Multiple-antenna technologies are evolving towards larger aperture sizes, extremely high frequencies, and innovative antenna types. This evolution is fostering the emergence of near-field communications (NFC) in future wireless systems. Considerable attention has been directed towards this cutting-edge technology due to its potential to enhance the capacity of wireless networks by introducing increased spatial degrees of freedom (DoFs) in the range domain. Within this context, a comprehensive review of the state of the art on NFC is presented, with a specific focus on its 1) fundamental operating principles, 2) channel modeling, 3) performance analysis, 4) signal processing techniques, and 5) integration with other emerging applications. Specifically, 1) the basic principles of NFC are characterized from both physics and communications perspectives, unveiling its unique properties in contrast to far-field communications. 2) Building on these principles, deterministic and stochastic near-field channel models are explored for spatially-discrete (SPD) and continuous-aperture (CAP) arrays. 3) Based on these models, existing contributions to near-field performance analysis are reviewed in terms of DoFs/effective DoFs (EDoFs), the power scaling law, and transmission rate. 4) Existing signal processing techniques for NFC are systematically surveyed, which include channel estimation, beamforming design, and low-complexity beam training. 5) Major issues and research opportunities in incorporating near-field models into other promising technologies are identified to advance NFC's deployment in next-generation networks. Throughout this paper, promising directions are highlighted to inspire future research endeavors in the realm of NFC, underscoring its significance in the advancement of wireless communication technologies.

Near-Field Communications: A Comprehensive Survey

—In this paper, we study a communication-centric integrated sensing and communication (ISAC) approach, where an access point (AP) communicates with users, while a passive radar (PR) is present in the environment. We investigate the deployment of a reconﬁgurable intelligent surface (RIS) to enable the PR to localize a target. We derive an optimization problem for updating the phase shifters of the RIS per epoch. Due to the limited information at the PR, such as unknown payload information and unknown number of targets in the scene, we propose two methods capable of performing joint angle of arrival estimation and detection of the targets. We demonstrate the superior performance of the methods onto the proposed setting through numerical simulations, in comparison to a no- RIS baseline scheme.

RIS-Enabled Passive Radar towards Target Localization

In this paper, an efficient power control based MF-TDMA resource allocation scheme is proposed for next generation military satellite communication systems. The proposed scheme has the flexibility is used to support heterogeneous terminals with differ in transmission capabilities. The method can be divided into two parts : burst size calculation and burst structure determination. At first, we estimate the link budget taken into account a dynamic satellite link state variation. Then, applicable ACM level and burst size is chosen. In burst structure determination phase, we reorganize the burst structure in time-frequency domain by controlling limited power, bandwidth, time resources. In particular, we compensate the power spectral density among different terminals to integrate them in same transponder, Furthermore, we increase the packing efficiency by controlling the ACM level of the burst in applicable power spectral density range. Simulation results show that the method increase the spectral efficiency and burst packing efficiency. In addition, slot allocation rejection ratio is successfully reduced.

/pdf/a-power-control-based-mf-tdma-resource-allocation-scheme-for-lbcsesp083.pdf

A Power Control-Based MF-TDMA Resource Allocation Scheme for Next Generation Military Satellite Communication Systems

There have been recently many studies demonstrating that the performance of wireless communication systems can be significantly improved by a reconfigurable intelligent surface (RIS), which is an attractive technology due to its low power requirement and low complexity. This paper presents a measurement-based characterization of RISs for providing physical layer security, where the transmitter (Alice), the intended user (Bob), and the eavesdropper (Eve) are deployed in an indoor environment. Each user is equipped with a software-defined radio connected to a horn antenna. The phase shifts of reflecting elements are software controlled to collaboratively determine the amount of received signal power at the locations of Bob and Eve in such a way that the secrecy capacity is aimed to be maximized. An iterative method is utilized to configure a Greenerwave RIS prototype consisting of 76 passive reflecting elements. Computer simulation and measurement results demonstrate that an RIS can be an effective tool to significantly increase the secrecy capacity between Bob and Eve.

Measurement-based Characterization of Physical Layer Security for RIS-assisted Wireless Systems

As the 6th-Generation (6G) wireless communication networks evolve, privacy concerns are expected due to the transmission of vast amounts of security-sensitive private information. In this context, a Reconfigurable Intelligent Surface (RIS) emerges as a promising technology capable of enhancing transmission efficiency and strengthening information security. This study demonstrates how RISs can play a crucial role in making 6G networks more secure against eavesdropping attacks. We discuss the fundamentals and standardization aspects of RISs, along with an in-depth analysis of Physical-Layer Security (PLS). Our discussion centers on PLS design using RIS, highlighting aspects including beamforming, resource allocation, artificial noise, and cooperative communications. We also identify the research issues, propose potential solutions, and explore future perspectives. Finally, numerical results are provided to support our discussions and demonstrate the enhanced security enabled by RIS. 

Overview of RIS-enabled secure transmission in 6G wireless networks

RIS-assisted MIMO secure communications with Bob's statistical CSI and without Eve's CSI

In modern satellite communication systems, because of the high efficiency and flexibility, MF-TDMA has become one of hot issues. The resource-allocation can be described as an optimal location problem in the MF-TDMA channel structure (MTCS). The effective timeslot management is the guarantee of the efficiency of the resource management in MF-TDMA system. This paper discusses the timeslot allocation problem in two aspects. Firstly, we proposed an organizing method of time slots in a timeslot bin-tree. Then, according to the timeslot tree structure, we put forward a Buddy-fit with Recursive Adjustment (BFRA) algorithm to improve the utilization rate of the system. The simulation shows that BFRA algorithm has a good performance in managing and utilizing timeslot fragments.

Optimal Timeslot Allocation Algorithm in MF-TDMA

Secrecy Rate Analysis for RIS-Aided Multi-User MISO System over Rician Fading Channel

Physical layer network code processing method

This paper proposes a new combinational technology which is feasible to apply physical-layer network coding (PNC) to wireless fading channel by employing the harmful interference strategically. The key step of PNC is that terminals embrace interference and recover original signals from the intervening signals. Generally, the signals from different sources are mutual independent. We exploit an enhanced Joint Diagonalization Separation named Altering Row Diagonalization (ARD) algorithm to maximize the cost function measuring independence, by which we can separate these independent signals by blind separation method without any priori information about channel in wireless fading environments. In conclusion, the proposed method APNC (ARD PNC) performs well in PNC with higher bandwidth utility and lower error rate.

A Joint Diagonalization Separation Approach to Physical-Layer Network Coding over Wireless Fading Channel

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