question about soft symbol mapper

I have came across a so-called soft symbol mapper in OFDM system, which I
understand it is modulation by soft values, but how to do it? for example,
QPSK modulation will make [0 0] [0 1] [1 0] [1 1] to [-0.7071-0.7071i]
[-0.7071+0.7071i] [+0.7071-0.7071i] [+0.7071+0.7071i], how about soft
symbol mapper?

anybody answer me?

>I have came across a so-called soft symbol mapper in OFDM system, which
I
>understand it is modulation by soft values, but how to do it? for
example,
>QPSK modulation will make [0 0] [0 1] [1 0] [1 1] to [-0.7071-0.7071i]
>[-0.7071+0.7071i] [+0.7071-0.7071i] [+0.7071+0.7071i], how about soft
>symbol mapper?
>

"totohaha" <wuxianguk@hotmail.com> wrote in message
news:r46dnXdaDqH-eOranZ2dnUVZ_h2pnZ2d@giganews.com...
> I have came across a so-called soft symbol mapper in OFDM system, which I
> understand it is modulation by soft values, but how to do it? for example,
> QPSK modulation will make [0 0] [0 1] [1 0] [1 1] to [-0.7071-0.7071i]
> [-0.7071+0.7071i] [+0.7071-0.7071i] [+0.7071+0.7071i], how about soft
> symbol mapper?

Usually it is just a look up table. If the I and Q values are 16 bit, for
example, a 4x32 memory can implement this function for you.

Typically it is a dual port memory so that the values can be reloaded on one
port while the data is processed on the other port.

-Clark

"totohaha" <wuxianguk@hotmail.com> writes:

> I have came across a so-called soft symbol mapper in OFDM system, which I
> understand it is modulation by soft values, but how to do it? for example,
> QPSK modulation will make [0 0] [0 1] [1 0] [1 1] to [-0.7071-0.7071i]
> [-0.7071+0.7071i] [+0.7071-0.7071i] [+0.7071+0.7071i], how about soft
> symbol mapper?

Perhaps they're implementing some sort of predistortion?
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