Augmented Affine Frequency Division Multiplexing for Both Low PAPR Signaling and Diversity Gain Protection

Abstract: Research results on Affine Frequency Division Multiplexing (AFDM) reveal that it experiences the same Peak-to-Average Power Ratio (PAPR) problem as conventional Orthogonal Frequency-Division Multiplexing (OFDM). On the other side, some references and also our studies demonstrate that AFDM involves an unneeded matrix, which is based on a parameter typically represented by $c_2$, for signalling. Hence, in this paper, an augmented AFDM scheme, referred to as A$^2$FDM, is proposed to mitigate the PAPR problem of AFDM, which is achieved by replacing the $c_2$ matrix in AFDM by a new unitary matrix that performs both sub-block-based Discrete Fourier Transform (DFT) and symbol mapping. Two symbol mapping schemes, namely interleaved mapping and localized mapping, are proposed for implementing A$^2$FDM, yielding the Interleaved A$^2$FDM and Localized A$^2$FDM. The input-output relationships of these schemes are derived and the complexity and the effects of system parameters on the performance of A$^2$FDM along with AFDM systems are analyzed. Furthermore, simulation results are provided to demonstrate and compare comprehensively the performance of the considered schemes in conjunction with different system settings and various operational conditions. Our studies and results demonstrate that, while A$^2$FDM is capable of circumventing the PAPR problem faced by AFDM, it is capable of attaining the achievable diversity gain, when AFDM is operated in its undesirable conditions resulting in the loss of the diversity gain available.