Nested Tensor-based Simultaneous Localization and Communication Method for RIS-assisted Near-field Integrated Sensing And Communication Systems
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摘要: 可重构智能表面(RIS)因其能够智能配置无线传输环境而成为增强通信和感知的革新技术。随着RIS孔径的增加,电磁场特性发生根本性变化,近场范围扩大。与远场通信和感知不同,近场通信和感知需要考虑更为复杂的信道结构特性,这使得RIS辅助的毫米波系统在近场通信和感知方面更具挑战。基于此,该文研究一种RIS辅助通信感知一体化(ISAC)的近场传输系统。首先,利用所考虑的ISAC场景的多维度资源和Khatri-Rao空时编码方法,将接收到的ISAC信号构造为4阶嵌套张量。然后,利用嵌套张量的代数结构和对近场信道模型的2阶菲涅耳近似,设计一种基于嵌套张量的同时定位和通信方案,在不发送专用导频的情况下实现近场环境散射点和用户定位以及信息符号检测。仿真结果表明,提出的方案具有较好的ISAC性能并优于现有方案。此外,即使是在高阶调制情况下,所提方案也有良好的定位精度和的误码率性能。Abstract:
Objective As wireless communication technology advances, sensing and communication systems are shifting toward higher frequency bands, larger antenna arrays, and miniaturization. This integration of hardware architecture, channel characteristics, and signal processing enables wireless infrastructure to support environmental sensing in addition to communication. Technologies such as millimeter-wave communication, Reconfigurable Intelligent Surface (RIS), and Integrated Sensing And Communication (ISAC) facilitate this development. Although extensive research has examined RIS applications in ISAC systems, expanding the RIS aperture fundamentally alters electromagnetic field characteristics, extending the near-field range. Unlike far-field scenarios, near-field communication and sensing exhibit more complex channel structures, posing challenges for RIS-assisted millimeter-wave systems. To address these challenges, this study proposes an ISAC framework and develops a nested tensor-based Simultaneous Localization And Communication (SLAC) scheme. This approach localizes scattering points and users while detecting information symbols in near-field environments, eliminating the need for dedicated pilot signals. Methods First, a near-field spherical wave transmission model is established. To mitigate the complexity introduced by spatial path variations across reflection units, a channel model based on the second-order Taylor approximation is derived, incorporating distance, direction of arrival, and angle of arrival. Next, to fully utilize the time redundancy of Khatri-Rao Space-Time (KRST) coding, the received signal is formulated as a nested tensor model comprising outer and inner PARAFAC tensors, enabling the development of a nested tensor-based SLAC scheme. For the outer PARAFAC tensor, an Alternating Least Squares (ALS) algorithm is employed for channel matrix estimation and information symbol detection. For the inner PARAFAC model, a two-stage algorithm is used for channel parameter estimation and User Equipment (UE) and scatterer localization. The Minimum Description Length (MDL) method determines the number of transmission channel paths. In the first stage, the ALS method decomposes the PARAFAC model to estimate channel parameters. In the second stage, the ESPRIT algorithm is applied to refine parameter estimation and perform localization. Finally, the estimated channel parameters are used to determine the locations of the UE and scatterer points. Results and Discussions The proposed scheme first utilizes the multi-dimensional resources of the ISAC scenario and the KRST coding method to structure the received ISAC signals into a fourth-order nested tensor. Leveraging the algebraic properties of the nested tensor and the second-order Fresnel approximation of the near-field channel model, the nested tensor-based SLAC scheme is designed to enable near-field localization of scattering points and UE, as well as information symbol detection. Simulation results demonstrate that the proposed scheme achieves superior ISAC performance compared with existing methods ( Fig. 2 ,Fig. 3 ,Fig. 4 ). Performance improves as the number of subcarriers increases (Fig. 2 ,Fig. 3 ). Additionally, the scheme maintains high localization accuracy and symbol detection performance even under higher-order modulation (Fig. 5 ,Fig. 6 ). Further improvements in ISAC performance are observed with an increased number of time slots and coding length (Fig. 7 ,Fig. 8 ). The results also indicate good convergence across various parameter configurations.Conclusions This paper proposes an RIS-assisted ISAC millimeter-wave near-field transmission scheme based on a nested tensor model and develops a nested tensor-based SLAC scheme leveraging the second-order Fresnel approximation of the near-field channel model. The constructed nested tensor model exhibits an algebraic structure, enabling the proposed scheme to operate without dedicated pilot signals. Moreover, the model integrates multiple dimensions of sensing and communication signals, enhancing information symbol detection and target localization accuracy by extracting additional useful information. Simulation results demonstrate that the proposed method achieves good convergence across various parameter configurations. Compared with existing methods, it exhibits superior sensing performance. Under higher-order modulation, it maintains excellent information symbol detection and achieves high-precision channel state information recovery, providing centimeter-level localization accuracy. Furthermore, the method is scalable and can be applied to larger-scale systems, such as expanding RIS or increasing the number of antennas. However, system scalability increases computational complexity, particularly for higher-order tensor models. To address this, optimizing the algorithm structure, such as introducing tensor-based closed-form algorithms (e.g., higher-order singular value decomposition), is a promising approach. -
1 基于嵌套张量的SLAC算法
初始化:相移矩阵$ {{\boldsymbol{\varPhi}} _k} $,编码矩阵$ {\boldsymbol{C}} $,信道矩阵$ {{\boldsymbol{H}}_{{\text{BI,}}k}} $,接收信
号$ {{\boldsymbol{Y}}_{k,p,q}} $(1)将接收信号$ {{\boldsymbol{Y}}_{k,p,q}} $构造成张量$ {\mathcal{Y}_{k,q}} $ (2)借助张量$ {\mathcal{Y}_{k,q}} $,使用ALS算法求解$ {\hat {\boldsymbol{S}}_k} $和$ {\hat {\boldsymbol{H}}_k} $ (3)将$ {\hat {\boldsymbol{H}}_k} $构造张量$ {\hat {\mathcal{H}}_k} $,通过伪逆计算未知信道矩阵$ {\hat {\boldsymbol{H}}_{{\text{IU,}}k}} $ (4)将$ {\hat {\boldsymbol{H}}_{{\text{IU,}}k}} $构造张量$ {\hat {\mathcal{H}}_{{\text{IU}}}} $,使用ALS算法分解因子矩阵得到
$ \left\{ {{{\hat {\boldsymbol{A}}}_{{\text{IT}}}},{{\hat {\boldsymbol{A}}}_{\text{U}}},\hat {\boldsymbol{B}}} \right\} $(5)使用MDL算法求解路径数目$ L $ (6)通过下采样方法得到$ {\hat {\boldsymbol{A}}_{{\text{IT}}}} $和$ {\hat {\boldsymbol{A}}_{\text{U}}} $对应的协方差矩阵 (7)使用ESPRIT算法和基于相关的算法估计信道参数
$ \left\{ {{{\hat \phi }_{{\text{U}},l}},{{\hat \theta }_{{\text{U}},l}},{{\hat \phi }_{{\text{IT}},l}},{{\hat \theta }_{{\text{IT}},l}},{{\hat \tau }_l}} \right\}_{l = 1}^L $(8)使用已估计的信道参数进行定位得到$ {\hat {\boldsymbol{\rho}} _{\text{U}}} $和$ \left\{ {{{\hat{\boldsymbol{ \rho}} }_{{\text{R,}}l}}} \right\}_{l = 1}^L $ 输出:发送信息符号$ {\hat S_k} $,信道参数
$ \left\{ {{{\hat \phi }_{{\text{U}},l}},{{\hat \theta }_{{\text{U}},l}},{{\hat \phi }_{{\text{IT}},l}},{{\hat \theta }_{{\text{IT}},l}},{{\hat \tau }_l}} \right\}_{l = 1}^L $,用户和散射点位置$ {\hat {\boldsymbol{\rho}} _{\text{U}}} $和
$ \left\{ {{{\hat {\boldsymbol{\rho }}}_{{\text{R,}}l}}} \right\}_{l = 1}^L $ -
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