Orthogonal Design of Cyclic Block Filtered Multitone Modulation

This paper deals with the orthogonal design of a cyclic block filtered multitone modulation (CB-FMT) system. CB-FMT is a filter bank modulation scheme that uses well frequency localized pulses as in FMT but the linear convolutions are replaced by circular convolutions. We derive the orthogonality conditions both in the time domain and in the frequency domain. Then, we show that such conditions can be fulfilled with a hyper-spherical parameterization of the pulse frequency components. Finally, optimal frequency localized orthogonal pulses are searched. It is shown that much higher in-band-to-out-of-band sub-channel energy is achieved for both critically sampled and non-critically sampled architectures compared to baseline solutions corresponding to either the use of a rectangular or a root-raised-cosine window in frequency. Finally, a comparison with OFDM shows that higher spectral efficiency can be provided by orthogonal CB-FMT.