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Nonlinear acoustic signals, specifically the parametric effect, offer significant advantages over linear signals because the low frequencies generated in the medium due to the intermodulation of the emitted frequencies are highly directional and can propagate over long distances. Due to these characteristics, a detailed analysis of these signals is necessary to accurately estimate the Time of Arrival (ToA) and amplitude parameters. This is crucial for various communication applications, such as sonar and underwater location systems. The research addresses a notable gap in the literature regarding comparative methods for analyzing nonlinear acoustic signals, particularly focusing on ToA estimation and amplitude parameterization. Two types of nonlinear modulations are examined: parametric Frequency-Shift Keying (FSK) and parametric sine-sweep modulation, which correspond to narrowband and broadband signals, respectively. The first study evaluates three ToA estimation methods—threshold, power variation (Pvar), and cross-correlation methods for the modulations in question. Following ToA estimation, the amplitude of the received signals is analyzed using acoustic signal processing techniques such as time-domain, frequency-domain, and cross-correlation methods. The practical application is validated through controlled laboratory experiments, which confirm the robustness and effectiveness of the existing methods proposed under study for nonlinear (parametric) acoustic signals. [ABSTRACT FROM AUTHOR]

The multifunctionality feature of graphene field-effect transistors (GFETs) is exploited here to design circuit building blocks of high-data-rate modulators by using a physics-based compact model. Educated device performance projections are obtained with the experimentally calibrated model and used to choose an appropriate improved feasible GFET for these applications. Phase-shift and frequency-shift keying (PSK and FSK) modulation schemes are obtained with 0.6   G Hz GFET-based multifunctional circuits used alternatively in different operation modes: inverting and in-phase amplification and frequency multiplication. An adequate baseband signal applied to the transistors' input also serves to enhance the device and circuit performance reproducibility since the impact of traps is diminished. Quadrature PSK is also achieved by combining two GFET-based multifunctional circuits. This device circuit co-design proposal intends to boost the heterogeneous implementation of graphene devices with incumbent technologies into a single chip: the baseband pulses can be generated with CMOS technology as a front end of line and the multifunctional GFET-based circuits as a back end of line. [ABSTRACT FROM AUTHOR]

With the development of body area network technology and brain neuroscience, the study of electroencephalogram signals has been increasingly emphasized by academics. However, more research on electrocorticography (ECoG) still needs to be carried out. In this study, the communication performance of ECoG signal transmission via the human body and the influence of port structure on their transmission are thoroughly investigated. First, we use the finite difference time domain method to model the head system accurately in conjunction with the electromagnetic properties of human tissues, which reveals the multipath propagation phenomenon in communication. Second, based on our previous research results, we compare the system bit error rate (BER) under phase shift keying (PSK) and frequency shift keying (FSK) modulation modes and further explore the link budget of the system under these two modulation modes. Finally, we analyze the potential impact of the transceiver structural parameters on the signal transmission characteristics. The results show that the power delay in the communication link exhibits a second-order exponential decay function distribution and that the inter-path delay and delay spread follow a Weibull distribution. Under certain BER conditions, PSK reduces the signal-to-noise requirement by 3.2 dB compared to FSK modulation, which is more suitable for head-end channel transmission. In addition, variations in the size and angle of the electrode disks at the transmitter and receiver have little effect on the transmission results. [ABSTRACT FROM AUTHOR]

With the development of super computation ability and invention of quantum computer, safeguarding network layer data confidentiality by computation based encryption method suffers great impact. As a result, people pay more attention to safeguarding data confidentiality in physical layer of wireless satellite communication system. In this paper, a groundbreaking method for enhancing physical layer security (PLS) by information hiding technology is proposed, that is, embedding secret information into chaotic frequency-hopping signal by multilevel frequency shift keying (MFSK) modulation. First, the secret information to be transmitted is encrypted with chaotic binary sequence. Secondly, according to frequency-hopping pattern and chaotic address sequence, select suitable modulation order and specific frequency point corresponding to each encrypted data block. Finally, the encrypted information is embedded into frequency-hopping Sine signal by MFSK modulation. Experimental results indicate that the proposed scheme is robust against various jamming attacks, such as power attenuation, noise adding, single-tone jamming, key exhaustive search, etc. [ABSTRACT FROM AUTHOR]

Harmonic generation and utilization are significant topics in nonlinear science. Although the progress in the microwave region has been expedited by the development of time‐modulated metasurfaces, one major issue of these devices is the strong entanglement of multiple harmonics, leading to criticism of their use in frequency‐division multiplexing (FDM) applications. Previous studies have attempted to overcome this limitation, but they suffer from designing complexity or insufficient controlling capability. Here a new space‐time‐coding metasurface (STCM) is proposed to independently and precisely synthesize not only the phases but also the amplitudes of various harmonics. This promising feature is successfully demonstrated in wireless space‐ and frequency‐division multiplexing experiments, where modulated and unmodulated signals are simultaneously transmitted via different harmonics using a shared STCM. To illustrate the advantages, binary frequency shift keying (BFSK) and quadrature phase shift keying (QPSK) modulation schemes are respectively implemented. Behind the intriguing functionality, the mechanism of the space‐time coding strategy and the analytical designing method are elaborated, which are validated numerically and experimentally. It is believed that the achievements can potentially propel the time‐vary metasurfaces in the next‐generation wireless applications. [ABSTRACT FROM AUTHOR]

Photonic Band Gap (PBG) crystals have shown their significant role in optical data processing. Again it is seen that in optical communication and computation, Frequency Shift Keying (FSK) can extend a potential application. In PBG also the FSK can show its usefulness. The main novelty of the proposed work is the implementation of an optical FSK system designed on a 2D PBG crystal. The proposed structure contains a square-shaped lattice formed by GaAsInP-doped rods placed in an air-based substrate along with photonic crystal-based Semiconductor Optical Amplifiers (pc-SOAs). The authors also presented a theoretical model that successfully demonstrates the operation of the FSK system in the optical domain with simulation experiment. This work uses a moderate input light power and operates at a very high-speed (Tbps). Here, a ring cavity resonator with a constant biasing signal is incorporated to realize the FSK model. The intensity-encoded Boolean signal and the photonic crystal-based two Semiconductor Optical Amplifiers (pc-SOAs) are used here to establish the FSK scheme where the Boolean 1 (presence of optical signal) is encoded by another light having a frequency υ1 and the Boolean 0 (absence of light) is encoded by another frequency of light υ2. As the FSK is developed in the optical domain using the switching character of PBG, hence a moderate light power is enough to conduct this implementation. In this communication, the optical FSK is designed and analyzed by a simulation process with Finite-Difference-Time-Domain (FDTD) and Plane Wave Expansion (PWE) techniques. [ABSTRACT FROM AUTHOR]

Direct wireless communication through sea–air media is essential for constructing an integrated communication network that spans space, air, land, and sea. The amplitude of acoustically induced micromotion surface waves is much smaller than the noise interference in complex sea states, making the accurate extraction of these signals from the raw signals detected by an FMCW millimeter-wave radar a major challenge. In this paper, Butterworth filtering is used to extract underwater acoustic signals from the surface waves detected by radar. The physical processes of the channel were simulated theoretically and verified experimentally. The results demonstrate a fitting coefficient of 0.99 between the radar-detected water surface waves and the simulation outcomes, enabling the effective elimination of noise interference and the extraction of acoustically induced micromotion signals in environments with a signal-to-noise ratio (SNR) of −20 dB to −10 dB. Experiments modifying frequency and linear frequency modulation have verified that the usable frequency range for underwater acoustic signals is at least 400 Hz, meeting the frequency requirements of Binary Frequency Shift Keying (2FSK) modulation encoding methods. This research confirms the accuracy of the simulation results and the feasibility of filtering and extracting underwater acoustic signals, providing a theoretical basis and an experimental foundation for building cross-media communication links. [ABSTRACT FROM AUTHOR]

To establish ubiquitous and energy-efficient wireless sensor networks (WSNs), short-range Internet of Things (IoT) devices require Bluetooth low energy (BLE) technology, which functions at 2.4 GHz. This study presents a novel approach as follows: a fully integrated all-digital phase-locked loop (ADPLL)-based Gaussian frequency shift keying (GFSK) modulator incorporating two-point modulation (TPM). The modulator aims to enhance the efficiency of BLE communication in these networks. The design includes a time-to-digital converter (TDC) with the following three key features to improve linearity and time resolution: fast settling time, low dropout regulators (LDOs) that adapt to process, voltage, and temperature (PVT) variations, and interpolation assisted by an analog-to-digital converter (ADC). It features a digital controlled oscillator (DCO) with two key enhancements as follows: ΔΣ modulator dithering and hierarchical capacitive banks, which expand the frequency tuning range and improve linearity, and an integrated, fast-converging least-mean-square (LMS) algorithm for DCO gain calibration, which ensures compliance with BLE 5.0 stable modulation index (SMI) requirements. Implemented in a 28 nm CMOS process, occupying an active area of 0.33 mm2, the modulator demonstrates a wide frequency tuning range of from 2.21 to 2.58 GHz, in-band phase noise of −102.1 dBc/Hz, and FSK error of 1.42% while consuming 1.6 mW. [ABSTRACT FROM AUTHOR]

We address the challenge of adaptable long-range underwater acoustic communications. Applications include defence, emergency response, environmental monitoring, and search and rescue. We have developed a communication system aiming to achieve long rage communications in the harsh conditions of the Canadian Arctic. We use low-frequency underwater acoustic waves that have the potential for long-range communications. Underwater propagation conditions can vary considerably. We define protocol elements for adaptable underwater communications. They comprise six frame formats with a wide range of robustness concerning underwater communication conditions. We vary the interval of symbols of 4-tone Frequency-Shift Keying modulation from one design to another. This has the effect of increasing the SNR. Hence, the ability to operate in less favourable conditions. We have simulation results. Moreover, we have obtained sea trial results. The communication system had been tested in sea trials in a test facility on the east side of Vancouver Island and the Canadian Arctic. [ABSTRACT FROM AUTHOR]

As wearable devices continue to proliferate, seamlessly integrating them into wireless body-area networks (WBANs) becomes increasingly crucial. Bodycoupled communication (BCC) emerges as a promising WBAN technology, utilizing the human body itself as a transmission channel. This paper presents a novel BCC transceiver designed for efficiency and miniaturization. The proposed transceiver prioritizes reliable data transmission with a convolutional encoder. It leverages a simple direct digital synthesizer (DDS) for frequency shift keying (FSK) modulation, minimizing chip area. At the receiver, a Viterbi decoder (VD) ensures accurate data recovery. This design shines in its resource efficiency. It occupies less than 1% of an Artix-7 FPGA, operates at 268.77 MHz with a mere 111 mW power consumption, and achieves a remarkable data rate of 13.78 Mbps. This translates to a hardware efficiency of 44.46 Kbps/slice, surpassing existing transceivers. Moreover, the BCC transceiver exhibits a stellar bit error rate (BER) of over 10-7 under realistic body channel conditions. Overall, this work presents a highly efficient BCC transceiver with significant improvements in chip area, power consumption, and data rate compared to existing designs. This paves the way for practical and miniaturized WBAN solutions for future wearable applications. [ABSTRACT FROM AUTHOR]

In ultraviolet (UV) communication, On–Off Keying (OOK) is the primary modulation technique. Compared to OOK, frequency modulation offers stronger resistance to path attenuation. Currently, research on frequency modulation demodulation schemes for UV communication is limited, mainly employing waveform detection and laser pulse response methods, which require high detection sensitivity to light. This study presents a novel frequency modulation communication scheme using discrete Poisson channel distribution and optical pulse signal processing algorithms, enhancing the signal processing sensitivity of the existing frequency modulation scheme to the level of photons. The proposed system model is rigorously evaluated through theoretical derivations and simulations. Additionally, a hardware system integrating optical pulse counting, frequency detection, and clock data recovery algorithms is developed. Experimental results show the system achieving a 5 kbps transmission rate under frequency modulation. In non-line-of-sight (NLOS) scenarios, communication reaches up to 65 m, with the receiver elevation angle ranging from 10° to 25° and the bit error rate (BER) stabilized at 10−4, while in line-of-sight (LOS) situations, the BER remains at 10−5 up to 400 m and 10−4 up to 700 m, achieving the farthest distance and fastest communication rate achievable in the current FSK modulation scheme of ultraviolet communication systems. The integrated components enhance its applicability in communication systems. This study offers a valuable addition to UV communication technology. [ABSTRACT FROM AUTHOR]

In this study, deep learning network technology is employed to solve the problem of rapid changes in underwater channels. The modulation techniques employed are frequency-shift keying (FSK) and the BELLHOP module of MATLAB; they are used to create water with multipath, Doppler shifts, and additive Gaussian white noise such that underwater acoustic receiving signals simulating the actual ocean environment can be obtained. The southwest coastal area of Taiwan is simulated in the manuscript. The results reveal that optimizing the environment by using the virtual time reversal mirror (VTRM) technique can generally mitigate the bit error rates (BERs) of the deep learning network's model receiver and traditional demodulation receiver. Lastly, seven deep learning networks are deployed to demodulate the FSK signals, and these approaches are compared with traditional demodulation techniques to determine the deep learning network techniques that are most suitable for marine environments. [ABSTRACT FROM AUTHOR]

A noise robust time-frequency representation based on the S-method (SM) and modified group delay (MGD) (S-MGD) is proposed in this article. The SM is free from cross-terms as it is the sum of individual Wigner distributions of different signal components and provides high-energy concentration both in time and frequency. The MGD reduces the Gibbs ripple and spurious spectral peaks because of noise, without using any frequency smoothing, and thus maintains the best frequency resolution as that of rectangular window. Hence, a combination of SM and MGD provides the desirable features of both the methods. The proposed method is tested for different signals like time varying random process, frequency shift keying, synthesized car engine sound/pressure signals using a solo combustion and a realtime echolocation pulse emitted by a big brown bat (Eptesicus fuscus) which indicate that the new S-MGD has improved noise immunity and frequency resolution compared to the method that uses frequency smoothing to suppress noise and Gibbs effects. [ABSTRACT FROM AUTHOR]

BLE-based (Bluetooth Low Energy-based) backscatter has received considerable attention, as it aims to communicate with everyday smart devices such as smartphones, smartwatches, and tablets in passive IoT. The state-of-the-art BLE backscatter systems enable communication using a specialized continuous wave (CW) generator or entirely using commodity BLE 4.0 radios as an RF source. However, the existing BLE communication systems suffer from several key issues, including a short carrier length and a large frequency shift. This paper presents a passive BLE (PBLE) backscatter communication system that utilizes commodity BLE 5.0 radios. The system uses a BLE 5.0 extended advertising packet with partial single tones as excitations transmitting on the secondary advertising channel of BLE 5.0, and the BLE backscatter tag produces bandpass frequency-shift keying modulation at 1 Mb/s, which enables compatibility with BLE advertising channels. The prototype is implemented using an NRF52832 BLE 5.0 commodity chip, smart devices, and tags with FPGAS and chips. In FPGA board-level verification, when the downlink distance is 0.5 m, the uplink distance can reach 10 m. In chip testing, the uplink distance can reach 7 m when the downlink distance is 1 m. The baseband power consumption is 2 μW, with a total power consumption of 10 μW. This system eliminates the need for expensive and costly specialized RF sources, unlike the BLE backscatter communication system that uses a specialized CW generator. Compared to the BLE backscatter communication system that uses commodity BLE 4.0 radios, this system reduces the minimum frequency shift from 24 MHz to 2 MHz and increases the length of the single tones as a CW by a factor of about seven, from 31 bytes to 254 bytes. [ABSTRACT FROM AUTHOR]

Since the coprime discrete time fractional Fourier transform (DTFrFT) spectral receiver can effectively intercept low probability of interception signals and its output shows favorable spectral characteristics in the discrete time fractional Fourier domain (DTFrFD), this paper presents an intrapulse modulation recognition method in the DTFrFD to process the coprime DTFrFT spectral receiver's output data, consisting of two banks, namely coarse recognition and fine recognition. The coarse recognition returns a coarse classification for the shift keying signals [binary phase shift keying (BPSK) and binary frequency shift keying (BFSK)] from the linear frequency modulation (LFM) and polyphase coded signals (Frank code, P1 code, P2 code, P3 code, P4 code) by addressing the optimal transformation order of the intercepted data in DTFrFD. In the fine recognition algorithm, the ridge line extraction function and the peak energy ratio function in the DTFrFD are defined to identify BPSK signals from BFSK signals and distinguish LFM signals and polyphase-coded signals. Compared to conventional recognition approaches in the Fourier domain, the proposed recognition method is always more efficient because it utilizes more spectral characteristics of the output data in the DTFrFD. Both theoretical analysis and simulation results demonstrate that the proposed algorithm shows better robustness and better recognition performance than the original coprime digital Fourier transform spectral receiver against SNR variation. [ABSTRACT FROM AUTHOR]

Marine communication has attracted widespread attention in the wake of global warming and national defense awareness in recent years, where acoustic systems enabling smooth underwater communication have become a popular research topic. In this study, we proposed an underwater communication system equipped with modulators and demodulators (modems). Specifically, the wireless communication software GNU’s Not Unix Radio (GNU Radio) was adopted to develop communication formats and architectures applied to a Raspberry Pi computer, on which we developed a communication format available for signal synchronization to increase system robustness against underwater channel interferences. We also developed hardware and software modems for the system. The hardware device was developed using the XR2206 function generator and XR2211 equipment for frequency-shift keying (FSK)-based modulation and demodulation, respectively. The software FSK modem was developed using GNU Radio. To increase the robustness of the transmitted data, we added a cyclic redundancy check through the Async CRC32 block, after which the power distribution unit (PDU) to the Tagged Stream block placed a tag to the start of data combined with effective loads and CRC32, facilitating the attachment of header generators. Four experiments with different underwater scenarios were then conducted to verify the proposed system. The hardware modem had a 0 bit error rate (BER) during experiments implemented in a laboratory sink, a 20-m-long indoor swimming pool, and a 50-m-long outdoor swimming pool, compared with BERs of 2.8 × 10−3 and 6.6 × 10−3 during the breeding water tank experiment under transmission rates of 1 and 2 kbps, respectively. Similarly, the software modem delivered 0-BER performance in the laboratory sink as well as in the indoor and outdoor swimming pools, with its BERs being 2.3 × 10−4 and 2.98 × 10−4 under 1 and 2 kbps transmission rates, respectively. The proposed system comprises preambles, headers, and effective load communication formats for signal protection. In particular, its directional ultrasonic cylindrical piezoelectric transducer can mitigate multipath effects and interferences, thereby enhancing system robustness. [ABSTRACT FROM AUTHOR]

In harsh operating environments such as mines and gas stations, intrinsically safe power converters are required for electronics devices. Reliable communication is the key ensuring good performance of monitoring and coordinated control for intrinsically safe converters. This paper proposes a power and signal dual modulation (PSDM)‐based communication method for intrinsically safe parallel‐connected Buck converters. The bidirectional communication between two parallel Buck converters is realized by combining the frequency shift keying (FSK) and phase shift keying (PSK) methods. In addition, switching frequencies are employed to identify the signals received from the power converters interfacing different sources. According to the intrinsic safety requirement, inductors and capacitors are redesigned based on the modulated voltage ripples during communication. Simulations and prototype experiments are performed to verify the feasibility of the proposed bidirectional communication for intrinsically safe converters. The amplitude of voltage ripples modulated for carrying data is restricted to less than 1.5% of the bus voltage. The transmission speed can be achieved from 0.5 to 2kbps depending on the adopted switching frequencies. The demodulation delay is less than 5% duration of one bit of transmitted data. [ABSTRACT FROM AUTHOR]

Hand gesture recognition, which is one of the fields of human–computer interaction (HCI) research, extracts the user's pattern using sensors. Radio detection and ranging (RADAR) sensors are robust under severe environments and convenient to use for hand gestures. The existing studies mostly adopted continuous-wave (CW) radar, which only shows a good performance at a fixed distance, which is due to its limitation of not seeing the distance. This paper proposes a hand gesture recognition system that utilizes frequency-shift keying (FSK) radar, allowing for a recognition method that can work at the various distances between a radar sensor and a user. The proposed system adopts a convolutional neural network (CNN) model for the recognition. From the experimental results, the proposed recognition system covers the range from 30 cm to 180 cm and shows an accuracy of 93.67% over the entire range. [ABSTRACT FROM AUTHOR]

The investigation of a decentralized radio network dedicated to unmanned aerial systems (UASs) was presented in the paper. Two frequencies (315 MHz; 434 MHz) and five different configurations of Gaussian frequency-shift keying (GFSK) were taken into account. Three different algorithms for decentralized networks were investigated and their influence on the network capacity was measured. The research was done both for static and dynamically changed unmanned aerial vehicle (UAV) positions. In order to quantify the research three different parameters were determined: RSSI, nP (number of data packets in one second), and F (frequency of data update). [ABSTRACT FROM AUTHOR]

In recent years, the nitrogen-vacancy (NV) center in diamonds has been demonstrated to be a high-performance multiphysics sensor, where a lock-in amplifier (LIA) is often adopted to monitor photoluminescence changes around the resonance. It is rather complex when multiple resonant points are utilized to realize a vector or temperature-magnetic joint sensing. In this article, we present a novel scheme to realize multipoint lock-in detection with only a single-channel device. This method is based on a direct digital synthesizer (DDS) and frequency-shift keying (FSK) technique, which is capable of freely hopping frequencies with a maximum of 1.4 GHz bandwidth and encoding an unlimited number of resonant points during the sensing process. We demonstrate this method in experiments and show it would be generally useful in quantum multi-frequency excitation applications, especially in the portable and highly mobile cases. [ABSTRACT FROM AUTHOR]

In this paper, a system was designed to simulate the study and analyze the effect of chlorophyll on the underwater wireless optical communication system. Chlorophyll was extracted and characterized by measuring absorption and fluorescence spectra, the performance of system was observed by mixing various volumes added to water. The optical beam was modulated at different frequencies by the frequency shift key, once through clean water and once through water mixed with chlorophyll and different metrics such as received power (Pr), attenuation coefficient (α), peak-to-peak voltage (Vp-p), voltage gain (Av), and signal-to-noise ratio were measured to assess the performance of the system. The results refer that the system exhibits a good link quality to the received frequencies under different conditions. [ABSTRACT FROM AUTHOR]

Ultrasonic sensors are inexpensive and provide highly accurate measurements, even with simple hardware configurations, facilitating their use in various fields. When multiple ultrasonic sensors exist in the measurement space, crosstalk occurs due to other nodes, which leads to incorrect measurements. Crosstalk includes not only receiving homogeneous signals from other nodes, but also overlapping by other signals and interference by heterogeneous signals. This paper proposes using frequency sweep keying modulation to provide robustness against overlap and a faster region-based convolutional neural network (R-CNN) demodulator to reduce the interference caused by heterogeneous signals. The demodulator works by training Faster R-CNN with the spectrograms of various received signals and classifying the received signals using Faster R-CNN. Experiments implementing an ultrasonic crosstalk environment showed that, compared to on–off keying (OOK), phase-shift keying (PSK), and frequency-shift keying (FSK), the proposed method can implement CDMA even with shorter codes and is robust against overlap. Compared to correlation-based frequency sweep keying, the time-of-flight error was reduced by approximately 75%. While the existing demodulators did not consider heterogeneous signals, the proposed method ignored approximately 99% of the OOK and PSK signals and approximately 79% of the FSK signals. The proposed method performed better than the existing methods and is expected to be used in various applications. [ABSTRACT FROM AUTHOR]

Multiple Gateways (GWs) provide network connectivity to Internet of Things (IoT) sensors in a Wide Area Network (WAN). The End Nodes (ENs) can connect to any GW by discovering and acquiring its periodic beacons. This provides GW diversity, improving coverage area. However, simultaneous periodic beacon transmissions among nearby GWs lead to interference and collisions. In this study, the impact of such intra-network interference is analyzed to determine the maximum number of GWs that can coexist. The paper presents a new collision model that considers the combined effects of the Medium Access Control (MAC) and Physical (PHY) layers. The model takes into account the partial overlap durations and relative power of all colliding events. It also illustrates the relationship between the collisions and the resulting packet loss rates. A performance evaluation is presented using a combination of analytical and simulation methods, with the former validating the simulation results. The system models are developed from experimental data obtained from field measurements. Numerical results are provided with Gaussian Frequency Shift Keying (GFSK) modulation. This paper provides guidance on selecting GFSK modulation parameters for low bit-rate and narrow-bandwidth IoT applications. The analysis and simulation results show that larger beacon intervals and frequency hopping help in reducing beacon loss rates, at the cost of larger beacon acquisition latency. On the flip side, the gateway discovery latency reduces with increasing GW density, thanks to an abundance of beacons. [ABSTRACT FROM AUTHOR]

In this study, the performance analysis of dual-hop power line communication (PLC)/ η − μ and PLC/ λ − μ L-branch systems by using the decode-and-forward (DF) protocol is presented in detail. The introduced work provides novel closed-form expressions of the probability density function (PDF) of the instantaneous signal-to-noise ratio (SNR) of the considered systems. Taking the proposed PDFs into account, we also derive closed-form expressions of the error rate and channel capacity (CC) performance for the dual-hop PLC/ η − μ and PLC/ λ − μ L-branch DF systems. Furthermore, an exhaustive comparative study of different modulation types such as non-coherent M-ary frequency-shift keying, square quadrature amplitude modulation (SQAM), and cross quadrature amplitude modulation (×QAM) is presented by using the proposed closed-form error rate expressions. Also, the exact expressions for the CC with channel inversion with a fixed-rate (CIFR) transmission policy are proposed. Finally, all the theoretical findings are confirmed through numerical results obtained by using the exact expressions. [ABSTRACT FROM AUTHOR]

Wireless electroencephalography (EEG) has emerged as a critical interface between human cognitive processes and machine learning technologies in the burgeoning field of sensor communications. This paper presents a comprehensive review of advancements in wireless EEG communication and analysis, with an emphasis on their role in next-generation green wireless networks and industrial IoT. The review explores the efficacy of modulation techniques, such as amplitude-shift keying (ASK) and frequency-shift keying (FSK) in EEG data transmission, and emphasizes the transformative role of deep learning in the joint transmission and restoration of EEG signals. In addition, we propose a novel, energy-efficient approach to deep learning-based EEG analytics, designed to enhance wireless information transfer for industrial IoT applications. By applying an autoencoder to sample the EEG data and incorporating a hidden layer to simulate a noisy communication channel, we assessed the energy efficiency and reliability of the transmission. Our results demonstrate that the chosen network topology and parameters significantly affect not only data fidelity but also energy consumption, thus providing valuable insights for the development of sustainable and efficient wireless EEG systems in industrial IoT environments. A key aspect of our study is related to symmetry. Our results demonstrate that the chosen network topology and parameters significantly impact not only data fidelity but also energy fidelity and energy consumption, thus providing valuable insights for the development of sustainable and efficient wireless EEG systems in industrial IoT environments. Furthermore, we realized that the EEG data showed mildly marked symmetry. Neural networks must also exhibit asymmetric behavior for better performance. [ABSTRACT FROM AUTHOR]

A space-time coding metasurface (STCM) operating in the sub-terahertz band to construct new-architecture wireless communication systems is proposed. Specifically, a programmable STCM is designed with varactor-diode-tuned metasurface elements, enabling precise regulation of harmonic amplitudes and phases by adjusting the time delay and duty cycle of square-wave modulation signal loaded on the varactor diodes. Independent electromagnetic (EM) regulations in the space and time domains are achieved by STCM to realize flexible beam manipulations and information modulations. Based on these features, a sub-terahertz wireless communication link is constructed by employing STCM as a transmitter. Experimental results demonstrate that the STCM supports multiple modulation schemes including frequency-shift keying, phase-shift keying, and quadrature amplitude modulations in a wide frequency band. It is also shown that the STCM is capable of realizing wide-angle beam scanning in the range of ±45°, which offers an opportunity for user tracking during the communication. Thus, the STCM transmitter with high device density and low power consumption can provide low-complexity, low-cost, low-power, and low-heat solutions for building the next-generation wireless communication systems in the sub-terahertz frequency and even terahertz band. [ABSTRACT FROM AUTHOR]

A 10 Gbps Continuous Phase Frequency Shift Keying (CPFSK) modulation is proposed for a Free Space Optical (FSO) communication system. The system performance is analyzed by considering effects of atmospheric conditions, beam divergence, transmitter and receiver antenna aperture diameters for 1550 nm operation. In this paper, we evaluate the system maximum Quality-factor (Q-factor), Bit Error Rate (BER), and received power, where the system is greatly affected by th e mentioned parameters. This simulation is performed by using the Optiwave system software. The obtained simulation results show that CPFSK modulated FSO system with low beam divergence and high aperture diameter is upgrading maximum Q-factor and degrading minimum BER. [ABSTRACT FROM AUTHOR]

Antiferromagnets exhibit ultrafast magnetization precession, which has the potential to enable the development of terahertz spin torque nano-oscillators. By utilizing perpendicularly magnetized magnetic nanopillars with a synthetic antiferromagnetic (SAF) free layer, we have demonstrated through theoretical and numerical analysis that stable out-of-plane precession states can be achieved by applying current and an electric field. In the case of small current, the two magnetic layers of the SAF are in antiparallel alignment and rotate around the z-axis with the precession frequency decreasing as the current strength increases. When the current-induced spin torque is strong enough to fully overcome the antiferromagnetic coupling, the SAF free layer is driven into a scissor-like precession state around the z-axis with the frequency increasing with current. By selecting the appropriate combination of the current and electric field, the magnetization precession orbits and precession frequencies can be adjusted. These controllable procession orbits with tunable frequencies and fixed magnetization precession amplitude may be a promising candidate for implementing binary frequency shift keying modulation techniques. [ABSTRACT FROM AUTHOR]

This paper proposes a novel automotive radar waveform involving the theory behind M-ary frequency shift key (MFSK) radar systems. Along with the MFSK theory, coding schemes are studied to provide a solution to mutual interference. The proposed MFSK waveform consists of frequency increments throughout the range of 76 GHz to 81 GHz with a step value of 1 GHz. Instead of stepping with a fixed frequency, a triangular chirp sequence allows for static and moving objects to be detected. Therefore, automotive radars will improve Doppler estimation and simultaneous range of various targets. In this paper, a binary coding scheme and a combined transform coding scheme used for radar waveform correlation are evaluated in order to provide unique signals. AVs have to perform in an environment with a high number of signals being sent through the automotive radar frequency band. Efficient coding methods are required to increase the number of signals that are generated. An evaluation method and experimental data of modulated frequencies as well as a comparison with other frequency method systems are presented. [ABSTRACT FROM AUTHOR]

Nonlinear acoustics offers a new range of acoustic applications that are currently being exploited. The parametric nonlinear effect—the occurrence of low frequencies with modulated high-frequency emission—is of particular interest. This work provides a systematic exposition of the theoretical framework on which the so-called parametric nonlinear effect is based. In relation to this behavior is an analytical discussion of how to solve the problem for two cases: (i) nonlinear behavior with modulation, and (ii) parametric emission of two monochromatic waves (bi-frequency). Subsequently, parametric emission experiments were carried out in air and water using the same transducer to compare the results with those obtained theoretically. In this sense, directivity and attenuation measurements are obtained. Conclusively, this research offers a proof of concept for underwater acoustic communications. It is characterized by the transmission of a binary sequence through Frequency Shift Keying (FSK) modulation, and the subsequent decoding of each received bit (either 1 or 0) utilizing advanced signal processing with the cross-correlation technique. This paper accentuates the significant potential of employing the parametric effect for specialized communication applications. [ABSTRACT FROM AUTHOR]

Concepts for two cooperative active reflector tags (ARTs) for joint ranging and communication in a linear frequency modulated continuous wave secondary radar system are presented along with corresponding theoretical derivations. To prove the concepts, the ARTs operating from 24 to 24.5 GHz are implemented using custom integrated superregenerative amplifiers (SRAs) designed in a 130 nm SiGe BiCMOS technology. The SRAs have a measured minimum detected input power greater than −80 dBm, and an output power greater than 3.2 dBm after wire‐bonding. The ARTs also feature roll invariance using bandwidth enhanced microstrip patch antenna diversity and a novel quench frequency shift keying based low data rate simplex communication. Indoor ranging experiments done to prove the concepts and the theoretical considerations show a maximum distance of 77 m in the ranging mode and a data rate of 0.5 symbols per second in the data transfer mode. For distances less than 5 m, the characterised accuracy is better than 12 cm and the precision is better than 2 cm. To the best of authors' knowledge this is one of the first reported scientific works leading to a proof of concept for integrated superregenerative amplifier based joint ranging and quench frequency shift keying. The combination of maximum range and precision are also one of the best reported among similar works in the literature. [ABSTRACT FROM AUTHOR]

This paper proposes a deep transfer learning (DTL)-based variable Doppler frequency-hopping binary frequency-shift keying underwater acoustic communication system. The system uses a convolutional neural network (CNN) as the demodulation module of the receiver. This approach directly demodulates the received signal without estimating the Doppler. The DTL first uses the simulated communication signal data to complete the CNN training. It then copies a part of the convolution layers from the pre-trained CNN to the target CNN. After randomly initializing the remaining layers for the target CNN, it is trained by the data samples from the specific communication scenarios. During the training process, the CNN learns the corresponding frequency from each symbol in the selected frequency-hopping group through the Mel-spectrograms. Simulation and experimental data processing results show that the performance of the proposed system is better than conventional systems, especially when the transmitter and receiver of the communication system are in variable speed motion in shallow water acoustic channels. [ABSTRACT FROM AUTHOR]

In this paper, we present a hybrid frequency shift keying and frequency division multiplexing (i.e., FSK–FDM) approach for information embedding in dual-function radar and communication (DFRC) design to achieve an improved communication data rate. Since most of the existing works focus on merely two-bit transmission in each pulse repetition interval (PRI) using different amplitude modulation (AM)- and phased modulation (PM)-based techniques, this paper proposes a new technique that doubles the data rate by using a hybrid FSK–FDM technique. Note that the AM-based techniques are used when the communication receiver resides in the side lobe region of the radar. In contrast, the PM-based techniques perform better if the communication receiver is in the main lobe region. However, the proposed design facilitates the delivery of information bits to the communication receivers with an improved bit rate (BR) and bit error rate (BER) regardless of their locations in the radar's main lobe or side lobe regions. That is, the proposed scheme enables information encoding according to the transmitted waveforms and frequencies using FSK modulation. Next, the modulated symbols are added together to achieve a double data rate using the FDM technique. Finally, each transmitted composite symbol contains multiple FSK-modulated symbols, resulting in an increased data rate for the communication receiver. Numerous simulation results are presented to validate the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

Floral trait evolution mediated by pollinators is important in the diversification of flowering plants, yet few studies have demonstrated the range‐wide geographic variation in both floral traits and pollinators which represents a predicted precursor for pollinator‐mediated speciation. This study explores whether geographic variation in pollinator interactions underlies the observed patterns of floral divergence both 1) among species of the Castilleja purpurea complex (C. purpurea, C. citrina and C. lindheimeri) and the congener C. sessiliflora, as well as 2) within C. sessiliflora, across its wide geographic range. We sampled floral visitors and floral traits (morphology and color) at 23 populations across a 1900 km‐wide study area in 1–3 years, with reproductive fitness (fruit set) data for 18 of these populations. A wide diversity of pollinator functional groups visited the focal species, including bees, butterflies, hawkmoths and hummingbirds, and visitor assemblages varied among species and across geography. We identified relationships between floral traits and visitation by certain pollinator groups, which often aligned with predictions based on pollination syndromes. Despite visitor assemblages being largely generalized across most populations, we found that the observed changes in floral traits were associated with shifts in the relative frequencies of key pollinator functional groups. Hence this study demonstrates that variation in pollinator assemblages across the distributions of taxa may underlie divergence in floral traits and suggests that highly specialized relationships may not be required for early stages of pollinator‐mediated floral divergence. Our extensive sampling of 23 populations over multiple years across a large geographic area highlights the value of range‐wide studies for characterizing patterns of divergence mediated by ecological interactions. [ABSTRACT FROM AUTHOR]

Moored buoys are important components of stereo platforms for ocean observation, which are crucial in underwater exploration. In complex marine environments, power supply and data transmission between moored buoys and underwater sensors are difficult. To solve these problems, an inductively coupled power and data transfer (ICPDT) scheme based on LCCL-S-LC hybrid compensation is proposed. The power transmission was analyzed by establishing an LCCL-S-LC compensation buoy ICPDT system model. The system efficiency and output power were analyzed when the load changed, and the optimal load resistor for maximum system efficiency was determined. A modulation and demodulation circuit used for data transmission was introduced, the compensation topology parameters of each loop of the buoy ICPDT system were deduced, and the crosstalk between power and data was analyzed and reduced. An ICPDT system prototype was built to verify the system's feasibility and effectiveness when it was powered by 24 V. The LCCL-S-LC topology reduced the interference between data and power transmission. When the measured output power of the system was 61.5 W, the power transmission efficiency was 78.1%, and the data receiving end could achieve correct demodulation when the transmission rate was 100 kb/s. [ABSTRACT FROM AUTHOR]

Visible light communications (VLC) are an emerging technology that is increasingly demonstrating its ability to provide wireless communications in areas where radio frequency (RF) technology might have some limitations. Therefore, VLC systems offer possible answers to various applications in outdoor conditions, such as in the road traffic safety domain, or even inside large buildings, such as in indoor positioning applications for blind people. Nevertheless, several challenges must still be addressed in order to obtain a fully reliable solution. One of the most important challenges is focused on further improving the immunity to optical noise. Different from most works, where on–off keying (OOK) modulation and Manchester coding have been the preferred choices, this article proposes a prototype based on a binary frequency-shift keying (BFSK) modulation and non-return-to-zero (NRZ) coding, for which the resilience to noise is compared to that of a standard OOK VLC system. The experimental results showed an optical noise resilience improvement of 25% in direct exposure to incandescent light sources. The VLC system using BFSK modulation was able to maintain a maximum noise irradiance of 3500 µW/cm2 as compared with 2800 µW/cm2 for the OOK modulation, and an improvement of almost 20% in indirect exposure to the incandescent light sources. The VLC system with BFSK modulation was able to maintain the active link in an equivalent maximum noise irradiance of 65,000 µW/cm2, as opposed to the equivalent 54,000 µW/cm2 for the OOK modulation. Based on these results, one can see that based on a proper system design, VLC systems are able to provide impressive resilience to optical noise. [ABSTRACT FROM AUTHOR]

Ultrasonic communication and power transfer are attractive solutions when conventional electromagnetic-based or wired connections are unfeasible. Most ultrasonic communication applications concern a single-solid barrier. Nevertheless, some relevant scenarios can be composed of several fluid—solid media, through which communication and power transfer are intended. Due to its multi-layer nature, insertion loss and, consequently, the system efficiency considerably decrease. This paper presents an ultrasonic system capable of simultaneously power transferring and transmitting data through a set of two flat steel plates separated by a fluid layer using a pair of co-axially aligned piezoelectric transducers on opposite sides of the barrier. The system is based on frequency modulation and adopts a novel technique for automatic gain and automatic carrier control. The modems used herein were developed specifically for this application, rendering the system able to transfer data at a rate of 19,200 bps, using the frequency shift keying (FSK) modulation scheme and simultaneously transferring 66 mW of power through two flat steel plates (5 mm) separated by a fluid layer (100 mm), which completely supplied a pressure and temperature sensor. The proposed automatic gain control allowed a higher data transmission rate and the automatic carrier control reduced power consumption. The former reduced the transmission error from 12% to 5%, while the latter reduced the global power consumption from 2.6 W to 1.2 W. The proposed system is promising for monitoring applications such as oil wellbore structural health monitoring systems. [ABSTRACT FROM AUTHOR]

Driven by increasing demands for the ultra‐compact interconnects of integrated electronics and the ultrafast information transfer of communication systems, research on spoof plasmonic metamaterials has attracted considerable attention. However, most efforts to date have been only achieved in individual modulation of amplitude or phase at a single frequency because of the limitation of structural design. Herein, an ultra‐thin reprogrammable modulator consisting of a spoof surface plasmonic polariton (SSPP) waveguide and spoof localized surface plasmon (SLSP) resonators is proposed and experimentally demonstrated. It allows controlling the amplitudes and phases of surface waves independently. By simultaneously manipulating the SSPP waveguide and SLSP resonators in real time, different modulations are realized in a programmable way, such as amplitude‐shift keying, phase‐shift keying, quadrature amplitude modulation, and frequency‐shift keying. Measured results confirm that the reprogrammable plasmonic metamaterial can modulate the surface electromagnetic waves, holding promising applications in integrated circuits and communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a new simultaneous wireless power and data transfer method is proposed based on 4FSK modulation using the four splitting frequencies of series–parallel combined resonant circuit (SPRC) based WPT system. Features of SPRC-based WPT systems, including two resonance frequencies, circuit quality factors, system topologies, system quality factors and four splitting frequencies, are investigated. Based on that an optimum condition of the system to have similar quality factors at the four splitting frequencies is derived and a 4FSK modulation-based simultaneous wireless power and data transfer system is designed. An experimental prototype of the proposed system is constructed and the simultaneous transfer feasibility of power and data based on 4FSK modulation is validated. The prototype shows stable power transfer and up to 4kbps data rate in the distance of 20 cm, where the carrier frequency hops between four splitting frequencies spreaded in 40 to 62 kHz range. [ABSTRACT FROM AUTHOR]

One of the problems with the pump at Paiton Power Plant is the vibration. Vibration occurs because the pump's natural frequency approaches its operational frequency, then resulting condition in resonance. If the pump is experiencing resonance, there will be a strengthening of the vibration which can cause damage to the components in it. The vibration absorber was chosen as a way to reduce the vibration. The purpose of the absorber design is to determine the constants and mass of the absorber so that the mass displacement of the equipment experiencing vibration becomes zero. Vibration absorber installation experiment was carried out to prove that there was a change in the natural frequency for the system installed with the absorber. Installation of the Vibration Absorber can reduce the vibration of the pump due to resonance up to 75% at the desired frequency. [ABSTRACT FROM AUTHOR]

In this article, a switching frequency-modulation-based inductive power transfer system that provides wireless charging of the scooters by magnetic in-band communication is newly proposed. Although the transmitter (Tx) and receiver (Rx) coils are misaligned, the scooters can be freely charged in the charging station by the proposed frequency modulation method without additional power converters in the Tx and Rx sides. In order to implement frequency modulation control, the Rx side can transmit the required information to the Tx side through the magnetic coupling between Tx and Rx coils, i.e., magnetic in-band communication, in the suggested approach. By virtue of the proposed magnetic in-band communication method, the switching frequency can be modulated so that the load power for charging the battery in the Rx side is appropriately controlled, considering the battery charging profile. Contrary to the Qi standard technology using both amplitude shift keying (ASK) and frequency shift keying, the proposed magnetic communication protocol is optimally and simply designed for targeting scooter wireless charging applications. Because the proposed communication method is based on only ASK technique for unidirectional information delivery, the coil misalignment sensitivity and the complexity of the communication process can be reduced, which guarantees the robust frequency modulation control for load power regulation. A 100 W power level prototype for the charging station and the scooters was fabricated and verified by simulations and experiments. The 97.3% of the coil-to-coil efficiency and 90.6% of the dc-to-dc efficiency were obtained at a nominal operating point of k = knom and PL = 100.8 W. As a result, the battery having 44.0–53.0 V and 13 Ah in the Rx side was charged under a wide range of battery charging conditions and coil misalignments. [ABSTRACT FROM AUTHOR]

A 27-MHz wireless system with binary frequency shift keying (BFSK) modulation at 400-kHz is reported. The receiver has been designed to handle in-band interference corrupting the BFSK signal with the use of complex filters and amplitude comparison method. The BFSK modulation is carried out with a voltage-controlled oscillator before up-converting with a 27-MHz local oscillator. The bipolar junction transistors (BJT-based) power amplifier with 30% efficiency pumps 220 mW into a spiral antenna. The inductive-degenerated low-noise amplifier with a voltage of more than 30 dB amplifies an incoming signal before feeding into a mixer for complex direct down conversion. With deliberate Gaussian interference injection, the minimum ratios between the signal with interference and the interference only at the distance of 2.5, 10 and 15 m are 3.3, 8.5 and 11.5 dB, respectively at a maximum data rate of 20 kbps. Without any interference included, the system can achieve a data rate of 40 kbps at the maximum transmission distance of 15 m. Conceptually agreed with the presented bit-error-rate (BER) analysis, the BER measurements with Gaussian and single-tone/two-tone in-band interferences also confirm superiority offered by the amplitude comparison method where the signal-to-noise ratio is at 1 dB for BER=10-3 at 10 kbps (10 dB better than the phase detection counterpart). [ABSTRACT FROM AUTHOR]

The current work is devoted to chaos oscillator employment in digital communication systems for IoT applications. The paper presents a comparative performance analysis of two different chaos data transmission systems: frequency-modulated chaos shift keying (FM-CSK) and quadrature chaos phase-shift keying (QCPSK), and a comparison to their non-chaotic counterparts: frequency-shift keying (FSK) and quadrature amplitude modulation (QAM). For both chaotic communication systems, the Vilnius oscillator and substitution method of chaotic synchronization are chosen due to simple circuitry implementation and low power consumption properties. The performance of the systems in the fading channel with additive white Gaussian noise (AWGN) is evaluated. Also, the systems' performance in the case phase noise is investigated, and the benefits of chaotic waveforms employment for data transmission are demonstrated. [ABSTRACT FROM AUTHOR]

This work addresses the fundamental concepts in the design of a voice communications system that uses the operating principles of direct current power line communications (DC-PLC: Direct Current - Power Line Communications) based on BFSK modulation. The system is composed of a transmission subsystem and a voice signal reception subsystem, these elements are interconnected through a DC-PLC channel referenced to a twisted copper pair. The transmission subsystem performs the functions associated with the conditioning, digitization and processing of the signal for its digital transfer with a BFSK modulation in the communication channel. The receiving subsystem performs the BFSK demodulation, processing and recovery of the voice signal for monitoring. For both subsystems a design based on the use of Silicon Laboratories 8051 core microcontrollers is proposed. The UART peripheral available in the 8051 microcontrollers is used for digital data transfer and is applicable as a transmission method in the DC-PLC channel type. In addition, the design criteria of the internal circuits are presented and exposed through their electrical schematics. [ABSTRACT FROM AUTHOR]

To solve the problem of bit error rate (BER) performance degradation over strong solar wind turbulence channel, this paper addresses to Gaussian minimum frequency shift keying (GMSK) demodulation using machine learning. First, by analyzing the scintillation characteristics of the telemetry signal caused by solar wind turbulence during the solar superior conjunction, the K distribution channel model is innovatively established over strong solar wind turbulence channel. Then, the approximate probability density function of the K distribution of the established channel is studied by using Laguerre orthogonal polynomial for convenience. Additionally, the BER performance of GMSK over strong solar wind turbulence channel is analyzed. Second, using a one-dimensional convolutional neural network (1D-CNN) and bidirectional long short-term memory network (Bi-LSTM), two demodulators for GMSK are proposed. By integrating the 1D-CNN and LSTM to extract local features and process the dynamic information of GMSK signals, we propose a novel GMSK demodulator over strong solar wind turbulence channel with combining 1D-CNN and Bi-LSTM. The simulation results show that, even if the solar wind turbulence has serious effects on the signal at a low signal-to-noise ratio, the proposed combining neural network demodulation can obtain better BER performance than the classical Viterbi algorithm, demodulation using only a single 1D-CNN or Bi-LSTM. The proposed GMSK demodulator is more suitable for the deep space exploration of the solar system. [ABSTRACT FROM AUTHOR]

This article proposed an underwater simultaneous wireless power transfer and data transfer system for the autonomous underwater vehicle. The double-sided LLCC compensation topology is proposed to effectively suppress the interference to the data channel at switching instant. With the increase of the size and turns of the coupling coils, the self-resonance frequency gradually decreases. However, the frequency of data carriers is usually much lower than the self-resonant frequency, which will reduce the data rate or improve the bit error rate at a high data rate. Moreover, the high voltage generated by coupling coils causes high voltage stress on the data channel. To deal with these two issues, the last turn of each coupling coil is used to transfer data in the proposed system. The two transceivers are, respectively, connected with the last turn of the two coupling coils, which excites the entire coils to self-resonate and generates two resonant frequencies. The two resonant frequencies are utilized to realize high-speed full-duplex communication. And the voltage stress of the data channel is effectively reduced. A 518-W full-duplex prototype is built, and the maximum data rate is 700 kb/s, which verifies the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]