Demodulation Scheme Research Articles

Asymmetric Reflection Spectrum of Fabry-Perot Interferometer and the Application in Pressure Sensing

The performance of a fiber optic Fabry-Perot (F-P) sensor largely depends on the spectral characteristics of F-P interference, nevertheless there is little research on the spectral characteristic, such as the asymmetry shapes which are often observed in practical experiments. Here, a simple analytical formula for simulating the reflected spectrum of a F-P resonator have been provided, based on which the asymmetry spectral shape can be diversified through adjusting the refined parameters in the analytical formula. In addition, the composite film of Pt/Ge with different thickness on fiber tip has been theoretically demonstrated to change the parameters, and the F-P interferometer composed by composite film of Pt/Ge on fiber tip and gold film has been simulated to exhibit variated asymmetric reflection spectra. Meanwhile, the reflection spectrum from fiber F-P interferometer based on the composite film deposited on the end face of optical fiber has been experimentally proven to change according to the thickness variation of Ge film. Finally, a fiber based miniature extrinsic Fabry-Perot interferometer (EFPI) showing a saw tooth wave shape spectrum has been fabricated to sense static pressure through a dual-wavelength based intensity demodulation scheme, which possesses the potential to overcome the offset between sensitive and dynamic range for a traditional sensor.

Suppressing backscattering noise of a resonant fiber optic gyroscope using coherent detection.

This paper provides a novel, to the best of our knowledge, method for suppressing backscattering noise of a resonant fiber optic gyroscope (RFOG) with a coherent detection technique. The light from the fiber ring resonator is mixed with a reference beam rather than being demodulated directly in traditional configurations, generating a coherent signal with a radio frequency. The central frequencies of the two reference lights used for the clockwise and counterclockwise waves are different to avoid the effect of backscattered waves. Besides, a common phase modulation is applied on the two counter-propagating waves to eliminate the parasitic effect due to the residual amplitude modulation in the phase modulator. Two demodulation schemes for the rotation rate detection from the coherent signals are then proposed and demonstrated, with performance on noise suppression tested. One is the beat-frequency demodulation, and the other is the self-mixing demodulation technique. The influence of backscattering intensity is reduced from 270°/h to 3°/h and 0.05°/h with the two demodulation techniques, respectively, showing a full suppression of backscattering noise.

Real-Time Self-Calibrating Phase-Shifted Demodulation Method Based on Polarized Low-Coherence Interference for Optical Fiber Acoustic Sensor

A real-time self-calibrating quadrature phase-shift demodulation method for external Fabry–Perot interferometric (EFPI) sensors is proposed and demonstrated. Two birefringent crystal blocks with matching lengths are used to generate two orthogonal interference signals, and the third rotating birefringent crystal block is used as a compensation path for real-time normalization of two orthogonal interference signals. The signals are finally processed by the differential cross multiplication (DCM) algorithm demodulation. Experimental results show that the demodulation scheme can not only correctly demodulate low-frequency dynamic signals but also demodulate ultrasonic signals with high stability and high speed, and has a signal-to-noise ratio (SNR) of up to 90 dB. When the sensor cavity length drifts between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 4.94\,\,\mu \text{m}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.584 ~\mu \text{m}$ </tex-math></inline-formula> , it still has stable demodulation performance and is suitable for EFPI sensors with different diaphragms. The demodulation scheme provides a simple, effective, high-speed, and robust solution for dynamic signal measurement in complex environments based on real-time self-calibrating, which demonstrates great potential in practical engineering applications.

Non-line-of-sight WDM-MIMO optical camera communications with the DBPWR algorithm

Non-line-of-sight (NLOS) optical camera communications (OCC) is a potential wireless communication technology, which offers robustness to blocking and blooming effect, higher data throughput over longer transmission distances compared with line-of-sight OCC. In this work, we propose a wavelength division multiplexing (WDM)-multiple inputs multiple outputs (MIMO) NLOS OCC system with multi-level pulse width modulation (MPWM) and difference-based pulse width recognition (DBPWR) schemes. Signals on different color channels are separated through the RGB filter of the CMOS camera, while MPWM signals on the same color channel are separated using the DBPWR algorithm. Compared with the conventional threshold-based demodulation scheme, the proposed DBPWR scheme has lower complexity, higher reliability, and improved sampling frequency offset tolerance. A total data rate of 10.8 kb/s is experimentally demonstrated over more than 2 m NLOS link using the proposed WDM-MIMO OCC system, which is sufficient in many Internet of things applications.

Digitalized phase demodulation scheme of [formula omitted]-OTDR based on cross-coherence between Rayleigh back-scattering beat signals

In this paper, a simple and low-cost phase demodulation scheme for phase sensitive optical time domain reflectometer (φ-OTDR) sensing system is proposed and investigated. By utilizing simulated coherence between different back-scattering beat signals, digital phase demodulation for vibration detection can be achieved without employing hardware phase demodulation components. Experiments were conducted and the results demonstrated that the vibration induced phase change within different lengths of sensing optical fiber can be obtained sensitively by the proposed digital processing demodulation scheme that effectively avoid the noise caused by the hardware and reduce the complexity of the distributed optical fiber sensing system.

Ultra-High SNR Demodulation Method for Optical Fiber Sensors Applied in Power Transformer Partial Discharge Detection

The demodulation method of optical fiber sensors utilized in power transformer partial discharge (PD) detection is insufficient for engineering applications. We design a distributed feedback fiber laser (DFB-FL) PD detection system with an asymmetric 3 × 3 coupler and propose an ultra-high signal-to-noise ratio (SNR) demodulation scheme by eliminating the main factors that affect the traditional method using an asymmetric 3 × 3 coupler. The power transformer PD detection results reveal that the proposed scheme is free from 3 × 3 coupler asymmetry issues, with an average SNR of 38.30 dB, which is much higher than the widely used demodulation method and the piezoelectric transducer sensor. The average SNR of the system is increased by 24.2 dB with the proposed method.

Frequency Modulated Signal’s Optimum Noncoherent Demodulator Performance

The article considers optimum noncoherent demodulator scheme. The symbol synchronization is key problem of demodulator’s performance. It is offered the resampler symbol synchronization sсhem. Modeling demodulator algorithm results is shown. The modeling results let to propose the optimum noncoherent demodulator scheme. It is shown that the demodulator provided near to ideal noncoherent performance. Based on the results presented in the paper, receivers of various broadband signals can be constructed.

Improved multi-channel interferometric fiber-optic sensor demodulation based on the Goertzel algorithm.

In a multi-channel interferometric fiber-optic sensor system using space-division multiplexing (SDM) and phase-generated-carrier (PGC) demodulation, the phase delay and phase modulation depth fluctuation of each channel will affect the amplitude consistency and harmonic distortion of the demodulation results. In this paper, an improved demodulation scheme based on the Goertzel algorithm is proposed to calculate the multi-channel phase delay and phase modulation depth and to compensate for their fluctuations simultaneously. First, the carrier's 1st to 6th harmonic amplitudes in the interference fringe are extracted using the Goertzel algorithm. Then, the phase delay is calculated using the real and imaginary components of the 1st harmonic amplitude. The phase modulation depth is calculated with a combinatorial operation of the 1st to 6th harmonic amplitudes. In addition, a reference channel is introduced to implement phase delay and modulation depth feedback control. The experimental results demonstrate that the improved scheme can effectively suppress the harmonic distortion and improve the amplitude consistency of multi-channel interferometric fiber-optic sensors with low resource consumption.

Artificial Neural Network-Based Scheme for 4-PWM OCC System

In the letter, an artificial neural network (ANN)-based scheme is proposed and experimentally demonstrated to alleviate the inter-symbol interference (ISI) from the overlap of the exposure time in 4-pulse width modulation (PWM) optical camera communication (OCC) system. By using ANN, it directly restores the gray value sequence to the corresponding data symbol. And down-sampling is not required. The experimental results show that, compared with the conventional demodulation scheme, the ANN demodulation scheme can effectively improve the data rate. When the symbol resolution is 6 pixels per symbol and the illuminance is 2440 lux, the bit error rate (BER) can be reduced to <inline-formula> <tex-math notation="LaTeX">$1.78\times 10^{-5}$ </tex-math></inline-formula> at the data rate of 15.84 kb/s in 4-PWM OCC system.

Demodulation of Fiber Bragg Grating Accelerometer Using In-Line Sagnac Interferometers

We proposed a fiber Bragg grating (FBG) accelerometer demodulation method based an in-line Sagnac interferometric structure. In this method, an electro-optical phase modulator (EOM) is used as a phase-generating carrier (PGC) modulation module. The principle of in-line Sagnac optical path interference based on EOM is theoretically analyzed by Jones matrix, and the modulation mechanism of EOM is described. The experimental results of an FBG accelerometer based on flexible hinge show that the system background noise is <inline-formula> <tex-math notation="LaTeX">$1 \times {10^{ - 5}}\,\,{{\mathrm {rad}}} \cdot {{\mathrm {Hz}}^{-1 /2}}$ </tex-math></inline-formula>. The EOM based modulation scheme solves the problem of distortion of demodulation response due to the unstable modulation performance of the conventional piezoelectric transducer, which also provides a fast response to the interferometric optical path changes. The sensitivity of the in-line Sagnac based demodulation scheme is doubled compared to the Sagnac ring structure. The proposed scheme provides an integrated phase modulator for demodulation system for FBG sensors.

Fiber fusion splicing error analysis of all-fiber optic current sensor with different demodulation schemes

Measurement accuracy is essential for the all-fiber optic current sensor. Angle errors of axis alignment in the fusion processing affect the measurement accuracy with different modulation and demodulation methods. The relationship between observed and theoretical values has been analyzed with sinusoidal modulation and square modulation, respectively. The error and the error tolerance are computed with different demodulations based on the application of measurement and protection. The four demodulations are ordered based on the complexity and the error tolerance requirement. The open-loop demodulation scheme of the all-fiber optic current sensor can be applied for the protection application because it can be easily achieved. For the measurement application, the closed-loop feedback demodulation is recommended when the current is to be measured significantly; Otherwise, the harmonic division demodulation could meet the requirements of the system.

Reaching the True Shot-Noise-Limited Phase Sensitivity in Self-Heterodyne Interferometry

The use of an acousto-optic modulator in an interferometer enables heterodyne detection and can alleviate technical issues such as laser intensity noise and photodetector flicker noise. However, it also introduces at least a 3 dB penalty to the shot-noise limited phase sensitivity when compared to that attainable through homodyne detection. In this paper, we show theoretically that this penalty can be lifted by implementing detection and demodulation schemes that exploit the cyclostationary nature of shot noise observed at the outputs of the self-heterodyne interferometer. We also discuss how expected departures from ideality, namely imperfect interferometric visibility, non-zero stationary noise, and finite detection bandwidth, affect the performance of these schemes and propose a simplified procedure relaxing the requirement for a rigorous instrument characterization. While two independent detectors are required to reach the true (classical-light) shot-noise limit for phase, single-detector instruments can also benefit from the introduced ideas to achieve up to 3 dB improvement in phase sensitivity.

Secure Transmission for Energy Efficient Parallel Mixed FSO/RF System in Presence of Independent Eavesdroppers

In this paper, the physical layer security (PLS) challenges for a decode and forward (DF) based dual hop mixed free space optical (FSO) / radio frequency (RF) communication system in the presence of multiple eavesdroppers has been investigated. In order to improve the PLS of the energy efficient co-operative communication system, diversity combining techniques have been introduced at the destination node. In addition to this, collusion and non collusion eavesdropper scenarios are considered to make the system more practical. The FSO and RF links are assumed to experience independent Málaga ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {M}$</tex-math></inline-formula> ) and Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> fading distributions, respectively. Additionally, the FSO link model considers the impact of boresigt and non-zero boresight pointing errors and type of optical demodulation scheme. To investigate the security performance, the lower bound for the secrecy outage probability (SOP) and effective secrecy throughput (EST) have been obtained in terms of Meijer’s G function. Thereafter, asymptotic expressions have been derived for the considered system and the numerical results have been verified by the Monte-Carlo simulation method. Finally, we have analyzed the secrecy energy efficiency (SEE) based on secrecy rate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R_s$</tex-math></inline-formula> ) of the considered system to provide practical insights into the effect of major parameters on the energy efficient secure transmission design.

Application of two-dimensional warped discrete Fourier transform to nonlinear two-dimensional amplitude demodulation

This study introduces a novel nonlinear two-dimensional (2D) warped discrete Fourier transform (WDFT) amplitude demodulation method that allows higher-resolution measurements on specific two-dimensional regions of interest. The specific application in this study addresses the need for the nonlinear 2D amplitude demodulation of fringe-wave fields acquired by a deformed Mach–Zehnder interferometer. The proposed method exploits the properties based on which the WDFT can obtain frequency spectra sampled at non-equidistant intervals and the symmetry of the Fourier transform. As a result, this 2D-WDFT-based method can be used to nonlinearly demodulate the amplitude of the 2D interference fringe wave field to obtain a high-resolution localized fringe envelope. This study describes the proposed analysis procedure and its application using this 2D WDFT-based demodulation scheme. Experimental verification of the proposed approach was conducted with the use of deformed Mach–Zehnder interferometry. The successful experimental validation proves the efficiency of the proposed algorithm for amplitude demodulation with dense sampling points located in the central part of the envelope. To the best of the authors’ knowledge, this is the first investigational report on a 2D nonlinear envelope demodulator.

Hybrid Chirp Signal Design for Improved Long-Range (LoRa) Communications

Long-range (LoRa) communication has attracted much attention recently due to its utility for many Internet of Things applications. However, one of the key problems of LoRa technology is that it is vulnerable to noise/interference due to the use of only up-chirp signals during modulation. In this paper, to solve this problem, unlike the conventional LoRa modulation scheme, we propose a modulation scheme for LoRa communication based on joint up- and down-chirps. A fast Fourier transform (FFT)-based demodulation scheme is devised to detect modulated symbols. To further improve the demodulation performance, a hybrid demodulation scheme, comprised of FFT- and correlation-based demodulation, is also proposed. The performance of the proposed scheme is evaluated through extensive simulation results. Compared to the conventional LoRa modulation scheme, we show that the proposed scheme exhibits over 3 dB performance gain at a bit error rate of 10−4.

Design of a SIMO Deep Learning-Based Chaos Shift Keying (DLCSK) Communication System.

This paper brings forward a Deep Learning (DL)-based Chaos Shift Keying (DLCSK) demodulation scheme to promote the capabilities of existing chaos-based wireless communication systems. In coherent Chaos Shift Keying (CSK) schemes, we need synchronization of chaotic sequences, which is still practically impossible in a disturbing environment. Moreover, the conventional Differential Chaos Shift Keying (DCSK) scheme has a drawback, that for each bit, half of the bit duration is spent sending non-information bearing reference samples. To deal with this drawback, a Long Short-Term Memory (LSTM)-based receiver is trained offline, using chaotic maps through a finite number of channel realizations, and then used for classifying online modulated signals. We presented that the proposed receiver can learn different chaotic maps and estimate channels implicitly, and then retrieves the transmitted messages without any need for chaos synchronization or reference signal transmissions. Simulation results for both the AWGN and Rayleigh fading channels show a remarkable BER performance improvement compared to the conventional DCSK scheme. The proposed DLCSK system will provide opportunities for a new class of receivers by leveraging the advantages of DL, such as effective serial and parallel connectivity. A Single Input Multiple Output (SIMO) architecture of the DLCSK receiver with excellent reliability is introduced to show its capabilities. The SIMO DLCSK benefits from a DL-based channel estimation approach, which makes this architecture simpler and more efficient for applications where channel estimation is problematic, such as massive MIMO, mmWave, and cloud-based communication systems.

Deep Learning-based Wireless Signal Classification in the IoT Environment

With the development of the Internet of Things (IoT), diverse wireless devices are increasing rapidly. Those devices have different wireless interfaces that generate incompatible wireless signals. Each signal has its own physical characteristics with signal modulation and demodulation scheme. When there exist different wireless devices, they can suffer from severe Cross-Technology Interferences (CTI). To reduce the communication overhead due to the CTI in the real IoT environment, a central coordinator can be able to detect and identify wireless signals existing in the same communication areas. This paper investigates how to classify various radio signals using Convolutional Neural Networks (CNN), Long Short-Term Memory (LSTM) and attention mechanism. CNN can reduce the amount of computation by reducing weights by using convolution, and LSTM belonging to RNN models can alleviate the long-term dependence problem. Furthermore, attention mechanism can reduce the short-term memory problem of RNNs by re-examining the data output from the decoder and the entire data entered into the encoder at every point in time. To accurately classify radio signals according to their weights, we design a model based on CNN, LSTM, and attention mechanism. As a result, we propose a model CLARINet that can classify original data by minimizing the loss and detects changes in sequences. In a case of the real IoT environment with Wi-Fi, Bluetooth and ZigBee devices, we can normally obtain wireless signals from 10 to 20 dB. The accuracy of CLARINet's radio signal classification with CNN-LSTM and attention mechanism can be seen that signal-to-noise ratio (SNR) exhibits high accuracy at 16 dB to about 92.03%.

Digitalized Phase Demodulation Scheme of

Digitalized Phase Demodulation Scheme of

An Improved Pgc Demodulation Scheme Based Efa and Dual Cosine Laser Frequency Modulation

An Improved Pgc Demodulation Scheme Based Efa and Dual Cosine Laser Frequency Modulation

Differential Data-Aided Beam Training for RIS-Empowered Multi-Antenna Communications

The Reconfigurable Intelligent Surface (RIS) constitutes one of the prominent technologies for the next generation of wireless communications. It is envisioned to enhance the signal coverage in cases when the direct link of the communication is weak. Recently, beam training based on codebook selection is proposed to obtain the optimized phase configuration of the RIS. After that, the data is transmitted and received by using the classical coherent demodulation scheme (CDS). This training approach is able to avoid the large overhead required by the channel sounding process, and it also circumvents complex optimization problems. However, the beam training still requires the transmission of some reference signals to test the different phase configurations of the codebook, and the best codeword is chosen according to the measurement of the received energy of the reference signals. Then, the overhead due to the transmission of reference signals reduces the spectral efficiency. In this paper, a zero overhead beam training for RIS is proposed, relying on data transmission and reception based on non-CDS (NCDS). At the BS, the received differential data can also be used for the determination of the best beam for the RIS. Therefore, the efficiency of the system is significantly enhanced since reference signals are fully avoided. After choosing the best codebook, NCDS is still more suitable to transmit information for high mobility scenarios as compared to the classical CDS. Analytical expressions for the Signal-to-Interference and Noise Ratio (SINR) for the non-coherent RIS-empowered system are presented. Moreover, a detailed comparison between the NCDS and CDS in terms of efficiency and complexity is also given. The extensive computer simulation results verify the accuracy of the presented analysis and showcase that the proposed system outperforms the existing solutions.