Analysis of low-PAR modulation schemes for wideband-CDMA

This paper examines a class of PSK-based, linear modulation schemes for application in direct-sequence CDMA systems with respect to the variation of the (complex) baseband signal envelope. A minimum peak-to-average ratio (PAR) of the envelope reduces the linearity requirements of the power amplifier and increases the power amplifier efficiency, which is of great importance especially for mobile terminals. A generalization of the PAR-efficient π/4-QPSK, denoted as φ-QPSK, was proposed for a wideband-CDMA concept for UMTS/IMT-2000 and is investigated here: fundamental mechanisms determining PAR are identified for both real and complex chip sequences. Theoretical PAR values are derived and lead the way to the design of new concepts for PAR-optimal spread spectrum modulation