Non-uniform FBMC - A Pragmatic Approach

Outgoing from the known uniform FBMC (Filter-Bank Multi-Carrier) formats with Nyquist spectral shaped sub-channels and its time-frequency dual Time-Limited Orthogonal (TLO) form, we introduce an orthogonal frequency division multiplex of non-uniformly spaced and unequal-width sub-channels. The goal is to attain potential gains in using relatively small number of sub-channels, but still allow for frequency gaps needed for channelization with a small decrease in overall spectral efficiency. The orthogonality conditions are evaluated through simulations using the extended OFDM framework, whereby the corresponding referent filter-bank impulse responses are defined in frequency-domain by straightforward aggregations of the pertaining uniform filter-bank sub-channels spectral shapes (for conventional FBMC with frequency limited sub-channels spectra), and by transforming to frequency-domain of adequately aggregated time-limited referent impulse responses of uniform TLO configuration. An analytical derivation, i.e. confirmation of the orthogonality conditions are also derived with reliance on the uniform FBMC and TLO orthogonality conditions. Non-symmetrical spectral shaped sub-channels in the case of FBMC format are also proposed.