02 Mar 2023
An option for Low Power Wide Area (LPWA) applications
The IoT ecosystem is experiencing a revolutionary phase. Most MNOs have announced or even executed the switch-off of legacy 2G and 3G cellular technologies, migrating the related frequencies to 4G or 5G networks. As a result, IoT developers must also adopt a new cellular standard. Although 5G is already under deployment, its use faces several challenges. Besides coverage issues, current 5G networks do not fit most IoT requirements: power consumption, cost, and design complexity (problems that 5G RC and MMTC will address in the future), to mention some. Therefore, 4G LTE is the only cellular technology sustaining global coverage and will take this role for at least the next five years.
In 2016, 3GPP Rel 13 specified new 4G cellular standards for the IoT. The aim was to compete with non-cellular Low Power Wide Area (LPWA) technologies, like SigFox or LoRaWAN. Thus, the new cellular standards that 3GPP launched were NB-IoT (aka LTE Cat-NB), LTE-M (aka LTE Cat-M), and LTE Cat 1bis (3GPP Rel 8 had already specified the standard LTE Cat 1).
Following 3GPP Rel 13, MNOs and chip manufacturers focused on NB-IoT and LTE-M, leaving aside LTE Cat 1bis. The reason behind this decision was because, comparing specs, the Cat 1bis pros/cons ratio was less favorable than the other two.
An intense debate arose around the new proposed cellular LPWA technologies for the IoT. One side pushed toward using NB-IoT, whereas the other toward LTE-M. In the past, countries agreed upon deployed technology, supported bands, and roaming agreements. And apart from a few exceptions like IMT-2000’s early rollout in Japan or the initial deployment of CDMA/EV-DO in North America before converging to UMTS/HSPA, the world was under global convergence. But more recently, that convergence was left out of the picture. APAC and most of EMEA chose NB-IoT implementations, while the Americas and Australia chose LTE-M.
The divergence created a bipolar world. China pushed hard for NB-IoT; indeed, China is the only country where NB-IoT has had a massive deployment. North America, on the other hand, deployed LTE-M quickly. Today, it dominates most of this market, although some MNOs have added NB-IoT support over the years. EMEA’s case is peculiar. Initially, it opted for NB-IoT. Later on, however, most MNOs in Western European countries also added LTE-M support.
While LTE-M characteristics fit most IoT requirements, this is not true for NB-IoT. Even if NB-IoT has better MCL (Maximum Coupling Loss) than LTE-M, its data rate is limited. In addition, the design of NB-IoT infrastructure does not support mobility (handover) and voice.
In the current scenario, we find regions where IoT applications benefit from excellent LTE-M coverage (like North America), whereas in others, it is partially or entirely absent. When the latter situation happens, NB-IoT cannot satisfy most use cases due to the abovementioned limitations.
In Europe, many IoT applications still connect to legacy 2G (where available). Customers ask for LPWA modules with 2G fallback because LTE-M coverage is unreliable and, in worst cases, absent. NB-IoT capabilities do not fulfill use case demands.
Until recently, LTE Cat 1 was the lowest-cost 4G cellular technology with global coverage. However, a disadvantage is that LTE Cat 1 chipsets cost much more than those for NB-IoT or LTE-M. Moreover, compared with LTE-M and NB-IoT, an LTE Cat 1 design is more complex and requires additional components, significantly impacting the total cost.
This situation has led IoT developers and MNOs to search for cost-effective alternatives and thus guarantee LPWA worldwide connectivity, mobility, and roaming for the IoT ecosystem—the result is a renewed interest in LTE Cat 1bis.
In a nutshell, LTE Cat 1bis is LTE Cat 1 with a single receive (Rx) antenna. All the other device characteristics, like uplink (UL) / downlink (DL) data rates and protocols, remain the same. On the contrary, standard LTE Cat 1 (3GPP Rel 8) supports Rx diversity. It thus requires two Rx vias.
Rx diversity improves RF reception capabilities, especially at the edge of the cell. But to support RX diversity, the LTE Cat 1 chipsets require two RF inputs with a sophisticated RF front-end and specific software. To some extent, this is why LTE Cat 1 chipsets cost more than those for LTE-M and NB-IoT. Consequently, LTE Cat 1 applications require more elaborated and extensive PCBs, additional components, and two antennas. All these features result in higher costs: an LTE Cat 1 solution could cost twice the corresponding LTE-M version.
On the other hand, removing the Rx diversity feature from the LTE Cat 1bis standard enables simpler and cost-optimized chipset designs. Developers leverage this to design simpler, smaller, and cheaper IoT applications than they could with the standard LTE Cat 1.
When comparing LTE-M and LTE Cat 1bis, LTE-M stands out due to several characteristics, making it the obvious choice for IoT applications in most use cases. Some of these are:
• Power consumption: LTE-M supports low-power modes like PSM and eDRX. It thus ensures a longer battery lifespan.
• Link budget: LTE-M has MCL (Maximum Coupling Loss) of -154 dBm vs. -149 dBm of LTE Cat 1. LTE Cat 1bis loses an additional 3-4 dB compared with Cat 1 due to the loss of the RX diversity antenna. This means that LTE Cat 1bis’ MCL is 8-9 dBm worse than LTE-M. The higher MCL of LTE-M ensures a better capability to keep connections active in poor signal conditions, like in harsh urban environments, garages, or at the edge of the cell. In addition, LTE-M is more robust for applications that stay in the field for prolonged periods, during which the network conditions are subject to change.
• Total solution cost: An LTE-M application costs half of what an equivalent would cost based on LTE Cat 1; LTE Cat 1bis reduces this gap, and in fact, in some situations, the difference is not significant.
• 5G compatibility: LTE-M and NB-IoT standards are already under the 5G umbrella. 5G networks will support them in the future, making them future-proof. This does not apply to LTE Cat 1 and 1bis, as they will disappear along with 4G networks.
LTE Cat 1bis outperforms LTE-M in characteristics like latency and data rate, but most use cases do not require these in the range of several Mbps.
To summarize, LTE-M meets the requirements of most IoT use cases previously powered by 2G and 3G technologies: medium bandwidth, low power consumption, and low cost, to cite some of them. It also improves MCL, ensuring deep building penetration.
Why consider LTE Cat 1bis as an LPWA alternative now? What driving factors could lead IoT developers to ponder LTE Cat 1bis as an LPWA option? We must consider the specific use case, price gap, and status of LPWA global deployments to answer these questions. When choosing the proper communication technology, four considerations are at stake. The following concise list summarizes them, although by no means is exhaustive:
• The amount of transmitted data and the impact on the battery
• Network coverage and availability
• Service lifespan
• Device size
LTE-M perfectly fits IoT applications requiring low and medium data rates by providing 375kb / 1Mb Downlink/Uplink capability, a simplified modulation scheme, and improved MCL. eDRX and PSM, innovative power-efficient modes, provide extended battery life that LTE Cat 1/1bis cannot match.
Nevertheless, we must consider that other IoT applications like video surveillance, alarm systems with video, or eHealth, produce considerable data volume. These use cases could leverage LTE Cat 1bis bandwidth.
With more bandwidth, devices transmit data faster. This translates into less time in the air and, consequently, less battery usage. Depending on the amount of data, a faster transmission implies staying in the air for less time, leading to better power efficiency. But this will only happen if the available bandwidth is limited compared to the data volume.
For applications that do not rely on a battery or can easily/frequently be plugged in, LTE Cat 1bis higher power consumption may be acceptable. A lower price gap and faster data rates could be fair reasons to choose LTE Cat 1bis over LTE-M.
The global portability that legacy 2G and 3G technologies ensured is ending due to the cellular standards’ sunset occurring in several countries. The lack of LPWA deployment coordination provoked a peculiar world situation. APAC and most Eastern European countries have only NB-IoT coverage, whereas the Americas, Australia, and a few European countries have both NB-IoT and LTE-M. Although in this latter case, the coverage faces several obstacles. 4G LTE is present in most African countries where neither NB-IoT nor LTE-M has been deployed. The exception to the rule is South Africa, where NB-IoT is currently active.
Implementing two standards, at first NB-IoT and later LTE-M, makes the situation in Western Europe challenging. Consider Italy as an example, although this applies to other Western European countries as well. Italian MNOs, like most European MNOs, initially deployed NB-IoT. But in recent times, Vodafone Italy added LTE-M support (2022). This does not necessarily mean that LTE-M is available everywhere, especially considering that the NB-IoT coverage is not comprehensive. So even if LTE-M is available, Italy’s territory lacks full coverage, without certainty on when this will occur.
Examples like this could push IoT developers to consider LTE Cat 1bis a valid LPWA option. Because even if they can rely on 2G today, an unclear commitment to keep it functioning beyond 2025 prevails.
One considerable advantage of LTE-M over LTE Cat 1 and 1bis is that the former belongs to the 5G spec. Being LTE-M forward-compatible with 5G networks means that some IoT applications could stay in the field for years. They could be deployed remotely or in locations without easy access (like in-house meters). For those use cases, LTE-M is the only future-proof choice. On the contrary, LTE Cat 1bis support will remain as long as the 4G network is in place (at least up to 2030).
LTE Cat 1bis is a valid LPWA alternative to ensure connectivity in the next few years. IoT developers should consider it for applications with a short or medium life span (compared to the 4G network’s sunset) and a reduced price gap. But it would be wise to keep an eye on LTE-M for a next-generation design, waiting for its full deployment. LTE Cat 1bis is the only choice for mobile applications traveling through countries with different LPWA deployed technologies (for instance, between Western and Eastern Europe).
Developers find it hard to address some use cases, even considering the current miniaturization of electronic components. This problematic situation impacts more LTE Cat 1 than LTE-M due to its RX Diversity support and the need for a dual-antenna design. For instance, LTE Cat 1 adapts well to the wearable market. LTE Cat 1, in fact, offers a good balance between enough bandwidth, coverage, and power consumption‒exactly what these devices need.
The fact that designers aim for small solutions forces them to find the equilibrium between performance and size. Thus, often they do not implement the RX Diversity line and remove the second antenna from the design.
With its simplified antenna, shorter parts list, and more affordability (compared with LTE Cat 1), LTE Cat 1bis can also replace LTE Cat 1. This applies well to size-constrained applications with better cost structures, nonetheless providing similar performance.
In light of 2G and 3G decommission already initiated (or completed) in most countries, and according to experts, LTE-M is in pole position to become the most suitable cellular LPWA technology for the Internet of Things.
Due to the NB-IoT limitations, experts are not surprised that APAC and EU experience an LTE Cat 1bis demand growth. Yet, paradoxically, these same areas initially deployed NB-IoT. To discover later that most mobile IoT applications kept using legacy 2G/3G whenever possible to ensure stable connectivity, mobility, and roaming. The only exception was China, where regulations drove migration.
u-blox offers a broad portfolio, including LTE-M, LTE Cat 4, LTE Cat 1, and LTE Cat 1bis modules. With a well-established market leadership based on the first certified LTE-M module series, SARA-R4, u-blox also developed its LTE-M chipset: the UBX-R5. This chipset has been used as a foundation of the u-blox SARA-R5 secure family, also embedding a secure element.
For LTE Cat 1, u-blox offers the LARA-R6 modules supporting full Rx diversity and the LENA-R8 series for LTE Cat 1bis. LENA-R8 is also available as a combo: LTE Cat 1bis + GNSS variant. The GNSS core is the new u-blox M10 GNSS platform. The LENA-R8 combo (LENA-R8M10) has two power supplies, providing customers with excellent power management flexibility. And thus, optimizing the overall performance.
u-blox does not see LTE Cat 1bis as a competitor but rather as an LTE-M complement within the cellular LPWA ecosystem. Wherever regions have deployed the LTE-M network, it can fulfill most IoT use cases. However, this does not apply in cases requiring increased bandwidth/speed, where LTE Cat1 bis or even LTE Cat 1/Cat 4 stand out as a better solution.
Senior Product Marketing Manager Cellular