Cellular IoT: Status of LTE CAT 1bis

Global Trends in Cellular IoT: The Rising Significance of LTE CAT 1bis

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By JJ DeLisle for Mouser Electronics

Published March 11, 2024

Wireless networking technologies constantly adapt to growing demands from both consumer and professional applications. Many of these are focused on or otherwise support Internet of Things (IoT) devices and features, ranging from smart home to industrial to military/aerospace applications. This includes deploying and adopting smart home interoperability standards like Matter, new automotive standards like ultra-wideband (UWB), and further developing LTE variants and non-cellular low-power wide area network (LPWA/LPWAN) technologies. Where wireless networking standards (e.g., Wi-Fi^®, Bluetooth^®, Thread) and proprietary standards such as Sigfox and LoRaWAN are well suited to local applications and areas that support proprietary wireless infrastructure, navigating cellular LPWA/LPWAN standards is more complicated.

This article delves into several aspects of cellular LPWA/LPWAN technologies, global trends, and other factors impacting cellular IoT. Furthermore, this article discusses the value of LTE CAT 1bis for cellular IoT applications and how it is a viable alternative to narrow-band IoT (NB-IoT) and LTE-M for many applications.

LPWA/LPWAN Tech: Navigating Regional Preferences

LPWA/LPWAN standards are rapidly becoming the backbone of mobility and dispersed IoT applications and will continue to play a significant role in IoT adoption and development. However, the shifting landscape of global factors has muddied the waters of the best approaches to building out LPWA/LPWAN IoT technologies. The past several years have seen intense debate and disharmony around cellular LPWA/LPWAN standards, namely between NB-IoT and LTE-M. As it turns out, most of the Asian-Pacific (APAC) and Europe, the Middle East, and Africa (EMEA) regions opted for NB-IoT implementations. In contrast, the Americas and Australia opted for LTE-M. Both competing technologies were rapidly deployed in their regions with minimal support initially available for both standards in any area (Figure 1). This divergence has led to backtracking and changes in the support and service coverage for these LPWA/LPWAN over the past few years since the 3GPP Rel 13 release.

Figure 1: Map of LTE-M and NB-IoT implementations worldwide. (Source: GSMA IoT^[1])

To further the complexity of the situation, 2G and 3G support is being eliminated in most countries, meaning that IoT developers need to rapidly adapt the 4G LTE and 5G technologies to replace legacy systems and capitalize on new market opportunities. Moreover, NB-IoT and LTE-M exhibit significantly different characteristics. LTE-M has slightly better data rates than NB-IoT and supports mobility handovers and voice, whereas NB-IoT exhibits better maximum coupling loss. LTE-M is suitable for most IoT use cases, whereas NB-IoT is more limited. This means there are areas in APAC and EMEA with limited cellular LPWA/LPWAN support for various IoT use cases. Specifically in Europe, many IoT developers rely on 2G fallback for their nominally LTE-M-based devices.

A legacy solution to this problem is LTE CAT 1, one of the lowest-cost 4G cellular options with global coverage. Nevertheless, LTE CAT 1 chipsets are a substantial premium over NB-IoT or LTE-M chipsets. Moreover, LTE CAT 1 devices require receiver (Rx) diversity, two antennas, and associated RF hardware. This increased complexity and component count are predominately why LTE CAT 1 exceeds NB-IoT and LTE-M in total cost. LTE CAT 1 has been a viable option since 3GPP Release 8 in 2008 for many IoT applications requiring higher bandwidths and throughput and can handle higher power usage.

LTE CAT 1bis vs. NB-IoT/LTE-M

NB-IoT is limited to a 200kbps peak downlink rate and 250kbps peak uplink rate, so NB-IoT is designed for fixed deployments. However, in practice, these rates are closer to 26kbps and 66kbps, respectively. LTE-M can handle mobile links to a maximum of 1Mbps uplink and downlink (Table 1). LTE CAT 1 is designed for a peak downlink rate of 10Mbps and peak uplink rate of 5Mbps, making LTE CAT 1 much more suited to high throughput IoT applications, such as security, monitoring, automation control, complex sensing applications, and high fidelity and high data rate sensing. LTE CAT 1 is also available anywhere 4G LTE networks are available, which is essentially global. However, it still may not cover some rural regions of the world with 2G/3G coverage (though this will soon become unavailable).

Table 1: Comparison of LTE CAT 1/LTE CAT 1bis, LTE-M, and NB-IoT

Though LTE CAT 1 was originally created for emerging IoT applications of the time, LTE-M and NB-IoT were designed to fill gaps left by the complexity, power consumption, and cost of LTE CAT 1 (but weren't evident until years later). Namely, LTE-M and NB-IoT modules are much more power efficient, with substantially extended battery lifetimes over LTE CAT 1, and the lower complexity of these cellular IoT modules compared to LTE CAT 1 modules means that they are typically more compact. A smaller battery, fewer thermal management requirements, and a smaller chipset or module mean that LTE-M and NB-IoT devices can be much more compact. This compactness and better power efficiency mean that LTE-M and NB-IoT devices are more suited to distributed machine-to-machine networks with low data rate requirements but might be quite numerous. This level of device density and power efficiency wasn't an application that was as apparent in the late 2000s as it was in the mid-2010s.

However, the wide divergence and spotty deployments of LTE-M and NB-IoT across many regions mean there is a coverage gap to consider on top of other technical cellular IoT device considerations. LTE-M and NB-IoT also require that network operators develop and deploy software support for these standards, where LTE CAT 1 has been supported for some time.

Fortunately, there is a bridge between LTE-M and NB-IoT in terms of complexity, power consumption, and size: LTE CAT 1bis. In most ways, LTE CAT 1 and LTE CAT 1bis are identical standards; they have the same peak data rates, bandwidths, duplex mode, transmission power, voice support, and power save features like extended discontinuous reception/power-saving mode (eDRX/PSM). With 3GPP Release 13 (Rel-13), LTE CAT 1bis was detailed with only needing a single Rx antenna and RF path, which is the major difference between LTE CAT 1 and LTE CAT 1bis. This means that unlike LTE CAT 1, LTE CAT 1bis RF requirements are roughly the same as LTE-M and NB-IoT. Moreover, requiring only a single antenna and RF path means that LTE CAT 1bis modules are similar in size to LTE-M and NB-IoT modules.

Additionally, LTE CAT 1bis chipsets and modules are less expensive than LTE CAT 1 chipsets and modules and are closer in cost to LTE-M and NB-IoT modules. This is because the half-duplex architecture of the LTE CAT 1bis Rx signal chain does not usually require additional filtering in the RF front end, which helps to make LTE CAT 1bis chipsets/modules more cost-competitive and accessible for areas that face inadequate LTE-M and NB-IoT coverage.

A trade-off of having only a single antenna and RF path means that LTE CAT 1bis sacrifices receiver diversity and loses 3dB or more of maximum coupling loss compared to LTE CAT 1. This loss results in Rx signal strengths that are marginally lower than those of LTE CAT 1 but much more than those of NB-IoT and LTE-M. This means that LTE CAT 1bis will theoretically have a lower operating range than other contemporary cellular IoT standards.

As obsolescence is an issue with 2G/3G devices, it is also a concern with LTE devices that may go obsolete as 5G deployments expand. However, obsolescence is not a concern with LTE CAT 1bis devices, and 3GPP Release 15 defined an option allowing for upgraded LTE devices (eLTE) to connect to a 5GC network with upgraded eLTE NB (eNB). This helps to ensure service continuity for LTE CAT 1bis devices even if 4G core networks are phased out and lowers the risk to cellular IoT developers and IoT network deployers using LTE CAT 1bis.

Generally, LTE CAT 1bis provides the following strengths:

• Peak download rate of approximately 10Mbps and upload rate of 5 Mbps—the same as LTE CAT 1 and greater than LTE-M/NB-IoT
• Less power consumption than LTE CAT 1 (but more than LTE-M/NB-IoT)
• Less complexity than LTE CAT 1 (but more than LTE-M/NB-IoT)
• Support for mobility applications
• Low obsolescence concerns due to being “baked” into 5G standards as eLTE
• Fills the gap for many applications that need compact and low-cost modules with higher data rates than LTE-M/NB-IoT can offer
• Requires no substantial software upgrades to 4G LTE systems to function, enabling it to work in areas that don’t support LTE-M/NB-IoT

LTE CAT 1bis In Action

The enhanced data rate of LTE CAT 1bis compared to LTE-M and NB-IoT means it is ideal for a wide range of contemporary applications and use cases. LTE CAT 1bis is likely the only choice for critical smart commercial building and industrial facility cellular IoT. This includes buildings with substantial amounts of automation and continuous or near-continuous monitoring of automated systems, such as automated production/processing, shipping/receiving/logistics systems, and even autonomous mobile robotic (AMR) systems.

Smart city applications with data-intensive smart features, like interactive kiosks, ATMs, digital signage, e-bike/e-scooter (urban mobility) systems, and vehicle-to-infrastructure (V2I) systems are another clear opportunity for LTE CAT 1bis technologies. Fleet management systems that include transportation and telematics features, one of the fastest areas of growth for IoT, can also be served by LTE CAT 1bis technologies.

Conclusion

Developers of LTE-M and NB-IoT cellular IoT devices must face fractured coverage in many regions around the globe. LTE CAT 1bis has the potential to serve as a reliable choice for IoT developers looking to support cellular IoT applications that may soon desperately require coverage as 2G/3G technologies are phased out.

Sources

[1]

“Mobile IOT Deployment Map,” GSM Association, September 5, 2023, https://www.gsma.com/iot/deployment-map/.