RedCap and eRedCap – standardizing simplified 5G devices for the Internet of Things

The cellular IoT enables wireless connection of devices as diverse as surveillance cameras, smart electrical grid devices, industrial sensors, smart glasses, health monitoring devices, and other wearables, as shown in Figure 1. These are just a few examples of the many potential cellular IoT use cases – the list could easily be extended to any use case that would benefit from wireless connectivity if the cost and capabilities of the available technologies allow.

Figure 1 – Examples of cellular IoT use cases

Ericsson has contributed actively to the definition of cellular IoT technologies from the start and acted as rapporteur in the 3GPP standardization organization during its work on RedCap and eRedCap.

After a thorough study by 3GPP starting back in 2020 (described in an earlier blog post), 5G support for RedCap devices was introduced in 3GPP Release 17 in 2022 to facilitate the expansion of the 5G device ecosystem to use cases with requirements that were outside the 5G specifications at the time. RedCap devices have low complexity and peak rates below 250 Mbps.

Following another study in 3GPP, the eRedCap device type introduced in 3GPP Release 18 in 2024 is a RedCap device with its peak rate capped to 10 Mbps. Since this lower peak rate is expected to be sufficient in many cases, it was deemed worthwhile to specify a new device type.

Both of these new device types (RedCap and eRedCap) are designed to enable cost-effective support for a vast array of use cases for both consumers and industries.

Different device types for different use case segments – why? 

The connectivity requirements of IoT use cases vary widely. While it might be tempting to try to use a single device type for all use cases, in many cases the solution would end up being over-dimensioned and unnecessarily expensive. To avoid this problem, different use case segments need to be targeted by different device types.

Figure 2 illustrates the main 4G/5G device types, with 4G on the left and 5G on the right. The radio technologies for 4G and 5G are named LTE (Long-Term Evolution) and NR (New Radio), respectively. The most advanced device types can be found at the top of the figure, and the simpler device types toward the bottom of the figure. Note that the two lowest device types in both 4G and 5G are based on the NB-IoT and LTE-M radio technologies and that the RedCap and eRedCap device types are intended for different use cases than those served by NB-IoT and LTE-M.

Figure 2: 4G/5G device types

Figure 3: Requirements of the use case segments

Figure 3 provides a simplified illustration of use case requirements. A use case that requires a high data rate would appear near the top, whereas a use case requiring low latency would be in the lower right corner. A use case requiring low device cost and/or long battery life would appear in the lower left corner.

The colored triangles inside the main triangle represent the four main use case segments:

The enhanced mobile broadband (eMBB) triangle corresponds to use cases that require high data rates and decent latency, which are well served by 4G LTE and 5G NR devices. Smartphones are a good example.

The ultra-reliable low-latency communications (URLLC) triangle includes use cases that require a very reliable connection with very low latency along with a decent data rate, which can also be supported by 5G NR. Alternative names for this segment are critical machine-type communications (cMTC) and time-critical communications (TCC). A typical example would be control of a robot in a factory, where there is little-to-no margin for errors and delays.

The massive machine-type communications (mMTC) triangle includes low-end IoT use cases with modest requirements on data rates and latency, but with more stringent requirements on one or more of the following: low device cost, small device form factor, long battery life, and deep coverage. Sometimes these are referred to as massive IoT (mIoT) or low-power wide-area (LPWA) use cases, and they are supported by the NB-IoT and LTE-M technologies. Smart electricity/water/gas metering devices are good examples.

The reduced capability (RedCap) triangle corresponds to use cases that require lower device cost and longer battery life than legacy 5G NR devices can provide, but at the same time they need higher data rates and lower latency than NB-IoT and LTE-M can offer. This segment sometimes goes under the name broadband IoT. Typical examples include smart wearables and industrial sensors.

Filling the device gap with RedCap and eRedCap

The use cases that fall within the RedCap triangle (the broadband IoT segment) in Figure 3 can be served adequately by the 4G LTE device categories 1/2/3/4 shown in Figure 2. However, the first release of the 5G standard did not include support for 5G NR devices with performance and complexity on par with these low-end 4G LTE devices. As a result, a decision was made to introduce support for 5G NR devices with reduced capabilities (RedCap) and enhanced RedCap (eRedCap) in the 5G standard.

Figure 4 shows a base station communicating with a RedCap device (RedCap user equipment or UE for short) and a standard 5G NR device (legacy UE), illustrating the differences in terms of maximum bandwidth, antennas, duplex and modulation.

Figure 4: Base station communicating with a RedCap device and a standard 5G device

RedCap simplifications and their implications 

The following simplifications were specified in 3GPP Release 17 to reduce 5G NR device complexity to a level that is comparable with 4G LTE device categories 1/2/3/4:

• Reduced bandwidth
• Reduced number of antennas
• Half-duplex operation
• Relaxed modulation

It is important to note that a RedCap device does not need to implement all of the simplifications. The reduced bandwidth is mandatory for all RedCap devices, while the use of the other simplifications is optional and up to the RedCap device implementation.

This blog post focuses on the simplifications that can be used for RedCap devices that support low-to-mid frequency bands (up to ~7 GHz), which is the most widely deployed frequency range for 5G. Note that similar but somewhat different simplifications have also been specified for RedCap devices supporting high frequency bands (~24 GHz and above), something that may be of interest especially for indoor industrial scenarios.

Within the low-to-mid frequency range, the lower bands (especially below 1.5 GHz) use frequency division duplex (FDD) and the higher bands (especially above 2.6 GHz) use time division duplex (TDD). FDD means that downlink and uplink communications take place in two different frequency bands separated by a duplex distance. TDD means that downlink and uplink communications take place in the same frequency band but in different time slots.

Reduced bandwidth

A RedCap device has a maximum bandwidth of 20 MHz for transmission and reception, whereas a normal 5G NR device has a maximum bandwidth of at least 100 MHz (or the maximum bandwidth specified for the frequency bands supported by the device, which may be smaller than 100 MHz). In addition, RedCap devices do not support simultaneous use of more than one carrier frequency – that is, they do not support carrier aggregation (CA) or dual connectivity (DC).

The 5G carrier bandwidth used by the base station can still be as large as before. It is only the bandwidth of the transmissions to and from a RedCap device that is limited, which puts a cap on the achievable data rates for RedCap devices.

Reduced number of antennas

A RedCap device can be implemented with a single receive antenna, whereas a normal 5G NR device is required to implement at least two receive antennas for bands below 2.5 GHz and typically at least four receive antennas for bands above 2.5 GHz. A device with fewer antennas can be smaller and less complex. RedCap devices also have a single transmit antenna, but this is allowed also for normal 5G NR devices, so there is no difference there.

Devices with multiple receive antennas can support parallel data streams (called layers) over the air using multiple-input multiple-output (MIMO) transmission. RedCap devices with a single receive antenna can only support a single layer, meaning that they don’t need to implement MIMO-related processing. However, the standard also allows more advanced RedCap device implementations with two receive antennas, supporting two layers, doubling the downlink peak rate compared to single-antenna devices.

Half-duplex operation

A RedCap device can be implemented with support for half-duplex FDD operation only, meaning that it doesn’t need to support simultaneous transmission and reception. (This simplification is not relevant for TDD, since transmission and reception never take place simultaneously in TDD.) Half duplex can result in lower data rate and higher latency, but it also means that the cost and size of the device can be reduced as it can implement a simple switch instead of the more advanced duplex filter(s) that would be required to support full duplex. This can make a big difference especially for devices that support many frequency bands, since each band may require its own filter.

The standard also allows more advanced RedCap device implementations that support full-duplex FDD operation, as a normal 5G NR device.

Relaxed modulation

When data bits are transmitted over the air, multiple bits can be combined into a modulation symbol, which is carried by a modulated radio wave. The number of values that the symbol can take is called modulation order. Normal 5G NR devices need to support (at least) up to modulation order 256 in downlink and 64 in uplink, using a modulation scheme called quadrature amplitude modulation (QAM). RedCap devices only need to support modulation order 64 in both downlink and uplink. This results in a 25% lower downlink peak rate but also a somewhat simpler receiver.

The standard also allows more advanced RedCap device implementations with 256 in downlink and/or uplink, as for normal 5G NR devices.

Key properties of RedCap devices

As mentioned earlier, a RedCap device does not need to implement all of the simplifications. The achievable peak rate will depend on the design choices. In case of TDD, it will also depend on how the network chooses to split the time between downlink and uplink.

• For a RedCap device in FDD, typical peak rates range from 85 to 225 Mbps in downlink and from 90 to 120 Mbps in uplink depending on design choices.
• For a RedCap device in TDD, typical peak rates range from 50 to 130 Mbps in downlink and from 35 to 45 Mbps in uplink depending on design choices, assuming a time split with 60% downlink and 40% uplink.

The following rough comparison can be made between RedCap and other technologies:

• The peak rates and device complexity for RedCap resemble those of 4G LTE device categories 2/3/4 (Cat-2/3/4).
• Normal 5G NR devices have much higher peak rates and higher complexity.
• NB-IoT and LTE-M devices have much lower peak rates and lower complexity.

The fact that RedCap poses similar requirements on the device hardware as 4G LTE Cat-2/3/4 facilitates implementation of dual-mode devices supporting both 4G (Cat-2/3/4) and 5G (RedCap). This may be useful for example in scenarios with spotty coverage or in roaming scenarios.

As a rule of thumb, based on the 3GPP study, the modem part of the simplest possible RedCap device can be expected to have about one third of the complexity of the modem part of the simplest possible ordinary 5G NR device. However, the exact numbers will depend on design choices such as what frequency bands the device supports.

The reduced complexity should translate into reduced bill-of-material cost, which in turn should translate into reduced overall device cost. Beside complexity, the importance of economies of scale should not be underestimated. If a single product can be used for many use cases and many markets worldwide, it can be produced and sold in large quantities. This tends to reduce the production cost and price of the product, which may increase demand even further.

On the cellular network side, support for RedCap devices is typically a software feature that can be rolled out throughout a network as part of an ordinary software upgrade.

Further simplifications for eRedCap devices

An important category of low-end IoT use cases is successfully served today by 4G LTE device category 1 – the lowest device category in 4G LTE – with a peak rate of 10 Mbps in downlink and 5 Mbps in uplink. It has two flavors: Cat-1 which has two receive antennas, and Cat-1bis which has a single receive antenna.

With this use case category in mind, a decision was made in 3GPP that all eRedCap devices have 10 Mbps peak rate (in both downlink and uplink), regardless of what other features they may support. Note that this is different from RedCap, where the peak rate depends on design choices such as the number of antennas. Again, the aligned device hardware requirements facilitate dual-mode device implementations supporting both 4G (Cat-1/1bis) and 5G (eRedCap). The maximum bandwidth for eRedCap is the same as for RedCap, that is, 20 MHz.

In addition, an eRedCap device can be implemented with a reduced maximum data channel bandwidth. The radio part of the device still supports 20 MHz, but the number of physical resource blocks (PRBs) that are used for data transmission is limited to a number that corresponds to approximately 5 MHz. This can provide further complexity reduction. It is a design choice whether or not to implement this restriction in the eRedCap device, however.

During the study preceding the Release 18 eRedCap specification work, other potential solutions which would have required larger standard changes were also studied, including a solution where the bandwidth would have been reduced to 5 MHz also in the radio part. However, the potential additional complexity reduction from this was estimated to be too small to motivate the required standard changes, which would have deviated more from the RedCap framework that had already been established in Release 17.

An eRedCap device only supports low-to-mid frequency bands, not high frequency bands. In principle, there is nothing preventing specifying standard support for eRedCap for high frequency bands as well, but so far there has not been a clear market need for devices that support a low peak rate in high frequency bands.

Apart from the differences mentioned above, eRedCap devices operate essentially in the same way as RedCap devices and can implement the same simplifications as RedCap devices (reduced number of antennas, half-duplex operation, etc.). This means that if a cellular network already supports RedCap devices, the required effort for upgrading the network to support eRedCap devices as well should be relatively modest.

Looking ahead

In the two years since support for RedCap devices was introduced in 3GPP Release 17, we have been pleased to see RedCap devices and 5G network support for RedCap devices being deployed throughout the world. We expect that eRedCap devices will follow, enabling even more cost-efficient support for a vast array of consumer and industrial use cases around the globe. At Ericsson, we look forward to continuing to work together with our standardization partners in 3GPP to continue to evolve cellular technologies to support the broadest possible range of future cellular IoT use cases.

If you are interested in learning more about RedCap, check out Ericsson’s product offering and our white paper that explains how RedCap expands the 5G device ecosystem. Among other topics, it describes possible device design choices including some minor additional simplifications not covered above, achievable peak rates, power saving techniques with the potential to help achieve substantially longer battery life, and network deployment aspects.

Read more:

• Read more about Ericsson's 5G RedCap offering
• Read our white paper about how RedCap expands the 5G device ecosystem: RedCap: Expanding the 5G device ecosystem
• Book providing detailed descriptions of the NB-IoT and LTE-M technologies: Cellular IoT: from massive deployments to critical 5G