However, notice that we actually
have an improvement in Eb/No when going to the higher number of modulation levels.
A more general observation is that as the number of modulation levels increases for PSK/QAM,
the required Eb/No increases as well. This is because the distance between neighboring constellation
points becomes closer as the number of modulation levels increases. The opposite effect is visible for
the FSK modulation scheme family, where increasing the number of modulation levels decreases the
required Eb/No. As discussed earlier, each addition to the FSK modulation alphabet does not allow a
smaller noise immunity vector to cause a decision error. The distance between the neighboring FSK
symbols is actually constant for the orthogonal signaling case we discussed above.
2.3.3 Some Wireless Standard Choices
In the above sections a comparison of some of the above modulation schemes was presented. First the
goals were outlined and then BER, Eb/No, and BW were discussed, in relation to the desired effects
with respect to the goals. It was shown that antipodal signaling with coherent detection produced the
lowest/best BER in the AWGN channel. We noticed that spectral efficiency can be increased by
increasing the number of modulation levels of PSK and QAM, at the expense of power (i.
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