What you’ll learn:
- Insight into 3GPP’s RedCap IoT devices.
- The benefits of using RedCap over traditional 5G devices.
- RedCap network deployment and migration.
It’s estimated that the number of connected IoT devices will reach nearly 39 billion by 2029, a significant increase over the number of expected smartphones at 7.7 billion. Both rely on wireless communication for network connections, placing the dependence on 5G as a necessity for both technologies.
Utilizing 5G for both ecosystems is an uphill battle, leaving little room for expansion while dealing with the throughput equivalent of a traffic jam. To help support the expected IoT device expansion, the 3rd Generation Partnership Project (3GPP), a conglomerate of developed protocols for mobile telecommunications, introduced RedCap 5G NR, a significant addition to the 5G family.
RedCap 5G NR, or reduced capability 5G NR, provides enhancements that allow for new classes of IoT devices to run on 5G networks. While the initial release of 5G targeted enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communication (uRLLC), and massive Machine Type Communication (mMTC), a solution was needed that could address devices falling outside of that protocol spectrum and handle the requirements of broadband IoT use cases with lower complexities and costs. In essence, this makes it possible for devices to operate more efficiently and use less bandwidth over traditional 5G devices.
How RedCap in Release 17 Surpasses Existing IoT Standards
RedCap technology was standardized in the 3GPP Release 17 and enables IoT devices, such as smartphones and modems, to utilize a subset of the capabilities of the 5G network to support applications that fall between the performance requirements of 5G and narrowband IoT (NB-IoT). It outperforms 5G eMBB in battery life and component costs and could be a viable alternative to a pair of 4G-based IoT standards, including LTE Category 1 through 4 and NB-IoT.
The RedCap Release 17 provides a number of benefits over existing IoT standards, which are listed below.
Reduced Device Cost and Complexity
Developing RedCap devices looks to provide lower-complexity alternatives over traditional IoT 5G NR devices, especially those that can be utilized by low-end LTE platforms. This includes reducing bill-of-materials (BOM) costs and hardware requirements while still retaining core functions.
RedCap devices are known for their limited capabilities, which land somewhere in the middle of the simplest and most advanced variants. The simplest “5G device” refers to a basic 5G NR device, such as a smartphone or modem, with only minimal capabilities that are mandatory to support the device. The simplest “RedCap device” corresponds to a basic RedCap device with only minimal capabilities that are enabled for it to function.
Of course, there’s the “most advanced RedCap device,” too, which translates to a RedCap device with the most advanced (but optional) capabilities that can be implemented.
They’re also the most constrained with limited bandwidth support, aren’t supported by major cellular carriers, and are restricted when it comes to networks' multiple-input, multiple-output (MIMO) layers and antenna branches. Complexity reduction techniques at the higher layers of the radio protocol will further streamline RedCap devices, including a drop in the maximum number of data radio bearers and sequence number length. But even with those reductions, peak data rates will remain unaffected while providing a balance between function and complexity.
Diverse Battery-Life Requirements
The key to extending the battery life for IoT devices can be done through a discontinuous reception (DRX) mechanism, which turns off its receiver circuitry over a period of time to save power. With 5G, this is done using a network that can configure DRX cycles from a few hundred milliseconds to up to 2.5 seconds, based on the downlink latency requirements.
Such a value range is extended by Release 17 via eDRX (extended-DRX), which provides up to around three hours for devices in radio resource control (RRC) Idle mode and 10 seconds while in RRC Inactive mode (see figure). The tradeoff when using eDRX is that it increases downlink latencies and devices won’t respond until the end of their sleep cycle, but in turn, extends battery life.
While that tradeoff may seem like a deal breaker, it's less critical for RedCap than other use cases, such as eMBB or URLLC, which require low latencies. What’s more, if there’s data activity in the uplink, the device can’t remain asleep, which reduces battery-life improvement with increased uplink transmissions.
To that end, the longer the eDRX sleep cycle, the greater the battery life is improved. For example, a two-hour eDRX cycle with reduced uplink data transmissions in a three-hour period could extend battery life by up to 80X versus not using eDRX.
Optimizing device and network performance requires a connection to base stations with a strong signal strength, which, in turn, needs frequent RRM mobility measurements. Reducing those measurements can also help to extend battery life. This can be accomplished via relaxed cell monitoring techniques based on device mobility and location within the cell.
Release 17 provides reduced relaxation scenarios for RedCap devices that can also help extend battery life. Combining eDRX with relaxed measurements in RRC Idle or RRC Inactive can push that battery life even further while still retaining specific use-case battery life requirements.
Network Deployment for RedCap Devices
When it comes to cellular networks, coverage for all devices is paramount. For those devices to have good coverage, they need to receive and transmit multiple data and control channels in both downlink and uplink.
In low- to mid-frequency bands (FR1), where RedCap devices feature reduced bandwidth and antenna branches, downlink performance can be negatively affected. Despite that impact, the RedCap devices should provide comparable coverage to typical 5G devices due to their enhanced downlink performance, meaning existing 5G networks shouldn’t need adjustments for deployment.
The same can be said for high-frequency bands (FR2), as RedCap devices maintain the same amount of receive antenna branches and provide similar coverage as traditional 5G devices. That said, RedCap devices may operate at a lower power class in FR2, which can affect the coverage of some uplink and downlink channels. However, those issues can be mitigated by utilizing conventional techniques such as retransmission.
Ensuring coverage while minimizing resource consumption for downlink transmissions is essential for efficient network scheduling. Identifying RedCap devices during initial access procedures allows for optimized resource allocation, meaning there’s a chance for the network to configure a RedCap device to identify itself in Message 1 of the random-access procedure.
For cellular networks, the frequency spectrum is a crucial resource for efficient data transmission. Base stations look to optimize data scheduling across different devices to maximize throughput and system capacity, a challenge primarily found in uplink scheduling due to contiguous frequency allocations. Moreover, the deployment of RedCap devices alongside typical 5G devices can lead to uplink resource fragmentation, which could have a negative impact on those 5G devices and their ability to utilize available bandwidth, transmission speeds, and peak data rates.
To overcome those issues, two mechanisms were introduced:
- First, networks can establish a RedCap-specific initial bandwidth part (BWP) positioned at the uplink frequency resource’s edge to free up contiguous resources for regular 5G devices. The RedCap-specific BWP, used briefly during initial access, can be configured without periodic downlink transmissions, thus minimizing signal overhead.
- Second, networks can turn off frequency hopping for all RedCap device transmissions to further reduce uplink resource fragmentation. While frequency hopping increases reception in challenging conditions, it may contribute to resource fragmentation when transmissions hop those frequencies. RedCap devices can deactivate resource hopping for all transmissions, which minimizes that fragmentation.
LTE-to-NR Migration for IoT Use Cases
3GPP’s introduction of RedCap devices in Release 17 aligns with low-end LTE devices, making them ideal as a replacement in future LTE-to-NR migrations. RedCap devices also feature hardware requirements similar to those of low-end LTE devices, enabling dual-mode devices to support both technologies.
What’s more, Release 18 will purportedly introduce a new RedCap device with a peak rate of around 10 Mb/s, catering to IoT use cases with reduced data-rate requirements. However, its complexity reduction is minimal compared to those introduced by Release 17.
In addition, Release 18 is expected to support RedCap devices with enhanced positioning support for location services for a myriad of IoT applications. By leveraging 5G NR’s broader frequency spectrum and deployment options, RedCap devices are set to enable IoT use cases in new scenarios where LTE-M/NB-IoT may lack support.
On the network end, support for RedCap devices could be introduced via software upgrades, minimizing the need for new hardware deployments. The devices will also inherit the spectrum-sharing techniques found with standard NR, allowing for different device types to share the same cellular carrier if needed.
3GPP’s Release 17 introduction marks a significant expansion to the 5G ecosystem, providing lower costs, reduced complexities, and increased battery life over traditional 5G NR devices. RedCap is designed to target IoT use cases that don’t require high-end capabilities while offering solutions that cater to market demand, including wearables, industrial sensors, low-end AR/VR headgear, and video surveillance applications.
These solutions are in a position to replace low-end LTE platforms in future LTE-to-NR migrations and are capable of serving as alternatives to LTE-M/NB-IoT frequency bands that lack support or product ecosystems. Release 18 aims to enhance support for RedCap devices even further with additional use cases and expansion into new market segments with minimal costs and hardware complexities.
Moreover, RedCap devices are engineered to coexist with other NR devices, leveraging the benefits of 5G NR, including wide frequency band support, low latencies, increased energy efficiencies and more.
