Time Division Multiplexing Technology Research Articles

A Quartz-Enhanced Photothermal Spectroscopy for C2H2 and CH4 Detection Based on Time Division Multiplexing Technology

A Quartz-Enhanced Photothermal Spectroscopy for C₂H₂ and CH₄ Detection Based on Time Division Multiplexing Technology

A temperature-insensitivity multi-channel strain sensor based on chirped fiber grating loop ring-down structure

This study proposes a novel multi-channel strain sensor, which combines the chirped fiber grating loop ring-down (CFGLRD) structure and time division multiplexing (TDM) technology. Each channel contains a CFGLRD cavity based on overlapping spectrum demodulation, which can convert measurements into ring-down spectra. All cavities are connected in series by delay fiber. The advantages of the sensor include simple structure, high light utilization, and temperature insensitive. A two-channel strain experimental setup is used in performance testing of the sensor. The strain measurement ranges of both channels extend from 0 to 3000 με. The resolutions of two channels are 18.3 με and 27.9 με, the linear correlation coefficients R2 are 0.997 and 0.996, the strain sensitivities are about 112.97 μs/ε and 280.03 μs/ε, and the temperature sensitivities are 0.37 ns/°C and 0.72 ns/°C. The experimental results show the structure has good performances on linearity of curve, measurement range, and temperature robustness.

Multi-point sensing system for cable fault detection using fiber Bragg grating

This study presents a multi-point sensing system for cable fault detection based on fiber Bragg grating (FBG). The system detects vibration signals caused by cable faults through changes in the reflected power of the FBGs. By integrating time division multiplexing (TDM) technology, the system achieves multi-point fault detection and distinguishes vibration signals from faults at different cable locations. To verify the system’s feasibility, different fault scenarios were simulated. The results show that the system can detect the vibration signals caused by cable joint faults, successfully demodulate the corresponding frequency components, and reconstruct the strain applied to the FBGs. Additionally, to address the impact of front-end FBG on back-end FBG, a power compensation method was developed to improve detection accuracy. The proposed cable fault detection system facilitates online detection of cable joint faults but also reduces system equipment costs, offering a novel approach to cable fault detection.

Simultaneous measurement of methane, propane and isobutane using a compact mid-infrared photoacoustic spectrophone

Hydrocarbon gas sensing is a challenging task using laser absorption spectroscopy due to the complex and broad structure of absorption lines. This application requires quick, accurate and highly sensitive detection of hydrocarbon gases concentrations. In this paper, a compact photoacoustic spectrophone was developed to simultaneously measure methane, propane and isobutane. This spectrophone uses wavelength modulation spectroscopy (WMS) with a single acoustic resonator and a single DFB laser emitting at 3368 nm, which greatly reduces the system complexity without using time-division multiplexing technology for multi-gas sensing. Due to the complex and broadband absorption of hydrocarbon gases, a novel signal processing method based on multilinear regression with Ridge regression (MLR-RG) is proposed to reduce the measurement error caused by the nonlinearity of spectra signal. For single gas measurement, the detection limits of methane, propane, and isobutane are determined to be 828 ppb, 419 ppb, and 619 ppb (SNR = 1, integration time = 20 s), respectively. For simultaneous multi-gas sensing in a gaseous mixture, the detection limits of propane and isobutane are determined to be 7 ppb, 68 ppb with an integration time of 860 s, 460 s, respectively. The measurement accuracy of propane and isobutane using MLR-RG is higher than that of ordinary least squares regression and partial least squares regression by 75% and 60%, respectively. The proposed algorithm based on MLR-RG provides a promising approach to process the broad overlapping absorption spectra for accurately retrieving hydrocarbon gases concentrations.

Maglev train high-precision positioning technology based on FBG array time division multiplexing

The positioning system is crucial in operating, controlling and monitoring maglev trains. This study proposes a maglev train positioning technology based on weak Fiber Bragg Grating (wFBG) sensing array time division multiplexing (TDM). The onboard Halbach permanent magnet array generates a traveling wave magnetic field that follows the train movement. The wFBG magnetic sensor array fixed on the track senses the magnetic field changes which cause periodical variation in sensors’ center wavelength. The relative position of the onboard Halbach array and the sensors on the track can be determined with the changes in center wavelength. Therefore, train positioning can be achieved. A rotating motor equipped with a circumferentially arranged magnet array is utilized for simulation experiment to verify the frequency response characteristics of the magnetic sensor. The result is that the operating frequency range of the sensor is at most 160 Hz so the sensor can be applied to positioning under the theoretical speed of 23 km/h. A small-scale experiment containing nine sensors is also conducted, which achieves relative positioning accuracy of 20 mm and absolute positioning accuracy of 540 mm, demonstrating the feasibility of the positioning technology. This study introduces the FBG TDM technology into maglev train positioning and provides new ideas about maglev train positioning.

Design of single-laser remote methane gas measurement system with distance measurement based on time-division multiplexing technology

Limited to the principle of Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, the existing open-path laser remote methane measurement system can only measure the integral concentration, and it needs to be matched with a laser rangefinder to complete the calculation of the average concentration, which increases the complexity of the system. To solve this problem, by driving the laser diode (LD) in time-division multiplexing mode, we complete the integral concentration of gas and distance measurement with the use of a single LD. We complete the design of the laser signal transceiver structure and finish the corresponding hardware circuit design, including the LD driving circuit, frequency generation, mixer circuit, and optoelectronic signal receiving circuit. The experiment shows the measurement error of the system is less than 2.5% while measuring the average concentration in the case of different concentrations and distances, and the system greatly reduces the system complexity while satisfying the performance requirements.

Simultaneous continuous-variable quantum key distribution and classical optical communication over a shared infrastructure

Integrating quantum key distribution (QKD) and classical optical communication for large-scale applications presents a significant challenge due to high cost and complexity. In this paper, we experimentally demonstrate the feasibility of simultaneous continuous-variable QKD (CV-QKD) and classical optical communication over a shared infrastructure. Through high-linearity modulators and detectors, we validated classical quadrature phase shift keying communication and CV-QKD protocol on a single platform by time-division multiplexing technology. Experimental results show that the classical communication achieved a bit rate of 200 Mbits/s, and the CV-QKD protocol achieved a secret key rate of 1.12 Mbits/s at 6 dB channel attenuation. This work reveals the feasibility of using a shared optical module to realize classical and quantum communication, leading to simplified integrating QKD and classical communication infrastructure.

Electromagnetic Transient Modeling Method of Photovoltaic Power Station Based on FPGA

The rapid development of renewable energy needs the effective support of simulation technology. Aiming at the shortage of both modeling scale and simulation accuracy of the current large-scale photovoltaic power station, an electromagnetic transient modeling and real-time simulation method suitable for large-scale photovoltaic power stations are proposed. The microsecond accurate real-time simulation of 24 photovoltaic power units is implemented on a single FPGA. Through an equivalent modeling method, the electromagnetic transient model of a photovoltaic power unit including a PV array, DC boost circuit, grid-connected inverter, filter, and grid-side transformer is established. Then, based on the FPGA parallel computing and pipeline time division multiplexing technology, the updating framework of the station collecting network and the power unit is constructed, and the real-time simulation model of the station including 24 photovoltaic power units in 4 sub-stations is built. Finally, the microsecond real-time simulation of the photovoltaic power station is realized through RTRES, a self-developed real-time simulator in China’s Southern Power Grid. The comparison with the detailed PSCAD model shows that the simulation error is within ± 2%, which verifies the correctness of the proposed method and model.

The intra‐cavity QEPAS sensor using fiber‐ring laser for C2H2 and CO2 detection

AbstractAn intra‐cavity quartz‐enhanced photoacoustic spectroscopy (QEPAS) sensor using fiber‐ring laser is demonstrated. The sensor includes an erbium‐doped fiber (EDF) intra‐cavity laser and a quartz tuning fork (QTF), and realizes wavelength scanning through a piezoelectric transducer (PZT). The acousto‐optic modulator (AOM) is used to modulate laser intensity at a frequency of 32.758 kHz. We use optical switches to detect acetylene (C2H2) and carbon dioxide (CO2) at 1530.37 and 1572.66 nm, respectively, based on the time division multiplexing (TDM) technology. The two‐component gas sensor showed good linearity of 0.9996 and 0.9966, and could achieve a minimum detection limit (MDL) of 180.64 ppbv and 145.45 ppmv for C2H2 and CO2 detection, respectively.

Random Time Division Multiplexing Based MIMO Radar Processing with Tensor Completion Approach

Automotive radar pursues low cost and high performance, and especially hopes to improve the angular resolution under the condition of a limited number of multiple-input–multiple-output (MIMO) radar channels. Conventional time division multiplexing (TDM) MIMO technology has a limited ability to improve the angular resolution without increasing the number of channels. In this paper, a random time division multiplexing MIMO radar is proposed. First, the non-uniform linear array (NULA) and random time division transmission mechanism are combined in the MIMO system, and then a three-order sparse receiving tensor of a range-virtual aperture-pulse sequence is obtained during echo receiving. Next, this sparse three-order receiving tensor is recovered by using tensor completion technology. Finally, the range, velocity and angle measurements are completed for the recovered three-order receiving tensor signals. The effectiveness of this method is verified via simulations.

Photoacoustic spectrometry and resonant frequency tracking based dual-mode gas sensor

Photoacoustic spectrometry has excellent advantages in trace gas detection. However, due to the influence of gas saturation absorption, when the gas concentration spikes to a certain level, this technology is difficult to achieve accurate detection. Therefore, a dual-mode gas sensor based on photoacoustic spectroscopy and resonant frequency tracking is developed by the features of both detection technologies. A tunable DFB diode laser in the 1654 nm wavelength range and a loudspeaker are used for the photoacoustic detection, and the resonant frequency tracking, respectively. A resonant photoacoustic cell is used as the sensing element to work in dual-mode by time-division multiplexing technology. The wavelength-modulated photoacoustic detection is enabled in the methane concentration below 30%. When the gas concentration exceeds 30%, it will be automatically switched to the measurement-mode of resonant frequency tracking by the fast Fourier transform. The double-range gas detection is realized by a single sensor with dual-mode detecting functionality. With the wavelength modulation and lock-in harmonic detection method, the minimum detectable limit (1σ) of 3.5 ppm CH4 was demonstrated under the photoacoustic detection mode. The response time of the sensor is about 10 s within the measurement range of double-range.

Multi-User Visible Light Communication and Positioning System Based on Dual-Domain Multiplexing Scheme

Visible light communication and positioning (VLCP) is a promising candidate for constructing a multi-functional wireless network with large-scale connectivity and centimeter-level positioning. However, there is still a lack of effective methods to offer simultaneous visible light communication (VLC) and visible light positioning (VLP) functions for multiple users. Thus, we propose a multi-user VLCP system based on a dual-domain multiplexing (DDM) scheme, where both the time and code resources are multiplexed to transmit VLCP signals for multiple users simultaneously. In the proposed system, the data of different users are distinguished by using code division multiplexing technology, while the VLCP signals transmitted from different LEDs are separated by adopting time division multiplexing technology. The performances, including bit-error rate and positioning error, are evaluated through both simulation and experimentation to verify the feasibility of the proposed multi-user VLCP system. In the experiment, a VLCP system with four LED transmitters was able to simultaneously support low-speed VLC with free error and accurate VLP with a 2 cm precision for eight users. This offers an effective solution to support a large number of users with simultaneous VLC and VLP functions in the future multi-functional wireless network.

The fiber ring laser intra-cavity gas sensor for C2H2 and CO2 detection based on photoacoustic spectroscopy

In this paper, a two-component gas sensing system in the resonant cavity of the fiber ring laser based on photoacoustic spectroscopy (PAS) is designed by embedding the PAS cell into the laser resonant cavity. A ring cavity erbium-doped fiber (EDF) laser is built in this system, combined with a longitudinal resonant PAS cell to detect the PAS signal, and a custom-designed wavelength modulator uses the fiber bragg grating (FBG) to paste the piezoelectric transducer (PZT) for scanning and modulating the gas absorption wavelength. The gas concentration is calculated by the second harmonic (2f) PAS signal. Based on time division multiplexing (TDM) technology, the acetylene (C2H2) and carbon dioxide (CO2) is detected respectively by the time-sharing operation of C-band and L-band EDFs for different wavelengths output. The time-sharing operation of the two wavelength laser is realized through optical switches, which effectively avoids the laser power loss and the instability of each wavelength caused by the mode competition phenomenon of multiple wavelengths. The detection performance of C2H2 and CO2 is implemented under normal temperature and pressure. The PAS signal intensity is further improved by optimizing the wavelength modulation amplitude and incident laser power. The linear fit (R2) and minimum detection limit (MDL) of C2H2 and CO2 are 0.99821, 728 ppbv, 0.9994 and 503 ppmv respectively. It shows that the two-component gas sensing system designed in this paper has a good linear response and high sensitivity, and plays an important role on the multi-component gas detection.

Design and Implementation of an Efficient Hardware Coprocessor IP Core for Multi-axis Servo Control Based on Universal SoC

The multi-axis servo control system has been extensively used in industrial control. However, the applications of traditional MCU and DSP chips in high-performance multi-axis servo control systems are becoming increasingly difficult due to their lack of computing power. Although FPGA chips can meet the computing power requirements of high-performance multi-axis servo control systems, their versatility is insufficient, and the chip is too costly for large-scale use. Therefore, when designing the universal SoC, it is better to directly embed the coprocessor IP core dedicated to accelerating the multi-motor vector control current loop operation into the universal SoC. In this study, a coprocessor IP core that can be flexibly embedded in a universal SoC was designed. The IP core based on time division multiplexing (TDM) technology could accelerate the multi-motor vector control current loop operation according to the hardware–software coordination scheme proposed in this study. The IP was first integrated into a universal SoC to verify its performance, and then the FPGA prototype verification for the SoC was performed under three-axis servo control systems. Secondly, the ASIC implementation of the IP was also conducted based on the CSMC 90 nm process library. The experimental results revealed that the IP had a small area and low power consumption and was suitable for application in universal SoC. Therefore, the cheap and low-power single universal SoC with the coprocessor IP can be suitable for multi-axis servo control.

The strategic analysis and operation of the multiservice model used for synchronous transmission in communication networks

The core idea of asynchronous transfer mode (ATM) technology was revealed a long time ago. The main technology under development at the time was time-division multiplexing (TDM) technology, which consisted of synchronous switching based on the sequence number of bytes in the integrated frame. The main disadvantage of TDM technology, also known as synchronous transport module (STM) synchronous transmission technology, is the inability to reallocate the bandwidth of the integrated channel between subchannels. During those periods when no user data is sent on the subchannel, the aggregated channel still sends the bytes of this subchannel filled with zeros. Efforts to load sub channels’ idle periods necessitate the introduction of a header for each subchannel’s data. In intermediate statistical time-division multiplexing (STDM) technology, which allows idle periods to be filled by transmitting bursts of traffic from other sub channels, headers that actually have a subchannel number are introduced. In this paper, the strategic analysis and operation of technologies used in multiservice networks were discussed. Simultaneously, the structure of data sets is drawn into sets resembling computer networks. The fact that each packet has an address allows it to be transmitted asynchronously since its location relative to data on other subchannels is not its address. Asynchronous packets from one subchannel are inserted into the free time slots of another subchannel, but they are not mixed with the data of this subchannel because they have their own address.

Capacity Analysis and Data Detection of OvTDM-MIMO System

It is well known that the channel capacity of traditional MIMO systems is positively correlated with the number of antennas, so MIMO systems usually use more antennas to meet higher system capacity requirements, which is increasingly conflicting with the miniaturization requirements of portable devices. To overcome the above problems, a new OvTDM-MIMO system is proposed, which can effectively improve the capacity of the system. This system introduces the overlapped time division multiplexing (OvTDM) technology into the MIMO system, which can further improve the channel capacity of the MIMO system by using a smaller number of antennas. This paper introduces the transceiver model of the OvTDM-MIMO system in detail and derives the channel capacity of the system based on mutual information theory. Compared with a conventional MIMO system, the OvTDM-MIMO system has the ability to improve channel capacity. Then, this paper proposes an OvTDM-MIMO symbol detection scheme based on an improved low-complexity Orthogonal Approximate Message Passing (OAMP) algorithm to solve the symbol detection problem caused by symbol correlation. The main design idea of this scheme is to use symbol correlation as the detection constraint and realizes joint symbol detection by combining adjacent symbols, avoiding the problem of excessive matrix size caused by Kronecker product operation. The simulation results show that the proposed detection algorithm can achieve similar performance to traditional MIMO system detection algorithms with low computational complexity.

Multiplexed Photonic Crystal Fiber Gas-Sensing Network Based on Intracavity Absorption.

A highly sensitive hollow-core photonic crystal fiber (HC-PCF) gas-sensing network based on intracavity absorption is designed and experimentally verified. The capacity of the multichannel sensing network is expanded by time division multiplexing and wavelength division multiplexing technology. The voltage gradient method is employed in the wavelength scanning process of Fabry-Perot (F-P) filter to enhance the detection efficiency up to six times. The proposed sensing network has 16 sensing points. Experimental results show that the minimum detection limit (MDL) of this sensing system is 25.91 ppm and 26.85 ppm at the acetylene gas absorption peaks of 1530.371 nm and 1531.588 nm, respectively. As far as we know, it is the first time to obtain an intracavity sensing network via the application of an optical switch and DWDM at the same time. The sensing network can be used for high-capacity, low-concentration dangerous gas detection. It has great potential in environmental monitoring, industrial manufacturing, safety inspection and similar occasions.

Two-parameter method for identification and location of leaks based on weak FBG for steam pipelines

In this paper, an online steam pipeline leakage monitoring method, based on a weak-reflectivity optical fiber Bragg grating (wFBG) array for temperature–vibration hybrid sensing, is presented. This method meets the requirements of long-distance, large capacity, low false positive rate (FPR), and low false negative rate (FNR). The drawing tower online-writing FBG technology was used to write the wFBG (−40 dB), which has the advantages of high strength and good consistency. A large-capacity sensor network is realized using mixed time-division multiplexing and wavelength-division multiplexing technology. A novel temperature–vibration composite optical cable structure was designed to realize multi-parameter pipeline leakage monitoring. A chirped wFBG array with a spatial resolution of 3 m and a narrowband wFBG array with a spatial resolution of 1 m were combined in the same optical cable to simultaneously monitor the vibration and temperature of the pipeline. Leakage of the steam pipeline is accompanied by changes in the temperature and vibration signals. The leakage and its location can be identified more accurately by changes in these two parameters in the wFBG wavelength and interferometric phase. The field experiment results show that this temperature–vibration two-parameter detection system can accurately identify and locate steam pipeline leaks and reduce the FPR. This validates the feasibility of the wFBG array-based temperature–vibration hybrid sensing technology for monitoring steam pipeline leakage.

Time-Division Multiplexing Ising Computer Using Single Stochastic Magnetic Tunneling Junction

A magnetic tunneling junction (MTJ) with very low energy barrier, which shows controllable stochastic property, is recently proposed to constitute the probability bit (P-Bit). With the P-Bit, Ising computation, which is a general and powerful computing platform for both conventional and non-conventional problems, is implemented. However, such hardware emulation suffers from the severe intrinsic variations of a stochastic MTJ device. The nonuniform probability switching curves of different stochastic MTJs hinder straightforward expansion of Ising computer to a large P-Bits array for solving more complicated problems. In this work, we propose a novel Ising computer using a single stochastic MTJ device. With the utilization of the time-division multiplexing (TDM) technology, a “Compute–Read–Switch” scheme is proposed, so that the single stochastic MTJ can act as multiple P-Bits during Ising computation. A design guide for the current magnitude and time duration of the “Compute–Read–Switch” scheme is investigated and provided. Furthermore, NOT and XOR logic gates are implemented with our proposal. An accuracy rate as high as 69% for the integer factorization is also achieved, which is comparable with conventional Ising computer. Meanwhile, the TDM Ising computer avoids the calibration process, which is mandatory in the conventional Ising computer.

Full color ghost imaging by using both time and code division multiplexing technologies

We propose a new full color ghost imaging scheme using both time and code division multiplexing technologies. In the scheme, the speckle patterns of three colors (red, green and blue) are modulated with different time slots and codes. The light intensity is sampled by one bucket detector. Then based on the modulated time slots and codes, we can effectively and simultaneously extract three detection component signals corresponding to three color components of objects from the sampling signal of the bucket detector. Finally, three component images resulting from the three component detection signals can be synthesized into a full color image. The experimental results verify the feasibility of our scheme under the limit of the number of time slots and codes. Moreover, our scheme reduces the number of bucket detectors and can realize high quality imaging even in a noisy environment.