What is the function and use of signal constellation?

Constellation diagram is a basic concept of digital modulation at present. People who have studied communication principles or digital communication should know that when sending digital signals, generally, 0 or 1 is not sent directly, but 0, 1 signals (bits) are grouped by one or several bits, for example, every two bits, that is, 00,010,65438. (If there are no three digits, there are eight states, and so on). At this time, you can choose QPSK (four-phase modulation, corresponding to the first four states of 00 ...11). Four points of QPSK form a QPSK constellation, and each point is 90 degrees (with the same amplitude) from its neighboring points. You can draw it yourself, and one constellation point corresponds to one modulation symbol.

When receiving and demodulating a QPSK signal, we can judge which signal is sent according to the distance between the received signal and four points on the constellation (commonly called Euclidean distance). If it is closest to 00, it is judged as 00, otherwise it is judged as other points.

Therefore, the function of constellation diagram is mainly used for mapping during modulation (such as QPSK, 16QAM, 64QAM, etc. ) and is used to judge which point is sent when receiving, so as to demodulate the data correctly.

If you don't understand, I suggest you start with the basics of communication principles and study hard.