A novel orthogonal transmission scheme for non-orthogonal multi-carrier signal

The orthogonality among sub-carriers and the minimum frequency span which satisfies the Nyquist criterion in frequency domain are foundational principles of conventional OFDM (Orthogonal Frequency Division Multiplexing) system. Although reducing the minimum frequency span in OFDM can improve the spectral efficiency, it is not practical previously because of large detection complexity which is derived from the non-orthogonality and considerable inter carrier interference among sub-carriers. Gram-Schmidt orthogonalization procedure proposed in the paper can transform the non-orthogonal sub-carriers into orthogonal waveforms and the bit error rate is not deteriorated in additive white Gaussian noise channel. Meanwhile, the total signal bandwidth becomes smaller than that of conventional OFDM, i.e., the spectral efficiency can be increased. In the paper, Gram-Schmidt orthogonalization procedure is explained by dirty paper coding in information theory and functional analysis in mathematics. Simulation results also verify the validity and correctness of this signal processing method - Gram-Schmidt orthogonalization procedure.