Since their introduction in the late 1970’s, cellular networks and technology have evolved tremendously, with successive generations (2G through 4G) representing significant milestones in the development of mobile connectivity. 5G, the latest incarnation, represents a step-change in performance over 4G, with throughputs of up to 10 Gbps (100 times faster than 4G networks) that aim to satisfy the growing hunger for bandwidth.
Along with the major jump in bandwidth, 5G offers latencies of 1 msec (compared that with 30 to 50 msec for 4G) that enable near-real time response rates, and connection densities of 1000 devices per square kilometer (100 times more than 4G) that can support the growing numbers of IoT devices and sensors.
Carriers are now sunsetting support for the older technologies. 2G, in particular, presents a security risk. It’s a lot like connecting to a WEP-secured Wi-Fi hotspot; the security is obsolete, so it’s easy to crack. In the U.S., carriers shut down 2G years ago, and the 3G shutdown is already underway. What does this mean for the cellular Internet of Things (IoT) — those devices and sensors that connect to the internet over a cellular network?
With 2G- and 3G- phaseout accelerating globally, two new technologies have emerged as viable migration paths. First up is Long-Term Evolution for Machines (LTE-M), a low-power, wide-area technology (LPWAN) that supports IoT through lower device complexity and provides extended coverage while allowing the reuse of the LTE installed base (which includes 2G, 3G and 4G). The second contender is Narrow Band Internet of Things (NB-IoT), a standards-based low-power, wide-area technology developed to enable a wide range of new IoT devices and services.
LTE-M and NB-IoT are positioned as future-proof alternatives for cellular IoT since both technologies deliver LPWAN benefits of enhanced coverage, longer battery life and reduced costs compared to previous cellular generations. But LTE-M and NB-IoT are not created equal; there are some distinct differences to consider when deciding between the two for your IoT or M2M application. In general, LTE-M can address most if not all NB-IoT use cases, but the opposite is not true.
There are five technology implications to factor into your connectivity strategy:
1. Is roaming a requirement?
LTE-M and NB-IoT are relatively new technologies for which dedicated roaming agreements are not yet widely in place among network operators. However, LTE-M roaming is possible over traditional 4G infrastructure (if the mobile operator already supports LTE-M in its network architecture), which can make it the best option in certain situations. For example, with the right IoT SIM, LTE-M modems can piggyback on existing national and global 4G roaming agreements to enable multi-network LTE-M connection in a wide range of countries worldwide.
This brings two important LTE-M benefits for IoT businesses:
- Improved coverage and service availability within a country
- Reduced complexity with a single SIM for cross-border network service
NB-IoT roaming, meanwhile, is limited to those areas where there are official agreements between network operators, and few are currently in place. There are many reasons for this, one of which is that operators have yet to work out their respective NB-IoT charging models, given the very low data consumption typically associated with IoT devices.
Another consideration: NB-IoT features like Power Save Mode (PSM) and Extended Discontinuous Reception (eDRX) have not been consistently deployed, which can lead to roaming issues when a device moves from a network with PSM to one where it is not available. Due to limited NB-IoT roaming, you will likely need separate operator contracts and SIMs if devices are distributed globally and are bound to one operator’s service within each country.
2. Determine your bandwidth and latency requirements
A low data rate may be sufficient for your use case today, but will this change over the next few years as your IoT solution evolves and new customer requirements come into play? Changing the connectivity module down the road is not only cost- and labor-intensive but also requires re-certification of devices
LTE-M boasts the highest bandwidth and data rate of all existing LPWAN technologies, which means it supports evolving device capabilities. Similarly, LTE-M delivers extremely low latency. Taking a long-term view of your evolving bandwidth requirements will help future-proof your solution.
3. Mobile applications require special consideration
For mobile use cases, LTE-M and NB-IoT differ in their ability to support cell handover. Handover (or handoff) is the technique that ensures the device remains attached to the network and data transmission is maintained as the service moves from one cell to another.
NB-IoT is not capable of handover; devices need to re-register with the network every time they move to a new cell, which consumes extra power and causes intermittent disconnections. Furthermore, cell re-selection happens only after the device has been completely disconnected from the last cell location. As it moves further away from a cell tower, the device will increase transmission output power (Tx) until the connection is lost, adding to overall power consumption.
With its excellent handover support, an LTE-M device can seamlessly switch to a new cell tower as soon as it is within proximity while staying attached to the network. LTE-M is therefore far more power-efficient and thus the better choice for use cases like asset tracking or fleet management.
4. Power consumption
LTE-M has (falsely) earned the reputation as the more power-hungry of the two technologies. Looking at this more closely, these factors emerge as key determinants:
- Transmission current (active mode)
- Sleep mode and idle mode current (with PSM and eDRX)
- Transmission time of each message (i.e., device wake-up time)
In dual modems, power usage during PSM and eDRX is around the same for each technology. Additionally, while the average transmission current of LTE-M is slightly higher than that of NB-IoT, this is somewhat mitigated by the significant difference in transmission time. In general, reduced transmission time improves battery life as devices can fall back to sleep mode faster to save power.
For use cases that require transmission of minimal data, NB-IoT conserves more energy due to the lower transmission current. Yet, when it comes to medium-sized messages like firmware updates, an NB-IoT transmission can last for minutes due to the low data rate, which consumes a lot of energy. Conversely, the higher bandwidth of LTE-M allows more data to be sent much faster, making it more power-efficient in medium-throughput applications.
5. SMS requirements
SMS is often used for remote IoT device configuration, device reboot, or getting specific device information. In certain scenarios, SMS is used for over-the-air SIM configuration. According to GSMA, SMS is not included as a key minimum feature for NB-IoT, and very few operators have so far deployed the technology with SMS support. Conversely, there is a clear consensus that SMS will be deployed in global LTE-M deployments — consistent with legacy 4G networks. If SMS is integral to your use case, you are better off using an LTE-M or a duo modem.
Summary
While the low-cost benefits of NB-IoT make it attractive compared to LTE-M, these come at the expense of other network functionalities. Eventually, it all boils down to your device requirements and your specific use case. Given that both technologies are still under roll-out and not yet available in all countries, fallback to older and more widely deployed cellular technologies may still need to be part of your IoT solution.
The move away from legacy technologies will undoubtedly be a significant transition for many IoT and M2M companies, because 2G and 3G connectivity is still the most used technologies for deployed devices. For the geographic updates on 2G sunsetting, consult our global 2G phase-out list.
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