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# In digital modulation, how did they get the magnitudes 0.22 and 0.821? Any explanation about how is it derived?

### 1 Answer

- Markus ImhofLv 71 month ago
A little more context would be extremely helpful.

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Still at a loss here - the symbols in QAM usually represent multiple bits, so there isn't a single numerical value (for whatever) that corresponds to a single bit, but rather a combination of numerical values for the i and q amplitudes that correspond to a set of bits (usually 2 to 8 bits per symbol). The values you are quoting _might_ be the amplitude values in a (specific) square 16-QAM, i.e. all possible combinations of these values (including negative sign) will give 16 points in i/q-space, denoting the 16 QAM symbols which can correspond to the binary symbols 0000...1111.

Although, if this is the case, I find the choice of amplitudes strange, as these will give a far lower distance between the points of the inner square.

Our professor can't elaborate how the values 0.821 and 0.22 derived. These were the magnitudes used in QAM that represents logic 1 and logic 0. I really want to know how is it derived.