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Home5G knowledgeWhat is the 5G RedCap technology ?

What is the 5G RedCap technology ?

Massive Machine-Type Communications (mMTC) is one of the three major 5G use cases, aiming to achieve the connectivity of everything. In regard to the transmission rate, 5G IoT technologies are used in low-rate and medium-rate scenarios.

In low-rate scenarios, 5G uses LTE MTC and NB-IoT to support a massive number of connections and low-rate data transmission, meeting the requirements of Low Power Wide Area (LPWA).

Figure 2-1 shows the evolution of LTE MTC and NB-IoT.

Figure 2-1 Evolution of LTE MTC and NB-IoT

In medium-rate scenarios, LTE MTC and NB-IoT are inadequate. So, what technologies can be used to support IoT services in 5G medium-rate scenarios?

Release 17, the third version for 5G standards, outlines IoT innovation in medium-rate scenarios. Based on existing 5G technologies, RedCap has been designed to reduce UE complexity and power consumption for medium-rate large-scale IoT use cases, such as wearables, industrial sensors, and video surveillance.

If LTE MTC is regarded as chopped LTE Category 1, RedCap can be regarded as chopped eMBB. RedCap cuts down costs at the physical layer and reduces power consumption at the upper layer. RedCap is designed for scenarios where both costs and capabilities fall between eMBB and LPWA, as shown in Figure 2-2.

Figure 2-2 Comparing LPWA, RedCap, and eMBB

3 Use Cases

RedCap can be widely used in three major cases: wearables, industrial sensors, and video surveillance. According to 3GPP TR 38.875, the three use cases have different performance requirements for RedCap, as described in Table 3-1.

Table 3-1 RedCap use cases

Use Case

Terminal Type

Data Transmission Rate

Latency

Battery Lifetime

Wearables

Smart watches, chronic disease monitoring devices, and medical monitoring devices

Downlink: 5 Mbit/s to 50 Mbit/s, peak rate of 150 Mbit/s

Uplink: 2 Mbit/s to 5 Mbit/s, peak rate of 50 Mbit/s

Multiple days or weeks

Industrial sensors

Sensors and remote controllers

Less than 2 Mbit/s

Less than 100 ms; 5 ms to 10 ms in remote control or security-related scenarios

Multiple years

Video surveillance

Surveillance devices for urban transportation, urban security, smart factories, and home security

Common video: 2 Mbit/s to 4 Mbit/s

HD video: 7.5 Mbit/s to 25 Mbit/s

Less than 500 ms

A dash (-) means that there is no specific requirement for this item in the protocol.

3.1 Wearables

Wearables, such as smart watches, chronic disease monitoring devices, and medical monitoring devices, are increasingly more popular. They require stronger network connection capabilities, lower power consumption, smaller device sizes, and richer software functions.

Considering the characteristics of wearables, 3GPP TR 38.875 proposes the following requirements on RedCap UEs:

  • The data transmission rate ranges from 5 Mbit/s to 50 Mbit/s in the downlink and from 2 Mbit/s to 5 Mbit/s in the uplink. In some scenarios, the peak rate must be 150 Mbit/s in the downlink and 50 Mbit/s in the uplink.
  • The battery needs to last for several days (up to one or two weeks).
  • The device should be small and compact.

3.2 Industrial Sensors

5G connectivity has become a catalyst for industrial Internet, which improves flexibility, enhances productivity and efficiency, reduces maintenance cost, and improves operational safety. Industrial Internet scenarios involve a massive number of terminal devices such as sensors and remote controllers.

3GPP TR 38.875 references the requirements of 3GPP TR 22.832 and 3GPP TS 22.104 on industrial sensor use cases as follows:

  • The data transmission rate is less than 2 Mbit/s. Symmetric uplink and downlink traffic or heavy uplink traffic scenarios must be supported.
  • The latency must be below 100 ms. The latency of remote controllers or security-related sensors must range between 5 ms and 10 ms.
  • The availability of communication services must reach 99.99%.
  • The battery needs to last for several years.

3.3 Video Surveillance

Video surveillance covers data collection and processing in various vertical industries, such as urban transportation, urban security, smart factories, and home security.

3GPP TR 38.875 references the requirements of 3GPP TR 22.804 on video surveillance scenarios as follows:

  • In most scenarios, the data transmission rate ranges from 2 Mbit/s to 4 Mbit/s. In some use cases (such as high-definition video) that have high requirements on uplink transmission, the rate must reach 7.5 Mbit/s to 25 Mbit/s.
  • The latency must be below 500 ms.
  • The communication service reliability must reach 99% to 99.9%.

4 Key Technologies

RedCap needs to meet the bandwidth, latency, and performance requirements of the preceding use cases. For this, RedCap cuts down UE performance to reduce complexity based on the price and size requirements of chip modules. It also enhances some power saving functions to reduce the power consumption of UEs and provide specific IoT UEs with a longer battery life.

4.1 Reducing UE Complexity

Compared with legacy NR UEs, RedCap UEs are less complex in terms of the number of transmit and receive antennas, duplex mode, bandwidth, maximum modulation order, maximum number of MIMO layers supported in the downlink, and UE capability, as shown in Table 4-1.

Table 4-1 Dimensions that reduce RedCap UE complexity

Dimension

RedCap UE

Legacy NR UE

Number of transmit and receive antennas

1T1R or 1T2R

1T2R, 1T4R, or 2T4R

Duplex mode

TDD frequency bands: only half-duplex mode

FDD frequency bands: half-duplex and full-duplex modes

TDD frequency bands: only half-duplex mode

FDD frequency bands: only full-duplex mode

Maximum bandwidth

FR1: 20 MHz

FR2: 100 MHz

FR1: 100 MHz per cell

FR2: 200 MHz per cell

Modulation scheme

64QAM or 256QAM

256QAM or 1024QAM

Maximum number of MIMO layers in the downlink

1 or 2

2 or 4

UE capabilities, including carrier aggregation (CA) and dual connectivity (DC)

Not supported

Supported

The following describes how tailoring these dimensions reduces the complexity of RedCap UEs.

  1. Reducing the number of UE’s receive antennas
    • In FR1, a legacy NR UE requires two or four receive antennas, while a RedCap UE requires only one or two.
    • In FR2, a legacy NR UE requires at least two receive antennas, while a RedCap UE requires only one.
  1. Adjusting the duplex mode

    The duplex mode of RedCap UEs is the same as that of legacy NR UEs in TDD frequency bands but not in FDD frequency bands. In FDD frequency bands, a legacy NR UE must work in full-duplex mode, and the UE requires a duplexer for simultaneous transmission and reception. In contrast, a RedCap UE can work in half-duplex mode and a duplex filter is not required at the RF end. A duplex is usually quite large, so removing it makes devices lighter.

  2. Reducing the maximum bandwidth supported by the UE

    Legacy NR UEs need to support 100 MHz in FR1 and 200 MHz in FR2. RedCap UEs support bandwidths of 20 MHz and 100 MHz, respectively.

  1. Lowering the modulation order

    Legacy NR UEs need to support at least 256QAM. RedCap UEs can use 64QAM, which is a simpler modulation mode and has lower requirements on RF and baseband.

  2. Reducing the maximum number of downlink MIMO layers supported by the UE

    The maximum number of downlink MIMO layers supported by a UE is less than or equal to the number of its receive antennas. Reducing the number of receive antennas in RedCap UEs also reduces the maximum number of downlink MIMO layers and the complexity of baseband signal processing.

  3. Reducing functions supported by UEs

    Considering the use cases and costs, 3GPP Release 17 explains that a RedCap UE can work only in one frequency band at a time and does not need to support carrier aggregation or dual connectivity.

The above methods are expected to reduce the 5G module cost of RedCap UEs by 60% to 70% compared with that of legacy NR UEs.

4.2 Reducing UE Power Consumption

Similar to legacy NR UEs, RedCap UEs adopt power saving technologies in the time, frequency, and space domains to reduce power consumption, as listed in Table 4-2.

Table 4-2 Power saving technologies used by RedCap UEs

Dimension

Related Technology

RedCap UE

Legacy NR UE

Time-domain power saving solutions

Discontinuous reception (DRX)

Supported

Supported

DRX + wake-up signal (WUS)

Supported

Supported

Cross-slot scheduling

Supported

Supported

UL skipping

Supported

Supported

Extended discontinuous reception (eDRX)

Supported

Supporteda

Frequency-domain power saving solutions

Bandwidth part (BWP) adaptation

Supported

Supported

SCell dormancy

Not supported

Supported

Reducing the number of SCCs

Not supported

Supported

Space-domain power saving solutions

Reducing the number of MIMO layers

Supported

Supported

BWP spatial adaptation

Supported

Supported

Other power saving solutions

RRC connection release of RRC_INACTIVE UEs

Supported

Supported

On-demand NR activation in NSA networking (SCG carrier addition policy)

Not supported

Supported

RRM measurement optimization

Supported in both connectedb and idle modes

Supported only in idle mode

a: Currently, eDRX is mainly used in IoT scenarios.

b: When a RedCap UE is in connected mode, the measurement relaxation condition can be determined only based on the data rate.

For details about the UE power saving technologies supported by both RedCap and legacy NR UEs, see UE Power Saving in the technology series. This document describes the eDRX UE power saving technology that is mainly used in IoT scenarios.

eDRX

A legacy NR UE uses DRX to periodically enter sleep mode and does not monitor the PDCCH. When the UE needs to monitor the PDCCH, it wakes up from sleep mode. This reduces the UE’s power consumption. The longer the UE is in sleep mode, the lower its power consumption, but also the longer its service transmission latency.

To adapt to IoT services that require low power consumption and are delay-insensitive, 3GPP Release 17 introduces eDRX based on DRX. eDRX extends the DRX paging cycle to minutes or hours, as shown in Figure 4-1. In an eDRX cycle, a UE stays in deep sleep mode for a long time, and monitors paging messages as it would in DRX mode but only within the paging time window (PTW). For details about DRX, see UE Power Saving in the technology series.

Figure 4-1 eDRX mechanism

5 Differences Between RedCap, LTE MTC, and NB-IoT

Table 5-1 lists the differences between RedCap, LTE MTC, and NB-IoT.

Table 5-1 Differences between RedCap, LTE MTC, and NB-IoT

Item

RedCap

LTE MTC

NB-IoT

Maximum bandwidth

20 MHz

1.4 MHz

180 kHz

TX/RX mode

1T1R or 1T2R

1T2R

1T1R

Maximum number of MIMO layers in the downlink

1 or 2

2

1

Modulation scheme

64QAM or 256QAM

16QAM

QPSK

Duplex mode

TDD frequency bands: only half-duplex mode

FDD frequency bands: half-duplex and full-duplex modes

TDD frequency bands: only half-duplex mode

FDD frequency bands: half-duplex and full-duplex modes

TDD frequency bands: not supported

FDD frequency bands: only half-duplex mode

 

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6 References

  1. 3GPP TR 38.875, Study on support of reduced capability NR devices (Release 17)
  2. 3GPP TR 22.832, Study on enhancements for cyber-physical control applications in vertical domains; Stage 1 (Release 17)
  3. 3GPP TS 22.104, Service requirements for cyber-physical control applications in vertical domains (Release 17)
  4. 3GPP TR 22.804, Study on Communication for Automation in Vertical Domains (Release 16)
  5. 3GPP TS 36.306, Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio access capabilities (Release 16)

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