文章目录
前言
介绍信噪比极限和如何计算接收灵敏度。
参考资料：《LoRa信噪比和接收灵敏度》
一、信噪比极限（SNR LIMIT）
信噪比极限，也可以理解为最小解调信噪比。即，接收机能够成功解调信号的最小信噪比，低于这个信噪比接收机将无法解调。
- 下表是不同的扩频因子对应码片数和信噪比极限：
| SF | chips/symbol | SNR limit(dB) |
|---|---|---|
| 7 | 128 | -7.5 |
| 8 | 256 | -10 |
| 9 | 512 | -12.5 |
| 10 | 1024 | -15 |
| 11 | 2048 | -17.5 |
| 12 | 4096 | -20 |
SF增加“1”， S N R l i m i t − 2.5 d B {SNR}_{limit}-2.5dB SNRlimit−2.5dB
二、接收灵敏度
S = − 174 + 10 × l o g 10 ( B W ) + N F + S N R l i m i t S = -174 + 10\times log_{10}(BW)+NF+SNR_{limit} S=−174+10×log10(BW)+NF+SNRlimit
接收灵敏度单位dBm，BW单位是Hz，接收机噪声系数（NF）单位是dB，且NF只受硬件性能影响。SX1272和SX1276的NF=6dB
- 举例：BW=125kHz，NF=6dB，SF7~12
S F = 7 : S N R l i m i t = − 7.5 d B SF = 7:SNR_{limit}=-7.5dB SF=7:SNRlimit=−7.5dB
S = − 174 + 10 × l o g 10 125000 + 6 − 7.5 = − 125 d B m S = -174 + 10\times log_{10}{125000} + 6 - 7.5 = -125 dBm S=−174+10×log10125000+6−7.5=−125dBm
S F = 8 : S N R l i m i t = − 10 d B SF = 8:SNR_{limit}=-10dB SF=8:SNRlimit=−10dB
S = − 174 + 10 × l o g 10 125000 + 6 − 10 = − 127 d B m S = -174 + 10\times log_{10}{125000} + 6 -10 = -127dBm S=−174+10×log10125000+6−10=−127dBm
S F = 9 : S N R l i m i t = − 12.5 d B SF = 9:SNR_{limit}=-12.5dB SF=9:SNRlimit=−12.5dB
S = − 174 + 10 × l o g 10 125000 + 6 − 12.5 = − 130 d B m S = -174 + 10\times log_{10}{125000} + 6 -12.5 = -130dBm S=−174+10×log10125000+6−12.5=−130dBm
S F = 10 : S N R l i m i t = − 15 d B SF = 10:SNR_{limit}=-15dB SF=10:SNRlimit=−15dB
S = − 174 + 10 × l o g 10 125000 + 6 − 15 = − 132 d B m S = -174 + 10\times log_{10}{125000} + 6 -15 = -132dBm S=−174+10×log10125000+6−15=−132dBm
S F = 11 : S N R l i m i t = − 17.5 d B SF = 11:SNR_{limit}=-17.5dB SF=11:SNRlimit=−17.5dB
S = − 174 + 10 × l o g 10 125000 + 6 − 17.5 = − 135 d B m S = -174 + 10\times log_{10}{125000} + 6 -17.5 = -135dBm S=−174+10×log10125000+6−17.5=−135dBm
S F = 12 : S N R l i m i t = − 20 d B SF = 12:SNR_{limit}=-20dB SF=12:SNRlimit=−20dB
S = − 174 + 10 × l o g 10 125000 + 6 − 20 = − 137 d B m S = -174 + 10\times log_{10}{125000} + 6 -20 = -137dBm S=−174+10×log10125000+6−20=−137dBm
