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With the rapid development of space–air–ground integrated networks (SAGIN), the synergy between the satellite and unmanned aerial vehicles (UAVs) in sensing environmental status information reveals substantial potential. In SAGIN, applications such as disaster response and military operations require fresh status information to respond effectively. The freshness of information, quantified by the age of information (AoI) metric, is crucial for an effective response. Therefore, it is urgent to investigate the AoI in real-time remote sensing systems leveraging satellite–UAV synergy. To this end, we first establish a comprehensive system model, corresponding to the satellite–UAV "multiscale explanation" synergy remote sensing system in SAGIN, in which we focus on the typical information transmission and fusion strategies of the system, the analysis framework of AoI, and the temporal evolution of AoI. Subsequently, the time-varying process of the system model is transformed into a corresponding finite-states continuous-time Markov chain, enabling a precise analysis of its stochastic behavior. By employing the stochastic hybrid system (SHS) approach, the moment generating functions (MGFs) and mean AoI, offering quantitative insights into the freshness of status information, are derived. Following this, a comparative analysis of AoI under different queuing disciplines, highlighting their respective performance characteristics, is conducted. Furthermore, considering transmit power and bandwidth constraints of the system, the AoI performances under full frequency reuse (FFR), and frequency division multiple access (FDMA) strategies are analyzed. The energy advantage and spectrum advantage associated with AoI are also examined to explore the superior AoI-related performance of the FFR strategy in SAGIN. [ABSTRACT FROM AUTHOR]

The competence of Non-Orthogonal Multiple Access (NOMA) to provide improved spectrum efficiency, support massive network elements, and low latency services make it attractive to Multiple Access (MA) technology for next-generation wireless networks. Single-Carrier Frequency Division Multiple Access (SC-FDMA) is an optimal technique in 4G wireless communication to enhance spectrum efficiency and user capacity. The amalgamation of SC-FDMA with NOMA can become a better choice for wireless communication for 5G and Beyond 5G (B5G). Discrete Wavelet Transforms (DWT) have been a better choice for improving the system's performance due to its outstanding orthogonality and spectral confinement characteristics. This study proposes a transceiver architecture that uses joint Discrete Fourier Transform (DFT) and DWT to outperform existing NOMA systems in terms of Bit Error Rate (BER). The transceiver architecture is symbolized as a joint DFT precoded DWT (JDPD) SC-FDMA NOMA System. Furthermore, we propose a Joint Low Complexity Regularized Zero forcing (JLC RZF) for JDPD SC-FDMA NOMA system to enhance the BER with low complexity. In order to illustrate the superiority of the proposed system over multipath channels, the system performance over a range of Carrier Frequency Offset (CFO) values and power allocation scenarios are also examined. [ABSTRACT FROM AUTHOR]

The integration of radar interference is an effective technical path to optimize radio frequency resources and realize directional interference. Radar interference integrated waveform design is a hot spot in radar interference integrated research. This paper presents an radar interference integrated waveform based on Zadoff-Chu sequence and orthogonal frequency division multiplexing (OFDM) architecture, and studies the waveform design and processing methods. The waveform uses OFDM as the modulation mode and time- frequency division multiplexing as the basic architecture. The frequency domain subcarriers are reasonably allocated and modulated through Zadoff-Chu and Mersenne-Twister sequences to achieve the integration of detection and interference functions. In signal processing, the first step in to separate the time and frequency of interference detection, and the second step in to conduct pulse compression and coherent processing, so as to achieve ranging and velocity measurement. Theoretical analysis and simulation test show that the proposed waveform has the advantages of high ratio of main lobe to side lobe of pulse compression, strong Doppler tolerance, flexible frequency alignment and strong interference randomness. [ABSTRACT FROM AUTHOR]

Multiple-Input Multiple Output (MIMO) systems require Orthogonal Frequency Division Multiplexing (OFDM) for effectively operating in multipath communication. Channel estimation is utilized in channel conditions where time-varying features are needed. However, Inter-Symbol Interference (ISI) occurs in MIMO-OFDM due to multi-path propagation, leading to inaccurate channel impulse response estimation. In this research, Improved Wild Horse Optimization (IWHO) is proposed based on three strategies namely, Random Running Strategy (RRS), Dynamic Inertia Weight Strategy (DIWS), and Competition for Waterhole Mechanism (CWHM) for pilot insertion which helps to estimate the channel accurately. IWHO increases the exploitation behavior and optimizes the global solution using three strategies. The input signal is encoded and decoded using Space Time Block Coding (STBC) to transmit data over noisy channels. Quadrature Phase Shift Keying (QPSK) is performed for modulation and demodulation in MIMOOFDM. The Additive White Gaussian Noise (AWGN) channel is employed to transmit signals from the transmitter to the receiver. When compared to the existing techniques, pilot-based interpolation method, Discrete Fourier Transform-Least Square-Wiener (DFT-LS-Wiener), and Binomial Distribution-based Grey Wolf Optimization (BDGWO), the IWHO achieves a lesser Bit Error Rate (BER) of 0.0025 with (dB) being 15. [ABSTRACT FROM AUTHOR]

Cyclic interleaved frequency division multiplexing (CIFDM) stands out as a promising solution for enhancing diversity reception over frequency-selective channels. Within the CIFDM framework, cyclic interleaving at the transmitter, followed by multipath detection at the receiver, collaboratively contributes to performance improvement. A recent advancement in this domain is the introduction of CIFDM-successive interference cancellation (CIFDM-SIC) (Anuthirsha and Stuwart in ETRI J, 1--11, 2024), a multipath multistage detection method. However, CIFDM-SIC leaves room for improvement, as it only partially mitigates multipath interference resulting from the semi-orthogonality of codes in CIFDM. To address this limitation, our current approach introduces a CIFDM-decorrelative successive interference cancellation (CIFDM-dSIC) method. In the proposed CIFDM-dSIC, a decorrelation process is employed to effectively eliminate non-orthogonal interference components arising from the cross-correlation of codes in the SIC output stages. Specifically, after the completion of the entire SIC operation, interference at each output stage, except the last one, is eliminated through path-specific decorrelation of the effective spreading codes. We have conducted a comprehensive evaluation of the performance of CIFDM-dSIC under various scenarios, comparing it with both existing CIFDM and traditional interleaved frequency division multiplexing methods. Simulation results unequivocally establish the dominance of the proposed CIFDM-dSIC, affirming its reliability in terms of bit error rate and diversity reception. [ABSTRACT FROM AUTHOR]

We present a subspace-based polynomial rooting algorithm to estimate the frequency bias (FB) of generalized frequency division multiplexing (GFDM) systems employing null subcarriers and repetitive sub-symbols. The estimation process is classified into fractional FB (FFB) and integer FB (IFB) estimation. The use of repetitive sub-symbols creates a quasi-periodic structure in the FB-distorted received signal, allowing the proposed algorithm to estimate the FFB using the root-MUSIC algorithm. Based on this, the proposed algorithm compensates for the FFB in the received signal and then estimates the null subcarrier pattern (NSP) in the frequency domain. As a result, the IFB estimate can be obtained in a maximum likelihood (ML) manner. Before the NSP estimation, this study uses a sub-symbol combiner to enhance signal strength of the FFB-aligned signal, ensuring the reliability of the IFB estimate. Computer simulations show that the proposed subspace-based algorithm has several advantages over traditional FB estimation methods: 1. Unlike some existing algorithms that use a training sequence to estimate FB, the proposed approach is a semi-blind algorithm because it can deliver information through repeated sub-symbols while estimating FB; 2. The proposed algorithm demonstrates excellent estimation accuracy compared to most traditional FB estimation algorithms; and 3. The proposed algorithm is computationally efficient, making it applicable to real-time applications in future communication systems. [ABSTRACT FROM AUTHOR]

Generalized frequency division multiplexing (GFDM) is a flexible block structured multicarrier scheme for next generation wireless systems featuring low out-of-band radiation and high spectrum efficiency. There are various approaches suggested for its analysis via simulations but testing in real time environments is necessary for its standardization. Traditional data aided methods of synchronization avoid the effect of egress noise in pilot preamble destroying its spectral advantage. To safeguard this advantage, preamble needs to be pulse shaped. The main contribution of this paper is the derivation of generalized maximum likelihood estimation of frequency and time offsets for receiver synchronization in GFDM systems, using the modified preamble by the application of matrix inversion lemma. The dependency of the choice of the filter on Cramer–Rao lower bound of frequency offset estimation is also emphasized. The performance of the system is analysed over additive white Gaussian noise and multipath channel environments. The authors carried out real time implementation of GFDM system using IEEE 802.11 short preamble in indoor environments by employing national instruments universal software radio peripheral 2953R boards as hardware platform which is interfaced with LABVIEW for practical validations of the results. [ABSTRACT FROM AUTHOR]

Spectrally efficient 16 quadrature amplitude modulation‐orthogonal frequency division multiplexing (QAM‐OFDM) system using specifications of commercially available high‐power phosphorous coated LED (PLED) is proposed in this study. To address the challenges of signal attenuation and limited bandwidth, systems integrated with a band pass filter (BPF) after the photodetector and optical preamplifier. The effect of BPF bandwidth and preamplifier gain on the performance of 16 QAM‐OFDM system have been investigated. Results demonstrated that 375 MHz bandwidth evaluated from 1.5 × symbol rate, offered an optimum performance achieving minimum bit‐error‐rate of 3.05 × 10−4. For preamplifier gain of 20 dB, we achieved a maximum distance of 3 m which is limited to 1.5 m for lower gain values. With BPF‐optimized bandwidth and a preamplifier gain of 20 dB, we have achieved a data rate of 5 Gbps for maximum distance up to 2 m while considering the super‐forward‐error‐correction limit of 1.863 × 10−2. With data rate of 6 and 7 Gbps, the distance lower down to 1.8 and 1.5 m, respectively. [ABSTRACT FROM AUTHOR]

Summary: The channel plays a significant role as the multipath in Multiple Input Multiple Output‐Orthogonal Frequency Division Multiplexing (MIMO‐OFDM) systems. The precoding‐based channel estimation algorithms estimate the channel capacity at the receiver node and they provide efficient channel estimates under worst case channel scenarios. To estimate the channel capacity in the mobile node, semi‐blind scenario is a crucial task in Multi User (MU) MIMO systems. Therefore, a semi blind sparse channel estimation algorithm is demonstrated in the MU‐MIMO system to provide better performance. In the transmitter side, the signal modulation is performed with the help of Quadrature Phase Shift Keying (QPSK), and the modulated signal is given to Pulse Shaping Algorithm (PSA) to reduce the inter‐carrier interference as well as inter symbol interference. At each transmitter, the Inverse Fast Fourier Transforms (IFFT) technique is used for mapping the symbols and then the mapped signal is send to the receiver. In the receiver side, the FFT, pulse reshaping, and QPSK demodulation blocks are serially connected and perform inverse operations of the transmitter in the receiver. Then, the sparse channel is estimated at the receiver by using the semi blind sparse algorithm, where the parameters are optimized by using the Hybridized Drosophila with Virus Colony Search Optimization (HD‐VCSO). The objective function of the developed sparse channel estimation is the reduction of Minimum Mean Square Error (MMSE) in the channel. The performance of the developed sparse channel estimation algorithm is analyzed through different conventional algorithms to validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In recent years, with the increasing number of terminal connections, high-density deployment scenarios have become important scenarios for future wireless networks. Ultra-high throughput (EHT) in high density deployment scenarios is the technical goal of IEEE 802.11be, the next-generation wireless local area network (WLAN) standard. However, in a high-density deployment scenario, interference suppression between BSSs is serious, which seriously affects the throughput of a WLAN. And the resources available are limited. Therefore, for the next generation WLAN standard, this paper proposes a downlink transmission scheme based on AP coordination and the orthogonal frequency division multiple access (OFDMA) protocol and the non-orthogonal multiple access (NOMA) protocol, named Co-OFDMA–NOMA scheme. The core idea is to transform the interference and suppression relationship between neighboring BSSs into the relationship of mutual coordination and assistance through the Co-OFDMA–NOMA protocol proposed in this paper. Firstly, a downlink transmission scheme named the Co-OFDMA–NOMA protocol is designed. In addition, the protocol and its framework structure have good backward compatibility. Theoretical analysis shows that the proposed Co-OFDMA–NOMA protocol has significant performance gain, and simulation results prove the effectiveness of the scheme. [ABSTRACT FROM AUTHOR]

As the speed of the communication system increases, there exist two kinds of fading simultaneously in the wireless channels, namely time-frequency double-selective fading. In this case, delay expansion and doppler shift will affect the channel, resulting in inter-carrier interference and inter-symbol crosstalk, which will affect the channel estimation performance of generalized frequency division multiplexing communication technology. This paper first analyzes the effects of time-selective fading and frequency-selective fading on transmitted signals. Then, a complex exponential basis extension model (CE-BEM) suitable for dual selective channels was selected, and the mean square error (MSE) was used to evaluate the CE-BEM model. The function order Q of GFDM channel estimation simulation was determined by the relationship between the number of sampling points in the transmission block and different order functions. Finally, the least square (LS) channel estimation algorithm and the least mean square error (MMSE) are used to complete the channel estimation of the GFDM communication system. The performance of channel estimation is improved by changing the way of pilot insertion, and the performance of channel estimation is measured by mean square error (MSE) when the characteristics of pilot insertion are changed. [ABSTRACT FROM AUTHOR]

Multiple Input Multiple Output (MIMO) is a technology that combines multiple antennas and Orthogonal Frequency Division Multiplexing (OFDM) modulation to increase the data rate and spectral efficiency of wireless communication systems. Equalization problems are one of the key issues with MIMO-OFDM systems, which are caused by multiple antennas and subcarriers. Optimal Power Allocation (OPA) in MIMO-OFDM is a critical component for achieving high spectral efficiency and improving the overall performance of the system. OPA refers to the process of allocating power to the different subcarriers and antennas in MIMO-OFDM systems in an optimal way. This study proposes the Dynamic OPA (DOPA) algorithm for MIMO-OFDM systems to dynamically adjust power allocation based on the changing channel conditions and reduce pilot contamination issues. This approach allocates more power to subcarriers and antennas with better channel conditions and less power to subcarriers and antennas with worse channel conditions. DOPA in MIMO-OFDM systems is necessary to maximize data rates, minimize interference, improve system capacity, and reduce power consumption. Simulation results showed that the proposed MIMO-OFDM-DOPA had reduced bit error rates, mean square error, and transmitter power and increased energy efficiency and capacity compared to existing state-of-the-art methods. [ABSTRACT FROM AUTHOR]

The growing fame and utilization of wireless multimedia approaches have led to the advancement of the wireless system. The fifth generation (5G) of wireless communication was developed to serve users with enhanced proficiency, low latency, reliable communication, and lesser battery exhausts. The non-orthogonal multiple access (NOMA) scheme is a proficient multiple access scheme to fulfil the requirement of a 5G mobile system. NOMA enables a remarkable enhancement in the systems throughput and ability to connect devices. NOMA distinguishes each user by allocating a distinct power level, superimposing all the user's signals utilizing superposition coding while transmitting and at the reception, each user's signals are decoded by employing successive interference cancellation (SIC). This study builds a real time downlink orthogonal frequency division multiplexing based NOMA (OFDM-NOMA) transceiver system using the NI USRP 2944R and 2901 platforms. The performance evaluation of the proposed OFDM-NOMA system is carried out in terms of signal to noise ratio by adjusting transmitting gain and the distance of users from the base station system. Experimental results show that the signal-to-noise ratio (SNR) of each user relies on the power allocation factor and proximity of users from the base station, and SIC output is compared with constellation variations. [ABSTRACT FROM AUTHOR]

Steady-state visual evoked potentials (SSVEPs) are widely used for brain-computer interfaces (BCIs) as they provide a stable and efficient means to connect the computer to the brain with a simple flickering light. Previous studies focused on low-density frequency division multiplexing techniques, i.e. typically employing one or two light-modulation frequencies during a single flickering light stimulation. Here we show that it is possible to encode information in SSVEPs excited by high-density frequency division multiplexing, involving hundreds of frequencies. We then demonstrate the ability to transmit entire images from the computer to the brain/EEG read-out in relatively short times. High-density frequency multiplexing also allows to implement a photonic neural network utilizing SSVEPs, that is applied to simple classification tasks and exhibits promising scalability properties by connecting multiple brains in series. Our findings open up new possibilities for the field of neural interfaces, holding potential for various applications, including assistive technologies and cognitive enhancements, to further improve human-machine interactions. Steady state visually evoked potentials enable EEG vision-based brain computer interfaces. We show that it is possible to encode information distributed across 100+ frequencies. We encode images and perform simple physical computing classification tasks. Connecting more than one in brain in series improves the classification capability. [ABSTRACT FROM AUTHOR]

In this study, the frequency down-conversion of terahertz waves is analytically and experimentally demonstrated at the temporal boundaries within a GaAs waveguide. The temporal boundary is established by photoexciting the top surface of the waveguide, thereby instantaneously increasing its electrical conductivity. This photoexcited waveguide supports a transverse electromagnetic (TEM) mode with a frequency lower than those of the transverse magnetic (TM) modes present in the original waveguide. At the temporal boundary, the incident TM mode couples with the TEM mode, resulting in frequency down-conversion. Subtracting the propagation loss from the frequency-converted components indicates that the frequency conversion occurs with an efficiency consistent with the analytical predictions. The propagation loss is primarily due to ohmic loss, caused by the finite electrical conductivity of the photoexcited region. Given that the frequency of transverse electric modes is up-converted at the temporal boundary, our findings suggest that the direction of frequency conversion (upward or downward) can be controlled by manipulating the incident polarization. The polarization-dependent frequency conversion in waveguides holds significant potential for applications in devices designed for the interconversion of terahertz signals across various frequency channels. This capability is instrumental in the development of frequency-division-multiplexed terahertz wave communication systems, thereby enabling high data transfer rates. [ABSTRACT FROM AUTHOR]

A flexible radio waveform, generalised frequency division multiplexing (GFDM) allows for significant degrees of freedom in adjusting the number of time slots, subcarriers, and pulse shaping filters. The GFDM is one of the multi-carrier techniques that has been proposed to achieve 5G requirements. Initially, this study discusses about the derivation of novel analytical expression of symbol error rate under α - μ fading channel using the GFDM system. The proposed derivation includes Rayleigh, Nakagami-m, and Nakagami-q fading channels as special cases for different α and μ values. Further, a simulation test-bed has been developed in MATLAB to access the simulation results and they are in good agreement with the derived theoretical results for various simulation parameters such as different roll-off factors, modulation orders and various fading parameters. [ABSTRACT FROM AUTHOR]

The Time Slotted Channel Hopping (TSCH) protocol, defined in the IEEE 802.15.4 standard, is tailored to meet the stringent communication requirements of industrial applications. TSCH combines Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) to efficiently allocate resources and schedule communications in IoT networks. In this paper, we conduct a comparative performance assessment of TSCH-based schedulers under varying traffic loads and patterns using the COOJA emulator. Our study focuses on two schedulers for TSCH: Minimal Scheduling and Orchestra, which includes two key variants - Orchestra Sender Based Shared (O-SBS) and Orchestra Receiver Based Shared (O-RBS). To comprehensively assess their performance in IoT networks, we conduct an in-depth evaluation across multiple key parameters: Packet Delivery and Acknowledgment Ratios, Radio-On duty cycle, End-to-End Latency, Stability, and Embedded Firmware's Memory footprint. Our results indicate that Orchestra SBS excels in ensuring high reliability and low latency in high-traffic scenarios. Meanwhile, TSCH Minimal Scheduling exhibits superior energy efficiency, and it boasts a smaller embedded firmware memory footprint. [ABSTRACT FROM AUTHOR]

The 2020 decadal review recognized the measurement of the polarization of the cosmic microwave background (CMB) to be a top priority for the decade. CMB experiments including POLARBEAR2/Simons Array, Atacama Cosmology Telescope/Advanced-ACT, SPT-3G, the Simons Observatory, and CMB-S4 have or will use transition edge sensor (TES) bolometer fabricated with Aluminum doped with Manganese (AlMn). AlMn is a popular material choice as the superconducting transition temperature ( T c ) and normal resistance ( R n ) of the TES can be tuned with Mn concentration, geometric patterning, film thickness, and thermal annealing. In addition the conductivity is appropriate for both time division multiplexing and frequency division multiplexing that require 10 m Ω and 1 Ω sensors respectively. In this paper we present work on the ability to tune the T c of a film based on its time and temperature thermal tuning profile combined with room temperature monitoring of film resistivity. Such control allows for the fabrication of a wide range of TES parameters from a single AlMn concentration. Scanning electron microscope (SEM) imaging shows that the AlMn film's grain boundaries are changed by thermal annealing making the film more conductive and raising its superconducting transition temperatures, and that at high enough temperatures will eventually recover the T c of bulk Al. We find that baking films at ∼ 200 ∘ C for tens of minutes yields a T c that is suitable for 100 mK base temperature experiments and we present on the thermal tune profiles of several different thicknesses of AlMn. [ABSTRACT FROM AUTHOR]

Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) is a familiar modern wireless broadband technology due to its resistance against multipath fading, high data transmission rate, and spectral efficiency. This technology delivers dependable communication as well as a large range of coverage. The precise recovery of Channel State Information (CSI) and synchronization among the receiver and transmitter are two major challenges for MIMO-OFDM systems. Several estimate procedures, like blind, pilot-aided, and semi-blind channel estimating, are used to recover channel state information. Yet, those systems have several flaws that cause them to perform poorly. Hence, this paper describes the basic introduction of the Channel Estimation (CE) process in the MIMO-OFDM system. The main goal of this survey is to study analyzing and categorizing the channel estimation algorithms, and simulation tools in different contributions. Further, the performance analysis with different performance metrics from diverse contributions is pointed out. Thus, this review article presents a detailed overview of the various channel estimation schemes that have been exploited in the OFDM channel to enhance the estimation of the CSI in the MIMO-OFDM systems. This work presents and discusses the relevant comparative results and computational complexity for all of these CE systems. Furthermore, there is a list of open study directions for further exploration. [ABSTRACT FROM AUTHOR]

Next to the legacy frequency division multiple access (FDMA) signals in the L1 and L2 band, modernized GLONASS satellites of the M+, K1, and K2 generation also transmit new code division multiple access (CDMA) signals on L3, and, in part, the L1 and L2 frequencies. Depending on the specific satellite platform, either a common antenna or two distinct antennas are used for the individual signals. As a novel feature, the new CDMA navigation messages provide information on the antenna phase center locations as well as the spacecraft orientation during rate-limited noon and midnight turns. We establish a comprehensive set of phase center positions for the individual GLONASS antennas from manufacturer data and information in the CDMA navigation messages, inferred from the comparison of FDMA and CDMA broadcast ephemerides, and obtained from antenna baseline estimates using a triple-frequency carrier phase combination. Based on these, reference values for the signal-specific PCOs of each block of modernized GLONASS spacecraft are derived that may be used to extend the current antenna model of the International GNSS Service (IGS) to all frequency bands. Complementary to the analysis of antenna phase center information, the new CDMA attitude model for GLONASS-K satellites is reviewed. Algorithms for computing relevant parameters of the rate-limited yaw slews including the ramp-up and -down phase based on the Sun/orbit geometry are derived that enable a concise attitude modeling in GLONASS orbit determination and precise point positioning. The model is validated through comparison with yaw angle estimates derived from triple-frequency observations showing consistency at the 1° level for the K2 satellite. On the other hand, unexpected accelerations during noon turns of GLONASS-M+ are identified, which may cause short-term yaw angle deviations of up to 20° relative to attitude models in common use within the IGS. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates an intelligent reflecting surface (IRS) assisted downlink short packet transmission system, where an access point sends short packets to multiple devices with the help of an IRS. Specifically, a performance comparison between the frequency division multiple access and time division multiple access is conducted for the considered system, from the perspective of average age of information (AoI). To minimize the maximum average AoI among all devices, the resource allocation and passive beamforming are jointly optimized. However, the formulated problem is difficult to solve due to the non‐convex objective function and coupled variables. Thus, an alternating optimization based algorithm is proposed by exploiting the semidefinite relaxation and bisection search techniques. Simulation results show that time division multiple access can achieve lower AoI by exploiting the time‐selective passive beamforming of IRS for maximizing the signal to noise ratio of each device consecutively. Moreover, it also shows that as the length of information bits becomes sufficiently large as compared to the available bandwidth, the proposed frequency division multiple access transmission scheme becomes more favourable due to more flexible power allocation.

This paper investigates an intelligent reflecting surface (IRS) assisted downlink short packet transmission system, where an access point sends short packets to multiple devices with the help of an IRS. Specifically, a performance comparison between the frequency division multiple access and time division multiple access is conducted for the considered system, from the perspective of average age of information (AoI). To minimize the maximum average AoI among all devices, the resource allocation and passive beamforming are jointly optimized. However, the formulated problem is difficult to solve due to the non‐convex objective function and coupled variables. Thus, an alternating optimization based algorithm is proposed by exploiting the semidefinite relaxation and bisection search techniques. Simulation results show that time division multiple access can achieve lower AoI by exploiting the time‐selective passive beamforming of IRS for maximizing the signal to noise ratio of each device consecutively. Moreover, it also shows that as the length of information bits becomes sufficiently large as compared to the available bandwidth, the proposed frequency division multiple access transmission scheme becomes more favourable due to more flexible power allocation. [ABSTRACT FROM AUTHOR]

Even though generalized frequency division multiplexing is an alternative waveform method expected to replace the orthogonal frequency division multiplexing in the future, its implementation must alleviate channel effects. Least‐squares (LS), a low‐complexity channel estimation technique, could be improved by using the discrete Fourier transform (DFT) without increasing complexity. Unlike the usage of the LS method, the DFT‐based method requires the receiver to know the channel impulse response (CIR) length, which is unknown. This study introduces a simple, yet effective, CIR length estimator by utilizing LS estimation. As the cyclic prefix (CP) length is commonly set to be longer than the CIR length, it is possible to search through the first samples if CP is larger than a threshold set using the remaining samples. An adaptive scale is also designed to lower the error probability of the estimation, and a simple signal‐to‐interference‐noise ratio estimation is also proposed by utilizing a sparse preamble to support the use of the scale. A software simulation is used to show the ability of the proposed system to estimate the CIR length. Due to shorter CIR length of rural area, the performance is slightly poorer compared to urban environment. Nevertheless, satisfactory performance is shown for both environments. [ABSTRACT FROM AUTHOR]

Radio Frequency Identification (RFID) technology plays a crucial role in various Internet of Things (IoT) applications, necessitating the integration of RFID systems into dense networks. However, the presence of numerous readers leads to collisions, degrading communication between readers and tags and compromising system performance. To tackle this challenge, researchers have proposed Medium Access Control (MAC) layer protocols employing different channel access methods. In this paper, we present a novel solution, the Distributed Time Slot Anti-Collision protocol (DTS-AC), which employs a new TDMA notification system to address Reader-to-Reader Interference (RRI), while incorporating FDMA-based frequency resource management to resolve Reader-to-Tag Interference (RTI) collision issues. Simulation results demonstrate that DTS-AC significantly improves performance in dense RFID networks by enhancing read rates, with scalability benefits based on the number of readers, channels, and Time Slots (TSs). Moreover, the cost-effectiveness of DTS-AC facilitates efficient deployment in RFID networks, emphasizing considerations of time delay and data sensitivity. [ABSTRACT FROM AUTHOR]

To address the problems of network congestion and spectrum resources shortage in multi-user large-scale scenarios, this paper proposes a twice random access OFDMA-NOMA-RA protocol combining the advantages of orthogonal frequency division multiple access (OFDMA) and non-orthogonal multiple access (NOMA). The idea of this protocol is that OFMDA is used to divide the entire frequency field into multiple orthogonal resource units (RUs), and NOMA is used on each RU to enable more users to access the channel and improve spectrum efficiency. Based on the protocol designed in this paper, in the case of imperfect successive interference cancellation (SIC), the probability of successful competition subchannels and the outage probability are derived for two scenarios: Users occupy the subchannel individually and users share the subchannel. Moreover, when two users share the channel, the decoding order of the users and the corresponding probabilities are considered. Then, the system throughput is obtained. To achieve better outage performance in the system, the optimal power allocation algorithm is proposed in this paper, which enables the optimal power allocation strategy to be obtained. Numerical results show that the larger the imperfect SIC coefficient, the worse the outage performance of weak users. Compared with pure OFDMA and NOMA, OFDMA-NOMA-RA always maintains an advantage when the imperfect SIC coefficient is less than a specific value. [ABSTRACT FROM AUTHOR]

Electromagnetic formation flight technology utilizes electromagnetic force and torque between satellites to control satellites' relative position and attitude without consuming propellant, thus having broad application prospects. However, the dynamics of electromagnetic formation flying are nonlinear and strongly coupled, posing challenges to the 6-DOF control of electromagnetic formation and the magnetic dipole allocation of satellites. The frequency division multiplexing method can approximate decoupling formation dynamics by loading multi-frequency AC carriers onto satellite magnetic dipoles and is likely to achieve more control functions. A design method for AC carriers based on frequency division multiplexing is proposed to decouple formation dynamics while controlling electromagnetic force and torque. This paper further provides an analytical solution for the magnetic dipoles of the electromagnetic force/torque equations. In addition, in response to external disturbances, model uncertainty, and the inability to obtain relative velocity and angular velocity information of the formation system, this paper establishes a 6-DOF coupling model based on dual quaternion and implements tracking control using the active disturbance rejection control method. Based on the internal force characteristics of the electromagnetic formation, an expression for the equilibrium distribution of reaction wheel torque is derived to avoid some reaction wheels' rapid accumulation of angular momentum. Numerical simulation results show the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Phase gradient metasurfaces (PGMs) have demonstrated powerful capacities for manipulating light waves freely. However, PGMs have limitations of bulky size and narrow bandwidth that hinder further applications. In this work, we present the design and analysis of a reflection-type PGM by utilizing the phase choice freedom in the supercell. It is found that in this well-designed PGM, perfect negative reflection including perfect retro-reflection can be observed not only at the initially designed frequency f1 = f0, but also at its double frequency, i.e., f2 = 2f0, which is named as the frequency-doubling perfect negative reflection. As a proof of concept, we design and fabricate a reflection-type PGM with 4π phase coverage in a supercell, with experimental results in perfect agreement with the theoretical ones. Our work offers an approach to design planar optical devices at multiple operating frequencies, holding potential applications for frequency division multiplexing communication, remote sensor technology, laser tracking, and more. [ABSTRACT FROM AUTHOR]

Aggregation and Orthogonal Frequency Division Multiple Access (OFDMA) are two fundamental features allowing access points and stations to benefit from the high physical transmission rates of the recent WiFi standards. They aim to pool frames with a unique overhead (mainly the physical header and the acknowledgment) to mitigate its impact on the throughput. Natural implementations of these features lead to nonFIFO (First In, First Out) service disciplines that may generate unfairness between frames. In this paper, we evaluate three stateless service disciplines that require a low level of resources (computation and memory). We prove that when OFDMA does not introduce additional delay, one of these greedy algorithms minimizes the overhead. Whereas this service discipline maximizes the system capacity, it generates strong unfairness between the stations. Instead, the two other algorithms may offer a good trade-off between capacity and fairness. These algorithms are evaluated through a theoretical framework and simulations that replay actual Wi-Fi traces. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel method for temperature measurement using surface acoustic wave (SAW) temperature sensors on curved or irregular surfaces. We integrate SAW resonators onto flexible printed circuit boards (FPCBs) to ensure better conformity of the temperature sensor with the surface of the object under test. Compared to traditional rigid PCBs, FPCBs offer greater dynamic flexibility, lighter weight, and thinner thickness, which make them an ideal choice for making SAW devices working for temperature measurements under curved surfaces. We design a temperature sensor array consisting of three devices with different operating frequencies to measure the temperature at multiple points on the surface of the object. To distinguish between different target points in the sensor array, each sensor operates at a different frequency, and the operating frequency bands do not overlap. This differentiation is achieved using Frequency Division Multiple Access (FDMA) technology. Experimental results indicate that the frequency temperature coefficients of these sensors are −30.248 ppm/°C, −30.195 ppm/°C, and −30.115 ppm/°C, respectively. In addition, the sensor array enables wireless communication via antenna and transceiver circuits. This innovation heralds enhanced adaptability and applicability for SAW temperature sensor applications. [ABSTRACT FROM AUTHOR]

Heterogeneous networks (HetNets) are essential in contemporary wireless communication networks as they help operators address challenges related to coverage, capacity, and quality. HetNets also enable the efficient use of resources and preparedness for future wireless technologies. The efficient allocation of limited resources to user equipments (UEs) is a critical problem that can be tackled using joint resource allocation and user association (JRAUA) techniques. However, this problem is challenging due to its non-convex and combinatorial nature, which is further complicated by the hybrid action space that involves both continuous actions and discrete actions. Consequently, determining the most efficient approach for JRAUA is a challenging endeavor. The objective of this study is to address the above challenge and improve the energy efficiency of networks by examining the JRAUA problem in downlink HetNets using orthogonal frequency division multiple access (OFDMA). This work presents a new strategy, called the Variable Hybrid Action Space—Deep Q-Network (VHAS-DQN), to optimize the learning policy and improve the average cumulative reward by incorporating constraints like wireless backhaul capacity of each UE and quality-of-service (QoS) into the learning process. To demonstrate the advantages of the JRAUA model in terms of energy efficiency while guaranteeing that the backhaul capacity constraints and quality of service (QoS) criteria are met, the simulation results from the VHAS-DQN were compared with other experimental case studies. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the timeliness of a multi-user system in terms of the age of information (AoI) and the corresponding stability region in which the packet rates of users lead to finite queue lengths. Specifically, we consider a hybrid OFDMA-NOMA system where the users are partitioned into several groups. While users in each group share the same resource block using non-orthogonal multiple access (NOMA), different groups access the fading channel using orthogonal frequency division multiple access (OFDMA). For this system, we consider three decoding schemes at the service terminals: interfering decoding, which treats signals from other users as interference; serial interference cancellation, which removes signals from other users once they have been decoded; and the enhanced SIC strategy, where the receiver attempts to decode for another user if decoding for a previous user fails. We present the average AoI for each of the three decoding schemes in closed form. Under the constraint of the stable region, we find the minimum AoI of each decoding scheme efficiently. The numerical results show that by optionally choosing the decoding scheme and transmission rate, the hybrid OFDMA-NOMA outperforms conventional OFDMA in terms of both system timeliness and stability. [ABSTRACT FROM AUTHOR]

This paper examines the performance of free space optical (FSO) communication systems in desert environments, focusing on the interaction between FSO technology and challenging atmospheric conditions like duststorms and fogs. The research aims to enhance the design and operation of FSO communication systems in these environments, where reliable connections are critical. The study evaluates the performance of the quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) technique to mitigate severe weather impacts on FSO communication links. We compare different modulation methods (AM, Duobinary RZ, Modified Duobinary RZ, OOK-RZ, and OOK-NRZ) in different weather conditions (light fog, moderate fog, heavy fog, light dust storm, and moderate dust storm). The results demonstrate that the 4QAM-OFDM modulation technique is highly effective in different fog conditions. It maintains an acceptable bit error rate (BER) in light fog, 0.5–1.5 km, and even at extended link distances. It achieves a BER of 2 × 10 - 5 at 2.4 km. In moderate fog, it achieves a BER of 6 × 10 - 5 at 1.75 km. In heavy fog, it maintains acceptable BER values within 0.5–0.8 km and a BER of 5 × 10 - 5 at 1.35 km. In moderate dust, specifically at a link range of 0.64 km, the achieved BER value is 7 × 10 - 7 . 4Qam-OFDM provides the most favorable values of received power compared to other modulation techniques. [ABSTRACT FROM AUTHOR]

Weak target detection is a great challenging in radar field. To detect weak targets via radar communication integrated signal, a method for constructed step-LFM (CStep-LFM) signal is proposed based on quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) echoes. First, a QAM-OFDM and CStep-LFM model is established, and then a bandpass filters bank is used to transform the QAM-OFDM echo into a Step-LFM signal. Finally, compared with several existing integrated signals, the analyses and the simulation results show that CStep-LFM signal not only improves the detection performance of weak targets but also has a better communication performance. [ABSTRACT FROM AUTHOR]

In the present work, orthogonal frequency division multiplexing (OFDM) is combined with wavelength division multiplexing-passive optical networks (WDMPONs) to obtain the combined benefits of both technologies for overall system improvement. performance of five OFDM signals using WDM is analyzed. An optical system is designed using the OFDM signal, and its performance is analyzed using various matrices like bit error rate (BER) and Q-factor under the effect of varying laser power. Mapping of OFDM signals is done using 16-QAM modulation. The system shows an enhancement in the performance by increasing the laser power but up to some limit, and efficient results are obtained in the 70–130 mW laser power range. [ABSTRACT FROM AUTHOR]

The efficient transmission of images, which plays a large role in wireless communication systems, poses a significant challenge in the growth of multimedia technology. High-quality images require well-tuned communication standards. The Single Carrier Frequency Division Multiple Access (SC-FDMA) is adopted for broadband wireless communications, because of its low sensitivity to carrier frequency offsets and low Peak-to-Average Power Ratio (PAPR). Data transmission through open-channel networks requires much concentration on security, reliability, and integrity. The data need a space away fromunauthorized access, modification, or deletion. These requirements are to be fulfilled by digital image watermarking and encryption. This paper ismainly concerned with secure image communication over the wireless SC-FDMA systemas an adopted communication standard. It introduces a robust image communication framework over SC-FDMA that comprises digital image watermarking and encryption to improve image security, while maintaining a high-quality reconstruction of images at the receiver side. The proposed framework allows image watermarking based on the Discrete Cosine Transform (DCT) merged with the Singular Value Decomposition (SVD) in the so-called DCT-SVD watermarking. In addition, image encryption is implemented based on chaos and DNA encoding. The encrypted watermarked images are then transmitted through the wireless SC-FDMA system. The linearMinimumMean Square Error (MMSE) equalizer is investigated in this paper to mitigate the effect of channel fading and noise on the transmitted images. Two subcarrier mapping schemes, namely localized and interleaved schemes, are compared in this paper. The study depends on different channelmodels, namely PedestrianAandVehicularA, with amodulation technique namedQuadratureAmplitude Modulation (QAM). Extensive simulation experiments are conducted and introduced in this paper for efficient transmission of encrypted watermarked images. In addition, different variants of SC-FDMA based on the Discrete Wavelet Transform (DWT), Discrete Cosine Transform (DCT), and Fast Fourier Transform (FFT) are considered and compared for the image communication task. The simulation results and comparison demonstrate clearly that DWT-SC-FDMAis better suited to the transmission of the digital images in the case of PedestrianAchannels, while the DCT-SC-FDMA is better suited to the transmission of the digital images in the case of Vehicular A channels. [ABSTRACT FROM AUTHOR]

In this work, a four-port directional filter (DF) with a broad passband and low reflection is proposed at the W-band, which comprises three unit filters at 92, 95, and 97 GHz, cascaded in series. Each unit consists of two microstrip lines in the top circuit layer for signal input and output, two pairs of apertures in the middle ground layer for directional coupling, and one square loop in the bottom layer as a selective resonator. By sweeping the working frequencies of the three units and optimizing the phase delays between them, the proposed filter achieves a 3-dB bandwidth as broad as 16%, an insertion loss of 2.5 dB at 95 GHz, and an out-ofband rejection of -28 and -23 dB at 80 and 110 GHz, respectively. The corresponding reflection attenuation is larger than 9.6 dB from 60 to 105 GHz. To verify our design, a prototype is fabricated and characterized, and its experimental data are consistent with the simulation. This work significantly expands the bandwidth of DFs and may find many applications in frequency division multiplexing and high-gain wireless systems. [ABSTRACT FROM AUTHOR]

This paper investigates methods for noise-canceling channel estimation (NC-CE) to track rapid time-varying channels in IEEE 802.11p/orthogonal frequency division multiplexing (OFDM) systems. To this end, we introduce a novel three-step channel estimation technique based on the estimated length of the channel impulse response (CIR). This approach aims to surpass the performance of conventional designs that rely on constructed data pilots (CDPs). In the first step, we not only eliminate noise components but also estimate the channel frequency responses (CFRs) of virtual subcarriers for long preamble parts. Moving on to the second step, we incorporate a modified CDP method without a frequency-domain reliability test and interpolation, taking into account the CFRs of virtual subcarriers obtained at the previous OFDM symbol time. The final step can be implemented as the operation of the inverse fast Fourier transform (IFFT)/nulling/FFT to reduce noise components from the CFRs obtained in the second step and generate CFRs for virtual subcarriers to be used in the next symbol time. The results of our simulations validate the effectiveness of our proposed channel estimation schemes. [ABSTRACT FROM AUTHOR]

Summary: The future generation of wireless communications systems uses the generalized frequency division multiplexing (GFDM) due to its viable candidate waveform to perform multiple user scheduling. It is a non‐orthogonal waveform susceptible to intercarrier and intersymbol interference (ISI); still, it offers flexible pulse shaping that enhances the efficiency of user scheduling. Here, to accomplish spatial diversity, the multiple‐input multiple‐output (MIMO) is incorporated with GFDM to enhance the performance; there is also an extra inter‐antenna interference problem that limits the model's performance. The issue concerning inter‐antenna interference can be resolved by adopting pilot‐based information transfer. The detection of a signal at the receiver based on the minimum mean square error has the issue of computational complexity while enhancing the estimation quality of a detector. Hence, a low‐complexity channel estimation technique is proposed in this research using the V‐degree polynomial‐based channel estimation technique, wherein the cubic order computation is reduced to square order. Also, the proposed adaptive pulse shaping technique, wherein the filter coefficient is optimized using the gazelle optimization algorithm (GOA) to provide optimal pulse shaping filter parameters by employing bit error rate (BER) as the objective function. The performance of a proposed V‐degree polynomial‐based channel estimation is analyzed based on various assessment measures like BER and MSE and acquired the minimal values of 5.75E‐05 and 2.07E‐05, respectively. [ABSTRACT FROM AUTHOR]

The advent of 5G technology has transformed the way that wireless networks and Internet of Things devices communicate, offering new opportunities in healthcare applications. Orthogonal frequency division multiplexing (OFDM) offers high data rates, low latency and robust communication in difficult settings, is one of the main 5G technologies. Healthcare applications face many difficulties despite 5G and OFDM's potential. The previously mentioned factors include reduced latency, dependability, energy conservation, data protection and privacy. To overcome this, we proposed wavelet-enhanced multiple input multiple outputs-orthogonal frequency division multiplexing (MIMO-OFDM). This study uses a variety of modulation schemes, including binary phase shift keying, quadrature phase shift keying, 8-PSK, quadrature amplitude modulation (QAM), 8-QAM and 16-QAM across additive white Gaussian noise channels. To simulate the proposed method by using MATLAB. The proposed systems in healthcare applications with limited resources may be restricted by the complexity of their implementation. To improve data transmission performance for healthcare applications, its viability depends on resolving complex difficulties and customizing it to particular medical applications. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the performance of multiple-input multiple-output (MIMO) communication systems applied with a non-orthogonal multiple access (NOMA)-based indoor visible light communication (VLC). We present two efficient user-pairing algorithms for NOMA in VLC, aiming to enhance achievable data rates effectively. Our investigation involves the application of three low-complexity power allocation techniques. Comparative analysis reveals performance enhancements when employing the proposed schemes, especially when contrasted with NOMA without user pairing and orthogonal frequency division multiple access (OFDMA). Additionally, we explore the performance of both algorithms in scenarios with both even and odd numbers of users. Simulation results demonstrate the superiority of NOMA in comparison to OFDMA. [ABSTRACT FROM AUTHOR]

This study develops an Enhanced Threshold Based Energy Detection approach (ETBED) for spectrum sensing in a cognitive radio network. The threshold identification method is implemented in the received signal at the secondary user based on the square law. The proposed method is implemented with the signal transmission of multiple outputs-orthogonal frequency division multiplexing. Additionally, the proposed method is considered the dynamic detection threshold adjustments and energy identification spectrum sensing technique in cognitive radio systems. In the dynamic threshold, the signal ratio-based threshold is fixed. The threshold is computed by considering the Modified Black Widow Optimization Algorithm (MBWO). So, the proposed methodology is a combination of dynamic threshold detection and MBWO. The general threshold-based detection technique has different limitations such as the inability optimal signal threshold for determining the presence of the primary user signal. These limitations undermine the sensing accuracy of the energy identification technique. Hence, the ETBED technique is developed to enhance the energy efficiency of cognitive radio networks. The projected approach is executed and analyzed with performance and comparison analysis. The proposed method is contrasted with the conventional techniques of the Whale Optimization Algorithm (WOA) and Grey Wolf Optimization (GWO). It indicated superior results, achieving a high average throughput of 2.2 Mbps and an energy efficiency of 3.8, outperforming conventional techniques. [ABSTRACT FROM AUTHOR]

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An equalization scheme employing convolutional neural networks (CNN) is proposed in generalized frequency division multiplexing (GFDM) for propagation in a hybrid microwave-optical system. Batch Gradient Descent is used to train the CNN equalizer quickly. The approach suggested eliminates nonlinearity and produces improved performance. By incorporating the GFDM network with successive interference cancellation (SIC)-based receiver, this solution greatly increases the storage ability of consumers and also offers a larger coverage range. The suggested CNN equalizer is correlated with other approaches, including statistical models and estimator techniques. The experimental finding shows that CNN produces the highest value that is marginally better than the other equalizers with a numerical difficulty reduced to zero. The simulation findings suggest that QAM-GFDM can attain the same bit error rate (BER) as cyclic-prefix (CP) OFDM without compromising spectrum economy. The tests obtained have shown that the new approach works much better than traditional techniques. [ABSTRACT FROM AUTHOR]

High-performance three-phase motor drives require accurate and robust acquisition of angular position and stator currents. A resolver sensor is widely used for angle measurement in harsh environmental conditions. This sensor receives a sinusoidal excitation signal and produces two amplitude-modulated outputs. Frequency division multiplexing is a useful alternative to simplify the data acquisition system (DAQ) to acquire the signals from stator current sensors and the resolver angular position sensor: a current signal and a resolver output are combined to produce a signal sent to the DAQ. In most cases, the sinusoidal excitation signal of the resolver is less than the switching frequency of the motor drive inverter. As a result, current signals may produce a significant interference in the angle estimation when the frequency of the resolver excitation signal is low. This paper describes an improved multiplexing approach where the resolver excitation frequency is 1.5 times the inverter switching frequency. Thus, the spectra of the resolver outputs and the stator currents are located further from each other, reducing the angle estimation interference. Synchronous sampling allows for the recovery of the current signals. A notch filter is added to an angle tracking observer to reduce even further this interference. Three different tests considering different operation conditions were performed. The proposed angle estimation method has less root mean square error in the angle estimation than other approaches (e.g., without using a notch filter or using a low resolver excitation frequency). Besides, the proposed multiplexing strategy allows recovering the fundamental component of the current signals. [ABSTRACT FROM AUTHOR]

Summary: Two fundamental aspects of wireless communication, which make it challenging and interesting, are fading and interference. Multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) techniques when utilized together effectively combat fading and interference thereby achieving the requirement of high data rate and high performance. In this paper, a 2 × 1 MIMO‐OFDM baseband model of the physical layer according to IEEE 802.16.1 standard employing 256 subcarriers capable of transmitting 192 Mbps in a 21‐MHz bandwidth frequency selective fading channel is designed. All essential blocks of the communication system like channel coding, modulation, time synchronization, frequency synchronization, channel estimation, residual carrier frequency offset (CFO) estimation, and channel decoding are covered at the algorithm level. A two‐step time synchronization method is used in this work to avoid any ambiguity in frame detection. A long preamble, consisting of three short preambles, is designed to aid in time synchronization, frequency synchronization, and channel estimation. To evaluate the performance of the proposed design, simulations were carried out in MATLAB‐SIMULINK. [ABSTRACT FROM AUTHOR]

Summary: This work presents the bidirectional and symmetric 40 Gbps wheel architecture comprising 16 channels‐based bidirectional hybrid next generation passive optical network with free space optics (NGPON/FSO) system using mode division multiplexing (MDM) scheme. The system incorporates a low‐cost high bandwidth and integrated time and wavelength division multiplexing with orthogonal frequency division multiplexing (TWDM‐OFDM) for data transmission over mixed fiber‐FSO links to various end users at donut modes 0 and 1. This system enhances the fifth generation (5G)‐based networks reliability, survivability, and flexibility, especially in rural places where the core fiber link may be damaged/destroyed under diverse turbulent and weather conditions. The obtained results depict the faithful multimode fiber range of 100 km with fixed FSO range of 100 m at −17 dBm receiver sensitivity and low power penalty of 0.2 dB at 10−9 bit error rate. Maximum FSO range of 2800 m under weak‐to‐strong Gamma‐Gamma turbulence and the effect of fog, rain, snow, and snow with rain can be obtained successfully with fixed 50 km fiber length. Also, the proposed wheel architecture provides superior performance over hybrid ring‐mesh architecture with high split ratio of 1:64. Moreover, the system can sustain up to 70 remote nodes at symmetric 10 Gbps throughput providing high gain, high optical signal‐to‐noise ratio, and low noise figure. The comparative literature work also reveals that the proposed architecture offers high bandwidth, security, long‐reach, and cost‐effectiveness in 5G fronthaul/backhaul networks. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the massive multiple‐input multiple‐output fractional Fourier transform‐based orthogonal frequency division multiplexing (MIMO FrFT‐OFDM) system is investigated using the Long Range (LoRa) modulation technique. The conventional system relies on quadrature amplitude modulated (QAM) modulation technology; high‐power amplifiers are needed to transmit the QAM signal. The LoRa modulation technique produces long‐range and low power signals. The two‐wave with diffused power (TWDP) fading channel is used to examine the system's performance. The expression of the bit‐error rate (BER) of the proposed system is also represented in a unique closed form. The proposed system is applied to a state‐of‐the art hospital, one of the Internet of Things (IoT) applications. As the problem of heart stroke is common, it needs to be monitored every second. The electrocardiogram (ECG) data are used to evaluate how well the proposed system is working. Using the proposed model, the physicians get the patient's ECG data while moving in the hospital, getting it at a high data rate, at a low cost because of the extended battery life, a long range, and a low BER. The data considered are from the MIT‐BIH Arrhythmia Database. The result displays that the proposed model achieves a BER of 0.0005 at 10 dB of signal‐to‐noise ratio (SNR), and the conventional model achieves the same BER at 15 dB of SNR. The BER performance of the proposed system is improved by nearly 5 dB. [ABSTRACT FROM AUTHOR]

Dual-polarization division multiplexing (DPDM) is considered to be a potential method to boost the secure key rate (SKR) of the continuous-variable quantum key distribution (CV-QKD) system. In this article, we propose a pilot alternately assisted local local oscillator (LLO) CV-QKD scheme based on multi-dimensional multiplexing, where time division multiplexing and frequency division multiplexing are combined with dual-polarization multiplexing techniques to dramatically isolate the quantum signal from the pilot tone. We establish a general excess noise model for the LLO CV-QKD system to analyze the influence mechanism of various disturbances (e.g., time-domain diffusion, frequency-domain modulation residual, and polarization perturbation) on the key parameters, such as the channel transmittance and excess noise. Specifically, the photon leakage noise from the reference path to the quantum path and that between quantum signals with two different polarization paths are simultaneously analyzed in the dual-polarization LLO CV-QKD scheme for the first time. Furthermore, a series of simulations are established to verify the performance of the proposed scheme. The results show that the maximal isolation degree achieves 84.0 dB~90.4 dB, and the crosstalk between pilot tones and quantum signals can be suppressed to a very small range. By optimizing the system parameters (e.g., modulation variance and repetition frequency), the SKR with 12.801 Mbps@25 km is achieved under the infinite polarization extinction ratio (PER) and 30 dB residual ratio of the frequency modulation in the nanosecond-level pulse width. Moreover, the performance of the proposed DPDM CV-QKD scheme under relatively harsh conditions is simulated; the results show that the SKR with 1.02 Mbps@25 km is achieved under a relatively low PER of 17 dB with the nanosecond-level pulse width and 20 dB residual ratio of the frequency modulation. Our work lays an important theoretical foundation for the practical DPDM LLO CV-QKD system. [ABSTRACT FROM AUTHOR]