Under what circumstances are 64QAM and QPSK better than 16QAM?

64QAM, 16QAM and QPSK are all modulation methods, but the mapping order on the constellation diagram is different.

64QAM, 16QAM, is an amplitude and phase modulation technology, that is, the signal is modulated into different amplitudes and phases, QPSK: only phase;

The higher the modulation order, the more bits it can carry. A 64QAM constellation point can carry 4 bits of information at the same time, while 16QAM is 4 bits and QPSK is 2 bits. Generally speaking, the higher the order, the better the performance, which is somewhat inappropriate, and the more appropriate the performance of the modulation method that matches the channel state.

Different modulation orders, the higher the order, the more bits can be carried, and the higher the frequency band utilization rate of transmission, but the higher the modulation order, the worse the anti-interference performance.