Reconfigurable Intelligent Surface-Aided Joint Spatial and Code Index Modulation Communication System
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摘要: 传统的可重构智能表面辅助的空间调制(RIS-SM)通信系统利用接收天线的索引来传输额外的信息比特,因此该系统数据传输速率的提升是以增加接收机天线数为代价。为了提高RIS-SM系统的数据传输速率和能量效率,该文提出可重构智能表面辅助的联合空间和码索引调制(RIS-JSCIM)通信系统。该系统利用多元正交幅度调制(M-QAM)符号、空域的接收天线索引和码索引传输信息比特。天线索引和码索引传输的信息比特不需要消耗能量,因此RIS-JSCIM系统能够获得良好的能量效率。该文对比了RIS-JSCIM系统和其他系统的能量效率、系统复杂度和误码率性能。对比结果表明,所提RIS-JSCIM系统以增加一定复杂度为代价,能够获得相比于其他系统更优异的能量效率和误码率性能。Abstract:
Objective The rapid growth of wireless communication traffic is pushing existing networks toward greener, more energy-efficient solutions. Therefore, research into wireless communication systems that balance low complexity with high energy efficiency is of significant importance. Index Modulation (IM) technology, which offers advantages in low complexity and high energy efficiency, has emerged as a promising candidate for future systems. Reconfigurable Intelligent Surfaces (RIS) provide benefits such as reconfigurability, simple hardware, and low energy consumption, presenting new opportunities for wireless communication development. However, traditional RIS- aided Spatial Modulation (RIS-SM) and RIS-aided Code Index Modulation (RIS-CIM) systems use the index of the receiver antenna or code to transmit additional information bits. Therefore, the data transmission rates of RIS-SM systems improve at the cost of increasing the number of receiver antennas. To enhance the data transmission rates and energy efficiency of RIS-SM systems, this paper proposes a RIS-Aided Joint Spatial and Code Index Modulation (RIS-JSCIM) communication system. Methods The proposed system utilizes M-ary Quadrature Amplitude Modulation (M-QAM) symbols, spatial antenna index, and code index to transmit information bits. The information bits transmitted through the antenna and code indices of RIS-JSCIM do not consume energy, enabling RIS-JSCIM to achieve high energy efficiency. At the receiver, both Maximum Likelihood Detection (MLD) and low-complexity Greedy Detection (GD) algorithms are employed. The MLD algorithm, although high in complexity, provides excellent Bit Error Rate (BER) performance, while the GD algorithm offers 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 uses Monte Carlo simulations to evaluate its BER performance. The performance metrics of the RIS-JSCIM system are also compared with those of other systems. The results show that, despite a slight increase in system complexity, the RIS-JSCIM system outperforms others in terms of energy efficiency and BER performance. Results and Discussions This paper compares the energy efficiency, system complexity, and BER performance of the RIS-JSCIM system with other systems. The comparison shows that, when the number of receiving antennas NR=4 and the number of Walsh codes L=8, the energy efficiency of the RIS-JSCIM system improves by 60% and 6.67% compared to the RIS-SM and RIS-CIM systems, respectively ( Table 2 ). The complexity of the RIS-JSCIM system with the GD algorithm is comparable to that of the GCIM-SM system and slightly higher than that of the RIS-CIM system (Table 3 ). Simulation results indicate that, at BER=10–5, the 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 show significant improvements in BER performance, with the RIS-JSCIM system outperforming the RIS-CIM system at high Signal-to-Noise Ratios (SNR). For example, at BER=10–5 and N=128, the RIS-JSCIM system offers 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 outperforms that of the RIS-SM system (Fig. 7 ).Conclusions The RIS-JSCIM system utilizes M-QAM symbols to transmit information bits and employs the receiver antenna and code indices to convey additional information. Both the MLD and GD algorithms are introduced for recovering the transmitted bits. The MLD algorithm explores all possible combinations of receiver antenna indices, code indices, and M-QAM symbols, offering improved BER performance at the cost of increased complexity. In contrast, the GD algorithm performs separate detection of antenna indices, code indices, and M-QAM symbols, providing a favorable trade-off between complexity and BER performance. The RIS-JSCIM system transmits receiver antenna index and code index bits without consuming energy, resulting in high energy efficiency. When the number of receiving antennas NR=4 and the number of Walsh codes L=8, the energy efficiency of the RIS-JSCIM system improves by 60% and 6.67% compared to the RIS-SM and RIS-CIM systems, respectively. Moreover, when the BER=10–5 and N=128, the RIS-JSCIM system offers a 5 dB SNR gain over the RIS-CIM system. -
表 1 本文所提RIS-JSCIM与其他方案的主要差异对比
表 2 本文所提RIS-JSCIM与RIS-SM, RIS-CIM方案的能量效率对比(%)
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