article explains why it’s important and how to do it.
Testing Bluetooth devices
Bluetooth continues to become more and more successful, as one of the main connectivity technologies chosen by developers of IoT solutions. Production numbers are increasing by over 1 billion units every year and the Bluetooth SIG estimates that more than 7.7 billion new Bluetooth devices will be made in 2028.
Bluetooth Low Energy (Bluetooth LE) technology, arriving in 2010, has enabled the role of Bluetooth to expand far beyond the original concept that envisaged a simple computer-mobile link. Diverse devices have emerged, benefiting from long communication range and long battery life that are ideal characteristics for IoT applications, including hearing aids, medical implantables, smart consumer accessories, and industrial sensors.
Each new product type must pass the Bluetooth IG’s qualification program, which includes tests for RF physical layer (PHY) conformance, protocol/profile conformance, and profile interoperability. New products must also pass relevant national or regional certification, as well as certifications specific to their application, such as medical devices. In addition, suitable test methodologies and test equipment are needed for fast and comprehensive production testing.
When Bluetooth LE was released, the Bluetooth SIG defined the Direct Test Mode (DTM) for verifying conformance to the specification. In DTM, a controller controls the device under test (DUT) and tester during RF tests. Control commands are sent via the Bluetooth host control interface (HCI) or a two-wire UART interface. However, the DUT and the tester do not have a real connection. Although this permits a fast test-cycle time, which is important for production testing, DTM does not show real RF behaviour in realistic operating conditions. Moreover, as Bluetooth LE has enabled developers to create devices that are extremely small, in many cases sealed for life, the absence of external ports prevents connecting a control cable.
Bluetooth LE non-signalling tests
As a non-signalling mode, DTM relies on sending commands to the DUT to test specific capabilities. Using a tester such as the R&S CMW platform, DTM sends the DUT a command for transmitter (TX) testing. The payload pattern, payload length and Bluetooth channel settings are configured on the tester and transmitted to the DUT via the control cable.
The DUT sends Bluetooth LE RF test packets back to the tester. In receiver (RX) testing, the tester sends the DUT a DTM command to switch to a specific Bluetooth channel in receive mode and sends a defined number of Bluetooth RF test packets at a suitably low level. Depending on the level, the DUT receives some packets correctly while others have bit errors. The DUT counts the number of correctly received packets by calculating a CRC checksum for each received packet and compares the checksum to the one transmitted by the CMW. At the end of the test, the CMW transmits a test end command. The DUT transmits the number of packets correctly received via the control cable to the CMW. It then calculates and displays the packet error rate (PER).
There is also a non-signalling advertiser mode that can be used for testing the DUT advertiser channels. In this mode, the DUT advertises itself by sending advertising packets and the tester performs RX and TX measurements on the primary and secondary (general-purpose) advertiser channels. While this test method is used to test the transmitter functions in production, data channel testing and qualification testing are not possible.
There is also a signalling test mode that uses DUT in a hopping connection where no control commands are exchanged. Instead, the RX and TX measurements use the exchange of arbitrary feature requests and feature response packages. As these are limited to data channels, the primary advertiser channels cannot be tested and pre-qualification tests cannot use this mode.
Unified Bluetooth testing over-the-air
Now, the Bluetooth SIG has standardised the Bluetooth OTA UTP Test Mode, as an alternative for OTA controlled device testing. As an LE test mode enhancement, the Unified Test Protocol (UTP) offers a common protocol for the existing DTM methods via HCI and two-wire UART and additionally the OTA test method as an alternative.
The DUT’s chipset needs to support the UTP test mode, so Rohde & Schwarz created a solution that leverages cutting-edge Bluetooth Low Energy hardware and software System-on Chip (SoC) IP and runs on the R&S CMW radio communication tester.
The R&S CMW radio communication tester supports Bluetooth Classic signalling and all Bluetooth Low Energy (LE) transmitter and receiver tests including the signalling specified by Bluetooth SIG.
Summary
Now, with Bluetooth Low Energy controller software running on the R&S CMW tester, users can perform Bluetooth Low Energy radio tests using the Bluetooth UTP Test Mode. All Bluetooth Low Energy and Bluetooth Classic Radio measurements can be performed with a single test setup over the air in a signalling connection. Comprehensive test automation and the highly accurate implementation of the Bluetooth test cases ensure compliance with the Bluetooth specifications and the solution can be used in development, pre-conformance, and production testing.
Rohde & Schwarz is actively involved in defining the specifications within the Bluetooth Core Specification Working Group, ensuring that the test solution will be in line with the specifications of the upcoming Bluetooth release. In addition, the solution is compatible with the already ratified Bluetooth releases up to release 6.0 Channel Sounding, supporting the existing DTM with the conducted control connection.
This article originally appeared in the April 25 magazine issue of IoT Insider.
