Reconfigurable Intelligent Surface-Aided Joint Spatial and Code Index Modulation Communication System

CHEN Pingping; ZHANG Yunxin; DU Weiqing

doi:10.11999/JEIT240987

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CHEN Pingping, ZHANG Yunxin, DU Weiqing. Reconfigurable Intelligent Surface-Aided Joint Spatial and Code Index Modulation Communication System[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240987

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CHEN Pingping, ZHANG Yunxin, DU Weiqing. Reconfigurable Intelligent Surface-Aided Joint Spatial and Code Index Modulation Communication System[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240987

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Reconfigurable Intelligent Surface-Aided Joint Spatial and Code Index Modulation Communication System

doi: 10.11999/JEIT240987

1.
School of Advanced Manufacturing, Fuzhou University, Quanzhou 362251, China
2.
College of Physics and Information Engineering, Fuzhou University, Quanzhou 350108, China

Funds: The National Natural Science Foundation of China (62171135)

Received Date: 2024-11-05
Rev Recd Date: 2025-02-11

Available Online: 2025-02-25

Abstract

Abstract

Objective The rapid growth of wireless communication traffic is driving existing communication networks toward greener and more energy-efficient solutions. Consequently, research into wireless communication systems that balance low complexity with high energy efficiency is of significant importance. Index Modulation (IM) technology, with its notable advantages in low complexity and high energy efficiency, has emerged as a promising candidate for future communication systems. Reconfigurable Intelligent Surfaces (RIS) offer benefits such as reconfigurability, simple hardware, and low energy consumption, presenting new opportunities for the development of wireless communication systems. However, Traditional RIS-aided Spatial Modulation (RIS-SM) communication systems and RIS-aided Code Index Modulation (RIS-CIM) communication systems utilize the index of the receiver antenna or code to transmit additional information bits. Therefore, the data transmission rates of the RIS-SM systems are improved at the cost of increasing the number of receiver antennas. In order to improve the data transmission rates and energy efficiencies of RIS-SM systems, a Reconfigurable Intelligent Surface-aided Joint Space and Code Index Modulation (RIS-JSCIM) communication system is proposed in this paper. Methods The proposed system leverages M-ary Quadrature Amplitude Modulation (M-QAM) symbols, spatial antenna index and code index to transmit information bits. The information bits transmitted by the antenna index and code index of RIS-JSCIM do not consume energy, and therefore RIS-JSCIM can achieve good energy efficiency. At the receiver, both Maximum Likelihood Detection (MLD) and low-complexity Greedy Detection (GD) algorithms are introduced. The MLD algorithm, while operating at a high complexity, delivers excellent Bit Error Rate (BER) performance; conversely, the GD algorithm provides a better trade-off between complexity and BER performance. Furthermore, this paper analyzes the energy efficiency and complexity of the proposed RIS-JSCIM system, and employs Monte Carlo simulations to assess the BER performance of the scheme. Additionally, the performance metrics of the RIS-JSCIM system are compared with those of other systems. The comparative results indicate that, despite a certain increase in system complexity, the RIS-JSCIM system achieves superior energy efficiency and BER performance relative to other systems. Results and Discussions This paper compares the energy efficiency, system complexity, and BER performance of the RIS-JSCIM system with other systems. The comparison results indicate that, when the number of receiving antennas ${N_R} = 4$ and the number of Walsh codes $L = 8$, the energy efficiency of the RIS-JSCIM system is improved by 60% and 6.66% compared to the RIS-SM and RIS-CIM systems, respectively (Table 2). The complexity of the RIS-JSCIM system when employing the GD algorithm is equivalent to that of the GCIM-SM system and slightly higher than that of the RIS-CIM system (Table 3).Simulation results demonstrate that at ${\text{BER}} = {10^{ - 5}}$, the proposed RIS-JSCIM system achieves a performance gain of over 6 dB compared to the RIS-CIM system (Fig. 5). As the number of RIS units $N$ increases, both the RIS-JSCIM and RIS-CIM systems exhibit significant improvements in BER performance, with the RIS-JSCIM system outperforming the RIS-CIM system at high Signal-to-Noise Ratios (SNR). For example, when the ${\text{BER}} = {10^{ - 5}}$ and $N = 128$, the proposed RIS-JSCIM system provides a 5 dB SNR gain over the RIS-CIM system (Fig.6). Similarly, at high SNR, the BER performance of the RIS-JSCIM system consistently exceeds that of the RIS-SM system (Fig.7). Conclusions This paper proposes a RIS-JSCIM system, which not only uses M-QAM symbols to transmit information bits but also utilizes the index of the receiver antenna and code to convey additional information bits. Furthermore, we introduce the Maximum Likelihood Detection (MLD) algorithm and the Gradient Descent (GD) algorithm for recovering the transmitted information bits. The MLD algorithm searches through all possible combinations of receiver antenna indices, code indices, and M-QAM symbols, thereby achieving improved bit error rate (BER) performance at the expense of increased complexity. In contrast, the GD algorithm recovers the received antenna index bits, code index bits, and M-QAM modulation bits through separate detection of antenna indices, code indices, and M-QAM demodulation, thus achieving a favorable trade-off between complexity and BER performance. The RIS-JSCIM system transmits receiver antenna index bits and code index bits without consuming energy, enabling the system to attain high energy efficiency. When the number of receiving antennas ${N_R} = 4$ and the number of Walsh codes $L = 8$, the energy efficiency of the RIS-JSCIM system is improved by 60% and 6.66% compared to the RIS-SM and RIS-CIM systems, respectively. Furthermore, when the ${\text{BER}} = {10^{ - 5}}$ and $N = 128$, the proposed RIS-JSCIM system provides a 5 dB SNR gain over the RIS-CIM system.

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References(21)

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