Large Intelligent Surface-Based Index Modulation: A New Beyond MIMO Paradigm for 6G
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Transmission through large intelligent surfaces (LIS), which modify the phases of incident waves in a deliberate manner to enhance the signal quality at the receiver, has been recently put forward as a promising candidate for future wireless communication systems and standards. In this paper, we bring the concept of LIS-assisted communications to the realm of index modulation (IM) by proposing LIS-space shift keying (LIS-SSK) and LIS-spatial modulation (LIS-SM) schemes. These two schemes are realized through not only intelligent reflection of the incoming electromagnetic waves to improve the signal quality at the receiver but also utilization of the IM principle for the indices of multiple receive antennas in a clever way to improve the spectral efficiency. Maximum energy-based suboptimal (greedy) and exhaustive search-based optimal (maximum likelihood) detectors of the LIS-SSK/SM schemes are formulated and a unified framework is presented for the derivation of the theoretical average bit error probability of the proposed schemes using both detectors. Extensive computer simulation results are provided to assess the potential of LIS-assisted IM schemes as well as to verify our theoretical derivations and remarks. Our findings also reveal that LIS-based IM, which enables ultra-reliable transmission with high spectral efficiency, can become a potential candidate for future wireless communication systems in the context of beyond massive multiple-input multiple-output (MIMO) solutions.
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