NB-IoT deployment modes — in-band, guard-band, standalone

In-Band — One LTE PRB Becomes NB-IoT

In in-band mode, NB-IoT reuses a single 180 kilohertz physical resource block of an existing LTE carrier. The eNodeB schedules one PRB exclusively for NB-IoT traffic; the rest of the LTE carrier continues serving smartphones and other LTE-class devices. From the operator perspective this is the cheapest NB-IoT deployment path because no new spectrum is required and existing LTE radios and base stations can support the feature with software upgrades. The cost is one PRB out of the carrier — roughly one percent of capacity on a 20 megahertz LTE carrier — which is rarely material in practice.