说明：  基于RSSI的距离测量 matlab 将接收信号强度RSSI转化为距离，发射信号经衰减到达接收端,根据接收信号的强弱计算T-R距离
(RSSI-based distance measuring the received signal strength RSSI matlab converted into distance, attenuated transmitted signal arrive at the receiver end, according to the strength of the received signal the calculation TR)