Differential Phase Shift Keying Research Articles

Using ADTS and CNN methods to effectively monitor CD, crosstalk, and OSNR in an optical network

The article presents the results of a method based on asynchronous delay-tap sampling (ADTS) and convolutional neural network (CNN) for determining simultaneously occurring disturbances described using the chromatic dispersion (CD), crosstalk and optical signal-to-noise ratio (OSNR) parameters. The ADTS method was used to generate training and test data for the convolutional network, which in turn was used to learn to recognize interference from said data. The tests were carried out for a transmission speed of 10 Gbit/s and for on-off keying (OOK) and differential phase shift keying (DPSK) modulation. Very good results were obtained in recognizing simultaneously occurring phenomena. Accuracy of over 99% was achieved for CD and crosstalk for DPSK modulation and over 98% for OOK modulation. In the case of amplified spontaneous emission (ASE) noise, slightly weaker results were obtained, above 95–96% for both modulations. Based on the conducted research, it was determined that the use of ADTS and CNN methods enables monitoring of simultaneously occurring CD, crosstalk, and ASE noise in the physical layer of the optical network, while maintaining the requirements for modern monitoring systems.

Performance analysis of nonlinear crosstalk of WDM systems using modulation schemes criteria

Abstract Nonlinearities in optical fibers are regarded as the most significant barriers that endanger the effectiveness of the optical transmission system and pose a threat to communication quality. Four-wave mixing (FWM) is one of the most important nonlinear effects that greatly reduces the wavelength-division multiplexing (WDM) system performance at high data rates over extended transmission distances. This research examines, and assesses, numerically, the behavior of a 4-channel, 40 Gbps WDM system under the effect of the FWM under various tuning parameters, including dispersion, input power, and wavelength spacing. The system model was built using OptiSystem software, and then three different modulation formats, namely, Non-return-to-zero-frequency shift keying, Return-to-zero frequency shift keying, and differential phase shift keying (DPSK) are used to assess the FWM power penalty. The results demonstrate that the FWM power penalty obtained with 1 nm wavelength separation in the DPSK method is dramatically reduced to −35 dBm. This study also demonstrates that when power variation is taken into consideration, the DPSK modulation scheme delivers a lower bit error rate in comparison to other modulation schemes.

The analysis of the non-Kolmogorov turbulence effect on the performance of uplink coherent DPSK laser satellite communication system in the presence of tilt-corrected beam wander

In the present study, a model for analyzing the performance of laser-based satellite uplinks that account for beam wander and atmospheric turbulence is presented. The developed scintillation index model is a continuation of the recent works considering the effects of non-Kolmogorov turbulence on the propagation of Gaussian beams across turbulent media. We specifically concentrate on the specific regime under the tilt-corrected beam wander. The on-axis scintillation index is developed assuming an isotropic non-Kolmogorov spectrum model where the power law exponent (PLE) effective value, α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document}, is taken to be 3 < α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha$$\\end{document} < 4. Within that regime, effective irradiance models for tilt-corrected beam wander are presented, using the Gamma and Gamma-Gamma distributions. Closed-form expressions of the average bit error rate (BER) are derived to evaluate the performance of the optical communication system considering coherent detection of differential phase shift keying. The obtained numerical results show the impact of the Gaussian beam radius at the transmitter, the PLE effective value, and the zenith angle on the on-axis scintillation index and the average BER of the system under consideration. Due to beam wander, the link performance in terms of scintillation index and average BER depends on the beam radius at the transmitter. With tilt-corrected beam wander the link performance becomes best at an intermediate value of beam radius. With the non-Kolmogorov turbulent medium model, the PLE effective value has a major effect on the beam radius with the best performance. The obtained results guide the choice of the optimum beam radius for best performance for each PLE effective value.

On chip broadband and high extinction ratios Mach-Zehnder interferometer for DPSK signal demodulation

Differential phase shift keying (DPSK) signals are widely employed in optical communication systems due to the high sensitivity and simple self-delay interference demodulation scheme. In this paper, we demonstrate a broadband on-chip Mach-Zehnder interferometer (MZI) for multiple channel DPSK signal demodulation. The chip is constructed using a single-mode high-index doped silica glass waveguide with fiber-to-fiber insert loss less than 3 dB and small second-order dispersion. The MZI interference fringe extinction ratio is over 25 dB in the range of C- and L-bands. The MZI is employed to demodulate four parallel DPSK signals simultaneously with similar performance, indicating that the broad bandwidth MZI is suitable for a receiver of massive parallel optical communications.

Investigation of IEEE 802.16e LDPC Code Application in PM-DQPSK System

With the development of the Internet and information technology, optical fiber communication systems need to meet people’s information demand for large capacity and high speed. High-order phase modulation and channel multiplexing can improve the capacity and data rate of optical fiber communication systems, but they also bring the problem of bit error. To improve the transmission quality and reliability of optical fiber communication systems, forward error correction (FEC) coding techniques are commonly used, which serve as the fundamental approach to enhance the quality and reliability of fiber optic communication systems, ensuring that the received data remain accurate and reliable. The FEC in optical fiber communication systems is divided into three generations. The first generation FEC is mainly hard decision codewords, represented as RS code. The second generation FEC is mainly cascaded code, which stands for interleaved cascaded code. The third generation of FEC mainly refers to soft decision codes, which are represented as low-density parity-check (LDPC) codes. As a kind of FEC, LDPC codes stand out as pivotal contributors in the field of optical communication and have gained remarkable attention due to exceptional error correction performance and low decoding complexity. Based on IEEE802.16e standard, LDPC code with specific code length and rate is compiled and simulated in MATLAB and VPItransmissionMaker 10.1 and successfully incorporated into polarization multiplexed differential quadrature phase shift keying (PM-DQPSK) coherent optical transmission system. The simulation results indicate that the bit error rate (BER) can be reduced to 10−3 when the optical signal-to-noise ratio (OSNR) reaches 14.2 dB, and the BER experiences a reduction by nearly three orders of magnitude when the OSNR is 17.2 dB. These findings underscore the efficacy of LDPC codes in significantly improving the performance of optical communication systems, particularly in scenarios demanding robust error correction capabilities. This study provides valuable, significant results regarding the potential of LDPC codes for enhancing the reliability of optical transmission in real-world applications.

O-band single-photon quantum key distributor master-to-slave injection-locked DFBLD pair

In comparison with the rapidly developing progress on the optical C-band (1525-1565 nm) master-to-slave injection-locked transmitter to perform the coherent single-photon quantum key distribution (QKD), the development on the O-band (1250-1350 nm) QKD transmitter is somewhat delayed as the commercially available wavelength-matched narrow-linewidth distributed feedback laser diode (DFBLD) pair is hardly accessible up to now. By using the DFBLDs with only sub-MHz linewidth and relatively deviated wavelength for the first time, this work demonstrates the optically differential-phase-shift-keying (DPS) QKD by an O-band master-to-slave injection-locked DFBLD pair. The master and slave DFBLDs with wavelength fluctuations of ±0.05% and ±0.2 pm are controlled by a thermo-electric cooler with a feedback gain of 100. The 1-bit delay interferometer (DI) under thermo-insulation maintains its visibility at &gt;96% with dPo/Po and dPo/dt measured below ±0.1% and ±1 × 10−3 mW/s. By RZ-OOK modulating the master DFBLD with step-like power coding at 150 µW to induce π phase shift in the injection-locked slave DFBLD, the rising-/falling-edge DPS envelope distortion of the slave DFBLD diminishes by decreasing the bias current of the master DFBLD from 7Ith (35 mA) to 2Ith (10 mA). This phenomenon enables the 128-bit DPS-QKD transmission with a quantum bit-error rate (QBER) of 3.57% and a secure key rate of 3.524 kbit/s in the 6-km SMF link. The O-band injection-locked single-photon DPS-QKD bit-stream with a mean photon number of 0.2 #/bit minimizes its decoding QBER to 3.88% and 4.84% for 512-bit and 1024-bit, respectively.

A new derivation of the Nakagami-m distribution as a composite of the Rayleigh distribution

Mobile communications systems are affected by what is known as fading, which is a well-known problem largely studied for decades. The direct consequence of fading is the complete loss of signal (or a large decrease of the received power). Rayleigh fading is a reasonable model for wireless channels although, Nakagami-m distribution seems better suited to fitting experimental data. In this paper we obtain the Nakagami-m distribution as a composite (mixture) of the Rayleigh distribution, a result which as far as we know it has not been shown in the literature. This representation of the Nakagami-m distribution facilitates computations of the average BER (Bit Error Rate) for DPSK (Differential Phase Shift Keying) and MSK (Minimum-Shift Keying) modulations for this distribution and higher moments of them, which is of great applicability to modeling wireless fading channels. Furthermore, a simple, not depending on any special function, apart of the Gamma function, bivariate version of the Nakagami-m distribution is also proposed as a special case of the multivariate version which is also presented. The proposed composite distribution is simulated through the standard procedure of summation of phasors, and results for the new closed-form measures for the MSK modulation are also shown. From that it is clear that the alternative formulation of the Nakagami-m distribution allows for easier modeling of fading fading-shadowing wireless channels through the new explicit second order statistics metrics. is well suited for modelling fading-shadowing wireless channels.

Investigation of Costas loop phase deviation effect on BER performance of space downlink coherent communication system with DPSK scheme

The Costas loop is an important technology for synchronous demodulation in space coherent communication. However, due to the limitation of the loop device and processing technology, it is difficult to achieve high-precision locking, which results in the Costas loop phase deviation and further affects the quality of the demodulation signal. In this paper, a closed-form bit error rate (BER) model is derived to evaluate the Costas loop phase deviation effect on BER performance in the space differential phase shift keying (DPSK) modulation and heterodyne detection communication system, considering laser phase noise, atmospheric turbulence, and detector noise. Based on the BER model, analytical solution simulation is conducted. The results show that the BER performance deteriorates varying with the increase of the Costas loop phase deviation. In addition, we research how to better balance the laser linewidth and Costas loop accuracy in the system design to ensure good communication status. We find that the wider the laser linewidth, the more stringent the Costas loop accuracy. Furthermore, the BER performance versus the Costas loop phase deviation under different satellite-to-ground communication system parameter settings including divergence angle, receiving aperture, signal laser power, and data rate are analyzed. This work provides valuable references for space optical coherent communication systems design.

Analysis of noise immunity of satellite communications under small-scale ionospheric disturbances and time-selective fading of received signals

The article develops a methodology for analyzing the noise immunity of satellite communication systems under small-scale disturbances of the ionosphere, taking into account the possibility of general and time-selective fading of received signals Differential Phase Shift Keying. The refined dependences of the intervals of time and space correlation of fading in the transionospheric radio channel on the parameters of transmitted signals and the state of the ionosphere are obtained. The analytical dependence of the probability of erroneous reception of signals with Differential Phase Shift Keying on the average signal-to-noise ratio at the receiver input, the frequency-time parameters of the signals and the characteristics of small-scale ionospheric inhomogeneities was obtained.

Design of Ultra Dense WDM Optical Communication System to Reduce Signal Impairments Using DCF and Repeater Techniques

Linear and non-linear impairments are the major problems that affected the dense wavelength division multiplexing (DWDM) system performance. In this simulation designs, two different compensation techniques have been proposed to eliminate signal impairments. The repeater technique was proposed to reduce non-linear effects like four-wave mixing (FWM) which cause transfer power from DWDM channels to another new channels. The dispersion compensation fiber (DCF) technique was used to reduce dispersion effects which cause signal pulse broadening over long transmission distances. Also, three different modulation formats and four frequency separations were used to determine which modulation scheme is more compatible with the compensation techniques. The results is calculated in term of quality factor against power and noetic that the carrier suppressed return to zero (CSRZ) format offers the best performance with the DCF technique with 32.1804 Q-factor at 15dBm threshold power then, the differential phase shift keying (DPSK) format is compatible with the repeater technique with 27.7959 quality factor and 14dBm threshold power. Index Terms— Dense Wavelength Division Multiplexing (DWDM), Dispersion Compensation Fiber DCF, Repeater, and Non-linear Effects.

All-optical wavelength and format conversion of DQPSK-to-PAM4 using DLI and pump assisted NOLM

An all-optical wavelength and format conversion scheme of 20 Gbps differential quadrature phase shift keying (DQPSK)-to-4-ary pulse amplitude modulation (PAM4) signals based on the delay line interferometer (DLI) and the pump assisted nonlinear optical loop mirror (NOLM) is proposed and numerically simulated. The input DQPSK signal is converted into two star-16-ary quadrature amplitude modulation (star-16QAM) signals (namely, star-16QAM-I and star-16QAM-Q) using DLI with the time delay of 1-symbol and different linear phase shifts of π/4 and −π/4, respectively. The star-16QAM signals are converted into the on-off keying (OOK) signals (namely, OOK-I and OOK-Q) using the pump assisted NOLM based on the self-phase modulation (SPM) and the cross-phase modulation (XPM) in the highly nonlinear fiber (HNLF). The two OOK signals can be aggregated into different types of PAM4 signals by adjusting their power ratio (PR) and relative phase shift (RPS) flexibly. Error vector magnitude (EVM) and bit error rate (BER) for the input and output optical signals are calculated to verify the scheme performance. Compared to the DQPSK signal with an input optical signal-to-noise ratio (OSNR) of 30 dB, there are about 2.5 dB penalty of receiver OSNR for the converted OOK-I and OOK-Q signals. For the corresponding aggregated equidistant PAM4 and equiamplitude PAM4 signals, they have about 6.3 dB and 12.1 dB penalty of receiver OSNR. The proposed scheme of DQPSK-to-PAM4 can be deployed at the all-optical gateway to bridge the long-hual and short-reach optical networks.

Investigation of 2.24Tbps full-duplex integrated multi-beam FSO/MDM-next generation PON under diverse atmospheric conditions

A full-duplex 2.24Tbps mode division multiplexing (MDM) based integrated multi-beam free space optics (FSO) and next generation passive optical network (NGPON) system to mitigate the atmospheric turbulence and fiber dispersion with enhanced network scalability as well as efficiency is proposed. In emergency scenarios the utilization of polarization shift keying (PolSK) and dual polarization (DP)-differential quadrature phase-shift keying (DQPSK) modulation in system offers high spectral efficiency, coherent detection, minimum link dispersion and less noise. The simulation results demonstrate the faithful MDM-FSO/NGPON signals transmission over 40 km fiber with 500 m multi-beam FSO links at −8 dBm received power and 2 dB maximum power penalty. Also, the maximum fiber & FSO range can be expanded upto 160 km and 1500 m respectively, considering fiber impairments and diverse weather conditions. The system also supports simultaneous 200 end users having 23–47 dB total channel loss. High optical to signal noise ratio of 36 dB in downlink and 44 dB in uplink is acquired successfully. The comparison of the designed system with other systems signifies its superiority to others.

Experimental study of the impact of carrying a telecom signal on LOCSET-based coherent beam combining.

We report on what is, to our knowledge, one of the first realizations of a CBC (coherent beam combining)-based laser emitter carrying a 10.66 Gb/s telecom signal in free-space optics, within the laboratory environment. Two telecom modulations have been tested: NRZ (non-return-to-zero, in amplitude) and DPSK (differential phase-shift keying, in phase). The modulated signal is split and amplified in three fiber amplifiers, delivering up to 3 W each. CBC of data amplified signals is achieved with residual phase errors well below < λ/60 RMS, using a phase-tagging technique (LOCSET). A first analysis of the influence of various parameters (such as phase-tagging modulation depth, optical path difference, number of channels, amplifier power) on the locking and data transmission quality is investigated. The study shows that the phase-tagging modulation depth and optical path difference are the main critical issues when carrying data on a CBC signal.

Receiver Design in Full-Duplex Joint Radar-Communication Systems

Full-duplex (FD) integrated sensing and communication (ISAC) has great potential in future vehicular networks. However, the FD requirement and the ISAC functions make the receiver processing extremely complicated, particularly when multiple transmissions are uncoordinated. In this paper, we study frequency-hopping (FH) based receivers in an FD ISAC system, where the arrivals of backscattered signals from one node may overlap with those of signals from another node. To mitigate the interferences caused by the overlapping signals, we consider two receiver options based on either conventional communications or frequency-modulated continuous-wave radars, and two signal modulations based on either fast FH or un-slotted ALOHA FH. Based on the different signal modulations, we develop two parameter estimation schemes via using FH-decoding and dechirp operations, respectively. To further improve the sensing accuracy, we proceed to propose an iterative algorithm, which refines the estimates of all parameters via using short-time-Fourier transform and maximizing the received power in desired frequency bands. After obtaining all channel parameters in sensing, bilateral communications between two nodes are realized by differential phase-shift keying. Finally, simulation results are provided and verify that the proposed FD ISAC can obtain parameters in high resolution and realize robust communication links.

Semiconductor Optical Amplifier (SOA)-Driven Reservoir Computing for Dense Wavelength-Division Multiplexing (DWDM) Signal Compensation

Optical signal processing (OSP) technology is a crucial part of the optical switching node in the modern optical-fiber communication system, especially when advanced modulation formats, e.g., quadrature amplitude modulation (QAM), are applied. However, the conventional on–off keying (OOK) signal is still widely used in access or metro transmission systems, which leads to the compatibility requirement of OSP for incoherent and coherent signals. In this paper, we propose a reservoir computing (RC)-OSP scheme based on nonlinear mapping behavior through a semiconductor optical amplifier (SOA) to deal with the non-return-to-zero (NRZ) signals and the differential quadrature phase-shift keying (DQPSK) signals in the nonlinear dense wavelength-division multiplexing (DWDM) channel. We optimized the key parameters of SOA-based RC to improve compensation performance. Based on the simulation investigation, we observed a significant improvement in signal quality over 10 dB compared to the distorted signals on each DWDM channel for both the NRZ and DQPSK transmission cases. The compatible OSP achieved by the proposed SOA-based RC could be a potential application of the optical switching node in the complex optical fiber communication system, where incoherent and coherent signals meet.

Simultaneous OSNR and chromatic dispersion monitoring based on optical tones power ratio

A novel technique is proposed for simultaneous monitoring of optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD). The scheme is based on the cross-phase modulation effect in a highly nonlinear fiber, which induces a change in the optical tones according to the impairments. The power ratio of the optical tones at two separate frequencies is utilized for monitoring. Improvements in the maximum measurable OSNR, CD and dynamic range can be obtained using only the clock tone for the non-return-to-zero, return-to-zero with a 50% duty cycle differential quadrature phase-shift keying, differential phase-shift keying and on-off keying signals at 80 Gb/s. For the return to zero differential quadrature phase shift keying (RZ-DQPSK) system, the OSNR of 4–40 dB can be monitored with a 36.73 dB dynamic range, and a chromatic dispersion of 0–117 ps/nm can be monitored with a 48.68 dB dynamic range. A correlation is built to describe the relationship of the power ratio with the OSNR and chromatic dispersion which has a root-mean-squared error of 1.41. The delay group dispersion insensitivity, the impact of the input signal power, and the filter selection are investigated. The design enables accurate monitoring, simple operation and may be used in a wide range.

A novel code shift keying for label superimposing in optical label switching

Optical label switching (OLS) is an attractive solution for the packet-based optical switching. A novel modulation method, i. e., code shift keying (CSK) is proposed for label modulation in this paper. The payload signal applies differential phase shift keying (DPSK) in Manchester code or NRZ format when the label data is “1” or “0”, respectively. The payload signal is detected by a Mach-Zehnder delay interferometer (MZDI) with two-bit delay difference between the two arms. The label signal is detected by another MZDI with a-half-bit delay difference between the two arms. The proposed CSK based OLS significantly increases the code efficiency of the payload signal without sacrificing the extinction ratio (ER). The feasibility of the CSK based OLS is verified by the simulation.

Investigation of MDRZ and DPSK modulation schemes employed in DWDM systems for smart city 5G access networks

Wavelength division multiplexing (WDM) is one of the emerging technologies for data transmission in 5G access network assembly between the antenna unit (AU) and the distribution unit (DU). Here, in this work, we evaluate and analyze a dense wavelength division multiplexing (DWDM) — passive optical networks (PONs) employing erbium–ytterbium-doped fiber amplifier (EYDFA) [Formula: see text] Raman hybrid optical amplifier (HOA) using two modulation schemes — modified duobinary return to zero (MDRZ) and differential phase shift keying (DPSK) for alternate channels, where the channel count has been varied from 8 to 40. The system has been analyzed over the wavelength span of 1550–1558.8[Formula: see text]nm with a channel spacing, input power and data rate of 25[Formula: see text]GHz, 0[Formula: see text]dB and 40[Formula: see text]Gb/s, respectively. An average gain, gain ripple and optical signal-to-noise ratio (OSNR) of 20.87, 0.95 and 30[Formula: see text]dB, respectively have been observed in the case of HOA along with the achievement of Q-factor of up to 9 at the receiving end of the system. The DPSK-modulated channels result in higher values of gain and OSNR along with lower gain ripple as compared to MDRZ channels making the proposed system a good option for 5G access network applications.

FWM crosstalk reduction and performance investigation of SC-DWDM system employing ML techniques

This article presents a comprehensive approach towards mitigation of four-wave mixing (FWM) induced crosstalk for a super-combined dense wavelength division multiplexing (SC-DWDM) system with in-line erbium-ytterbium doped fiber amplifier (EYDFA) + Raman hybrid optical amplifier (HOA). The performance of modified duo-binary return to zero (MDRZ) and differential phase-shift keying (DPSK) modulation formats employed on alternate channels of the 40-channel system have been compared considering equal (ECSA) and unequal channel spacing allocation (UECSA) schemes at a data rate of 40 Gbps. In the case of the UECSA scheme, the DPSK modulated channels have shown a reduction of FWM crosstalk components and intensities of up to 80% and 40 dB, respectively at a low bit error rate (BER) of 2.5 × 10−14. Different artificial neural network (ANN) techniques have been compared for gain spectrum estimation of HOA has been carried out based on input features of channel spacing, the number of channels and wavelength. Levenberg-Marquardt's (LM) model proves to be the best fit as compared to other ANN techniques. The k-nearest neighbours (KNN), support vector machine (SVM) and decision tree (DT) algorithms have been applied for the estimation of impairments based on root mean square error (RMSE) and coefficient of determination (R2) values as performance metrics. The best-performing model results applying an ANN approach with predicted R2 values of quality - factor (Q-factor) and noise figure (NF) of 0.74 and 0.56, respectively.

Inter-Dimensional Interference-Tolerant 4-D Set-Partitioning QAM-MDPSK optical access network transmission

Multidimensional optical modulation (MOM) is one of the promising techniques for spectrally efficient optical access network transmissions. However, inter-dimensional interference (IDI) in MOM limits the signal-to-interference-plus-noise ratio (SINR) giving trade-off between each dimension. In this paper, we propose IDI-tolerant four-dimensional (4-D) set-partitioning quadrature amplitude modulation with M−ary differential phase shift keying (SP-QAM-MDPSK) based on direct-detection (DD) systems. We compared the proposed scheme with QAM-MDPSK without set-partitioning and experimentally demonstrate SP-16QAM-16DPSK over 20-km single-mode fiber, results in nearly 3 dB signal-to-noise ratio (SNR) gain at 3×10-2 symbol error rate (SER) compared to 16QAM-4DPSK, which shows that SP-QAM-MDPSK is tolerant to the possible IDI.