Blind Channel Estimation for RIS-Assisted Millimeter Wave Communication Systems

In the research of RIS-assisted communication systems, channel estimation is a problem of vital importance for further performance optimization. In order to reduce the pilot overhead to the greatest extent, blind channel estimation methods are required, which can estimate the channel and the transmit signals at the same time without transmitting pilot sequence. Different from existing researches in traditional MIMO systems, the RIS-assisted two-hop channel brings new challenges to the blind channel estimation design. Hence, a novel blind channel estimation method based on compressed sensing for RIS-assisted multiuser millimeter wave communication systems is proposed for the first time in this paper. Specifically, for accurately estimating the RIS-assisted two-hop channel without transmitting pilots, we propose a block-wise transmission scheme. Among different blocks of data transmission, RIS elements are reconfigured for better estimating the cascade channel. Inside each block, data for each user are mapped to a codeword for realizing the transmit signal recovery and equivalent channel estimation simultaneously. Simulation results demonstrate that our method can achieve a considerable accuracy of channel estimation and transmit signal recovery.