RedCap 5G: Reduced Capability, Increased Potential

Currently, the 5G market revolves around 3GPP Release 15 networks and devices, a form of enhanced mobile broadband which is essentially a faster LTE system. Subsequently, an eagerly anticipated evolution of 5G is support for Reduced Capability, or RedCap, devices.

RedCap 5G was standardized in 3GPP Release 17 — frozen in June 2022, and set for issue in new and upgraded 5G systems by the end of 2024. It’ll bring a new dimension to 5G networks and could be a massive boost for 5G in Internet of things (IoT) and private mobile networks applications, as it promises simpler hardware and lower device costs.

RedCap is one of the core service areas enabled by 5G Advanced and is expected to be essential in developing 6G. It can expand the 5G device ecosystem to incorporate smartwatches, augmented reality glasses, wearable medical devices, industrial wireless sensors, CCTV cameras, smart grid devices and more (see The Potential Role of 5.5G in Scaling Passive IoT), enabling a greater range of applications to be served by 5G specifications.

Many of these uses have medium-speed data rate requirements rather than the higher speeds offered by enhanced mobile broadband 5G. Still, they need higher data rates than those addressed by low-power wide-area options such as LTE-M and narrowband-IoT solutions. Also, wearables, IoT sensors and surveillance cameras don’t have the stringent latency requirements of ultrareliable low-latency communications scenarios. There’s always a trade-off between such requirements and the functional complexity of a device versus its cost, with cost being critical in scaling up applications to thousands of devices.

This means there’s a sweet spot for RedCap 5G, with more scope for balancing functional performance with cost-effectiveness. This has been difficult to achieve in 5G standards to date, with the 5G non-smartphone device ecosystem suffering from overkill — devices need to support a lofty set of performance requirements which increases their cost, making it harder to scale up their use and control budgets.

So, what do RedCap requirements look like, and how does reducing capabilities help to lower costs?

RedCap uses a simpler radio in the terminals, which reduces the cost of the radio itself as well as the supporting components, such as antennas. Crucial aspects of the simplification are:

Device bandwidth: A RedCap device is only required to support a 20 MHz band in frequency range 1 (FR1) and 100 MHz in frequency range 2 (FR2) for transmission and reception, reduced from 100 MHz and 200 MHz bands respectively.

Receive branches: By reducing the number of receive branches, the number of corresponding receive antennas is also reduced, saving costs. Typically, 5G FR1 frequency-division duplex (FDD) bands, some FR1 time-division duplex bands and all FR2 bands require a device to be equipped with two receive branches, but a RedCap device is only required to have one.

Downlink multiple-input multiple-output (MIMO) layers: The maximum number of downlink MIMO layers required for a RedCap device is the same as the number of receive branches, so again, this is lower than a typical 5G device.

Downlink modulation order: Quadrature amplitude modulation (QAM) is a method of combining two amplitude modulation signals into a single channel, effectively doubling its potential bandwidth. Regular 5G devices are required to support 256 QAM in the downlink in FR1, but this is optional for a RedCap device.

Duplex operation: This refers to the operating method in which transmission is possible simultaneously in both directions. 5G devices are required to support a full-duplex operation in an FDD band, receiving in the downlink frequency and transmitting in the uplink frequency and vice versa. For RedCap devices, full-duplex-FDD support is optional, removing the need for a duplex filter. Instead, a cheaper switch can be used to select the transmitter or receiver to connect to the antenna.

But what does this mean for the market?

In terms of positioning, RedCap lands somewhere between massive machine-type communications, enhanced mobile broadband and ultrareliable low-latency communications, arguably the most demanding version of IoT in the 3GPP landscape. Of these, only the latter two are 5G-native.

Massive machine-type communications are currently underpinned by two low-power wide-area technologies that are LTE-based, albeit compatible with 5G networks: ultralow-power narrowband-IoT and the higher data rate LTE-M. RedCap presents a commercial pathway for such LTE-based communications to migrate to single 5G-based networks yet retain support for no-frills, scalable, long-term and cost-effective options for IoT. This will allow the technology to fill the gap between enhanced mobile broadband and existing LTE-based massive machine-type communications without encroaching on the opportunity for high-fidelity ultrareliable low-latency communications.

LTE-based IoT competes with a fragmented assortment of non-cellular (but cheaper) standards like Wi-Fi and long-range wide-area networks (LoRaWAN) in unlicensed bands. But RedCap’s support of IoT applications using wearables, sensors and surveillance cameras means it could have a fundamental impact on the business case for private 5G networks. Reducing 5G capabilities could bring device prices to mass-market levels, enabling the mobile industry to offer lower-cost mass-scale sensor networks.

RedCap 5G and passive IoT add 5G variations equivalent to existing non-5G radio options, with RedCap offering a replacement for and improvement on LTE Cat M4 and Cat M1. Passive IoT is potentially a better substitute for Amazon Sidewalk, bar codes, Bluetooth, Mesh IoT, Sigfox and others. Together, this allows 5G to deliver a full range of IoT connectivity on a single infrastructure.

RedCap incorporates the deterministic networking features and spectral efficiency of licensed spectrum, but also supports the cost-effectiveness, coverage and mobility that massive machine-type communications require, which could go a long way to enhancing 5G’s Industry 4.0 credentials and boost adoption of private 5G networks. Although the future of IoT, enterprise networking and private mobile networks is likely to be an amalgamation of multiple technologies, we expect RedCap 5G to play a significant role.