QAM demodulation , hard vs soft if there is any
There are techniques that use soft or hard decisions.

The most usual is a hard decision, where some sort of circuit guesses from that symbol alone which constellation point is closest, and outputs that one.

The soft decision output is where the circuit, instead of stating that X symbol is the most likely result, states that the received symbol is x distance away from X symbol. 

The soft decisions have use further downstream, they allow error detection/correction circuits to know which symbols were reliable, and which were marginal. A sufficiently sophisticated error correcter would weight reliable symbols more strongly than dodgy ones, and so gain a small performance improvement over those that worked with only hard decisions.

The performance gain is small, and needs a more complicated error corrector, which is why both hard and soft decision systems are in use.