The R&S®CMW wideband radio communication tester platform (R&S®CMW500, R&S®CMW270) uses high accuracy distance measurements (HADM) with phase‑based ranging (PBR) to provide a comprehensive and fully automated test solution to verify Bluetooth® Low Energy physical layer functionality.
Channel sounding (CS) principle for high accuracy distance measurements
The Bluetooth Special Interest Group (SIG) plans to extend positioning capabilities with a new channel sounding feature. The feature will be added along with advertising, RSSI-ranging and direction finding (DF) capabilities. Bluetooth® channel sounding (CS) will enable high accuracy distance measurements (HADM) between two Bluetooth® Low Energy devices. CS uses the phase shift between received and transmitted radio signals of different channels. Typical HADM applications include keyless entry systems, indoor navigation and asset tracking with new use cases sure to come in the future.
Phase based measurement principle
PBR uses the phase shift (Θ) of a radio signal as it travels over distance D on a frequency f. When two or more signals with different frequencies are used, the measured phase difference (ΔΘ) between the signals can be used to accurately estimate a distance. When estimating a distance with channel sounding, one device initiates (initiator) the procedure and a second device reciprocates the radio transmission (reflector) without modifying the phase. For every transmission with the frequency fi, the phase change (ΔΘi) between the transmitted and the received signal is measured by the initiator. Uncoded narrowband constant envelope signals can be sent or received using a single antenna for easy implementation in standard Bluetooth® Low Energy radio chips.
Ensuring best in class accuracy
The Bluetooth SIG defined RFPHY test cases (TC) to verify the accuracy of distance measurements when a Bluetooth® DUT is assuming either the initiator or reflector roles, meaning test solutions must operate both roles. Measurements must show that an initiator can generate the CS packets and tones with the required phase stability, that a reflector transmits signals with the correct phase and that the general DUT phase measurements are accurate. When using an antenna array, the antenna switching function also needs to be verified.
Bluetooth® Low Energy channel sounding physical layer verification setup with R&S®CMW and R&S®CMWrun
R&S®CMW wideband radio communication testers can generate and analyze all required channel sounding packets and tones in a one-box solution. This solution can be used to manually or automatically perform all RFPHY TCs. The DUT is controlled via an UART/USB interface with the HCI protocol in direct test mode (DTM). All transmitter and receiver RFPHY measurements can be performed simply with the intuitive, user-friendly graphical user interface. All HCI reports can be logged for further analysis and debugging purposes.
An off-the-shelf test plan with full coverage of all CS preconformance RFPHY TCs is included with the R&S®CMWrun sequencer software tool. Test cases can be run separately or with full preconformance testing and a test report. The R&S®CMWrun sequencer software tool also generates logfiles after each test run that make regression and preconformance testing easier than ever.
A fully automated Bluetooth® channel sounding test setup for user equipment with more than one antenna includes the R&S®CMW wideband radio communication tester and the R&S®OSP open switch and control platform. Both are controlled by R&S®CMWrun (installed on a separate controlling PC) via LAN/GPIB connections. The fully automated solution is especially suited for antenna switching integrity (ASI) testing, where multiple RF connection/disconnections are required. R&S®CMWrun sequencer software supports all Bluetooth® channel sounding test cases along with legacy Bluetooth® Low Energy and Bluetooth® Classic testing.
Transmitter testing
Receiver testing
The Bluetooth® Low Energy channel sounding test and measurement solution from Rohde & Schwarz uses the R&S®CMW platform to fully cover all verification needs during product design, including functional tests and RF parametric measurements and production requirements. Together with R&S®CMWrun, an off-the-shelf test plan ensures the regression and preconformance test efficiency.
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