Network-Controlled Repeater Type 1-C

Description

NCR type 1-C is a classification of network-controlled repeater (NCR) defined in 3GPP TS 38.106 and TS 38.114. A network-controlled repeater is an advanced repeater that maintains a control link with the gNB, allowing the network to configure and manage its forwarding behavior rather than operating as a purely transparent amplifier. The NCR comprises two functional entities: the NCR-MT (mobile termination), which handles the control link with the gNB, and the NCR-Fwd (forwarding), which performs the actual amplification and forwarding of the donor link signals. NCR type 1-C specifically denotes an NCR that includes both NCR-MT and NCR-Fwd operating at FR1, with a requirements set consisting only of conducted requirements defined at individual antenna connectors.

Operating at FR1 means the NCR type 1-C works in the sub-7 GHz frequency range, which covers the primary NR coverage bands such as 3.5 GHz and lower. The conducted requirements aspect is significant: conformance is assessed at the antenna connectors rather than as over-the-air radiated requirements. This simplifies testing and certification, because the repeater's RF performance can be measured directly at its ports without an anechoic chamber or radiated test setup. It also implies that the antenna is treated separately from the repeater's conducted interface, giving vendors flexibility in antenna selection and installation.

The NCR-MT establishes and maintains a control connection to the gNB, similar in principle to a UE's access link. Through this link, the gNB can send configuration commands, such as on/off control, beamforming or forwarding direction settings, and possibly power control parameters. This network control distinguishes NCRs from conventional repeaters, which typically operate with fixed or locally configured amplification and cannot be dynamically managed by the RAN. The NCR-Fwd then applies the configured forwarding behavior to the donor and service links.

In deployment, NCR type 1-C units are used to extend FR1 coverage in a controlled manner, for example filling coverage gaps, extending cell edges, or providing coverage in indoor or dense urban environments. Because the network controls them, they can be coordinated with the gNB's scheduling and beam management, reducing interference and improving overall network performance compared with uncontrolled repeaters. The conducted-requirements-only profile makes them particularly attractive for cost-sensitive deployments where radiated testing would be prohibitive.

NCR type 1-C sits within a broader family of NCR types that may differ by frequency range (FR1 vs FR2), by whether requirements are conducted or radiated, and by which functional entities are included. Understanding the type designation is essential for selecting the right conformance test suite and for ensuring interoperability with the gNB's NCR control procedures.

Purpose & Motivation

NCR type 1-C exists to provide a cost-effective, network-manageable coverage extension solution for FR1 deployments while keeping conformance testing practical. Traditional repeaters amplify signals without any control from the network, which can lead to uncontrolled interference, inefficient resource usage, and difficulty in coordinating with the gNB's transmission. Network-controlled repeaters solve this by adding a control link, but they introduce new testing and specification challenges, especially regarding how RF requirements are defined and verified.

The type 1-C designation addresses the testing challenge by restricting the requirements set to conducted requirements at individual antenna connectors. Radiated requirements, which demand complex and expensive over-the-air test environments, are avoided. This makes NCR type 1-C devices cheaper to develop, test, and certify, accelerating their availability for commercial FR1 networks. At the same time, including both NCR-MT and NCR-Fwd ensures the device has full control-plane and forwarding functionality.

Historically, coverage extension in cellular networks relied on repeaters, remote radio heads, or small cells. Repeaters were the cheapest option but lacked intelligence; small cells were capable but costly and required backhaul. NCRs, introduced in Rel-18 and refined in Rel-19, strike a balance by giving repeaters a control link to the gNB without requiring full base station functionality. NCR type 1-C specifically targets the FR1 conducted-requirements niche, where many operators need affordable coverage extension for sub-7 GHz spectrum.