Cooperative Diversity Research Articles

A comprehensive review of performance analysis of RF-FSO hybrid communication systems

The combination of radio frequency (RF) and free-space optical (FSO) communication has grown in importance as a study area for wireless communication systems in recent years. This technology has the ability to address the rising need for high-speed, high-capacity wireless communication in a variety of applications by successfully integrating the benefits of both RF and FSO communication. The performance analysis of various communication systems based on RF-FSO hybrid technology is covered in detail in this research. An overview of the RF-FSO hybrid technology and its many architectures follows the introduction of the key features and benefits of RF and FSO communication. The performance analysis of several RF-FSO hybrid communication systems, including relay-assisted RF-FSO systems, cooperative diversity RF-FSO systems, and dual-hop RF-FSO systems, are discussed in detail. The performance metrics, such as bit error rate (BER), outage probability, and channel capacity, is analyzed and compared for these systems. Based on the analysis of existing literature, several key conclusions are drawn. First, RF-FSO hybrid technology can provide higher data rates and greater reliability than traditional communication systems. Secondly, the performance of the RF-FSO hybrid system, which combines the advantages of RF technology and FSO technology, has bright development prospects. Finally, the RF-FSO hybrid system can also be combined with other systems for better performance and wider application scenarios.

Two wavelength band emission WGM lasers via photo-isomerization.

Wavelength switchable microcavity is indispensable component for various integrated photonic devices. However, achieving two wavelength band emission of the whispering gallery mode (WGM) laser is challenging. Here, we propose a strategy to realize two wavelength band emission WGM lasers activated by photo-isomerization based on excited-state intramolecular proton transfer (ESIPT) process in isolated/coupled polymer microfiber cavities. The WGM microcavity is built by highly polarized organic intramolecular charge-transfer (ICT) dye molecules. The two cooperative gain states of ICT dye molecules can be controlled by optimizing energy levels. Thereby, the lasing wavelength can be reversibly switched under photo-isomerization activated in the ESIPT energy-level progress. The photonic bar code can be generated by following the strategy of proposed design. This work provides a promising route to achieve switchable WGM laser in on-chip photonic integration.

Performance analysis of dual‐hop dual‐branch amplify‐and‐forward relaying cooperative diversity system using best‐path selection technique over Nakagami‐m fading channels

AbstractOne of the promising technologies for achieving virtual diversity gains is cooperative relaying. This study considers a dual‐hop dual‐branch cooperative diversity system with an amplify‐and‐forward mechanism where the hop count here means the total number of relays between source and destination which equals two. Utilizing the best‐path selection combining technique, a closed‐form formula for the average bit error rate and outage probability is obtained. Furthermore, between the nodes in the two branches, we consider independent non‐identical Nakagami‐m slow flat fading channels. The Monte Carlo simulation results are confirmed with the analytical ones.

UAV-Aided Wireless Energy Transfer for Sustaining Internet of Everything in 6G

Unmanned aerial vehicles (UAVs) are a promising technology used to provide on-demand wireless energy transfer (WET) and sustain various low-power ground devices (GDs) for the Internet of Everything (IoE) in sixth generation (6G) wireless networks. However, an individual UAV has limited battery energy, which may confine the required wide-range mobility in a complex IoE scenario. Furthermore, the heterogeneous GDs in IoE applications have distinct non-linear energy harvesting (EH) properties and diversified energy and/or communication demands, which poses new requirements on the WET and trajectory design of UAVs. In this article, to reflect the non-linear EH properties of GDs, we propose the UAV’s effective-WET zone (E-zone) above each GD, where a GD is assured to harvest non-zero energy from the UAV only when the UAV transmits into the E-zone. We then introduce the free space optics (FSO) powered UAV with enhanced mobility, and propose its adaptive WET for the GDs with non-linear EH. Considering the time urgency of the different energy demands of the GDs, we propose a new metric called the energy latency time, which is the time duration that a GD can wait before becoming fully charged. By proposing the energy-demand aware UAV trajectory, we further present a novel hierarchical WET scheme to meet the GDs’ diversified energy latency time. Moreover, to efficiently sustain IoE communications, the multi-UAV enabled WET is employed by unleashing their cooperative diversity gain and the joint design with the wireless information transfer (WIT). The numerical results show that our proposed multi-UAV cooperative WET scheme under the energy-aware trajectory design achieves the shortest task completion time as compared to the state-of-the-art benchmarks. Finally, the new directions for future research are also provided.

Rethinking Premodern Governance: Passing the Torch

During his long, prolific career, Henri J. M. Claessen was a major contributor to the comparative study of political organizational change. Starting with The Early State (1978), edited with Peter Skalník, Claessen's writings served to broaden and enrich evolutionary approaches in anthropology by recognizing key axes of diversity in political forms and variation in temporal sequences. Furthermore, he recognized that studies of long-term political change required multiscalar concepts that included analytical lenses larger in size than single polities. Claessen drew on his encyclopedic knowledge of ethnographic and historical cases in challenging and expanding the mid-twentieth century approaches to social evolution. With his passing, now is an appropriate time to build on the theoretical advances that Claessen forged, most specifically by taking fuller account of what archaeological research has discovered during the years coincident with his academic career. Grounded in these findings, further steps toward a comparative framing aimed at understanding diversity and change in human political organization and cooperation are advanced.

Performance Analysis of UAV-Assisted Hybrid FSO/RF Communication Systems under Various Weather Conditions.

Nowadays, unmanned aerial vehicle (UAV) communication systems are commonly considered as one of the key enabling technologies for 6G. The hybrid free space optical (FSO)/radio frequency (RF) system has the advantages of both FSO and RF links to improve communication system performance, and the relay-assisted system adopts multi-hop transmission and cooperative diversity methods to extend communication coverage. Thus, a joint consideration of UAV-assistedUAV assisted relay in hybrid FSO/RF transmission is meaningful. In this paper, we aim to analyze the performance of UAV-assisted multi-hop parallel hybrid FSO/RF communication systems with and without pointing errors (PE) in terms of Bit Error Rate (BER) and outage probability. In our considered system, the FSO sub-link adopts the Exponential Weibull turbulence model and the RF sub-link suffers the Nakagami fading model. With these, new mathematical formulas of both BER and outage probability are derived under the UAV-assisted hybrid FSO/RF with different modulation methods. Through numerical evaluationnumerical simulations, the performances of UAV-assisted hybrid FSO/RF systems are analyzed under different weather conditions, modulation methods, optical receiver aperture, RF fading parameters, pointing errors, and relay structures. The results demonstrate that (1) compared to hybrid FSO/RF direct links, UAV-assisted hybrid FSO/RF systems can further improve system performance; (2) the performance of UAV-assisted hybrid FSO/RF systems varies with different relay structures; (3) large receiver aperture and RF fading parameters can further improve the communication performance of hybrid FSO/RF direct links and UAV-assisted hybrid FSO/RF systems.

Uplink CoMP Transmission for Cellular-Connected UAV Networks

In this letter, we study the coordinated multipoint (CoMP) scheme in the uplink cellular-connected UAV network. By considering the LoS and NLoS components in air-to-ground (A2G) transmission, we adopt the strongest average received signal strength (RSS)-based CoMP scheme. We then develop an analytical framework to evaluate the network performance in terms of coverage probability and area spectral efficiency (ASE) for the case of two cooperative base stations (BSs), followed by an extension to a generalized number of cooperative BSs. Compared to the CoMP scheme with single UAV tier and Non-CoMP baseline, the considered CoMP scheme is able to leverage favored Line-of-Sight (LoS) transmission, lower path loss and BS cooperation gain.

Microfluidic Immuno-Serolomic Assay Reveals Systems Level Association with COVID-19 Pathology and Vaccine Protection.

How to develop highly informative serology assays to evaluate the quality of immune protection against coronavirus disease-19 (COVID-19) has been a global pursuit over the past years. Here, a microfluidic high-plex immuno-serolomic assay is developed to simultaneously measure50 plasma or serum samples for50 soluble markers including 35proteins, 11 anti-spike/receptor binding domian (RBD) IgG antibodies spanningmajor variants, and controls. Thisassay demonstrates the quintuplicate test in a single run with high throughput, low sample volume, high reproducibilityand accuracy. It is applied to the measurement of 1012 blood samples including in-depth analysis of sera from 127 patients and 21 healthy donors over multiple time points, either with acute COVID infection or vaccination. The protein analysis reveals distinct immune mediator modules that exhibit a reduced degree of diversity in protein-protein cooperation in patients with hematologic malignancies or receiving B cell depletion therapy. Serological analysis identifies that COVID-infected patients with hematologic malignancies display impaired anti-RBD antibody response despite high level of anti-spike IgG, which canbe associated with limited clonotype diversity and functional deficiency in B cells. These findings underscore the importance to individualize immunization strategies for these high-risk patients and provide an informative tool to monitor their responses at the systems level.

Fault diagnosis of inter-turn short circuit in turbogenerator rotor windings based on vibration-current signal fusion

The inter-turn short circuit of rotor winding is a common fault of turbogenerator, and fault diagnosis in the early stage is of great significance to ensure the safe and reliable operation of turbogenerator. In this paper, an inter-turn short circuit fault diagnosis model based on vibration-current fusion is proposed by using the real-time state data collected by the distributed control system (DCS) of turbogenerators. Firstly, Pearson correlation coefficient (PCC) analysis method is used to analyze the correlation characteristics between the square of generator excitation current and the shaft radial vibration when the inter-turn short circuit occurs in the rotor winding of the turbogenerator. Then, the method of cooperative gain transformation is adopted to fuse current-vibration correlation coefficient which can amplify the weak correlation between the square of the excitation current and the vibration signal during the early defect, and the residual between the measured and predicted excitation current is combined to further calculate the cooperative gain residual, and an early warning signal can be issued when cooperative gain residual exceeds threshold. Finally, the model is verified by the historical DCS data of a 600 MW large turbogenerator. The results show that the proposed model can sensitively and accurately diagnose the early defects of inter-turn short circuit in turbogenerator rotor windings and ensure the safe operation of the generator.

A low complexity distributed differential scheme based on orthogonal space time block coding for decode-and-forward wireless relay networks

<span lang="EN-US">This work proposes a new differential cooperative diversity scheme with high data rate and low decoding complexity using the decode-and-forward protocol. The proposed model does not require either differential encoding or channel state information at the source node, relay nodes, or destination node where the data sequence is directly transmitted and the differential detection method is applied at the relay nodes and the destination node. The proposed technique enjoys a low encoding and decoding complexity at the source node, the relay nodes, and the destination node. Furthermore, the performance of the proposed strategy is analyzed by computer simulations in quasi-static Rayleigh fading channel and using the decode-and-forward protocol. The simulation results show that the proposed differential technique outperforms the corresponding reference strategies.</span>

Optimal sequential decision rule for cooperative spectrum sensing of CUAVNs

AbstractCognitive radio (CR) technology is beneficial for unmanned aerial vehicles (UAVs) to access the spectrum resources needed for communication. Then, in order to integrate CR technology into UAVs without causing excessive interference to the primary users (PUs), cooperative spectrum sensing (CSS) is used as a key function of CR technology to detect the PUs for the UAV's available spectrum. However, the flexible locations of UAVs may significantly degrade the performance and efficiency of CSS within them. Hence, on the basis of a cognitive UAV networks (CUAVN) framework, we propose an internal cooperation paradigm to achieve the cooperative gain of CSS within an UAV. Furthermore, we convert the decision rule as an optimal stopping problem to optimize the decision rule for CSS. The optimization problem is carried out by the error probability regarding the PU presence of the phenomenon and the stopping time required to reach a global decision about the PU status. By optimizing the error probability respectively under the condition of a fixed sensing time, the optimization problem is transformed into an optimal stopping problem and solved by Markov stopping theory. Following this, we further determine a pair of thresholds in the optimal sequential decision rule from the minimal cost function. At last, numerical simulation results verify the correctness and effectiveness of the optimal sequential detection rule, and corroborate that in contrast to the external cooperative paradigm, the superiority of the internal cooperative paradigm under various network environments and parameters, in terms of the CSS performance and the stopping time.

Novel cooperative localization method of over-the-horizon shortwave emitters based on direction-of-arrival and time-difference-of-arrival measurements

The location of long-distance shortwave radiation sources is practically significant in national defense security. Shortwave multistation-positioning systems mainly include direction-of-arrival (DOA) and time-difference-of-arrival (TDOA) intersection locations. These two systems have their advantages and disadvantages in terms of performance. To combine the advantages of these two positioning technologies, this study focuses on the cooperative positioning problem based on DOA and TDOA measurements. First, the two-dimensional DOA and TDOA observation models are established for the over-the-horizon propagation scenario. Subsequently, the Cramér-Rao lower bound (CRLB) of positioning accuracy is derived in the presence of measurement errors in virtual ionosphere height. Aiming at the strong nonlinear characteristics of the observation equations, a new DOA/TDOA cooperative localization method is proposed. Finally, the asymptotic efficiency of the new estimator is proved using the first-order error analysis theory. The new method comprises two stages. In the first stage, the shortwave DOA observation equation is transformed into a pseudo-linear observation equation by introducing an auxiliary variable, as well as solving a quadratic equation with one unknown. Next, an optimization model with two quadratic equality constraints is constructed, and an iterative optimization algorithm based on matrix $~\bf{QR}$ decomposition is proposed to obtain an intermediate estimate of the emitter position. The second stage transforms the shortwave TDOA observation equation into a pseudo-linear observation equation by combining the intermediate estimates given in the first phase. Also, an iterative-constrained weighted-least-squares estimator based on the matrix decomposition is proposed again to localize the emitter. Simulation results show that the new cooperative localization method has good global convergence, the localization performance can reach the CRLB, and the obtained cooperative gain is quite high.

The Population Flow under Regional Cooperation of “City-Helps-City”: The Case of Mountain-Sea Project in Zhejiang

Regional cooperation has been increasingly recognized as indispensable in promoting coordinated regional development in China’s new urbanization. The “city-helps-city” cooperation arises as an important type of regional approach to reduce regional inequalities. This study focuses on the “city-helps-city” cooperation of the Mountain-Sea Cooperation Project in Zhejiang province and aims to examine how this type of cooperation affects the interjurisdictional linkages of backward places. First, based on the cellphone signaling data from China Mobile and social network analysis, we capture the interjurisdictional linkages represented by the population flow between poverty counties and other municipalities as our dependent variables, which are expected to be stimulated by the regional cooperation of Mountain-Sea projects. Second, through text semantic analysis on the news data of Mountain-Sea cooperation, we further identify three measures of cooperation, including the diversity of cooperation fields, the intensity of different cooperation focuses, and the legitimacy of cooperation as our main explanatory variables. Last, we run regression models to show differentiated impacts of cooperation diversity, intensity, and legitimacy on the linkages between poverty counties and developed places. The findings interrogate whether and how Mountain-Sea cooperation effectively engages backward localities in the regional network of economic production, social affairs, and institutional arrangements to enhance their linkages with other places. This study not only contributes to theoretical and empirical understandings of the state-driven “city-helps-city” cooperation as the new regional institution in transitional China, but also attempts to provide policy implications on reducing regional inequalities from the perspective of intercity cooperation.

Secrecy sum-rate based illegitimate relay selection

ABSTRACT This study presents the secrecy performance of sum-rate-based illegitimate relay selection policy for the two-way relay-assisted network. Two-hop multiple half- and full-duplex two-way illegitimate relay network and a limited number of friendly jammers, affecting to the illegitimate relays, are considered in the system model. Extensive computer simulation results reveal that the secrecy sum-rate-based full-duplex illegitimate relay selection policy outperforms the half-duplex-based counterpart in terms of outage performance. Simulation results also show that the secrecy sum-rate-based relay selection policy provides a better secrecy performance than the max-min-based selection algorithm. The obtained performance results also show that secrecy max-min- and sum-rate-based selection strategies achieve a cooperative diversity order, equal to the number of paths between legitimate and illegitimate terminals, in high signal-to-noise ratios. Also, results indicate that secrecy sum-rate-based selection provides better throughput performance than the max-min-based alternative for half-duplex and full-duplex modes. Finally, results show that a large number of friendly jammers do not severely affect the system secrecy performance if they are located relatively far from the illegitimate relay terminal.

The Investigation of Cooperation Diversity for Communication Exploiting Evaporation Ducts in the South China Sea

To improve the communication quality and reliability in the South China Sea (SCS), we proposed a method to exploit the combination of cooperative diversity and evaporation ducts. The simulation results show that the reliability of 300 km ranges at 12 GHz increases from the lowest 43.08% to 94.90% by using space diversity. Communication-link reliability for 100 km ranges may approach 100% or 98% for 200 km ranges. Furthermore, communication effects get significantly improved, and the ratio of signal-to-noise ratio (SNR) exceeds 40 dB that is up to 84.52% with diversity reception. By investigating the cooperation diversity for communication, we could find a favorable condition to realize optional-wide-frequency, long-range, and high-reliability transmission, which supports the scenario of sparse mobile communication in the SCS.

Coded Caching for Broadcast Networks with User Cooperation.

Caching technique is a promising approach to reduce the heavy traffic load and improve user latency experience for the Internet of Things (IoT). In this paper, by exploiting edge cache resources and communication opportunities in device-to-device (D2D) networks and broadcast networks, two novel coded caching schemes are proposed that greatly reduce transmission latency for the centralized and decentralized caching settings, respectively. In addition to the multicast gain, both schemes obtain an additional cooperation gain offered by user cooperation and an additional parallel gain offered by the parallel transmission among the server and users. With a newly established lower bound on the transmission delay, we prove that the centralized coded caching scheme is order-optimal, i.e., achieving a constant multiplicative gap within the minimum transmission delay. The decentralized coded caching scheme is also order-optimal if each user’s cache size is larger than a threshold which approaches zero as the total number of users tends to infinity. Moreover, theoretical analysis shows that to reduce the transmission delay, the number of users sending signals simultaneously should be appropriately chosen according to the user’s cache size, and always letting more users send information in parallel could cause high transmission delay.

Performance Analysis of Dual-Hop THz Transmission Systems Over α-μ Fading Channels With Pointing Errors

In this article, the performance of a dual-hop relaying terahertz (THz) wireless communication system is investigated. In particular, the behaviors of the two THz hops are determined by three factors, such as the deterministic path loss, fading effects, and pointing errors. Assuming that both THz links are subject to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> fading with pointing errors, we derive exact expressions for the cumulative distribution function (CDF) and probability density function (PDF) of the end-to-end signal-to-noise ratio (SNR). With these statistical expressions, some important performance metrics are evaluated, such as the outage probability (OP), average bit error rate (BER), and average channel capacity (ACC). Moreover, the asymptotic analyses are presented to obtain more insights. The results show that the dual-hop relaying scheme has better performance than the single THz link. Furthermore, the system diversity order depends on the fading parameters and pointing errors of both THz links. In addition, we extend the analysis to a multirelay cooperative diversity system and derive the asymptotic symbol error rate (SER) expressions. Finally, the derived analytical expressions are verified by the Monte Carlo simulation.

Impact of Co-channel Interference on the Performance of Cooperative Diversity Systems over α–μ Fading Channels

This paper investigates the impact of the co-channel interference on the performance of cooperative diversity networks. Selection combination technique is applied to the paths from multiple relay branches with no link directly connects the source and destination nodes. In addition, we derive the statistical characteristics of the upper bound of the SINR under the α–μ fading channel model, which then were used to derived the outage (P_{out}) and error (P_b(e)) probabilities for the cooperative network.

Full-Duplex Cooperative Rate-Splitting for Multigroup Multicast With SWIPT

We propose a full-duplex cooperative rate-splitting (FD-CRS) scheme in a downlink two-group multicast system. At the transmitter, two distinct messages requested by the two groups respectively are split and then encoded into one common stream and two private streams, based on the principles of rate splitting multiple access (RSMA). The cell-center-users (CCUs) in one group decode the common stream and their own private stream successively, then cooperatively form a distributed beamformer to assist the cell-edge-users (CEUs) in common stream transmission. To make full utilization of the time resources during cooperation, all the CCUs operate in FD mode to enable information receiving and forwarding simultaneously. Moreover, since it is unfair to sacrifice the cooperator’ energy to forward, each CCU is enabled to harvest energy from the received signal by adopting power-splitting protocol. With the objective of minimizing the system transmission power while guaranteeing all the groups’ target rates, an optimization problem is formulated to jointly design the beamformers, message splitting and power-splitting ratio. We reformulate the non-convex problem by using the difference of convex (DC) programming, and then propose an iterative algorithm based on successive convex approximation to solve it to obtain a local minimum. Further, a robust algorithm combining the semi-positive definite relaxation (SDR) technique and penalty function method is developed for the case with imperfect channel state information. Although our proposed FD-CRS scheme adopts the seemingly energy-wasting wireless power transfer technique, the simulation results still confirm the superiority of the proposed scheme, i.e., it outperforms the other baseline schemes in terms of power consumption under various user deployment, network loads and target rates. That is attributed to the comprehensive utilization of FD cooperation gain, spatial multiplexing gain as well as power multiplexing gain.

Interest of the Sharia Insurance Community in Prudential Syariah Binjai

Sharia insurance is one form of Islam's role in building community welfare by providing diversity and forms of cooperation in financing and financial management. Islamic insurance which is in line with the teachings of Islam. There are also new innovations that cannot be separated from maysir gharar and usury.