  Affine frequency division multiplexing (AFDM) and orthogonal AFDM access
(O-AFDMA) are promising techniques based on chirp signals, which are able to
suppress the performance deterioration caused by Doppler shifts in
high-mobility scenarios. However, the high peak-to-average power ratio (PAPR)
in AFDM or O-AFDMA is still a crucial problem, which severely limits their
practical applications. In this paper, we propose a discrete affine Fourier
transform (DAFT)-spread AFDMA scheme based on the properties of the AFDM
systems, named DAFT-s-AFDMA to significantly reduce the PAPR by resorting to
the DAFT. We formulate the transmitted time-domain signals of the proposed
DAFT-s-AFDMA schemes with localized and interleaved chirp subcarrier allocation
strategies. Accordingly, we derive the guidelines for setting the DAFT
parameters, revealing the insights of PAPR reduction. Finally, simulation
results of PAPR comparison in terms of the complementary cumulative
distribution function (CCDF) show that the proposed DAFT-s-AFDMA schemes with
localized and interleaved strategies can both attain better PAPR performances
than the conventional O-AFDMA scheme.
