Understand how wireless access technology works

Knowing how network search time varies between different connectivity technologies is also important when designing IoT Devices.

For example, the time it takes an IoT Communications Module to find an NB-IoT network increases nearly linearly with the size of the band being used. A 10MHz band (such as Band 13) takes around 4 seconds to scan, while a 60MHz band (such as Band 1 or Band 2) takes six times longer to scan.

Thus, a communications module that has enabled NB-IoT Bands 1, 2, and 13 will need to scan for roughly 50 seconds before connecting to a network — or 10 times longer (or even more) with more bands enabled, or when signal quality is poor.

This compares to 2G, 3G, and LTE technologies, where a communications module can typically complete a full network search and connect to a network within 2-3 minutes. An IoT Device Application that assumes the module should be connected within 3 minutes and is designed to restart if not, may never be able to successfully finish scanning NB-IoT networks.

This is why NB-IoT is described as being suited for devices that will be installed in a permanent location, as it avoids the need to constantly search for networks the way devices in mobile use cases do when they move around.

As many LPWAN communications modules support LTE-M, NB-IoT, and 2G technologies, developing IoT Device Applications that adjust timeouts according to the connectivity technology, as well as limiting the number of bands to use and adapting the application to technology-specific behaviors (such as NB-IoT network latency and Coverage Enhancement), is critical to success, as recommended in TS.34_4.0_REQ_008 and 009.