What are the similarities and differences between square QAM constellation and constellation QAM constellation

The distribution of signal vector endpoints is called constellation. In general, constellation diagram can be used to describe the signal spatial distribution state of QAM signal. For M= 16? For 16QAM, there are many signal constellations. ? The picture shows two representative signal constellations? 9? -? 2? As shown in the figure. In the photo? 9? -? 2(a)，？ The distribution of signal points is square, so it is called square 16QAM constellation, also known as standard 16QAM. In the photo? 9? -? In 2(b), the distribution of signal points is star-shaped, so it is called star 16QAM constellation. ?

If the minimum distance between signal points is 2A, and all signal points appear with equal probability.

The power difference between them is1.4db. In addition, there are important differences in their constellation structures. First, the star 16QAM has only two amplitude values, while the square 16QAM? There are three amplitude values; Second, star 16QAM has only 8 phase values, while square 16QAM has 12 phase values. These two points make the star 16QAM analogy more attractive in fading channels.