May 19, 2022
Narrow-Band IoT (NB-IoT) – Understanding Network and Security for Far-Edge Computing
NB-IoT is a specification devised by 3GPP that defines a low-powered WAN (LPWAN) technology that rides on top of existing 4G/LTE and 5GC networks. It is meant to provide a lower cost level of service for IoT devices that do not need the full throughput of an MNO’s standard 4G/LTE or 5G data service offering.
Because it piggybacks on top of existing mobile networks, it shares the same licensed frequency spectrum, and normally the same cell towers/antennas. However, at a signal level, it functions a bit differently. The specification limits each device to a maximum of 200KHz of bandwidth. Contrast this with 4G/LTE, which can have 20MHz channels, and 5G, which can go as high as 400MHz, and the reason it is called “narrow-band” becomes evident. An MNO can support as many as 100 NB-IoT devices using the same amount of bandwidth needed to support a single 4G/LTE phone using a 20MHz channel.
How much throughput an NB-IoT device can squeeze out of that 200KHz channel depends on the version. 3GPP Release 17 was published in 2022 and specifies the latest revision, known as NB-IoT Enhanced. This version specifies a maximum throughput of 250 kbps down and 20 kbps up. It achieves this by using TDD to time-slice the transmit phase as FDMA and the receive phase as OFDMA.
Another difference is that NB-IoT is typically deployed using the guard band slots of an MNO’s network. While this is not always true, it is important to ask your MNO whether they deploy NB-IoT using “in-band mode” or “guard-band mode” as the latter will inevitably suffer from a higher signal-to-noise ratio than you could expect from an NB-IoT channel provisioned in a standard slot. Guard bands exist for a reason. At the time of writing, few NB-IoT offerings do not use guard-band mode:
Figure 3.28 – NB-IoT-capable pressure sensor
In most other ways, NB-IoT works like any 4G/LTE or 5G mobile device. Each device needs a SIM (although eSIMs are becoming the standard) to access the MNO’s network. Each device is also paired with one cell tower/radio at a time. Finally, the connection is synchronous, which means it is constantly on, regardless of whether the device has data to send or receive.
The narrowness of the band allows the MNO to charge less for the service, but it also means NB-IoT devices need less power for the transceiver than if they were using standard 4G/LTE or 5G. However, because of the synchronous connection, NB-IoT devices as a rule consume more power than LPWAN technologies that use an asynchronous connection model.
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