Continuous-Phase Modulation for DFT-Spread Localized OFDM

Massive machine-type communications to support a large number of low-cost, low-power, and/or low-rate radio-frequency transceivers such as Internet-of-Things (IoT) devices is a major usage scenario of the 5G mobile communication system. To save cost and power, highly nonlinear power amplifiers (PAs) are expected to be used in the devices. However, the envelope fluctuation of the input of a PA may make the output suffer from severe nonlinear distortion. In this paper, a continuous-phase modulation is proposed for discrete-Fourier transform (DFT)-spread localized orthogonal frequency-division multiplexing (OFDM) of π/2-BPSK symbols. In particular, the combination of a spectrum shaping vector and an extra rotation angle is proposed, which enables the use of a receiver that is fully compatible with the current standard. It is shown that the proposed design significantly outperforms the conventional designs in terms of effective signal-to-distortion ratio and error vector magnitude at the cost of a negligible increase in out-of-band emission.