Long term evolution (LTE) is a fourth-generation (4G) wireless standard that was introduced by the 3GPP consortium to provide higher network capacity and increased speed for cellular communication.
LTE-M, also known as LTE Cat M1 or eMTC, is a variant of the LTE standard that has been specifically introduced to support IoT applications that require less battery power and wider coverage.
NB-IoT is a narrow band LPWAN technology that operates in the licensed band and can coexist with LTE or GSM bands. The NB-IoT protocol is built on the LTE paradigm where it reuses the different building blocks and components of the physical and upper layers of the LTE protocol stack. NB-IoT reduces the protocol stack functionalities of LTE to a minimum and modifies them to fit the requirements of IoT applications.