Know the risks in your use case before choosing a cellular LPWAN
Picking the right cellular low-power wide area technology for an IoT deployment can be a challenge. While you are looking for the right fit for your use case, you must bypass the technology push. If you know what to look for, you’ll see the subtle differences and their advantages to your case.
LTE-M and Narrowband-IoT (NB-IoT) are types of cellular connectivity intended to save power consumption. Both technologies tweak various network parameters in favor of power consumption, but both come with a sacrifice in latency and speed.
This concept remains when comparing LTE-M and NB-IoT among themselves. In the Narrowband-IoT standard, parameters are tweaked even further in favor of power consumption. But this comes at a disadvantage for power-efficient communication when the cellular modem moves.
Devices on the move? No NB-IoT
There are two major reasons why NB-IoT is not right for mobile IoT use cases:
- It does not support roaming
- It does not support handovers between cells
Roaming might not be an issue for every use case. If you deploy your assets in the U.S., for example, the lack of roaming functionalities is generally not an issue. But if you deploy GPS trackers in Europe, chances are that a vehicle will cross a geographical border many times a day.
Deutsche Telekom and Vodafone completed successful roaming tests on both networks. Although this is a promising accomplishment, we are far from publicly available roaming. The NB-IoT standard requires a small radio band of 200 kHz. Operators can choose from three implementing approaches for its core network — this brings flexibility on the network operator’s side. The NB-IoT modem needs to handle these different approaches — a fact that is irreconcilable with the aim to be cheap, simple and energy-efficient.
The absence of handover support in the standard brings similar problems. When a cell becomes out of reach of an NB-IoT device, it has to go through a full registration cycle again. This can take up to 30 seconds, making it a power-hungry and slow procedure. This contradicts the big advantage for NB-IoT: battery life.
So, is NB-IoT less useful than LTE-M?
No, that’s not the case. When used on a fixed location use case, NB-IoT can be efficient. The simple, cost-efficient hardware combined with deep indoor penetration brings great value. But to unlock its full potential, prepare to go all-in on the technology. There are several ways to use its protocols. Finding the perfect setup with NB-IoT can lead into a deep dive of application layer protocols.
The other answer of the 3GPP to non-cellular LPWAN is LTE-M. It focuses on saving power with two functionalities. The first is its deep-sleep, mode called power savings mode. The second technique wakes up the device only periodically while connected, a mode is called extended discontinuous reception. Since LTE-M follows a similar access scheme to 4G LTE, it has a head start with operators already having deployed an LTE-M network.
These two features make LTE-M an attractive option when looking for power efficiency alongside performance. The ubiquity of already-deployed LTE networks acts a big plus.
Cellular modules tell the story
Both technologies have their own advantages, making them suitable for different use cases, but they are hardly interchangeable. One of the leading providers, uBlox, offers both technologies on the same cellular module — this already tells you that the market hasn’t decided which is winning yet.
To make a well-considered decision, knowing whether your devices will often move is an important factor. Just like power-saving, it is crucial to know what you try to achieve. Knowing the true purpose of your systems will help give you decide if low-power cellular is an appropriate option.
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