Noise Floor Calculator

The thermal noise floor is the minimum theoretical noise power that a perfect receiver would measure at temperature T0 = 290 K. Its formula is N (dBm) = 10 x log10(k x T0 x B) + 30, which is approximately -174 dBm / Hz. For a 20 MHz bandwidth, N = -174 + 10 x log10(20e6) = -174 + 73 = -101 dBm.

Receiver sensitivity Rx_min = N + NF + SNR_min, where N is the thermal noise floor, NF is the receiver noise figure (typically 5-10 dB) and SNR_min is the minimum SNR for the target demodulator. For an LTE UE at 20 MHz with NF = 9 dB and SNR min -7 dB: Rx_min = -101 + 9 + (-7) = -99 dBm. The 3GPP specs provide reference sensitivities per UE category.

Thermal noise is white noise, its spectral density is constant (kT = -174 dBm/Hz). Doubling the bandwidth doubles the total noise power, adding 3 dB to the noise floor. Going from 10 MHz to 20 MHz adds 3 dB of noise. This is why the required SNRs are lower for wider 5G NR bandwidths (100 MHz, 400 MHz).