The elimination of peak-to-average power ratio concerns in OFDM via carrier interferometry spreading codes: a multiple constellation analysis

Abstract

Orthogonal frequency division multiplexing (OFDM) demonstrates symbol-by-symbol fluctuations in peak-to-average power ratio (PAPR), a direct consequence of independently modulated carriers. This, in turn, leads to inefficient operation of the transmit power amplifier, and/or in-band and out-of-band distortion due to power amplifier saturation. This paper extends our previous work, which explains how carrier interferometry (CI) spreading codes may be applied to OFDM (creating CI/OFDM) to eliminate PAPR fluctuations. Specifically, we analyze the PAPR benefits of CI codes in higher-order constellation OFDM systems (QPSK, 16-QAM, and 64-QAM OFDM). This work confirms that the proposed technique (of spreading the data symbols onto all carriers) ensures the elimination of high peaks in the signal envelope (thereby eliminating the PAPR problem): It is further shown that the choice of constellation size does little to change the PAPR benefits of the CI spreading technique.