LTE Category M1 protocol was introduced by the 3GPP in the Release 13. It adopted the previous set of IoT features defined for LTE Cat 0 in the Release 12 and reduced its complexity while improving the coverage and power efficiency. LTE Cat M1 complexity has been reduced by 80%, compared to that of LTE Cat 0.
From a coverage viewpoint, the LTE Cat M1protocol offers a new optional power amplifier of 20 dBm as specified as a power class, taking the overall coverage enhancement to over 15 dB, enabling LTE Cat M1 to reach locations previously unreachable for lower powered devices. Power efficiency remains source of discomfort for IoT devices. The target to aim for is now over 10 years of lifecycle for battery powered IoT devices. This is probably more than sufficient for most IoT applications, given the current pace of technology evolution.
In addition to the coverage and power consumption targets, the new Cat M1 based IoT devices are compatible with the existing LTE installed based on appropriate software updates. The backwards compatibility helps to keep deployment costs at a reasonable level.
Power saving mode, extended idle mode, connected mode, discontinuous reception, additional small data transmission and low latency are among the other optimization features that make LTE Cat M1 a key IoT communication protocol.
Maximum data rates for Cat M1 have remained the same as for LTE Cat 0, i.e. 1 Mbps for both, uplink and downlink directions (in practice, variable data rates between 10 kbps to 1 Mbps are possible, depending on the context requirements). However, now the latency optimization features provide for an expected latency range in the region of 10-15 msec. The 3GPP release 13, with Cat M1, has brought back the design focus onto latency.
In LTE Cat M1, most of the design effort for the overall system is placed on the user equipment, and the radio interface has seen new elements added, as the main factor for limiting the costs has been the reduction of bandwidth to six physical resource blocks. This now leaves the User Equipment (UE) bandwidth at 1.4 MHz, as opposed to the 20 MHz of UE bandwidth available in Cat 1 and Cat 0. This reduction has effectively made LTE Cat M1 a bandwidth-limited UE technology as per 3GPP definition.
LTE Cat M1 is a great solution for cellular IoT devices. It has removed many of the previous limitations, following the evolution path familiar with 3GPP standardization works.