Adaptive digital phase modulation schemes using transition-initiated phase acceleration

Link adaptation (LA) schemes, where signal transmission features, such as, modulation, coding rate, etc. are dynamically selected based on the feedback information from receiver regarding the channel condition, have recently emerged as powerful tools for increasing data rate and spectral efficiency of wireless networks. In this paper, we examine an adaptive modulation scheme for LA, based on digital phase-modulation techniques, employing a novel phase-shifting scheme. In the proposed technique, the abrupt phase shift of carrier waveform, required after each data transition, is realized by incrementing the frequency of the voltage-controlled oscillator (VCO) for a short duration, immediately following the data transition. The momentary increase in VCO frequency is realized by feeding the VCO with narrow control pulses, derived from the baseband data stream using a simple supporting circuit. The proposed technique can be used for very large scale integration (VLSI) of adaptive modulation schemes, and one such candidate scheme has been designed for VLSI implementation with triple options of binary phase-shift keying (BPSK), quadrature PSK (QPSK), and quadrature amplitude modulation (QAM).