  The recently developed affine frequency division multiplexing (AFDM) can
achieve full diversity in doubly selective channels, providing a comprehensive
sparse representation of the delay-Doppler domain channel. Thus, accurate
channel estimation is feasible by using just one pilot symbol. However,
traditional AFDM channel estimation schemes necessitate the use of guard
intervals (GI) to mitigate data-pilot interference, leading to spectral
efficiency degradation. In this paper, we propose a GI-free pilot-aided channel
estimation algorithm for AFDM systems, which improves spectral efficiency
significantly. To mitigate the interference between the pilot and data symbols
caused by the absence of GI, we perform joint interference cancellation,
channel estimation, and signal detection iterately. Simulation results show
that the bit error rate (BER) performance of the proposed method can approach
the ideal case with perfect channel estimation.
