[Paper Review] Large Intelligent Surface-Based Index Modulation: A New Beyond MIMO Paradigm for 6G

Ertuğrul Başar|arXiv (Cornell University)|Apr 14, 2019

Advanced Wireless Communication TechnologiesEngineering34 citations

TL;DR

This paper proposes LIS-SSK and LIS-SM, novel index modulation schemes using large intelligent surfaces (LIS) to enhance spectral efficiency and reliability in 6G systems. By combining intelligent reflection with index modulation on receive antenna indices, the schemes achieve high spectral efficiency and ultra-reliable communication, validated through optimal and suboptimal detection and theoretical bit error rate analysis.

ABSTRACT

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.

Motivation & Objective

• To address the need for higher spectral efficiency and reliability in future 6G wireless systems beyond massive MIMO.
• To overcome the limitations of conventional MIMO and index modulation by integrating large intelligent surfaces (LIS) into index modulation.
• To propose novel LIS-assisted index modulation schemes—LIS-SSK and LIS-SM—that exploit both wavefront manipulation and antenna index selection.
• To develop optimal (maximum likelihood) and suboptimal (maximum energy-based greedy) detection techniques for the proposed schemes.
• To derive a unified theoretical framework for the average bit error probability of LIS-SSK and LIS-SM under both detection methods.

Proposed method

• Proposes LIS-SSK and LIS-SM as new modulation schemes that combine intelligent reflection via large intelligent surfaces with index modulation on multiple receive antennas.
• Employs intelligent phase shifts on the LIS to steer and enhance the signal at the receiver, improving signal-to-noise ratio and reliability.
• Utilizes the indices of active receive antennas as information-bearing symbols, thereby increasing spectral efficiency without increasing bandwidth.
• Designs a maximum energy-based suboptimal detector that selects the antenna index with the highest received signal energy for low-complexity detection.
• Develops an exhaustive search-based optimal detector that minimizes bit error probability by evaluating all possible antenna index combinations.
• Derives a unified theoretical expression for the average bit error probability of both schemes using both detection methods, enabling performance analysis and comparison.

Experimental results

Research questions

• RQ1 How can large intelligent surfaces be integrated with index modulation to enhance spectral efficiency in 6G systems?
• RQ2 What are the performance gains of LIS-SSK and LIS-SM compared to conventional MIMO and index modulation schemes?
• RQ3 How do optimal and suboptimal detection techniques affect the bit error rate and complexity of LIS-based index modulation?
• RQ4 Can a unified theoretical framework accurately model the average bit error probability of LIS-SSK and LIS-SM under both detection strategies?
• RQ5 What is the potential of LIS-assisted index modulation as a beyond-massive MIMO solution for future wireless networks?

Key findings

• LIS-SSK and LIS-SM achieve high spectral efficiency by exploiting both intelligent reflection and antenna index selection, enabling data transmission without increasing bandwidth.
• The proposed schemes demonstrate ultra-reliable communication due to enhanced signal quality from intelligent phase control on the LIS.
• Theoretical analysis confirms the accuracy of the derived average bit error probability expressions, validated through extensive computer simulations.
• The suboptimal maximum energy-based detector offers a good trade-off between performance and complexity, approaching the performance of the optimal maximum likelihood detector.
• Simulation results confirm that LIS-based index modulation outperforms traditional MIMO and index modulation in terms of spectral efficiency and reliability.
• The unified framework enables consistent performance evaluation and comparison of LIS-SSK and LIS-SM across different detection strategies.