results: 通过 simulations，本文证明了 CFO 对 SCMA-OFDM 系统的影响，并显示了当正常化 CFO 超过 0.02 时，系统的 BER 性能会受到显著的降低。Abstract
Sparse code multiple access (SCMA) building upon orthogonal frequency division multiplexing (OFDM) is a promising wireless technology for supporting massive connectivity in future machine-type communication networks. However, the sensitivity of OFDM to carrier frequency offset (CFO) poses a major challenge because it leads to orthogonality loss and incurs intercarrier interference (ICI). In this paper, we investigate the bit error rate (BER) performance of SCMA-OFDM systems in the presence of CFO over both Gaussian and multipath Rayleigh fading channels. We first model the ICI in SCMA-OFDM as Gaussian variables conditioned on a single channel realization for fading channels. The BER is then evaluated by averaging over all codeword pairs considering the fading statistics. Through simulations, we validate the accuracy of our BER analysis and reveal that there is a significant BER degradation for SCMA-OFDM systems when the normalized CFO exceeds 0.02.
摘要
稀疏码多ступ存取（SCMA）基于对幂频分多址（OFDM）是未来机器类通信网络中支持大量连接的承诺技术。然而，OFDM对幂频偏移（CFO）的敏感性 pose a major challenge，因为它会导致orthogonality loss和产生intercarrier interference（ICI）。在这篇论文中，我们研究SCMA-OFDM系统在CFO的存在下的比特错误率（BER）性能。我们首先模型了SCMA-OFDM中ICI的分布为Gaussian变量，conditioned on a single channel realization for fading channels。然后，我们通过平均所有codeword pair来评估BER。通过实验，我们验证了我们的BER分析的准确性，并发现了CFO的normalized值超过0.02时，SCMA-OFDM系统的BER受到了显著的下降。
Design and Performance Analysis of Index Modulation Empowered AFDM System
for: 本研究旨在提高 affine frequency division multiplexing (AFDM) 的 bit error rate (BER) 和能效率 (EE) 性能，通过 incorporating index modulation (IM)。
methods: 该方案使用 $M$-ary constellation symbols 和滤波器偏振信号 (SCs) 的活动来传输信息，并提出了两种功率分配策略（power reallocation (PR) 策略和 power saving (PS) 策略）来提高 BER 和 EE 性能。
results: simulations 结果表明，提案的 AFDM-IM 方案在 BER 性能方面比 conventional AFDM 方案更高。Abstract
In this letter, we incorporate index modulation (IM) into affine frequency division multiplexing (AFDM), called AFDM-IM, to enhance the bit error rate (BER) and energy efficiency (EE) performance. In this scheme, the information bits are conveyed not only by $M$-ary constellation symbols, but also by the activation of the chirp subcarriers (SCs) indices, which are determined based on the incoming bit streams. Then, two power allocation strategies, namely power reallocation (PR) strategy and power saving (PS) strategy, are proposed to enhance BER and EE performance, respectively. Furthermore, the average bit error probability (ABEP) is theoretically analyzed. Simulation results demonstrate that the proposed AFDM-IM scheme achieves better BER performance than the conventional AFDM scheme.
摘要
在这封信中，我们将索引调制（IM）引入了分形频分多路传输（AFDM），称之为AFDM-IM，以提高比特错误率（BER）和能效率（EE）性能。在该方案中，信息比特不仅由$M$-ary符号传输，而且还由快速抽象（SC）的索引活动决定。然后，我们提议了两种功率分配策略，namely power reallocation（PR）策略和power saving（PS）策略，以提高BER和EE性能。此外，我们还 theoretically analyze了均值比特错误概率（ABEP）。实验结果表明，我们的AFDM-IM方案比传统AFDM方案表现更好。
Joint Multiple FMCW Chirp Sequence Processing for Velocity Estimation and Ambiguity Resolving
paper_authors: Tarik Kazaz, Karan Jayachandra, Arie Koppellar, Yiting Lu
for: This paper aims to improve the accuracy and resolution of velocity estimation in FMCW automotive radar systems by jointly processing multiple chirp sequences and resolving possible ambiguities.
methods: The proposed algorithm uses a novel approach that combines the strengths of multiple chirp sequences with co-prime delay shifts, while avoiding the limitations of classical spectral estimation techniques based on FFT.
results: The proposed algorithm achieves statistically efficient and gridless velocity estimation with super-resolution properties, outperforming traditional methods in terms of resolution and accuracy. These results are validated through numerical simulations and experiments with an automotive radar IC.Abstract
In FMCW automotive radar applications, it is often a challenge to design a chirp sequence that satisfies the requirements set by practical driving scenarios and simultaneously enables high range resolution, large maximum range, and unambiguous velocity estimation. To support long-range scenarios the chirps should have a sufficiently long duration compared to their bandwidth. At the same time, the long chirps result in ambiguous velocity estimation for targets with high velocity. The problem of velocity ambiguity is often solved by using multiple chirp sequences with co-prime delay shifts between them. However, coherent processing of multiple chirp sequences is not possible using classical spectral estimation techniques based on Fast Fourier Transform (FFT). This results in statistically not efficient velocity estimation and loss of processing gain. In this work, we propose an algorithm that can jointly process multiple chirp sequences and resolve possible ambiguities present in the velocities estimates. The resulting algorithm is statistically efficient and gridless. Furthermore, it increases the resolution of velocity estimation beyond the natural resolution due to its super-resolution properties. These results are confirmed by both numerical simulations and experiments with automotive radar IC.
摘要
在汽车FMCW雷达应用中，设计一个适合实际驾驶情况的滤波序quence是一个长期挑战。要支持长距离enario，滤波序quence应该具有足够的持续时间，但长滤波序quence会导致高速目标的干扰估计带有很大的偏差。为解决速度偏差问题，通常使用多个滤波序quence的差分延迟来解决这个问题。然而，使用多个滤波序quence的协同处理是不可能使用基于快速傅立叶变换（FFT）的经典 spectral estimation技术来实现。这会导致 estatisticamente不有效的速度估计和数据损失。在这项工作中，我们提出了一种可以同时处理多个滤波序quence并解决可能存在的速度估计偏差的算法。该算法具有 statistically efficient和gridless的特点，同时具有超分辨能力，可以超越自然的分辨能力。这些结果通过数值仿真和汽车雷达IC实验得到了证明。
Prior-Aware Robust Beam Alignment for Low-SNR Millimeter-Wave Communications
results: 对于使用这种技术的 simulate 结果，我们在使用 DeepMIMO 数据集中的动态低SNR 通信环境中发现了与现有扩散对齐技术相比的更高稳定性。Abstract
This paper presents a robust beam alignment technique for millimeter-wave communications in low signal-to-noise ratio (SNR) environments. The core strategy of our technique is to repeatedly transmit the most probable beam candidates to reduce beam misalignment probability induced by noise. Specifically, for a given beam training overhead, both the selection of candidates and the number of repetitions for each beam candidate are optimized based on channel prior information. To achieve this, a deep neural network is employed to learn the prior probability of the optimal beam at each location. The beam misalignment probability is then analyzed based on the channel prior, forming the basis for an optimization problem aimed at minimizing the analyzed beam misalignment probability. A closed-form solution is derived for a special case with two beam candidates, and an efficient algorithm is developed for general cases with multiple beam candidates. Simulation results using the DeepMIMO dataset demonstrate the superior performance of our technique in dynamic low-SNR communication environments when compared to existing beam alignment techniques.
摘要
Hybrid Hierarchical DRL Enabled Resource Allocation for Secure Transmission in Multi-IRS-Assisted Sensing-Enhanced Spectrum Sharing Networks
paper_authors: Lingyi Wang, Wei Wu, Fuhui Zhou, Qihui Wu, Octavia A. Dobre, Tony Q. S. Quek
For: The paper is written to explore the potential of intelligent reflective surfaces (IRSs) in enhancing spectrum sharing and secure transmission performance in wireless networks.* Methods: The paper proposes an intelligent resource allocation scheme based on double deep Q networks (D3QN) algorithm and soft Actor-Critic (SAC) algorithm to maximize the secure transmission rate of the secondary network by jointly optimizing IRS pairings, subchannel assignment, transmit beamforming of the secondary base station, reflection coefficients of IRSs, and the sensing time.* Results: The paper shows that the proposed intelligent scheme can efficiently enhance the secrecy rate and spectrum utilization of the secondary network, and the hierarchical reinforcement learning method can effectively tackle the sparse reward problem caused by a significant amount of reflection elements of multiple IRSs. The paper also demonstrates the superiority of multi-IRS design in enhancing security performance and spectrum utilization, but inappropriate deployment of IRSs can reduce the security performance with the presence of multiple eavesdroppers (Eves).Here is the information in Simplified Chinese text:* For: 本文是为探讨智能反射表面（IRS）在无线网络中提高频率分享和安全传输性能而写的。* Methods: 本文提议一种基于double deep Q networks（D3QN）算法和soft Actor-Critic（SAC）算法的智能资源分配方案，以最大化次要网络的安全传输率，并jointly 优化IRS的匹配、频率分配、次要基站的发射扬anner、反射率和感知时间。* Results: 本文显示，提议的智能方案可以高效地提高次要网络的机密率和频率利用率，而层次学习法可以有效地解决由多个反射元件引起的罕见奖励问题。同时，本文也示出了多个IRS的设计可以在存在多个伪装者（Eves）的情况下提高安全性和频率利用率，但是不当部署IRS可能会降低安全性表现。Abstract
Secure communications are of paramount importance in spectrum sharing networks due to the allocation and sharing characteristics of spectrum resources. To further explore the potential of intelligent reflective surfaces (IRSs) in enhancing spectrum sharing and secure transmission performance, a multiple intelligent reflection surface (multi-IRS)-assisted sensing-enhanced wideband spectrum sharing network is investigated by considering physical layer security techniques. An intelligent resource allocation scheme based on double deep Q networks (D3QN) algorithm and soft Actor-Critic (SAC) algorithm is proposed to maximize the secure transmission rate of the secondary network by jointly optimizing IRS pairings, subchannel assignment, transmit beamforming of the secondary base station, reflection coefficients of IRSs and the sensing time. To tackle the sparse reward problem caused by a significant amount of reflection elements of multiple IRSs, the method of hierarchical reinforcement learning is exploited. An alternative optimization (AO)-based conventional mathematical scheme is introduced to verify the computational complexity advantage of our proposed intelligent scheme. Simulation results demonstrate the efficiency of our proposed intelligent scheme as well as the superiority of multi-IRS design in enhancing secrecy rate and spectrum utilization. It is shown that inappropriate deployment of IRSs can reduce the security performance with the presence of multiple eavesdroppers (Eves), and the arrangement of IRSs deserves further consideration.
摘要
“安全通信是谐 spectrum sharing 网络中的关键因素，因为spectrum resource的分配和共享特性。为了更深入探讨智能反射表面（IRS）在增强spectrum sharing和安全传输性能方面的潜力，本文提出了一种多智能反射表面（multi-IRS）帮助的感知增强广泛频率共享网络。通过物理层安全技术，提出了一种基于double deep Q networks（D3QN）算法和soft Actor-Critic（SAC）算法的智能资源分配方案，以最大化次网络的安全传输率。通过联合IRS对策、子频分配、次基站的发射形式、反射率和感知时间的优化，提高了次网络的安全传输率。为了解决多个反射表面的稀疏奖励问题，利用了层次学习法。并 introduce了一种基于传统数学方法的可alternative optimization（AO）方法，以验证我们提出的智能方案的计算复杂性优势。实验结果表明，我们的智能方案效果高，并且多个IRS设计能够提高机密率和频率利用率。研究结果还表明，不当部署IRS可能会降低安全性性，并且IRS的布置需要进一步考虑。”
Covert Communications in STAR-RIS-Aided Rate-Splitting Multiple Access Systems
paper_authors: Heng Chang, Hai Yang, Shuobo Xu, Xiyu Pang, Hongwu Liu
for: investigate covert communications in a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided rate-splitting multiple access (RSMA) system
methods: derive analytical expression for the minimum average detection error probability of Willie, based on which a covert rate maximization problem is formulated
results: optimize transmit power allocation, common rate allocation, and STAR-RIS reflection/transmission beamforming to maximize Bob’s covert rate while confusing Willie’s monitoring, subject to Grace’s quality of service (QoS) requirementsHere’s the format you requested:
for: <what are the paper written for?>
methods: <what methods the paper use?>
results: <what results the paper get?>I hope that helps! Let me know if you have any other questions.Abstract
In this paper, we investigate covert communications in a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided rate-splitting multiple access (RSMA) system. Under the RSMA principles, the messages for the covert user (Bob) and public user (Grace) are converted to the common and private streams at the legitimate transmitter (Alice) to realize downlink transmissions, while the STAR-RIS is deployed not only to aid the public transmissions from Alice to Grace, but also to shield the covert transmissions from Alice to Bob against the warden (Willie). To characterize the covert performance of the considered STAR-RIS-aided RSMA (STAR-RIS-RSMA) system, we derive analytical expression for the minimum average detection error probability of Willie, based on which a covert rate maximization problem is formulated. To maximize Bob's covert rate while confusing Willie's monitoring, the transmit power allocation, common rate allocation, and STAR-RIS reflection/transmission beamforming are jointly optimized subject to Grace's quality of service (QoS) requirements. The non-convex covert rate maximization problem, consisting of highly coupled system parameters are decoupled into three sub-problems of transmit power allocation, common rate allocation, and STAR-RIS reflection/transmission beamforming, respectively. To obtain the rank-one constrained optimal solution for the sub-problem of optimizing the STAR-RIS reflection/transmission beamforming, a penalty-based successive convex approximation scheme is developed. Moreover, an alternative optimization (AO) algorithm is designed to determine the optimal solution for the sub-problem of optimizing the transmit power allocation, while the original problem is overall solved by a new AO algorithm.
摘要
在这篇论文中，我们研究了同时发送和反射的可配置智能表面（STAR-RIS）支持的秘密通信系统。在RSMA原则下，在Alice发送器上，用于Bob和Grace用户的消息被转换为公共流和私有流，以实现下行传输。同时，STAR-RIS被部署，不仅为Alice发送器提供帮助，还为Bob用户的秘密传输屏蔽了外部监视（Willie）。为了描述考虑STAR-RIS的潜在性能，我们得出了Willie监视下的最小平均检测错误概率的分析表达。基于这个表达，我们定义了一个潜在秘密率最大化问题。要 Maximizing Bob的秘密率， transmit power allocation, common rate allocation, 和STAR-RIS反射/传输扩散被 jointly 优化，以满足Grace用户的服务质量要求。这个不对称的潜在秘密率最大化问题，包括高度相互关联的系统参数，通过将其分解为三个互不相关的互斥问题： transmit power allocation、common rate allocation、和STAR-RIS反射/传输扩散。为了获得STAR-RIS反射/传输扩散优化问题的rank-one constrained optimal solution，我们开发了一种罚偿基于successive convex approximation scheme。此外，我们还设计了一种代替优化（AO）算法，用于解决 transmit power allocation优化问题，而原始问题则通过一种新的AO算法得到解决。
Perceptive, Resilient, and Efficient Networks assisted by Reconfigurable Intelligent Surfaces
results: 研究发现，通过使用高级波前工程技术和RIS，可以实现高频无线通信系统中的聚集、折叠和自我修复功能，超过了现有技术的限制。此外，本研究还提出了一种基于混合波前成形/波前聚焦方法的位置确定技术。Abstract
Wireless communications are nowadays shifting to higher operation frequencies with the aim to meet the ever-increasing demand for bandwidth. While reconfigurable intelligent surfaces (RISs) are usually envisioned to restore the line-of-sight of blocked links and to efficiently counteract the increased pathloss, their functionalities can extend far beyond these basic operations. Owing to their large surface and the multitude of scatterers, RISs can be exploited to perform advanced wavefront engineering, essentially transforming the incident beam into a non-trivial reflected beam that is able to address the challenges of high frequencies more efficiently than conventional beam-forming. In this paper it is demonstrated how advanced wavefront engineering with RISs enables beam profiles that are able to focus, bend and self-heal, thus offering functionalities beyond the current state-of-the-art. Their potential as enablers of perceptive, resilient, and efficient networks is discussed, and a localization technique based on a hybrid beam-forming/beam-focusing scheme is demonstrated.
摘要
无线通信现在正在转移到更高的运作频率，以满足不断增长的带宽需求。而可配置智能表面（RIS）通常被视为恢复受阻链路的视线和高效地减少碰撞的方法。但RIS的功能不仅Stop there，它们可以被利用来进行高级波前工程，使入射ibeam变成一种非常复杂的反射ibeam，可以更高效地处理高频信号than conventional beam-forming。本文示出了通过RIS进行高级波前工程所带来的 beam profile，可以弯曲、集中和自我修复，从而提供了现有状态艺术的功能以上。RIS的潜在作用是使网络更加敏感、可靠和高效，这一点会在文中进行讨论。此外，我们还示出了基于混合射频/射频聚焦的地址技术，可以帮助实现高级网络的地址。
Securing the Sensing Functionality in ISAC Networks: An Artificial Noise Design
results: 实验结果表明，我们的提议方法可以提高探测器的敏感信息积累量，同时限制Eve的探测积累量，相比于基eline方案。另外，使用噪声增强技术可以进一步提高探测安全性。Abstract
Integrated sensing and communications (ISAC) systems employ dual-functional signals to simultaneously accomplish radar sensing and wireless communication tasks. However, ISAC systems open up new sensing security vulnerabilities to malicious illegitimate eavesdroppers (Eves) that can also exploit the transmitted waveform to extract sensing information from the environment. In this paper, we investigate the beamforming design to enhance the sensing security of an ISAC system, where the communication user (CU) serves as a sensing Eve. Our objective is to maximize the mutual information (MI) for the legitimate radar sensing receiver while considering the constraint of the MI for the Eve and the quality of service to the CUs. Then, we consider the artificial noise (AN)-aided beamforming to further enhance the sensing security. Simulation results demonstrate that our proposed methods achieve MI improvement of the legitimate receiver while limiting the sensing MI of the Eve, compared with the baseline scheme, and that the utilization of AN further contributes to sensing security.
摘要
integated sensing and communications (ISAC) 系统使用双功能信号同时完成雷达探测和无线通信任务。然而，ISAC 系统开放了新的探测安全漏洞， allowing malicious illegitimate eavesdroppers (Eves) to exploit the transmitted waveform to extract sensing information from the environment。在本文中，我们研究了束形设计，以增强 ISAC 系统的探测安全性。我们的目标是最大化各自信息（MI） для合法的雷达探测接收器，同时考虑了黑客（Eve）的探测MI和服务质量 для用户（CU）。然后，我们考虑了人工噪声（AN）-aided 束形设计，以进一步增强探测安全性。实验结果表明，我们的提议方法可以提高合法接收器的MI，同时限制黑客的探测MI，相比基eline scheme。此外，使用 AN 进一步提高了探测安全性。
Optimal Placement of Transmissive RIS in the Near Field for Capacity Maximization in THz Communications
results: 模拟结果表明，RIS的最佳布置不仅取决于发射器和接收器之间的距离，还取决于发射器和接收器之间的天线间距。Abstract
This study centers on Line-of-Sight (LoS) MIMO communication enabled by a Transmissive Reconfigurable Intelligent Surface (RIS) operating in the Terahertz (THz) frequency bands. The study demonstrates that the introduction of RIS can render the curvature of the wavefront apparent over the transmit and receive arrays, even when they are positioned in the far field from each other. This phenomenon contributes to an enhancement in spatial multiplexing. Notably, simulation results underline that the optimal placement of the RIS in the near-field is not solely contingent on proximity to the transmitter (Tx) or receiver (Rx) but relies on the inter-antenna spacing of the Tx and Rx.
摘要