Modified TRFI Channel Estimation Scheme in OFDM-IM for 802.11p

IEEE 802.11p is developed to support cooperative intelligent transport systems. In such systems, channel estimation is a challenging problem due to the channel's double dispersive nature. In this paper, a modified time domain reliable test frequency domain interpolation (M-TRFI) scheme for 802.11p orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems is proposed. Unlike OFDM, OFDM-IM can achieve better performance in vehicular communication environments. However, due to the in-active subcarriers, channel estimation for OFDM-IM is more difficult than OFDM. Inspired by the OFDM TRFI and the structure of OFDM-IM, the proposed M-TRFI utilizes preambles and least square (LS) methods to fill in the missing channel information on in-active subcarriers, reducing the serious performance degradation caused by the conventional TRFI used in OFDM-IM. Simulation results show that the proposed M-TRFI achieves a similar estimation performance as that of the OFDM TRFI. Moreover, the proposed M-TRFI significantly outperforms the existing channel estimation performance designed for OFDM-IM systems.