This is the motivation for the development of RedCap (Reduced Capability). RedCap is the 3GPP IoT wireless specification designed to address several generic and specific use cases for 5G NR. The current state of RedCap can be traced back to several requirements in industry that culminated due to multiple and overlapping requirements from use cases and IoT verticals.
3GPP 5G NR Release 15 (Rel-15) was primarily designed to address use case areas requiring lower latency, higher peak data rates, and ultra-reliability beyond legacy 4G wireless networks. This was supplemented by 5G NR Rel-16 which added Time-Sensitive Networking (TSN), and further enhancements of 3GPP reliability and latency specifications.
These two releases were very beneficial for IoT use cases, but they still did not come close enough to already existing 4G 3GPP Rel-13 and 14 specifications which addressed energy efficiency, coverage, and lower device cost. There was a clear need for a protocol that allowed use cases involving Time
Sensitive Communications (TSC) and which could take advantage of 4G efficiency and costs as well as 5G reliability and latency.
The result was RedCap, which was officially adopted into 3GPP specifications in June 2022.
Why operators need RedCap
There are several reasons why operators need RedCap.
Although 5G networks are being deployed globally, they are not all the same. There are two distinct types: Stand Alone (SA) and Non-Stand Alone (NSA). The SA networks rely completely on 3GPP 5G specifications for all device and infrastructure equipment, while NSA networks rely on both 3GPP 4G and 5G specifications.
This means that “SA only” devices are specifically designed for 5G networks, and do not support 4G technologies such as LTE-M and NB-IoT. This can be a problem for operators of pure green-field 5G networks who have no legacy 4G installations.
For a device to be compliant with 5G specifications it must meet minimum requirements, which
include 100 MHz of bandwidth and four RX antennas. This is much more capability than needed for many IoT use cases – by increasing the power demand, these requirements make devices unsuitable for low power wide area (LPWA) networks. These 5G device minimum requirements are in place for both SA and NSA networks.
RedCap offers a migration path from 4G to 5G as spectrum is migrated to new bands and also bridges the gap between 4G IoT and 5G NR technologies.
Benefits of RedCap
The primary benefits of RedCap are the new use cases that enables the development of cost-effective devices. There are three initial IoT 3GPP Rel-17 use cases required by industry: industrial wireless sensors, video surveillance, and wearables. Each of these has slightly different demands in data rate, latency, reliability, and battery life as shown in the Table below.
Since the technical capabilities of RedCap based devices are less than those of 5G smart phones, they can use less complex modem and RF designs, which in turn lowers device cost, power consumption, and size.
The less complex wireless hardware in the devices means simpler modem and RF front end architectures, while the reduced number of antennas and less MIMO allows lower device costs. Fewer duplexers, amplifiers, and filters can also greatly simplify the component count of RedCap devices.
With reduced hardware requirements and lower costs, we should expect to see many new 5G devices and use cases in the next few years and there may even be much lower cost 5G smart phones based on RedCap.
RedCap compared to 5G and LTE
Looking at the Table below which shows how RedCap reduces device complexity and required features, we can get an overview of how the RedCap requirements compare to 5G minimum UE requirements and to LTE.
Some of the highlights include:
Bandwidth:
Maximum of 20 MHz in FR1 and 100 MHz in FR2 will achieve reduced power consumption and lower cost components – however, they will not achieve the high data rates of full NR devices.
Deployments:
- SA networks are the only ones for RedCap devices to support. This means there is no 2G/3G/4G connectivity requiring complex RF hardware, thus lowering power consumption and size.
- NR smart phones typically must support dozens of frequency bands for global use. RedCap devices will be designed for specific use cases, which can be stationary locations.
- However, these two points can be a drawback until SA network deployment grows. Inherent NR capabilities such as Sub- Carrier Spacing (SCS) do lower the latency.
Antennas:
Up to two receive antennas can be designed into RedCap devices, much lower than the 4x4 requirements in NR smart phones. This can limit coverage as MIMO can be used to increase downlink performance.
Maximum TX power:
Lower TX levels than NR smart phones will reduce power consumption, allowing for smaller batteries and giving lower cost. However, this can cause reduction of coverage at the cell edge.
Carrier Aggregation (CA):
No support for CA means a RedCap device only needs to use one frequency channel at a time. This will lower energy consumption, cost and size.
Current and future developments
RedCap specifications were included in 3GPP Rel-17 and finalised in June of 2022 and it will take around a year for modems and RF front ends to arrive.
Eventually, modules and end devices will take another year or less, so we should expect to see some of the first RedCap devices to appear around the end of 2023 to the middle of 2024, depending on the level of complexity and integration of the RedCap device. This is timely, as global operators will continually be deploying 5G SA networks over the next several years.
Rel-17 RedCap has only started the process of reducing complexity to lower cost and increase battery life and there remains much to be done. 3GPP has started studying items for RedCap Rel-18 (NR Advanced), with this RedCap Phase 2 planned for initial release in early 2024.
Some of the features under study include:
- Sidelink – direct 5G device to device communication.
- Positioning – better location for accuracy applications.
- Unlicensed Band – availability of shared spectrum.
- Multicast & Broadcast (MBS) – point to multi-point services.
- RedCap device types – classification of RedCap devices.
RedCap clearly has an exciting future and we can expect additional use cases to be defined that will address challenges such as drones, power grids, robotics, industrial, transportation, asset tracking, AGVs, and many more.
Author details: Brian Davis, Technology Strategy Manager, Anritsu Corporation
