Spectrally Efficient Orthogonal Frequency Division Multiplexing with Cyclic Prefix and Postfix, and Pilots

In this paper, we propose a precoding scheme for 6^th generation (6G) mobile communications, which can enhance the spectrum efficiency by overcoming the shortcoming of OFDM of power flowing out to adjacent channels and estimate the channel state with pilots. The proposed scheme is the first trial to have spectral efficiency by having orthogonality between subcarriers in the in-band as well as out-of-band (OOB) spectral efficiency. The precoding is realized with a matrix that consists of a cyclic prefix matrix, a central matrix, and a cyclic postfix matrix. The cyclic prefix and postfix matrices, and the central matrix play roles to provide the packet with the guard interval and to carry an information-bearing signal, respectively. The fade in and fade out properties of cyclic prefix and postfix can confine the spectrum of OFDM signals and prohibit the power leakage to adjacent channels. A good autocorrelation characteristic of the precoding scheme can guarantee the frequency offset estimation with high quality. Since the columns of the central matrix in the time domain are orthogonal to each other, the pilot symbols can be inserted in the same manner as in the conventional OFDM scheme.We will show that the proposed precoding scheme is useful in terms of out-of-band power leakage blocking, autocorrelation, and BER performance compared with OFDM.