This is the second of a two-part tutorial to derive bit error rate expressions for certain linear modulation schemes.

http://liquidsdr.org/blog/modem-ber-calc/

The modem module implements a set of (mod)ulation/(dem)odulation schemes for encoding information into signals. For the analog modems, samples are encoded according to frequency or analog modulation. For the digital modems, data bits are encoded into symbols representing carrier frequency, phase, amplitude, etc.

http://liquidsdr.org/doc/modem/