Performance Analysis of an Angle Differential-QAM Scheme for Resolving Phase Ambiguity

An angle differential-QAM (ADQAM) scheme is proposed to solve phase ambiguity problem in non-data-aided continuous transmission system with square QAM constellation. Starting from the 16-ADQAM case, we derive differential encoding and decoding schemes in terms of two differential angles, and use a solar system analogy for explanation. The 16-ADQAM system incurs only about 0.5-dB performance degradation as compared to the coherent 16-QAM system under AWGN channel. Generalization to flat fading channel and higher-level ADQAM are straightforward. For educational purpose, a demonstrative 16-ADQAM system is realized in terms of an audio-band software-defined-radio approach, and experimental result shows the feasibility of real-time speech transmission.