文章目录
前言
本文解释什么是链路预算，最大链路预算和链路裕度。
一、调制和解调
- 信号加载到载波上的过程为调制，调制后的信号被广播到接收端；
- 解调是反向的，原始信号从已调制的载波上恢复；
二、链路预算和链路裕度
- 一个简单的链路预算等式： R e c e i v e d P o w e r = T r a n s m i t t e d P o w e r + G a i n s − L o s s e s Received Power = Transmitted Power + Gains - Losses ReceivedPower=TransmittedPower+Gains−Losses如， R e c e i v e d P o w e r = 20 − 5 + 10 − 115 + 12 − 2 = − 80 d B m Received Power = 20 - 5 + 10 - 115 + 12 - 2 = -80dBm ReceivedPower=20−5+10−115+12−2=−80dBm
- 接收灵敏度是指接收端接收到所能解调最小的已调制信号： R e c e i v e r s e n s i t i v i t y = − 90 d B m Receiver sensitivity = -90dBm Receiversensitivity=−90dBm
- 链路裕度是指接收灵敏度与接收到的信号功率之差： L i n k m a r g i n = R e c e i v e d p o w e r − R e c e i v e r s e n s i t i v i t y Link margin = Received power - Receiver sensitivity Linkmargin=Receivedpower−Receiversensitivity 如， L i n k p o w e r = − 80 d B m Link power = -80dBm Linkpower=−80dBm R e c e i v e r s e n s i t i v i t y = − 90 d B m Receiver sensitivity = -90dBm Receiversensitivity=−90dBm L i n k m a r g i n = − 80 − ( − 90 ) = 10 d B m = 10 m W Link margin = -80 -(-90) = 10dBm =10mW Linkmargin=−80−(−90)=10dBm=10mW
- 链路裕度必须是正值（Received > Receiver sensitivity）并且至少有几个dB才能被正确解调；
- 由于采用扩频技术，Lora接收机的灵敏度可以达到-148dBm；
