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.

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.

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%.

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.

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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

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.

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