What is 5G RedCap, and can it save cellular IoT?

Regardless, in theory the latest version of the 5G New Radio (NR) standard has finally addressed the issue of cellular-based sensor communications, resulting in a stripped-down version of 5G for large-scale IoT deployments. But in reality, the news simply confirms an upcoming waypoint, pointing to a commercial path by 2024, with existing LTE-based massive machine-type communications (mMTC) migrating to a single 5G-based network.

The bigger question is, will it save the cellular-based IoT as a commercially viable technology that brings about massive industrial change? Because (if one thing is clear), of all the hype about future technologies that will save the planet, none has had longer-lasting promise and greater hype than the IoT — and the cellular market has been a bit of a mess so far, though more non-cellular operators have gotten in on the action, and they have the power to do so.

Release 17 standards, frozen in June, included a provision to allow IoT sensors to connect to 5G and significantly reduce the network (and therefore the hardware and cost pegged to it). This new specification, called Reduced Capability (RedCap; previously “NR-light” and its variants, in 3GPP work items), tentatively sits at a 5G NR power level between mMTC and eMBB.

But before we make more comments and quibble over details, we should review that the 17th version of the standard, which was frozen in June, included provisions for connecting IoT sensors to 5G, which significantly reduced network capabilities - and therefore reduced related hardware costs. This new specification is called RedCap (Reduced Capability). It is a new technology standard protocol specially launched by 3GPP in the 5G R17 stage for 5G application scenarios with low speed and latency requirements. It aims to comprehensively improve the quality and coverage of 5G networks, and can also be understood as "lightweight 5G".

To add context; it’s two rungs below URLLC that offer the most exciting view of IoT communications in this 3GPP ladder – indeed, it’s most commonly found as three points in the 5G NR family. The problem with these three types of specifications, however, is that only two are 5G native. The dual low-power wide-area (LPWA) technologies that underpin the massive (machine type) IoT segment, mMTC, are based on LTE, albeit compatible with 5G NR radios.

Only these technologies, ultra-low-power NB-IoT and 2G/3G-like LTE-M, can support lean, cheap, long-lived, ultra-large-scale IoT. So for now and the future, cellular IoT needs LTE to win over traditional IoT — and it competes with entrenched non-cellular standards like LoRaWAN in unlicensed bands. But RedCap promises to solve this problem — in some places, just like cellular networks.

On the surface, RedCap is designed to turn this familiar 5G NR family technology triangle into a Venn diagram (see above), overlapping with the other three operating scenarios. This is actually Ericsson's diagram, from an article about the new NR release. In terms of capabilities, it should be plugging a hole. Ericsson commented: "RedCap is positioned to address use cases that are not optimally served today using eMBB, URLLC or LPWA (mMTC over LTE) solutions."

RedCap is positioned as “lower than eMBB… but higher than LPWA,” it wrote in a blog post. Huawei says the same. Elsewhere, Qualcomm positions RedCap between mission-critical IoT (see figure below), currently served by consumer-like NR-based eMBB but soon to be served by developing URLLC provisions, and massive IoT (served by non-NR NB-IoT or non-cellular LPWA technologies such as LTE-M or LoRaWAN).

Analyst firm Omdia calls RedCap “the missing piece of the 5G IoT puzzle.” But operationally it’s closest to LTE-M (see Qualcomm chart below), described by Omdia as “the most popular and widely used cellular IoT standard,” and therefore closest to 2G/3G, still used for traditional cellular M2M devices. Of course, many of the use cases sound the same: the standard 3GPP product line is about industrial sensing, video surveillance, and wearable technology.

“In some ways, 5G RedCap attempts to address the needs currently met by LTE-M [Cat 1 to Cat 4],” Telit wrote in a blog post. “It is a lightweight version of the 5G standard. 5G RedCap is designed for use cases that do not require ultra-low latency but do require reasonable throughput to ensure data flows that support next-generation applications. It is expected to be used in wireless industrial sensors, video surveillance, and smart wearable technology.”

Omdia suggests that LTE-M-class pricing for NR-based IoT gadetry to serve similar mid-level IoT use cases is just the cellular industry’s ticket to continued development of massive sensor networks. It notes a 10x (1000%) difference between LTE-M and eMBB module costs, which, as of now, range from $30 to $300 per unit, respectively; and that, to date, there is no NR provision for such “mid-speed (IoT) applications.”

“The price gap between 4G and 5G modules is one of the fundamental factors – if not the most critical factor – that will continue to limit the adoption of 5G in IoT applications… In order to close the price gap… it is necessary to develop a 5G standard with fewer features and less hardware complexity.” RedCap is the answer. “Without RedCap, 5G NR lacks a key technology for IoT.”

Qualcomm also talks about “applications in smart grids, environmental sensors, predictive maintenance, utility meters, high-resolution monitoring, etc.” This sounds very LPWA, actually—perhaps even more NB-IoT and LoRaWAN than LTE-M. Still, the discussion of its near-term (post-2024) use cases is all about filling in the technology/application gaps; Huawei, for example, mentions “middle-tier applications…with capabilities that fall between these extremes.”

Ericsson does a good job of wrapping itself around what RedCap gave up: for example, bandwidth requirements were reduced to 20 MHz and 100 MHz in frequency range 1 (FR1; 4.1 GHz to 7.125 GHz) and FR2 (24.25 GHz to 52.6 GHz); the number of “receive branches” was reduced, which also means fewer receive antennas; and the maximum number of downlink MIMO layers, which is equal to the number of receive branches, was also reduced.

There are other innovations that make 5G useful for low-power IoT sensor applications, notably more flexibility in modulation order, duplex operation/support. Ericsson writes: “Substantial cost and complexity reductions can be achieved… establishing RedCap as a distinct equipment segment from eMBB or [URLLC].” The result is reduced equipment complexity, which reduces costs, extends longevity, and has enough capacity to do most IoT work.

But the information about the missing patch could be considered a smokescreen; from a technology perspective, most industrial IoT applications associated with RedCap are well served by LPWA network solutions using NB-IoT, LTE-M or LoRaWAN, or Sigfox or MIOTY (TS-UNB), or whatever. The 2024 timeframe for the release of Class 17 RedCap-equipped IoT devices also gives wiggle room to the rest of the market.

With key RedCap advances — including higher transmission rates, advanced positioning, “sidelink” near-field communications, and even support for unlicensed spectrum — defined only in Release 18 (see Qualcomm graphic below), which will be available in the second half of the decade, the IoT game for the cellular crowd is still a long way off. The big driver in the short term (2024) is that industrial companies, including those deploying private 5G, will be able to go two-for-one on IoT networks.

Omdia explains: “Enterprises looking to deploy a mix of… high- and medium-speed devices must deploy two [5G and 4G/LTE] standalone networks… incurring additional cost and complexity. There is no upgrade path to 5G NR for existing… [LTE-M] devices. This issue is not a major concern as most operators have no immediate plans to retire 4G networks. However, this issue will become a more critical factor in a few years.”

However, as Omdia points out above, RedCap’s real motivation is to migrate new and legacy M2M/IoT contracts to 5G NR in time for the sunsetting of LTE and the subsequent NB-IoT and LTE-M. Qualcomm said: “As the evolution of 5G continues, there will inevitably be a moment in the future when communications service providers begin the migration from 4G to 5G. With this in mind, 5G NR-Light becomes the platform of choice for new mid-range IoT designs for the future.”

Or does it? It sounds like a long way off — like another futuristic technology without an ecosystem, or an easy sales pitch, and a track record that doesn’t inspire much optimism.