Phase-Synchronize Operations

Since R2025a

Phase synchronization is the process of aligning the phase of signals across multiple RF channels, either on a single NI™ USRP™ radio or across multiple radios. Use the phase alignment process to achieve phase coherent signal processing in multi-antenna applications such as:

• Multiple-input multiple-output (MIMO)

• Direction-of-arrival (DOA) estimation

• Beamforming

You achieve phase synchronization by running a phase calibration routine that aligns the instantaneous phase of signals across RF channels so that they maintain phase alignment during operation.

Ensure Channels are Phase Coherent

Whether and how you can achieve phase coherence depends on your radio.

• Some radios are phase stable across RF channels on a single radio or across multiple radios if they are time synchronized.

• Some radios provide mechanisms for sharing a local oscillator (LO) signal between RF channels on a single radio or across multiple radios. For details about how to leverage LO sharing with Wireless Testbench™ on radios that support this feature, see Configure LO Sharing.

For details about the phase stability that you can achieve with specific hardware configurations, consult the manufacturer's documentation.

Calibrate Phase

You calibrate the phase between RF channels by measuring and correcting static phase offsets, enabling phase-aligned captures or transmissions. Both phase-coherent and non-coherent systems can be calibrated, although non-coherent systems require more frequent recalibration to maintain synchronization.

For transmit and capture workflows, Wireless Testbench provides functionality that enables you to measure the phase offset between antennas on a single radio, or across multiple radios, by using the basebandPhaseAnalyzer object (since R2026a). The object connects basebandTransceiver application objects to antennas for phase analysis.

Measure relative phase offsets using the measureAntennaPhase object function and apply a correction to future transmissions or captures.

For an example of how to estimate the direction of arrival of a signal using multiple RF channels phase-synchronized using the basebandPhaseAnalyzer object for calibration, see Estimate Direction of Arrival Using MUSIC Algorithm and TwinRX Daughterboards.

For other workflows, you can implement your own phase calibration algorithm.

Repeat Calibration

Recalibrate channels as required depending on the phase stability of your hardware configuration. For details, consult the manufacturer's documentation. You can test the phase stability of your hardware configuration by rerunning the phase calibration at timed intervals or after retuning, reinitializing, or power cycling your radio, and comparing the measured phase against previous measurements.