Abstract: Methods, apparatus, and systems for alternating quadratures differential binary phase shift keying (AQDBPSK) modulation and demodulation radically increase overall energy efficiency of a communication system due to the combined effect of efficient utilization of transmitter power, high noise immunity of modulation and demodulation, fast synchronization, and simple implementation. Efficient utilization of transmitter power is achieved because radical reduction of side lobe regeneration provided by AQDBPSK allows operation of all amplifiers of the transmitter analog signal path, including power amplifiers, in energy efficient nonlinear mode (for example, they can operate as class C amplifiers) without causing interchannel interference. AQDBPSK radically reduces side lobe regeneration by limiting phase transitions between adjacent in time modulator output symbols to .+?.90.degree and smoothly executing the transitions.

Abstract: A method of performing alternating quadratures differential binary phase shift keying modulation involves limiting phase changes between adjacent in time modulator output symbols to ±90 °, and transmitting modulator input data by 0° and 180° phase differences between non-adjacent in time modulator output symbols.