NR SA RedCap

This tutorial shows how to how to configure and test RedCap. RedCap stands for Reduced Capability which is introduced in 3GPP release 17. Followings are high level feature of RedCap

Designed for simplified / low cost device
Narrower bandwidth comparing to regular NR use case (eMBB), but narrowband here means up to 20 Mhz in sub-7 Ghz and 100 Mbps in mmWave
Half Duplex (optional)
a single receive antenna, with 2 antennas being optional,
lower-order modulation, with 256-QAM being optional

The main feature that Amarisoft callbox support for RedCap are

TDD/FDD
halfduplex
initial BWP Redcap
NCD-SSB

The key requirements driving RedCap development include moderate data rates, reasonable latency (not ultra-low), extended battery life, low device cost and complexity compared to eMBB devices. RedCap fills the gap between the high-end eMBB and ultra-reliable URLLC use cases, and the low-throughput mMTC use cases served by LTE-M and NB-IoT.

NR RedCap (Reduced Capability NR) is designed to address several key use cases for 5G NR networks:

Industrial Wireless Sensors

Temperature, pressure, motion, humidity, proximity sensors
Latency < 100ms (5-10ms for safety applications)
Reliability of 99.99%
Battery life ~2 years

Video Surveillance

For smart cities, agriculture, factories, retail, commercial
Latency < 500ms
Reliability 99-99.9%

Wearables

Smart watches, health monitors, AR/VR headsets
Battery life of multiple days up to 1-2 weeks

NR SA RedCap

Introduction
Summary of the Tutorial
Test Setup

< Setup A >
< Setup B >

Key Configuration Parameters
Test 1 : 20Mhz BW, Single BWP

Configuration
Perform the test
Log Analysis

Test 2 : 40Mhz BW, Two BWPs with a RedCap-only BWP

Configuration
Perform the test
Log Analysis

Test 3 : 40Mhz BW, Three BWPs with two RedCap-only BWP and NCD-SSB

Configuration
Perform the test
Log Analysis

RRC / NAS Signaling

SIB1
RrcSetup

Introduction

NR RedCap (Reduced Capability New Radio) is a specialized feature introduced in 3GPP Release 17 to enable 5G connectivity for simplified, lower-cost devices that do not require the full capabilities of enhanced Mobile Broadband (eMBB). RedCap is engineered to bridge the performance and complexity gap between high-end 5G use cases, such as eMBB and ultra-reliable low latency communications (URLLC), and the lower data rate requirements addressed by LTE-M and NB-IoT. Architecturally, RedCap introduces significant modifications to the NR protocol stack and radio access configuration, including the use of narrower bandwidths (up to 20 MHz in sub-7 GHz and 100 MHz in mmWave), optional half-duplex operation, and support for devices with a single receive antenna. Modulation schemes are typically limited to lower orders, with 256-QAM available as an option. The Amarisoft callbox supports key RedCap features such as Time Division Duplex (TDD), Frequency Division Duplex (FDD), half-duplex operation, initial Bandwidth Part (BWP) configuration, and New Control-Data Synchronization Signal Block (NCD-SSB). RedCap is specifically designed to meet requirements for moderate data rates, reasonable latency, extended battery life, and reduced device cost and complexity, making it an ideal solution for industrial sensors, video surveillance, and wearable devices. By enabling efficient 5G connectivity for these use cases, RedCap plays a pivotal role in broadening the ecosystem of 5G NR deployments and expanding the reach of 5G-enabled applications.

Context and Background
- RedCap was introduced in 3GPP Release 17 as a response to industry demand for NR devices with reduced complexity and cost, targeting markets not addressed by traditional eMBB or legacy IoT technologies.
- It provides a standardized approach for manufacturers and network operators to deploy 5G NR in application areas previously served by LTE-M and NB-IoT, but with enhanced 5G features and scalability.
- RedCap leverages the existing NR framework but restricts certain capabilities, optimizing for device simplicity, power efficiency, and cost-effectiveness.
Relevance and Importance of the Tutorial
- This tutorial addresses the practical aspects of configuring and testing NR RedCap using Amarisoft callbox solutions.
- Understanding RedCap is critical for engineers and technical professionals involved in the development, deployment, and validation of 5G NR devices targeting industrial IoT, surveillance, and wearable markets.
- The content is aligned with the latest 3GPP standards, ensuring learners gain up-to-date knowledge applicable to real-world 5G NR deployments.
What Learners Will Gain
- Insight into the architectural modifications and protocol optimizations introduced by RedCap in the 5G NR stack.
- Hands-on understanding of how to configure RedCap features on an Amarisoft callbox, including support for TDD/FDD, half-duplex, and initial BWP RedCap settings.
- Knowledge of RedCap use cases and deployment scenarios, enabling learners to assess its suitability for various applications.
- Practical skills for testing and validating RedCap devices, essential for product development and network integration.
Prerequisite Knowledge and Skills
- Familiarity with 5G NR architecture, including the radio protocol stack and key features of 3GPP Release 15 and later.
- Basic understanding of the Amarisoft callbox platform and its configuration workflow.
- General knowledge of wireless communication principles, such as duplexing schemes, bandwidth, and modulation techniques.
- Experience with device testing and validation in mobile network environments is recommended for best results.

Summary of the Tutorial

This tutorial demonstrates various test scenarios for RedCap (Reduced Capability) UE operation in NR SA networks, focusing on Bandwidth Part (BWP) configurations and RedCap-specific features. The procedures span three main tests, each building in complexity and feature coverage.

Test Setup:
- SIM card supplied with the system is used.
- Configuration changes can be made with reference to the Configuration Guide.
- Two physical setups are shown: Setup A (Callbox, UE, 2 SDRs) and Setup B (Callbox, UEsim, 1 SDR).
Key Configuration Parameters:
- dl_bwp_access, ul_bwp_access: Downlink/Uplink BWP access configuration.
- half_duplex and associated parameters: Control half-duplex operation and guard symbols.
- dl_bwp_list, ul_bwp_list: Lists of BWPs for DL/UL, respectively.
- initial_dl_bwp_id, initial_ul_bwp_id: Initial BWP selection for DL/UL.
Test 1: 20MHz BW, Single BWP
- Procedure:
  - Configure the network using gnb-sa-redcap.cfg and mme-ims.cfg as provided.
  - Set FDD mode (NR_TDD 0), 2x2 MIMO (N_ANTENNA_DL 2), and 20MHz bandwidth (NR_BANDWIDTH 20).
  - Use a single BWP shared by both regular and RedCap UEs.
  - RedCap UE configuration uses the simplest default: half_duplex: { }.
  - For UEsim, match FDD, bandwidth, and band settings to the Callbox.
  - Ensure as_release is set to 17 and redcap to true in the UE list.
  - Start LTE service, check NR cell configuration, and power on UEsim.
  - Wait for initial connection completion.
- Methodology Highlights:
  - All RedCap traffic uses the single initial BWP (20MHz).
  - RedCap-specific BWP is not used since channel bandwidth is not greater than 20MHz.
Test 2: 40MHz BW, Two BWPs with a RedCap-only BWP
- Procedure:
  - Use gnb-sa-redcap-2bwp.cfg and corresponding UE config.
  - Set FDD mode (NR_TDD 0), 2x2 MIMO, and 40MHz channel bandwidth.
  - Configure two BWPs: one for regular UE, one dedicated for RedCap UE.
  - Enable full PHY/MAC scheduling (e.g., force_dl_schedule, force_full_bsr) for layer conformance checks.
  - Configure two CSI reports: one for the initial BWP, one for RedCap BWP.
  - For RedCap BWP, set ra_type to type0 (Bitmap) for non-contiguous allocation support.
  - Create dedicated dl_bwp and ul_bwp for RedCap with 20MHz width.
  - Assign initial BWP IDs and RedCap-specific BWP lists to RedCap UEs.
  - For UEsim, match FDD, bandwidth, and band/frequency configuration.
  - Start LTE service, verify NR cell configuration, and power on UEsim.
  - Wait for initial connection completion.
- Methodology Highlights:
  - RedCap UEs use their dedicated BWPs for PRACH and subsequent PUSCH/PDSCH transmissions.
  - Half-duplex scheduling is observed by default, with transition to full-duplex if not declared in UE capability.
Test 3: 40MHz BW, Three BWPs with Two RedCap-only BWPs and NCD-SSB
- Procedure:
  - Use gnb-sa-redcap-3bwp-ncdssb.cfg and corresponding UE config.
  - Set up FDD mode, 2x2 MIMO, and 40MHz channel bandwidth.
  - Configure three BWPs: one for regular UE, two for RedCap (one for initial attach, one for NCD-SSB transmission).
  - Enable full PHY/MAC scheduling as in Test 2.
  - Configure additional dl_bwp and ul_bwp for RedCap, each 10MHz wide. The second BWP for NCD-SSB includes ssb_nr_arfcn configuration.
  - Assign initial and half-duplex BWP IDs to BWP 1 and 2 for RedCap UEs.
  - For UEsim, ensure matching FDD, bandwidth, and band/frequency configuration.
  - Start LTE service, check NR cell configuration, and power on UEsim.
  - Wait for initial connection completion.
- Methodology Highlights:
  - RedCap UEs initiate PRACH on their dedicated BWP and perform all PUSCH/PDSCH operations in RedCap-only BWPs.
  - One of the RedCap-only BWPs is used specifically for NCD-SSB, with position either automatically or explicitly configured.
  - Half-duplex scheduling is used by default and switches to full-duplex if UE capability does not declare half-duplex support.

General Notes:

For all tests, ensure the UE’s configuration matches the Callbox (cell bandwidth, band/frequency, FDD/TDD).
RedCap features are enabled by setting as_release to 17 and redcap to true for the UE.
Log analysis focuses on confirming RedCap feature signaling, BWP assignments, PRACH initiation, and operational mode (half/full duplex).
Tests demonstrate stepwise extension from basic RedCap operation with a shared BWP to advanced scenarios with multiple RedCap-only BWPs and NCD-SSB handling.

Test Setup

Test setup for this tutorial is as shown below.

SIM Card used in this tutorial is the one delivered with the system as it is.
If you want to change the configuration, The tutorial Configuration Guide would help

< Setup A >

TestSetup Callbox UE 2sdr 01

< Setup B >

Key Configuration Parameters

Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.

Test 1 : 20Mhz BW, Single BWP

In this test, I will show on a simple redcap test scenario where only one BWP is configured and it is shared by both regular UE and RedCap devices.

Configuration

I used the gnb-sa-redcap.cfg which is provided with the installation package

LTE HO Inter Config 01

I also used mme-ims.cfg as it is.

LTE HO Intra Config 02

I used the ue-nr-sa-redcap.cfg which is provided with the installation package

Configure gnb-sa-redcap.cfg as below.

You can configure this part in any way you like. In this test, I used FDD (NR_TDD 0), 2x2 MIMO(N_ANTENNA_DL 2) and bandwidth 20 Mhz (NR_BANDWIDTH 20).

LTE HO Intra Config 03

Since FDD is used in this test, a FDD band (n7) is used and 15Khz SCS(Sub Carrier Spacing) is used.

This is just for information. dl_bwp dedicated for RedCap is not used in this specific test since total channel bandwidth (NR_BANDWIDTH) is not greater than 20 Mhz.

Same as with dl_bwp, ul_bwp dedicated for RedCap is not used in this specific test since total channel bandwidth (NR_BANDWIDTH) is not greater than 20 Mhz.

Now specify RedCap specific features in redcap_ue configuration. In this specific test, only the simplest default redcap_ue:{ half_duplex: { } } is used.

ue-nr-sa-redcap.cfg is configured as follows. (NOTE : If you are using a mobile phone as DUT, you may skip this part)

Configure FDD (TDD 0), Cell Bandwidth (CELL_BANDWIDTH 20) and band/frequency(band, dl_nr_arfcn, ssb_nr_arfcn) to match the configuration of Callbox.

The configuration for ue_list is simple. Just make it sure that as_release is set to 17 and redcap is set to true.

Perform the test

Start LTE service and check basic cell configuration. Any cell configuration is OK as long as they are all NR cell. (NOTE : If you are using UEsim as a DUT instead of mobile phone, make it sure that the cell configuration on UEsim matches the configurations shown here)

LTE HO Inter Run 01

On UEsim, power_on (NOTE : you may try rx_gain -1 before power on UE to let UEsim automatically adjust RX power. You may set a specific value to rx_gain if you know exact channel condition of your setup. Otherwise, rx_gain -1 can be easy option for rx gain setting)

Wait until the initial connection is complete.

Log Analysis

Sample Log

First, gNB broadcast redcap feature support via SIB1. Check out redCap-ConfigCommon IE and look into the detailed configurations L halfDuplexCapAllowed, cellBarredRedCap, intrafreqSelectionRedCap IEs.

Set the initialDownlinkBWP with the entire 20Mhz BW configured in this test case (28875 is for StartRB 0 and NRB 106 with 15Khz Subcarrier Spacing (20Mhz).

Set the initialUplinkBWP with the entire 20Mhz BW configured in this test case (28875 is for StartRB 0 and NRB 106 with 15Khz Subcarrier Spacing (20Mhz).

gNB send UE capability enquiry for NR (bandNR 7 for this specific test case).

Confirm that UE support RedCap feature by checking out redCapParameters in UE capability Information message.

NOTE : For the remainder of the initial attach procedure and data traffic part is not different from any other regular NR SA since the UE is using the same BWP as initialDownlink and initialUplink BWP.

Test 2 : 40Mhz BW, Two BWPs with a RedCap-only BWP

In this test, I will show on a little bit extended redcap test scenario where two BWP are configured. One of the BWP is for regular UE and another one is dedicated for RedCap UE.