Implementation of Nondifferential Coding in a 64 QAM Digital Radio System with Forward Error Correction

Because of recovered carrier phase ambiguity, differential coding is commonly used in QAM systems. Differential coding eliminates the need for an absolute carrier reference phase, but it causes received bit error rate (BER) degradation. The BER degradation caused by differential coding (a factor of two or less) is usually significant unless the transmission system employs forward error correction.