This paper proposes a novel waveform for the uplink of massive machine-type communications (mMTC) in 5G. It has a halved subcarrier spacing than that of the orthogonal frequency division multiplexing (OFDM) with a discrete cosine transform (DCT) matrix based precoder on the transmitter side. It can keep the subcarriers orthogonal in the real domain and is called DCT precoded real domain OFDM (DCT-r-OFDM) in this paper. When the real valued modulation schemes such as binary phase shifting keying (BPSK) are applicable, it has doubled spectral efficiency than that of OFDM. In addition, thanks to the energy compaction property of DCT, it can have a lower peak-to-average-power-ratio (PAPR) than that of discrete Fourier transform matrix spreading OFDM (DFT-s-OFDM), which is used in the uplink of long term evolution (LTE). These two advantages can be beneficial for mMTC services, which do not require high data rate but have main optimization goals on connection density and PAPR. Simulation results based on LTE uplink parameters are presented to show the superiority of this waveform to the DFT-s-OFDM in terms of spectral efficiency and PAPR.
