A geometric approach to higher-order differential phase shift keying

Modulation/demodulation techniques which are robust in the presence of channel-induced phase and frequency uncertainties, accommodate slow channel phase and frequency variations with minimal performance degradation, and alleviate the need for phase and frequency tracking loops in the receiver are considered. The authors study the performance sensitivity for frequency offsets of a technique known as second-order differential phase shift keying and compare it to that of classical differential phase shift keying (DPSK) in additive white Gaussian noise. The results are generalized to include n^th order DPSK