The article presents QOFDM-SP (Subcarrier Permutation) as a further development of quasiorthogonal frequency access on subcarrier frequencies. The method does not introduce a new physical-layer signal and does not change the frequency plans, subcarrier spacing, subcarrier positions, or threshold admissibility condition of the base QOFDM ensemble. The proposed method adds a systematic channel-block assignment layer over already defined frequency plans. In this layer, each frequency plan is divided into logical channel blocks, and the assignment of channels to these blocks is varied between plans by permutations. A reproducible structural experiment is performed for an ensemble with K = 24, L = 4, ΔF = 20 MHz. The selected values of the number of subcarriers are the first 24 prime integers not smaller than 23. Since these values are pairwise coprime, each pair of plans has one endpoint coincidence at the upper edge of the common band, and the maximum same-channel coincidence count remains equal to one for all tested strategies. The main structural effect is therefore observed in the accumulated number of same-channel coincidences and in the number of plan pairs with such coincidences: both the cyclic and all-factorial assignments reduce these values from 276 to 60 and from 276/276 to 60/276, respectively. Thus, within the adopted discrete structural model, the proposed QOFDM-SP method provides a more uniform channel-block organization of QOFDM signal ensembles and reduces the concentration of same-channel frequency-position coincidences without modifying the base QOFDM frequency plans.
Харченко et al. (Thu,) studied this question.