  Probabilistic Amplitude Shaping (PAS) is a coded-modulation scheme in which
the encoder is a concatenation of a distribution matcher with a systematic
Forward Error Correction (FEC) code. For reduced computational complexity the
decoder can be chosen as a concatenation of a mismatched FEC decoder and
dematcher. This work studies the theoretic limits of PAS. The classical joint
source-channel coding (JSCC) setup is modified to include systematic FEC and
the mismatched FEC decoder. At each step error exponents and achievable rates
for the corresponding setup are derived.
