原文：https://liudongdong1.github.io/2020/07/01/aiot/mmwave/signalbase/

0. 數字訊號調製

字通訊系統需要將資訊0-1位元流（例如 0101110101），從發端通過無線通道傳送到收端。在發端傳送前，需要將0-1位元流調製到模擬訊號上。常用的調製方式有BPSK, QPSK, 16QAM, 64QAM等。其理論基礎是通過圖1所示的星座圖，根據位元流確定調製訊號：

An object at a distance d results in an IF tone of frequency S2d/c;

two tones can be resolved in frequency as long as the frequency difference θ f > 1 / T \theta f> 1/T

θf>1/T;

range resolution( d r e s d_{res} dres​) depends on the bandwidth(B): d r e s = c / 2 b d_{res}=c/2b dres​=c/2b;

the ADC sampling rate F s F_s Fs​ limits the max range ( d m a x d_{max} dmax​) to