Real-Time Kinematic

Description

Real-Time Kinematic (RTK) is an advanced positioning method standardized within 3GPP, particularly in specifications like TS 36.305 (LTE), TS 37.355 (LTE/NR), TS 38.305 (NR), and TS 38.859. It operates by comparing the phase of the carrier wave from Global Navigation Satellite System (GNSS) signals received at a rover (e.g., a UE) with those received at a fixed, known-location reference station. This differential approach cancels out common errors such as satellite clock drift, atmospheric delays, and orbital inaccuracies, enabling positioning accuracy at the centimeter level in real-time.

The architecture for RTK in 3GPP systems involves several key components: the UE (rover) equipped with a GNSS receiver capable of carrier-phase tracking, one or more reference stations with precisely known coordinates, and a communication link—typically provided by the mobile network (LTE or 5G NR)—to deliver correction data. The reference station calculates error corrections by comparing its known position with the measured GNSS data. These corrections, often formatted using standards like RTCM (Radio Technical Commission for Maritime Services) or 3GPP-defined protocols, are then transmitted to the UE via point-to-point or broadcast methods. The UE applies these corrections to its own GNSS measurements to compute a highly accurate position.

How RTK works involves the UE performing carrier-phase ambiguity resolution, a process of determining the integer number of wavelengths between the satellite and receiver. Once resolved, the carrier-phase measurements provide extremely precise range information. The 3GPP standards define protocols for delivering correction data, such as the LTE Positioning Protocol (LPP) and NR Positioning Protocol (NRPP), which support RTK as a high-accuracy method. The network can assist the UE by providing auxiliary data like approximate location, satellite ephemerides, and atmospheric models to speed up ambiguity resolution and improve reliability. RTK's role is integral to 5G's support for ultra-reliable low-latency communication (URLLC) and massive machine-type communication (mMTC), enabling precise positioning for critical applications.

Purpose & Motivation

RTK was integrated into 3GPP standards to meet the escalating demand for high-precision positioning in commercial and industrial applications. Traditional GNSS methods, such as standard GPS or Assisted-GPS (A-GPS), offer meter-level accuracy, which is insufficient for emerging use cases like autonomous driving, precision agriculture, drone navigation, and augmented reality. These applications require centimeter-level accuracy to ensure safety, efficiency, and functionality. The limitations of previous approaches included susceptibility to atmospheric errors, multipath interference, and the need for prolonged observation times to achieve high accuracy.

The motivation for its creation stems from the convergence of telecommunications and positioning technologies, leveraging mobile networks' ubiquitous coverage and low-latency connectivity to deliver RTK correction data reliably. Before 3GPP standardization, RTK systems often relied on dedicated radio links or internet connections, which were not optimized for mobility, scalability, or integration with cellular devices. By standardizing RTK support within LTE and 5G, 3GPP enables seamless, network-assisted high-accuracy positioning as a native service, reducing deployment costs and complexity.

Historically, RTK has been used in surveying and geodesy for decades, but its adoption in mass-market devices was hindered by the cost and complexity of receivers and correction data delivery. 3GPP's work, starting in Release 15 with 5G, addresses these barriers by defining efficient protocols and network architectures that support low-latency correction data transmission over cellular links. This solves the problem of providing real-time, high-accuracy positioning to a vast number of devices, unlocking new vertical markets and enhancing existing location-based services with unprecedented precision.