Receiver sensitivity in dBm equals the thermal noise floor plus the noise figure plus the minimum required SNR: Sensitivity = -174 + 10·log10 (B) + NF + SNR_min. Compute thermal noise floor (kTB) from. In optical communication systems, sensitivity is a measure of how weak an input signal can get before the bit-error ratio (BER) exceeds some specified number. The standards body governing the application sets this specified BER. Exceeding the BER value indicates signal degradation, rendering it unsuitable for data communication. More often than not, designers.