A Novel Optimized Affine Frequency Division Multiplexing Design for Future High-mobility Communications

As one of the recently proposed attractive multi-carrier waveforms towards high-mobility scenarios for 6G and beyond, the chirp-based affine frequency division multiplexing (AFDM) is capable of adapting to cope with large Doppler frequency shifts, which drastically deteriorates the orthogonality between orthogonal frequency division multiplexing (OFDM) subcarriers. Under doubly selective channels with given delay-Doppler profiles, existing works have proved that the classic AFDM requires a minimum number of subcarriers (such as the number of subcarriers is no less than 6, i.e.,
$N\geq 6$
) to achieve its full diversity. In this paper, we propose a novel optimized waveform design based on AFDM by combing the concept of index modulation (IM) and repetition coding (RC) in order to achieve additional diversity gain for the case that fewer subcarriers are available, and the proposed scheme is termed as index modulation-repetition coding-aided AFDM (IMRC-AFDM), where the main design idea is to perform the RC to complex-valued symbols to achieve diversity gain, while the transmission rate loss resulting from RC is compensated by exploiting the benefits of IM. Simulations results validate the benefits of our IMRC-AFDM scheme and show the performance gain of the proposed scheme over the original plain scheme.