TEC Units

Description

TEC Units (Timing Error Characterization Units) are a fundamental concept defined in 3GPP specification 37.355 for the purpose of standardizing the measurement and reporting of timing errors within positioning architectures, particularly for the LTE Positioning Protocol (LPP) and NR Positioning Protocol A (NRPPa). They serve as a normalized, dimensionless unit that quantifies the error in timing measurements, which are critical for methods such as Observed Time Difference of Arrival (OTDOA) and Round-Trip Time (RTT). By converting raw timing measurements (e.g., in nanoseconds) into TECUs, the system abstracts hardware-specific variations and provides a consistent scale for error assessment across different network elements and UE implementations.

The operation of TECUs is integrated into the positioning measurement reporting framework. When a User Equipment (UE) or a Location Management Function (LMF) calculates a timing measurement for positioning, it also computes an associated timing error. This error is then expressed in TECUs based on predefined conversion formulas or tables that relate physical timing uncertainty (influenced by factors like signal-to-noise ratio, bandwidth, and multipath) to the standardized unit. The LMF or other network functions use these TECU values to assess the quality of positioning fixes, apply error mitigation algorithms, and make decisions about positioning method selection or hybrid data fusion.

Key components involved with TECUs include the positioning protocols (LPP/NRPPa) that carry the TECU-quantified error reports, the positioning measurement engines in the UE and gNB/ng-eNB that generate the raw timing data, and the location servers (LMF) that process these reports. The role of TECUs is to enable interoperability and performance benchmarking. They allow network operators to set quality thresholds, compare positioning performance across different releases or deployments, and facilitate advanced features like enhanced location-based services and emergency positioning with known accuracy bounds. Without such a standardized unit, error reporting would be implementation-dependent, hindering network optimization and service level agreements.

Purpose & Motivation

TEC Units were introduced in 3GPP Release 16 to address the growing need for standardized and quantifiable accuracy metrics in cellular positioning systems. As location-based services, emergency calling (e.g., E911), and industrial IoT applications demanded higher precision, the limitations of proprietary or ambiguous error reporting became apparent. Previous approaches often relied on vendor-specific indicators or raw statistical values (like variance) that were difficult to compare across different UE chipsets or network infrastructure, complicating network planning, troubleshooting, and service assurance.

The creation of TECUs was motivated by the requirement to support advanced positioning techniques in 5G NR and evolved LTE, such as multi-RTT and angle-based positioning, where timing accuracy is paramount. By defining a common unit, 3GPP enabled consistent performance evaluation, certification testing, and minimization of interoperability issues. It solves the problem of ambiguous positioning quality of service (QoS) by providing a clear metric that can be used in positioning QoS parameters, allowing the network to request positioning with a specific accuracy target expressed in TECUs. This standardization is crucial for meeting regulatory requirements for emergency services and enabling commercial location-based applications that depend on reliable accuracy information.