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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]

This article proposes using in-phase and quadrature frequency-shift keying (IQFSK) modulation for low-power optical wireless communications (OWC). IQFSK independently leverages both cosine and sine basis functions to enhance the system's spectral efficiency (SE). It uses only the odd harmonic frequencies for these basis functions, allowing the clipping of negative amplitude excursions without losing information, making the waveform compatible with OWC The work presents optimal maximum likelihood and low-complexity sub-optimal detection mechanisms for IQFSK. The proposed scheme is analyzed analytically and with numerical simulations. The simulation and analytical results indicate that the proposed scheme is more energy-efficient, can attain a better energy and SE trade-off by exploiting the frame structure of the waveform, and has a lower minimum squared Euclidean distance relative to other state-of-the-art FSK-based counterparts, thus establishing it as one of the most efficient FSK approaches for low-power OWCs. [ABSTRACT FROM AUTHOR]

Future 6G communication systems are envisioned to expand their carrier frequency to the THz region, where a broad unexplored region of spectrum is available. With this expansion, THz wireless communication has the potential to achieve ultra-high data transmission rates of up to 100 Gbit/s. However, as large amounts of data are transmitted in an open wireless environment, there are significant concerns regarding communication security due to the susceptibility to eavesdropping, interception, and jamming. In this work, we proposed a secure approach for THz wireless communication based on spatial wave mixing and flexible beam steering. To achieve this, two frequency-modulated THz waves, which are generated by photonic THz sources and carry encrypted information with true randomness, are mixed at a THz envelope detector with an exclusive-OR logic operation. We analyzed the possible spatial location for the THz detector to ensure a secure microcell network deployment. Our results demonstrate that the size of the decryptable region is directly dependent on the directivity and width of the emitted THz beam. To address this, we have developed an array antenna with integrated uni-traveling-carrier photodiodes (UTC-PDs), which is capable of generating THz waves while also improving the flexibility of beam pointing, allowing for greater control over the location and size of the decodable region. By controlling fiber-optic delay lines, we successfully demonstrated that the directional gain of a 200 GHz wave is increased by 8 dB through a 1 × 3 UTC-PD-integrated planar bowtie antenna (PBA) array, together with continuous beam steering from -20° to 10°. Additionally, using a 1 × 4 UTC-PD-integrated PBA array to emulate two encryption transmitters and a Femi-level managed barrier diode to detect spatially mixed THz waves, we successfully achieved a feasibility experiment for real-time 200 Mbit/s location-based decryption in the 200 GHz band. These results indicate that the proposed scheme is feasible for secured THz communication, and would be a powerful candidate to mitigate security risks in 6G microcell networks. [ABSTRACT FROM AUTHOR]

Satellite based communication either in GEO or LEO based system are prominently employed for voice, video, data communication. Demand of more traffic necessitates the data rate of satellite to be enhanced which can be implemented by the proper choice of modulation scheme. Presently ground systems are also wireless based which include direct broadcast satellite (DBS),television service, wireless local area networks (WLANs), global positioning satellite (GPS), radio-frequency identification systems which is either point-to-point or point-to-multipoint. Modern day communication systems are digital; based rather than analog to have better noise immunity. Further with the limited spectrum availability the choice of modulation scheme plays an important role for faithful transmission of the signal. The digital communication can be categorized as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK) whereas for higher bit data rate Phase Shift Keying (PSK) such as BPSK, QPSK and OQPSK are employed. This article overview of various modulation schemes which are employed in satellite communication apart from its selection criteria along with the concept of bit error rate. [ABSTRACT FROM AUTHOR]

Spectrum sensing is an essential step in cognitive radio-based dynamic spectrum management. Spectrum sensing to detect the presence of the licensed signals in a particular frequency band is one of the most important research topics in cognitive radio. To identify primary user (PU) presence, we propose a low cost and low power consumption implementation of spectrum sensing operation based on real signals. These signals are generated by smart embedded devices at 433 MHz wireless transmitter using ASK (Amplitude-Shift Keying) and FSK (Frequency-Shift Keying) modulation type. The reception interface is constructed using an RTL-SDR dongle connected to MATLAB software. The signal detection is done by using four techniques: the artificial neural network (ANN), support vector machine (SVM), Decision Trees (TREE), and k-nearest neighbors (KNN). This article comparatively analyzed the performance of the classifiers to identify the best method for spectrum sensing between the three techniques. The performance evaluation of our proposed model is the probability of detection (P d) and the false alarm probability (P fa). Results show also that the sensing is susceptible to signal to noise ratio value. This comparative study has been demonstrated that the spectrum sensing operation by ANN and SVM can be more accurate than KNN, TREE, and some other classical detectors. [ABSTRACT FROM AUTHOR]

One of the most important applications of network coding is the Multiple Access Relay Channel (MARC) technique in which source terminals transmit independent data blocks over one or more relay terminals to a common destination terminal. In recent years, MARC has become one of the vital network coding applications in the area of innovative wireless cooperative communications for enhancing spectral efficiency. In this paper, non-coherent binary frequency shift keying (BFSK) modulation and differential binary phase shift keying (DPSK) modulation techniques are applied to the decode-and-forward (DF)-based MARC model and the average bit error rate (BER) of the proposed system is derived theoretically by using the maximum likelihood (ML) decision rule. The simulation results show that the BER performance of DPSK modulation is better than the non-coherent BFSK and full diversity gain is achieved in both modulation techniques. We also propose a power allocation scheme for the proposed system model which optimizes the power allocated to the source and relay transmissions. Depending on the location of the relay, performance gains up to 1.25 dB are achieved with the proposed optimum power allocation (OPA) scheme. Also, the mathematical derivations are verified through Monte-Carlo simulations and the superior performance of the OPA over equal power allocation (EPA) is observed. [ABSTRACT FROM AUTHOR]

To improve the separation performance of time-frequency overlapped radar and communication signals from a single channel, this paper proposes an effective separation method based on an improved empirical wavelet transform (EWT) that introduces a fast boundary detection mechanism. The fast boundary detection mechanism can be regarded as a process of searching, difference optimization, and continuity detection of the important local minima in the Fourier spectrum that enables determination of the sub-band boundary and thus allows multiple signal components to be distinguished. An orthogonal empirical wavelet filter bank that was designed for signal adaptive reconstruction is then used to separate the input time-frequency overlapped signals. The experimental results show that if two source components are completely overlapped within the time domain and the spectrum overlap ratio is less than 60%, the average separation performance is improved by approximately 32.3% when compared with the classic EWT; the proposed method also improves the suitability for multiple frequency shift keying (MFSK) and reduces the algorithm complexity. [ABSTRACT FROM AUTHOR]

Given the rapidly increasing market penetration of photovoltaic (PV) systems in many fields, including construction and housing, the effective maintenance of PV systems through remote monitoring at the panel level has attracted attention to quickly detect faults that cause reductions in yearly PV energy production, and which can reduce the whole‐life cost. A key point of PV monitoring at the panel level is cost‐effectiveness, as the installation of the massive PV panels that comprise PV systems is showing rapid growth in the market. This paper proposes an implementation method that involves the use of a panel‐level wireless PV monitoring module (WPMM), and which assesses the cost‐effectiveness of this approach. To maximize the cost‐effectiveness, the designed WPMM uses a voltage‐divider scheme for voltage metering and a shunt‐resistor scheme for current metering. In addition, the proposed method offsets the effect of element errors by extracting calibration parameters. Furthermore, a design method is presented for portable and user‐friendly PV monitoring, and demonstration results using a commercial 30‐kW PV system are described. [ABSTRACT FROM AUTHOR]

A high security chipless RFID tag designed using E shaped resonator is presented in this paper. The tag identity is encoded using Frequency Shift Coding technique. 144 different code words are possible in 2.78 to 3.85 GHz band using two E shaped resonators. The tag identity can be decoded from either amplitude or group delay information. The resonators are designed and fabricated on substrate C-MET LK4.3 of dielectric constant 4.3 and loss tangent 0.0018. Different tag combinations are designed and tested using bistatic measurement setup. Measurement results on realized prototypes are provided to ensure the reliability of the proposed design. [ABSTRACT FROM AUTHOR]

A design of the exciter of weather fax chart and NAVTEX is described in this paper, which has the advantages of miniaturization, low power consumption, high reliability. The exciter is made up of hardware equipment and PC client. The hardware principle and the working process of PC client are listed respectively. Finally, a receiving and launching experiment is used to verify the validity of the exciter's function; moreover, the power and volume of the exciter are given to support its advantage. [ABSTRACT FROM AUTHOR]

In this paper a modified ESPRIT algorithm, which bases on time subspace (T-ESPRIT) and spatial subspace of estimate 2D-DOA (azimuth and elevation) of a radiated source, that can increase the estimation accuracy with low computational load is introduced. Using the algorithm, the planar array is divided into a multiple uniform sub-planar arrays with the common reference point, and the T-ESPRIT method is applied for each sub-array. Secondly, Doppler frequency shift (fd) resulted from the target movement is estimated using displacement invariance technique (DIT). Then, in order to increase the estimation accuracy; the estimated Doppler frequency is used to correct the DOAE values according to target movement. Moreover, the proposed algorithm is combined the refined T-ESPRIT method with time differential of arrival (TDOA) technique to calculate an optimum DOA. It is found that the estimated results are better than the traditional ESPRIT methods leading to the estimator performance enhancement. [ABSTRACT FROM AUTHOR]

Software Defined Radio (SDR) is the technology which has given researchers the opportunity and flexibility of integration and intercommunication of existing and future networks together. The radio spectrum is the most vital resource for a mobile operator in today’s world of modern wireless communications. After analyzing the spectrum allocation map one can conclude that the most of the prime spectrums falling under the licensed bands have already been allocated for licensed users for exclusive use. There are very few unlicensed bands for the unlicensed users. SDR offers a perfect solution to this problem of spectrum scarcity being experienced in wireless communication systems. The demand for reliable, high data rate transmission has increased significantly these days, which leads the way to adoption, of different digital modulation techniques. The aim of this paper was to analyze Frequency Shift Keying (FSK) Transceiver built using Laboratory Virtual Instrumentation Engineering Workbench (LabVIEW) and to measure the reduction in data errors in the presence of Forward Error Correction (FEC) channel coding algorithms namely the Convolution and the Turbo Codes. Through this design a graphical representation of Bit Error Rate (BER) vs E b / N 0 where ( E b ) is Energy per bit and ( N 0 ) is Spectral noise density has been given in the presence of Additive White Gaussian Noise (AWGN) introduced in the channel. FSK is widely used for data transmission over band pass channels; hence, we have chosen FSK for the implementation of SDR. The SDR transceiver module designed has been fully implemented and has the ability to navigate over a wide range of frequencies with programmable channel bandwidth and modulation characteristics. We are able to build an interactive FSK based SDR transceiver in a shorter time with the use of LabVIEW. The outputs achieved show a low BER for very high data rates in the presence of AWGN noise. [ABSTRACT FROM AUTHOR]

In this paper we propose a new method that is suitable for shifting the frequency of Moving Picture Experts Group audio layer-3 (MP3) by changing the input of the inverse modified discrete cosine transform (IMDCT) in the process of MP3 decoding. The proposed method gives us a high quality frequency shift from the mathematical model devised by us that can extract the frequency, amplitude, and phase of the frequency component located in the subband boundary. The proposed method gained 3.8 points in a mean opinion score (MOS) test from professional composers, as well as a 0.33 and a 0.42 credit in a comparison MOS (C-MOS) test with a commercial sound editor and synchronized overlap-add (SOLA), respectively. The proposed method has a computation complexity of approximately 43% of the synchronized overlap-add (SOLA) algorithm for MP3 music, which is known as a simple frequency shift algorithm. The complexity improvement of the overall frequency shift system, including the MP3 decoder, is 23% compared with the MP3 decoder plus the SOLA system at the better audio quality. [ABSTRACT FROM AUTHOR]

In this study, local dynamic characteristics of mountable PZT interfaces are numerically analyzed to verify their feasibility on impedance monitoring of the prestress-loss in tendon anchorage subsystems. Firstly, a prestressed tendon-anchorage system with mountable PZT interfaces is described. Two types of mountable interfaces which are different in geometric and boundary conditions are designed for impedance monitoring in the tendon-anchorage subsystems. Secondly, laboratory experiments are performed to evaluate the impedance monitoring via the two mountable PZT interfaces placed on the tendon-anchorage under the variation of prestress forces. Impedance features such as frequency-shifts and root-mean-square-deviations are quantified for the two PZT interfaces. Finally, local dynamic characteristics of the two PZT interfaces are numerically analyzed to verify their perfonuances on impedance monitoring at the tendon-anchorage system. For the two PZT interfaces, the relationships between structural parameters and local vibration responses are examined by modal sensitivity analyses. [ABSTRACT FROM AUTHOR]

Design, technology and properties of a completely ceramic piezoelectric pressure sensor are described. The sensor is made of the LTCC (Low Temperature Co-fired Ceramics) with PZT (Lead Zirconate Titanate) transducer and is designed to withstand pressure up to 10 MPa. The device is a sensor and a package simultaneously. It can be directly screw mounted to a flat surface with a hole supplying a pressure. Two methods of detection are considered: shift of the resonant frequency for static loads detection and charge response for dynamically changing load. Measurements are carried out for maximum 6 MPa pressure. The sensor exhibits linear charge response and resonant frequency shift in tested range. [ABSTRACT FROM AUTHOR]

This paper presents a new four-node composite element, which incorporates nd delaminations through its thickness. Based on the extended finite element method (X-FEM) technology, the element is particularized on a CLT (classical laminate theory). Delamination is considered in the kinematic equations with additional degrees of freedom. The result is a four-node quadrilateral element requiring only two single FEM (finite element method) formulations, a bending one and a membrane one. An important result is that this formulation has the same accuracy as when separate elements are considered ("four region approach" ). It is furthermore proven that the delaminated element passes the "patch test" if the selected FEM formulations to build the element pass the test in the pure single problems, making this methodology very attractive to develop other fractured elements. To illustrate this result, two benchmark problems were studied: first a complete delaminated cantilever plate, and second a complete delaminated circular plate. The element was tested in the context of SHM (structural health monitoring). Frequency shifts, damage indexes, and changes in mode shapes and frequency response functions (FRF) were obtained to quantify the severity of damage due to delaminatio. [ABSTRACT FROM AUTHOR]

Abstract: A new classification algorithm of M-ary FSK signals based on the extraction of signals’ features is presented in this paper. The implementation of the methodology does not require any apriori information. By extracting some basic features of intermediate frequency signals both in time domain and frequency domain, the classification of M-ary FSK signals is achieved. Simulation result shows that the proposed algorithm can classify 2FSK, 4FSK and 8FSK signals effectively under AWGN and and still keeps a good performance even at low input SNR. [Copyright &y& Elsevier]

Abstract: Most existing underwater networks target deep and long range oceanic environments, which has led to the design of power hungry and expensive underwater communication hardware. Because of prohibitive monetary and energy cost of currently over-engineered communication hardware, dense deployments of shallow water sensor networks remain an elusive goal. To enable dense shallow water networks, we propose a network architecture that builds on the success of terrestrial sensor motes and that relies on the coupling of software modems and widely available speakers and microphones in sensor motes to establish acoustic communication links. In this paper, we analytically and empirically explore the potential of this acoustic communication system for the underwater environment. Our experimental approach first profiles the hardware in water after waterproofing the components with elastic membranes. The medium profiling results expose the favorable frequencies of operation for the hardware, enabling us to design a software FSK modem. Subsequently, our experiments evaluate the data transfer capability of the underwater channel with 8-frequency FSK software modems. The experiments within a 17×8m controlled underwater environment yield an error-free channel capacity of 24bps, and they also demonstrate that the system supports date rates between 6 and 48bps with adaptive fidelity. [Copyright &y& Elsevier]

In this paper, soft-decision (SD) decoders of permutation trellis code (PTC) with M -ary frequency shift keying are designed using three optimization algorithms and presented in four decoding schemes. In a concatenated code such as PTC, the Viterbi decoder for the outer convolutional code provides maximum likelihood decoding. Hence, the error correction performance is dependent on the decoding scheme used for the inner code. Due to the structure of the encoder with the modulation scheme, the channel output can be interpreted as an assignment problem. SD decoding can then be designed accordingly, using the presented, low-complexity optimization-based schemes. The bit error rate (BER) performance of the schemes are simulated in an additive white Gaussian noise (AWGN) and powerline communication (PLC) channel. The complexities of the schemes are also presented. The performance of the SD schemes are compared with the existing SD threshold detector, with BER results showing significant coding gain for certain codebooks. From the results, a reasonable trade-off between the complexity and coding gain is observed for a noisy channel such as the PLC channel. [ABSTRACT FROM AUTHOR]

In this paper, we propose a secure hybrid pulse compression method for radar waveform design. This method uses a confidential code as the phase-code for the binary-shift keying modulation. We also use another confidential code for the frequency-code. This code is replaced in the frequency control register of a direct digital synthesizer to perform the narrow-band frequency-shift keying. We exploit the output of an encryption algorithm, e.g. a block cipher, as the binary code, which fulfills security and confidentiality requirements of electronic warfare scenarios. In contrast to other proposals that use only confidential phase-codes, we propose a method that considers both the frequency and phase codes to be confidential. We evaluate the proposed method's performance in the presence of a jammer for three cases: where the jammer has access only to the phase-code, only the frequency code, and has access to neither. Our method effectively decreases the probability of false alarms, while improving detection probability. [ABSTRACT FROM AUTHOR]

In a multi-carrier power line communication (mPLC) with dominant Narrowband and Impulse noise, crisscross errors can be clearly observed. In this work, mPLC employing Rank codes with Index modulation (mPLC-IM) has been considered to provide a reliable high data rate communication over the powerline channel. The rank codes required for this implementation have been derived from cyclic codes over G F (q m) viewed as m × n matrices over G F (q). Encoding has been performed by employing the Galois Field Fourier Transform (GFFT) domain description of cyclic codes. This scheme is able to correct a variety of crisscross errors in mPLC-IM The GFFT approach provides an additional degree of freedom that is offered by choice of free transform component indices. It can be used to design an index key scheme which can enhance the physical layer security of an mPLC system. In the absence of knowledge of the index key, it is observed that the probability of error reaches an error floor of ≈ 1 0 − 2 , highlighting the need for index key for appropriate decoding. Further, a novel check matrix construction is proposed and used in devising a decoding strategy. It is observed that the proposed decoder is capable of correcting any errors of rank ≤ ⌊ m − 1 2 ⌋. In mPLC-IM with OFDM, the proposed codes over G F (2 4) provide an asymptotic gain of approximately 3 dB when compared to the uncoded system. For mPLC-IM with multi-tone Frequency Shift Keying (FSK), the proposed RC over G F (2 4) provides a 25% improvement in symbol error rate (SER) at lower values of p (probability of occurrence of narrowband noise) when compared to Reed-Solomon (RS) based Constant Weight (CW) C W (13 , 6 , 5) 2 ∘ R S [ 15 , 14 , 2 ] 16 codes. Further, a SER improvement of around 30% is achieved using rank codes (RCs) over G F (2 8) when compared with C W (9 , 4 , 4) 2 ∘ R S [ 15 , 14 , 2 ] 16 . In the presence of dominant background noise, the BER graphs show that the proposed codes are equivalent (slightly superior) in performance as that of Low Rank Parity Check (LRPC)/Gabidulin based designs. In the presence of dominant impulse noise, the proposed system is providing significant gain when compared with the Linearly Pre-coded Orthogonal Frequency Division Multiplexing (LP-OFDM) system and LRPC based scheme. Additionally, simulation results show that, in the absence of an index key, the probability of error reaches the error floor, highlighting the need for index key for appropriate decoding. This can be viewed as the code capable of providing an additional layer of security. [ABSTRACT FROM AUTHOR]

In this study, a novel digital modulation classification model has been proposed for automatically recognizing six different modulation types including amplitude shift keying (ASK), frequency shift keying (FSK), phase-shift keying (PSK), quadrate amplitude shift keying (QASK), quadrate frequency shift keying (QFSK), and quadrate phase-shift keying (QPSK). The determination of modulation type is significant in military communication, satellite communication systems, and submarine communication. To classify the modulation types, we have proposed a two-stage hybrid method combining short-time Fourier transform (STFT) and convolutional neural network (CNN). In the first stage, as the data source, the time–frequency information from these modulation signals have been extracted with STFT. This information has been obtained as 2D images to feed the input of the CNN deep learning method. In the second stage, the obtained 2D time–frequency information has been given to the input of the CNN algorithm to classify the modulation types. In this work, noises at various SNR values from 0 dB to 25 dB were created and added to the modulated signals. Even in the presence of noise, the proposed hybrid deep learning model achieved excellent results in the noised-modulation signals. • A novel hybrid model based on STFT and CNN is proposed for AMC. • SNR rates in the range of 0 dB and 25 dB were considered to validate the model success. • A comparison was realized to measure the performance of the different CNN models. • The CNNs achieved over 99% of classification accuracy. • The study proved that CNNs have a high capacity in recognizing the modulation types. [ABSTRACT FROM AUTHOR]