NB-IoT Link Budget Calculator
Calculate NB-IoT link budget, Maximum Coupling Loss (MCL), and coverage radius for downlink and uplink paths.
Frequently Asked Questions
What is NB-IoT MCL (Maximum Coupling Loss)?
Maximum Coupling Loss (MCL) is the maximum total path loss (in dB) that a link can sustain while still maintaining a connection. It includes all losses and gains between the transmitter and receiver: transmit power, antenna gains, cable losses, path loss, and noise/sensitivity margin. The 3GPP target MCL for NB-IoT is 164 dB, which is 20 dB better than GPRS (144 dB), enabling NB-IoT to reach devices deep inside buildings, basements, or underground.
How do NB-IoT repetitions improve coverage?
NB-IoT uses repetitions (retransmissions) to improve link budget at the cost of latency. Each doubling of repetitions adds approximately 3 dB of gain (10×log₁₀(Nrep)). With up to 2048 repetitions in the uplink (NPUSCH), NB-IoT can achieve gains of up to 33 dB, allowing deep indoor and underground coverage. This is the key mechanism behind the 164 dB MCL target — repetitions allow the receiver to combine energy across multiple transmissions using HARQ combining.
What is the difference between NB-IoT and LTE-M (Cat-M1)?
NB-IoT (Cat-NB1/NB2) and LTE-M (Cat-M1) are both LPWAN technologies defined in 3GPP Release 13. NB-IoT uses a 180 kHz channel and targets very low data rate, low cost, and maximum coverage (MCL 164 dB). LTE-M uses a 1.4 MHz channel, supports voice and mobility handover, and offers higher data rates (up to 1 Mbps DL) with MCL of 156 dB. NB-IoT is better for static deep indoor sensors; LTE-M is better for mobile or voice-capable IoT devices.