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Network-Controlled Repeater -- An Introduction

Fco. Italo G. Carvalho, Raul Victor de O. Paiva, Tarcisio F. Maciel, Victor F. Monteiro, Fco. Rafael M. Lima, Darlan C. Moreira, Diego A. Sousa, Behrooz Makki, Magnus Astrom, Lei Bao

TL;DR

This work introduces the Network-Controlled Repeater (NCR), a low-complexity, beamforming-enabled amplify-and-forward relay defined in 3GPP Rel-18 to mitigate mmWave coverage gaps in 5G. It situates NCR relative to IAB and RIS, detailing the architecture (NCR-MT, NCR-Fwd, C-link, backhaul/access links) and SCI-driven beam management that enables centralized control and energy-efficient operation. Through system-level simulations in urban scenarios, the paper demonstrates significant improvements in $SINR$ and throughput for both direct and NCR-forwarded paths, with the largest gains for cell-edge UEs and UL links, especially under higher interference when properly planned. The study also discusses practical challenges—testbeds, self-interference, and cost tradeoffs with competing solutions—and emphasizes that deployment planning and beamforming design are critical to realizing NCR benefits; it points to future work on field trials and comparative analyses with RIS and IAB to establish deployment guidelines.

Abstract

In fifth generation (5G) wireless cellular networks, millimeter wave spectrum opens room for several potential improvements in throughput, reliability, latency, among other aspects. However, it also brings challenges, such as a higher influence of blockage which may significantly limit the coverage. In this context, network-controlled repeaters (NCRs) are network nodes with low complexity that represent a technique to overcome coverage problems. In this paper, we introduce the NCR concept and study its performance gains and deployment options. Particularly, presenting the main specifications of NCR as agreed in 3rd generation partnership project (3GPP) Rel-18, we analyze different NCR deployments in an urban scenario and compare its performance with alternative deployments. As demonstrated, with a proper network planning and beamforming design, NCR is an attractive solution to cover blind spots the base stations (BSs) may have.

Network-Controlled Repeater -- An Introduction

TL;DR

This work introduces the Network-Controlled Repeater (NCR), a low-complexity, beamforming-enabled amplify-and-forward relay defined in 3GPP Rel-18 to mitigate mmWave coverage gaps in 5G. It situates NCR relative to IAB and RIS, detailing the architecture (NCR-MT, NCR-Fwd, C-link, backhaul/access links) and SCI-driven beam management that enables centralized control and energy-efficient operation. Through system-level simulations in urban scenarios, the paper demonstrates significant improvements in and throughput for both direct and NCR-forwarded paths, with the largest gains for cell-edge UEs and UL links, especially under higher interference when properly planned. The study also discusses practical challenges—testbeds, self-interference, and cost tradeoffs with competing solutions—and emphasizes that deployment planning and beamforming design are critical to realizing NCR benefits; it points to future work on field trials and comparative analyses with RIS and IAB to establish deployment guidelines.

Abstract

In fifth generation (5G) wireless cellular networks, millimeter wave spectrum opens room for several potential improvements in throughput, reliability, latency, among other aspects. However, it also brings challenges, such as a higher influence of blockage which may significantly limit the coverage. In this context, network-controlled repeaters (NCRs) are network nodes with low complexity that represent a technique to overcome coverage problems. In this paper, we introduce the NCR concept and study its performance gains and deployment options. Particularly, presenting the main specifications of NCR as agreed in 3rd generation partnership project (3GPP) Rel-18, we analyze different NCR deployments in an urban scenario and compare its performance with alternative deployments. As demonstrated, with a proper network planning and beamforming design, NCR is an attractive solution to cover blind spots the base stations (BSs) may have.
Paper Structure (5 sections, 4 figures, 2 tables)

This paper contains 5 sections, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. 3GPP NCR
  3. Performance Evaluation of NCR-assisted Networks
  4. On the Challenges of NCR-assisted Networks
  5. Conclusions and Future Perspectives

Figures (4)

  • Figure 1: gNB to UE connection via an NCR.
  • Figure 2: Scenarios of interest.
  • Figure 3: CDF of SINR for the direct and forwarded link for Scenarios A and B on Downlink and Uplink, respectively.
  • Figure 4: