About LTE-M IoT
LTE-M is a type of LTE network published by 3GPP in Releases 13 to 15 specifications. LTE-M is a low power wide area technology which supports IoT through lower device complexity and provides extended coverage, leveraging a mobile operator's existing LTE base stations. LTE-M finds its place as a (comparatively) high data rate service for more data-hungry IoT applications.
LTE-M is simply an extension to the existing 3GPP LTE standards, with Release 13 specifying a brand new Cat-M1 UE capable of operating on a bandwidth 1.08 MHz (i.e., 6 PRB's) within an existing LTE deployment, or 1.4 MHz in standalone deployment. This is a significant development from previous Release 12 specification of LTE Cat-0, which while containing a number of simplifications from conventional UE, still had to operate on standard LTE channel bandwidths.
Cat-M1 devices are limited to a 1000 bit transport block, and operate in either half-duplex or full duplex. This gives Cat-M1 a hard limit of 1 Mb/s and 375 kb/s for the two duplexing modes respectively. In practice, scheduling overheads strip about 20% off the DL throughput.
Supported by all major mobile equipment, chipset, and module manufacturers, LTE-M networks co-exist with 3G, 4G, and 5G mobile networks. LTE-M benefits from all the security and privacy features of mobile networks, such as support for user identity confidentiality, entity authentication, confidentiality, data integrity, and mobile equipment identification.
LTE-M allows an extended battery life of more than 10 years for a wide range of machine type communication use cases through the use of power saving mode (PSM), Discontinuous Reception (eDRX), Cellular IoT (CIoT) control plane, and user plane EPS optimisations for small data transmission.
- PSM (Power Save Mode)
- eDRX (Extended Discontinuous Reception)
- High Latency Communication
- Support for extended coverage
- LTE-M Half Duplex Mode/Full Duplex
- Support of Category M1 device
- VoLTE support
- Connected Mode Mobility
LTE-M was extended in 2018 with 3GPP publishing LTE Release 14. The new standard included Cat-M2 which increased the maximum channel size to 5 MHz (24 PRB), and TBS to 4008 bits in DL and 6968 bits in UL. Understandably however the use of the wider 5 MHz channel to support higher data rates has implications on receive sensitivity and consequently range.
Cat-M1 UL TBS was also increased to 2984 bits, increasing uplink data rates to 3 Mb/s.
The introduction of Release 14 saw the implementation of VoLTE for Cat-M1 devices, allowing for the first time voice services to be provided over an IoT network. VoLTE is not a mandatory feature of an LTE-M network, operators will choose to implement voice technology based on foreseeable business cases. Most LTE-M operators do however provide VoLTE.