An Enhanced Channel Estimation Scheme in OFDM-IM Systems With Index Pilots for IEEE 802.11p Standard

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is emerging as a robust technology, especially valued in vehicular communication scenarios for its resilience. In such dynamic environments, reliable channel estimation becomes critical to maintain system performance due to the fast time-varying and double dispersion channel nature. Despite the harsh conditions, OFDM-IM enhances system performance by leveraging inactive sub-carriers to convey additional information. However, these idle sub-carriers complicate channel estimation compared to traditional OFDM systems. In response to these challenges, this paper introduces an enhanced channel estimation scheme tailored for the IEEE 802.11p standard, which supports cooperative intelligent transport systems (C-ITS). Our proposed method, the enhanced time-domain reliable test frequency-domain interpolation with index pilots (E-TRFI-IP), strategically places pilots and utilizes the positions of inactive sub-carriers to facilitate accurate detection and prevent performance degradation from inadequate channel tracking. Additionally, to further improve channel estimation performance, a comparison threshold methodology for reliable sub-carriers test is introduced by utilizing the structure of IM and joint interpolation method. Extensive simulation results demonstrate that E-TRFI-IP significantly surpasses existing channel estimation methods for both OFDM and OFDM-IM in terms of channel estimation performance. Notably, OFDM-IM systems employing the E-TRFI-IP estimation scheme also exhibit superior performance in bit error rate (BER) compared to those using conventional OFDM-IM and other channel estimation techniques.