An Embedded Single-Pilot-Aided Channel Estimation Scheme Based on Interference Position Indices for AFDM-IM in Delay-Doppler Channels

Affine frequency division multiplexing with index modulation (AFDM-IM) system enhances the energy efficiency and bit error rate (BER) performance. To facilitate data detection in the AFDM-IM system, it is necessary to obtain the channel state information. We propose an embedded pilot-assisted channel estimation (CE) scheme based on interference position indices for AFDM-IM systems under low signal-to-noise ratio conditions, where CE and data detection are conducted within the same frame. In the proposed scheme, the AFDM-IM system only activates a portion of subcarriers for transmitting constellation modulation symbols, while the rest subcarriers stay inactive. Therefore, the pilot can be inserted into the silent subcarriers for CE. To fully exploit the high energy efficiency and spectral efficiency in the AFDM-IM system for information transmission, we design a frame structure for the transmitted signal. Aiming at the issue of insufficient guard intervals between pilot and data caused by this structure, we incorporate an interference position indices determination method into the channel estimation scheme to directly identify the elements for channel estimation in the received signal, which enables more accurate channel estimation and more efficient interference cancellation. Then, CE, interference cancellation, and data detection are iteratively performed. Simulation results show that the proposed channel estimation scheme achieves favorable BER performance by gaining more precise CE in a low signal-to-noise ratio condition.