Power efficiency, phase noise, and DC offset in constant envelope OFDM transceivers

This paper considers constant envelope orthogonal frequency-division multiplexing (CE-OFDM) that is an attractive candidate for the future Long Term Evolution over satellite and device-to-device communications in merging public safety and commercial networks. The constant envelope modulation allows power amplifier (PA) to operate near saturation levels thus maximizing power efficiency. Because the phase noise transforms just into an additive noise term after the phase detector, the CE-OFDM has significant advantage compared with phase noise sensitive OFDM. The transceiver power efficiency is evaluated by measuring the bit error rate as a function of average PA input signal-to-noise ratio so that the effects of the PA nonlinearities are taken into account in the performance evaluation. Our simulation results show that with a typical nonlinear satellite amplifier, the CE-OFDM has up to 6.0dB gain compared with the OFDM. This is beneficial especially in a channel having high attenuation. The consistent gains for the ideally linearized amplifier and common terrestrial three-way Doherty amplifiers are 2.2 and 2.5dB, respectively. The enhanced PA efficiency enables battery to be smaller or last longer in mobiles devices. For CE-OFDM implementation, a simple transmitter and receiver structure with novel direct current offset removal is presented by keeping in mind that the key factor for the rapid uptake of the future fifth generation systems is the maximization of technology commonalities with existing systems. Copyright © 2016 John Wiley & Sons, Ltd.