Receiver Sensitivity Sensitivity describes the weakest signal power

Receiver Sensitivity • Sensitivity describes the weakest signal power level that the receiver is able to detect and decode – Sensitivity is dependent on the lowest signal-to-noise ratio at which the signal can be recovered – Different modulation and coding schemes have different minimum SNRs • Range: <0 d. B to 60 d. B • Sensitivity is determined by adding the required SNR to the noise present at the receiver • Noise Sources – Thermal noise – Noise introduced by the receiver’s pre-amplifier

Thermal Noise • Thermal Noise = N = k. TB (Watts) • k=1. 3803 x 10 -23 J/K • T = temperature in Kelvin • B=receiver bandwidth – So Thermal Noise can be expressed by following formula N = -228, 6 d. Bw + 10 log T + 10 log B – Thermal noise is usually very small for reasonable bandwidths • Noise introduced by the receiver pre-amplifier – Noise Factor = Noise Figure = SNRin/SNRout (positive because amplifiers always generate noise)

Receiver Sensitivity Calculation • The smaller the sensitivity, the better the receiver • Sensitivity (W) = k. TB * NF(linear) * minimum SNR required (linear) • Sensitivity (d. Bm) = 10 log 10(k. TB*1000) + NF(d. B) + minimum SNR required (d. B)

Sensitivity Example • Example parameters – Signal with 200 KHz bandwidth at 290 K – NF for amplifier is 1. 2 d. B or 1. 318 (linear) – Modulation scheme requires SNR of 15 d. B or 31. 62 (linear) • Sensitivity = Thermal Noise + NF + Required SNR – Thermal Noise = k. TB = (1. 3803 x 10 -23 J/K) (290 K)(200 KHz) = 8. 006 x 10 -16 W = -151 d. BW or -121 d. Bm – Sensitivity (W) = (8. 006 x 10 -16 W )(1. 318)(31. 62) = 3. 33 x 10 -14 W – Sensitivity (d. Bm) = -121 d. Bm + 1. 2 d. B + 15 d. B = -104. 8 d. Bm • Sensitivity decreases when: – Bandwidth increases – Temperature increases – Amplifier introduces more noise