hard and soft demappers

soft demapper

hi all,

can anyone explain me whats the differnece between hard and soft demappers.
which has the better performance and lower BER.

soft demapper algorithm

hard demapper works on symbol by symbol basis
soft demapper uses the information from previous decisions (e.g. uses the viterbi algorithm)

the soft demapper has lower BER , hence better performance , but it is more complex

soft demapper

"amihomo" has described soft decoding, where a decision on a recived symbol is not taken immediately after receiving one symbol, but a whole sequence is examined before a decision is taken (viterbi decoding being the prime example).

However, I guess what the OP is asking about is soft demapper. The demapper associates the recieved signal to a constellation point. In hard decoding, it choses the nearest valid constellation point and decalres that as the recieved symbol. When soft decoding is done, the demapper gives out a set of values (each being a few bits), each being the quantised distance of the recieved signal from all, or a subset of, valid constellation points. The ECC decoder that follows the demapper usually gives a better performance if soft info is used.

So soft decoding can be done with both soft and hard demapping.
-b