Receive Timing Error

Description

Rx Timing Error is a key parameter in 5G NR positioning, defined in 3GPP Release 17 and maintained in later releases. It represents the error in time measurement due to the Rx Time Delay that is not compensated by internal calibration. Specifically, it is the result of the Rx Time Delay involved in the reception of a signal before reporting measurements obtained from that signal. It can be either the uncalibrated Rx Time Delay or the remaining delay after the UE/TRP has performed internal calibration/compensation. The calibration may also account for relative time delays between different RF chains within the same device and the offset of the Rx antenna phase center to the physical antenna center.

In positioning procedures, the UE measures the time of arrival of DL-PRS from multiple TRPs, and the TRP measures the time of arrival of UL SRS from the UE. These measurements are used to compute position. However, the measured times include the Rx Time Delay. If the device calibrates its internal delay, the residual error is the Rx Timing Error. This error must be reported to the network (e.g., via LPP or NRPPa) so that the positioning server can correct the measurements. The accuracy of the reported Rx Timing Error affects the overall positioning accuracy.

The 3GPP specifications 37.355 (LPP) and 38.305 (NG-RAN positioning) define the signaling and procedures for reporting Rx Timing Error. The UE may report a measured value with an uncertainty, and the network uses this to weight the measurements in the positioning calculation. The error can be caused by temperature variations, aging, or imperfect calibration. Therefore, devices may need to perform periodic calibration.

Rx Timing Error is closely related to Rx Time Delay. While Rx Time Delay is the physical delay, Rx Timing Error is the error that remains after attempting to compensate it. The calibration process may involve injecting known signals and measuring the delay, or using a reference receiver. The 3GPP error models specify the maximum allowed Rx Timing Error for different positioning accuracy classes.

In multi-RTT, both the UE and TRP have Rx Timing Errors that contribute to the round-trip time error. In TDOA, the UE's Rx Timing Error affects the time difference measurements. Hence, minimizing Rx Timing Error is crucial for high-accuracy positioning. The concept also includes compensation for RF chain mismatches and antenna phase center offsets, which are important for mmWave and massive MIMO systems.

In summary, Rx Timing Error quantifies the residual timing error in a receiver after calibration, and its accurate reporting is essential for 5G positioning to meet performance requirements.

Purpose & Motivation

Rx Timing Error was introduced to provide a standardized way to report and compensate for residual timing errors in positioning receivers. In time-based positioning, any error in the measured time translates directly to a distance error. While Rx Time Delay can be calibrated, perfect calibration is impossible due to hardware variations, temperature, and aging. Therefore, a residual error remains, and the network needs to know its magnitude to correct measurements or assess measurement quality.

Before Release 17, there was no standardized parameter for reporting such errors, leading to inconsistent positioning performance across devices. The definition of Rx Timing Error allows devices to report the uncalibrated or residual delay, enabling the network to apply corrections. This improves accuracy and interoperability, especially for high-precision use cases.

The concept also encourages vendors to implement calibration mechanisms and to specify the error bounds. It supports advanced positioning techniques like multi-RTT and TDOA by providing a means to account for receiver imperfections. By addressing Rx Timing Error, 3GPP ensures that 5G positioning can achieve the reliability and accuracy needed for emergency services, industrial automation, and consumer applications.