This paper describes a transformation technique aimed at solving the peak-to-average power ratio (PAPR) problem associated with OFDM (orthogonal frequency-division multiplexing). Constant envelope OFDM (CE-OFDM) transforms the OFDM signal, by way of phase modulation, to a signal designed for efficient power amplification. At the receiver, the inverse transformation - phase demodulation - is applied prior to the conventional OFDM demodulator. The performance of CE-OFDM is analyzed in additive white Gaussian noise (AWGN) and fading channels. CE-OFDM is shown to achieve good performance in dense multipath with the use of cyclic prefix transmission in conjunction with a frequency- domain equalizer (FDE). By way of computer simulation and hardware realization, CE-OFDM is shown to compare favorably to conventional OFDM.

Signal clipping has been suggested as an effective peak-to-average power ratio (PAPR) reduction scheme for orthogonal frequency-division multiplexing (OFDM). This paper analyzes clipped M-ary differentially encoded phase-shift keying (M-DPSK) OFDM. The impact of input power backoff (IBO) of a nonlinear power amplifier (PA) is evaluated. An effective PAPR reduction scheme should provide one of the two equivalent enhancements: 1) a reduced error floor at a given backoff, or 2) a reduced required IBO to achieve a target BER. The later is addressed by determining the total degradation (TD) of the system at various IBO. By this measure, it is shown that clipping is ineffective. Moreover, it is shown that clipping PAPR reduction doesn't improve the spectral broadening caused by the PA. The linearity of the amplifier is viewed at various backoff ratios, defined as K = IBO/PAPR. Since K is best viewed statistically, so is the linearity of the PA. As a side note, the formula suggested by A. J. Cann (1980) is shown to be equivalent to the often referenced Rapp solid-state PA model

A noncoherent constant envelope orthogonal frequency-division multiplexing (CE-OFDM) receiver is proposed. It is shown that CE-OFDM is naturally noncoherent since the effect of an unknown phase shift at the receiver is eliminated by the matched-filter bank following the front-end phase demodulator. The noncoherent receiver demodulates continuous phase CE-OFDM signals-which produce less adjacent channel interference-with no added complexity. Performance is evaluated in flat fading channels having both Rayleigh and Ricean statistics. Simulation results are compared to analytical approximations1.