5G RedCap, short for 5G Reduced Capability, also called 5G NR-Light, is a significant addition the 5G family. What exactly is RedCap? To answer this question, we need to start with the evolution of cellular IoT technology.

Since Release 8, while the rate of mobile broadband (MBB/eMBB) has continued to grow, 3GPP has also introduced a variety of cellular IoT technologies such as LTE Cat 1, Cat 1 bis, eMTC, NB-IoT, EC-GSM, and RedCap.

These cellular IoT technologies reduce the complexity, cost, size, and power consumption of terminals and modules through different degrees of "functional tailoring", so as to "tailor" to different IoT needs.

A brief introduction:

LTE Cat 1/LTE Cat 1 bis: LTE Cat 1 is a cellular IoT technology developed by 3GPP Release 8 specifically for M2M IoT applications, with a channel bandwidth of 20MHz, a downlink peak rate of 10Mbps, and an uplink rate of 5Mbps.

LTE Cat1 bis was proposed in Release 13. As an evolution of Cat 1, it further cuts the dual receiving antennas of LTE Cat 1 terminals to a single receiving antenna.

LTE Cat 0/eMTC: LTE Cat 0 is a UE type proposed by 3GPP Release 12 for IoT applications, with a channel bandwidth of 20MHz and an uplink and downlink peak rate of 1Mbps. LTE Cat 0 supports a single receiving antenna and half-duplex mode, so the terminal complexity is reduced by at least 50% compared to LTE Cat 1.

In Release 13, LTE Cat 0 evolved into eMTC or LTE-M (Cat M1). As the maximum channel bandwidth is reduced to 1.4MHz, the complexity of LTE Cat M1 is further reduced compared to LTE Cat 0, and the coverage capability is further improved.

Later, eMTC evolved to Release 15 and Release 16 in the 5G era, and its functions continued to be enhanced.

NB-IoT: NB-IoT is a narrowband IoT technology introduced in 3GPP Release 13, with a channel bandwidth of 180KHz and a peak rate of tens to 200Kbps.

Like eMTC, NB-IoT has also evolved from Release 13 and Release 14 in the 4G era to the 5G era, with its functions continuously enhanced, jointly promoting the development of 5G Massive IoT.

EC-GSM-IoT: EC-GSM-IoT is part of the 3GPP Release 13 specification, mainly evolved from 2G technology upgrades, and can be implemented through 2G GSM network software upgrades. The channel bandwidth is 200KHz and the peak rate is about 70 to 240Kbps.

RedCap: RedCap was formulated in 5G Release 17, and its full name is Reduced Capability NR, which means "cutting NR capabilities", so it is also called a lightweight and simplified version of 5G NR.

Why introduce RedCap?

As we all know, 5G initially defined three scenarios: eMBB, uRLLC and mMTC. Correspondingly, the types of IoT in the 5G era include broadband IoT, mission-critical IoT and large-scale IoT.

eMBB is mainly aimed at high-bandwidth applications such as high-definition video, VR/AR, etc., and the network downlink peak rate is usually as high as Gbps and the uplink rate is several hundred Mbps.

uRLLC is mainly aimed at mission-critical IoT applications such as remote control and unmanned driving, requiring the network end-to-end latency to be as low as milliseconds and reliability to be as high as 5 9s.

mMTC evolved from the NB-IoT and eMTC low-power wide-area IoT technologies of the 4G era, and is mainly aimed at large-scale IoT scenarios such as smart meter reading and smart street lights. It has very low requirements for data transmission rate and latency, with a network speed of less than 2Mbps and a latency that can be tolerated to 10 seconds.

Although these three scenarios differentiatedly match the requirements of high-speed, low-latency and low-speed IoT applications, you must have noticed that those IoT applications with medium requirements for rate and latency have not yet been covered.

For example, industrial wireless sensors used to measure and collect data such as temperature, humidity, and pressure require a data transmission rate of about 2Mbps, a latency of less than 100 milliseconds, and a reliability of only 99.99%; wearable devices such as smart watches, medical monitoring equipment, and AR/VR glasses require a data transmission rate of about 2 to 10Mbps; surveillance cameras require a data transmission rate of about 2 to 25Mbps, a latency of less than 500 milliseconds, and a reliability of only 99% to 99.9%.

If these IoT scenarios are supported by eMBB and uRLLC capabilities, it would be a waste of resources, and the rate and latency capabilities of mMTC cannot meet the requirements.

RedCap is a cellular IoT technology that was created to fill the "blank area" between eMBB, mMTC, and uRLLC. If 5G cellular IoT is divided into low, medium, and high levels based on technical indicators such as bandwidth, latency, cost, terminal power consumption, and coverage distance, then RedCap is the "mid-range" IoT technology in the 5G era.

What capabilities does RedCap cut?

Release 17 RedCap mainly cuts the following functions, thereby reducing terminal complexity and cost by 50% to 65%.

• The maximum bandwidth is reduced from NR's 100MHz to 20MHz

• The antenna configuration is reduced from NR's 2T4R to 1T1R or 1T2R

• The minimum number of downlink MIMO layers is reduced to 1

• The maximum modulation order can support at least 64QAM

• Half-duplex mode is introduced

In order to achieve higher peak rates, RedCap terminal devices do not need to be cut so drastically, and more advanced functions can be selected, such as supporting 2 receiving antennas, 2 downlink MIMO layers, 256QAM, full-duplex FDD, etc.

Through these capability cuts, the network connection requirements of IoT applications such as wearable devices (including wearable watches, AR/VR glasses, etc.), industrial wireless sensors, and surveillance cameras can be matched more cost-effectively and efficiently.

Conclusion

5G RedCap is a new 5G standard that is designed to address the use cases in between the high speed Enhanced mobile broadband (eMBB), the ultra-reliable low latency communications (uRLLC) and the low throughput and battery efficient Massive Machine-Type Communication (mMTC) technologies. 5G RedCap is well-suited for a wide range of IoT applications and will probably play an important role in future IoT deployments. For the time being, LTE Cat 1 and Cat 4 are the most suitable for those IoT scenarios.