Coverage classes and the IoT link budget

Maximum Coupling Loss as the Coverage Yardstick

Maximum Coupling Loss (MCL) is the standard 3GPP metric for coverage capability. It expresses the difference in decibels between the device transmit power and the lowest signal level the network can reliably decode. Standard LTE Cat-4 targets a 144 decibel MCL — sufficient for most outdoor and shallow-indoor users. NB-IoT and LTE-M target a 164 decibel MCL — twenty decibels deeper. Twenty decibels is a hundred-fold improvement in link budget, the difference between a meter that works in a ground-floor utility room and one that works three storeys underground in a building basement.