Phase-shift Keying Signals Research Articles

Maximum Probability of Detection of a Broadband Phase-Shift Keyed Signal with Allowance for Distortions in the Single-Loop Input Circuit of a Receiver

Maximum Probability of Detection of a Broadband Phase-Shift Keyed Signal with Allowance for Distortions in the Single-Loop Input Circuit of a Receiver

DNN-assisted phase distance tuned PSK modulation for PAM4-to-QPSK format conversion gateway node.

This paper proposes an optical gateway that converts pulse amplitude modulation (PAM) format to phase shift keying (PSK) modulation format, enabling flexible intensity-to-phase mapping without relying on optical-electrical-optical data conversion at heterogenous network connections. A proof-of-principle experiment shows that optically converted PSK signals from regular PAM signals will induce non-uniform irregular phase noise distortion. The proposed optical gateway is designed to provide an optimized phase distance for PSK signals such that an achievable information rate is maximized by a deep learning-based decision on the receiver side. The phase distance-tuned PSK signals offer performance improvement of about 4 dB gain at a target generalized mutual information by making use of a digital neural network recovery.

Modulation Scheme Classification in Cognitive Radio Networks Using the Long Short Term Memory (LSTM) of Deep Learning

Cognitive Radio (CR) system has been adopted for efficient utilization of radio frequency spectrum. The classification of signal modulation schemes is one of the main characteristics of the CR for appropriate demodulation of sensed signals. However, conventional Modulation Classification (MC) techniques require extensive extraction of signal features, which is not often guaranteed. Thus, Deep Learning (DL) has been seen as a promising solution to this drawback in MC. This paper proposes a DL-based MC technique using the Long Short-Term Memory (LSTM) network architecture. The proposed LSTM model was trained on M-ary Phase Shift Keying (MPSK) and M-ary Quadrature Amplitude Modulation (MQAM) signal types. The LSTM directly learns the features of a given modulation scheme of a signal sample during training. The signal samples were generated via computer simulation for Signal-to-Noise Ratios (SNRs) from -10 dB to 20 dB with an interval of 5 dB over flat fading channel and Additive white Gaussian noise (AWGN). Simulation results show that the proposed LSTM model achieves an average classification accuracy of 95% at SNRs above 0 dB.

Optimal nonlinear filtering of MPSK signals in the presence of a Doppler frequency shift

Objectives . Phase-shift keyed (PSK) signals are widely used in many telecommunication, communication, and cellular information transmission systems. Phase-shift keying provides a higher noise immunity than amplitude and frequency modulations do. An increase in the modulation order of such a signal leads not only to an increase in its spectral efficiency, but also to a certain decrease in the noise immunity of reception. To ensure a high noise immunity of reception of multiple phase-shift keyed (MPSK) signals, a demodulator should provide the coherence of the reference oscillation with the carrier. Ignorance of the frequency and phase of the received signal leads to significant energy losses. The purpose of this work was to synthesize and analyze algorithms for receiving MPSK signals with phase fluctuations caused by changes in the carrier frequency due to the Doppler effect against the background of white Gaussian noise. Methods . The problem was solved using the apparatus of optimal nonlinear filtering and methods of statistical radio engineering. Results . A demodulator was synthesized, which includes two interconnected units. One of them is a discrete symbol estimation unit, at the output of which a decision on the received symbol is issued, and the other is a phase-lock circuit. Analytical expressions were derived to estimate the characteristics of the receiver noise immunity as functions of the signalto-noise ratio and fluctuation parameters. It was shown that the synthesized quasi-coherent algorithm compensates well for the MPSK signal phase fluctuations caused by the instability of the master oscillator and the Doppler effect. Conclusions . Comparison of the results of this work with results obtained in the case of the absence of fluctuations in the initial phase showed that, at a high relative speed of the transmitter and the receiver (satellite radio channel), the energy loss is no more than 1 dB, and at lower speeds of the objects, it is about 0.2 dB and less.

Simple and Robust Log-Likelihood Ratio Calculation of Coded MPSK Signals in Wireless Sensor Networks for Healthcare

The simple and robust log-likelihood ratio (LLR) computation of coded Multiple Phase Shift Keying (MPSK) signals in Wireless Sensor Networks (WSNs) is considered under both phase noncoherent and Rayleigh fading channels for healthcare applications. We first simplify the optimal LLR for phase noncoherent channel, the estimation of the instantaneous channel state information (CSI) for both the fading amplitude and the additive white Gaussian noise (AWGN) is successfully avoided, and the complexity-intensive process for zero-order Bessel function of the first kind is also perfectly eliminated. Furthermore, we also develop the simplified LLR under Rayleigh fading channel. Correspondingly, the variance estimation for both AWGN and the statistical characteristic of the fading amplitude is no longer required, and the complicated process for implementation of the exponential function is also successfully avoided. Compared to the calculation of optimal LLR with full complexity, the proposed method is implementation-friendly, which is practically desired for energy-limited WSNs. The simulations are developed in the context of low-density parity-check (LDPC) codes, and the corresponding results show that the detection performance is extremely close to that of the full-complexity LLR metrics. That is, the performance degradation is efficiently prevented, whereas complexity reduction is also successfully achieved.

Waveform optimization technology of missile borne radar based on FSK-PSK composite modulation for anti repeater jamming

Aiming at the waveform of missile borne radar is simple and easy to be affected by the repeater jamming in the terminal guidance, an anti-jamming waveform optimization algorithm based on the frequency shift keying(FSK) and phase shift keying(PSK) composite modulation is proposed. The model function of FSK-PSK composite modulation signal is analyzed. Based on the orthogonality of sub pulses, an optimization algorithm of intra pulse PSK modulation based on the alternating direction multiplier method(ADMM) is designed. The simulation results show that comparing with PSK signal, the intra pulse sub pulse orthogonality of FSK-PSK signal optimized by modulation is improved by about 10 dB, which can effectively suppress the intra pulse forwarding interference.

Capacity expansion of chaotic secure transmission system based on coherent optical detection and space division multiplexing over multi-core fiber.

We propose and experimentally study a coherent optical chaotic secure transmission system through a multi-core fiber (MCF). The messages are encrypted by the chaotic carrier and transmitted through the outer cores of the MCF, whereas the chaotic carrier signal is concealed by transmitting through the center core. The MCF provides large transmission capacity expansion and security enhancement against eavesdroppers due to its physical structure. In addition, the designed optical chaos self-homodyne coherent detection strategy has high detection sensitivity and simple physical structure. Due to the prevalence of devices and digital signal processing (DSP) algorithms used in this system, it can be well compatible with a commercial coherent optical communication system. Error free 40 Gb/s/core encrypted 16 quadrature amplitude modulation (QAM) signal transmission over 10 km 7-core fiber is achieved, and 20 Gb/s quadrature phase shift keying (QPSK) signal transmission over a 100 km standard single-mode fiber (SSMF) is demonstrated to verify the long-distance transmission capability. The sensitivity to the secret key is also studied.

Transmission of High-Frequency Terahertz Band Signal Beyond 300 GHz Over Metallic Hollow Core Fiber

Terahertz band has become a promising research field due to its advantages such as high frequency and large available bandwidth. In this paper, we realized the transmission of the 325 GHz 30 Gbaud terahertz quadrature phase shift keying (QPSK) signal with a bit error ratio (BER) less than the 7% hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10^−3, and 325 GHz 16 Gbaud 16-ary quadrature amplitude modulation (16QAM) signal with a BER less than the 20% soft-decision forward-error-correction (SD-FEC) threshold of 2.0 × 10^−2 over 1 m metallic hollow core fiber. In addition, the performances of the metallic hollow core fiber transmission system under different frequencies from 300 to 380 GHz have also been measured. With the help of the Volterra nonlinearity compensation (VNC) algorithm, the highest net transmission rate can be up to 140.625 Gbit/s for 300 GHz 30 Gbaud 64QAM signal with satisfying the 28% spatially coupled low density parity check (SC-LDPC) threshold of 5.2 × 10^−2. By comparing the performances of the metallic hollow core fiber transmission system and wireless transmission system, we also proved the superiority of the hollow core fiber to transmit terahertz signals. The experimental results show that compared with the commonly used free space transmission, the hollow core fiber can be a promising candidate to transmit high-frequency terahertz signals with a high speed and a low loss, and is worthy of further study in the future.

Fast Feed-Forward Optical and Electrical Gain Control to Extend the Dynamic Range of the Burst-Mode Digital Coherent Receiver for High-Speed TDM-PON Systems

This paper introduces a new burst-mode coherent receiver configuration that drastically widens the receiver input dynamic range. Its key advance is a fast feed forward gain control scheme for both a semiconductor optical amplifier (SOA) used as a preamplifier and trans-impedance amplifiers (TIAs) set at the coherent receiver. The two-stage optical and electrical gain control greatly decreases the received burst signal's power variations and increases the receiver dynamic range which attenuates the quantization errors in analogue-to-digital conversion (ADC). To elucidate the receiver sensitivity characteristics, bit error rate (BER) calculations are conducted on 10 Gbit/s single polarization quadrature phase shift keying (SP-QPSK) signal coherent reception. The calculations focus on two significant parameters that greatly impact the quantization noise; ADC vertical resolution and received signal's state of polarization (SOP). The calculation results confirm that the proposed configuration achieves high sensitivity, better than −44 dBm, and wide dynamic range of 30 dB in the worst SOP condition, even when 5-bit ADC is used. Transmission experiments verify the calculated sensitivities and extremely high loss budget of 48.6 dB is achieved in 40-km single mode fiber (SMF) transmission. These results show that the proposal has the potential to realize 10 Gbit/s class long-reach and high splitting ratio PONs; the extremely wide dynamic range yields 40 km reach PON systems with 512- or 1024-way splits with no change in receiver configuration.

Optical 8‐ary phase shift keying modulation format generator based on three microring modulators

AbstractWe have proposed an 8PSK modulator based on three microring modulators (MRM). The design consists of three MRMs, each with a radius of 11.1 μm. Of these three, two MRMs are connected in parallel and they together generate a quadrature phase shift keying (QPSK) signal. While at the output port of the QPSK, a third MRM is connected in series works as an angle modulator, which is basically a 45° phase shift modulator; that is, the output of the MRM varies by 45° depending on the bit pattern fed to it, ‘0’or ‘1’ respectively. We have simulated and shown the performance of the proposed 8PSK modulator after transmitting the modulated signal through various lengths of optical. Constellation diagrams and eye diagrams at different fiber lengths are analyzed. Bit error rate (BER) versus optical signal to noise ratio curve shows that, 10−3 BER has been achieved at 13.5 dB optical signal to noise ratio.

6G Indoor Network Enabled by Photonics- and Electronics-Based sub-THz Technology

We propose an indoor network with a sub-terahertz- band wireless link for 6G applications. In our proposed indoor network, an optical hub unit (OHU) that controls the entire system is optically linked to THz remote nodes (RNs) over optical distribution fibers. The THz RNs communicate with the user equipment through a sub-THz wireless link. The function of the THz RNs is to provide an interface between the optical link and the sub-THz wireless link. For downlink transmission, a photonics-based sub-THz-band signal generation method is adopted to take advantage of the broadband characteristics of the optical components. An electronics-based sub-THz mixer is also used for uplink transmission because of its cost-effectiveness and low energy consumption. A digital signal processor (DSP) is designed to recover the original transmitted baseband signal. The DSP provides frequency offset compensation over a wide frequency range and reduces the probability of cyclic slip. The performance of the proposed system was investigated experimentally with commercially available optical/electrical components. We demonstrate 100 Gb/s 2.5-m wireless transmission with a 16-quadrature amplitude modulation (16-QAM) signal for configuring the downlink. The optical transmission distance was set to 10 km, and the power penalty measured by optical transmission was negligible. We also investigated the scalability and tunability of the photonics-based sub-THz transmitter to confirm the upgradability of our proposed indoor network to consider future capacity expansion. To establish an uplink, a 25 Gb/s 1.5-m wireless transmission with a quadrature phase shift keying (QPSK) signal was employed. A directly modulated laser was used for cost-effective optical transmission. Unlike downstream transmission, a measured bit error rate (BER) penalty caused by the optical transmission was observed. This is due to the interplay between the frequency chirp of the directly modulated laser and the chromatic dispersion in the fiber. Despite this penalty, BERs less than the soft-decision forward error correction (FEC) threshold (2 × 10^−2) with 20% overhead were achieved. We discuss several remaining technical challenges in real-field deployment. These include THz Tx power improvement, photonic integration, reducing form-factor, polarization insensitivity, and automatic beam steering. Our recent efforts to address these issues are also introduced and examined.

Demonstration of an optical phase conjugation based dual‐hop PDM‐QPSK free‐space optical communication link

The dual-hop free-space optical (FSO) communication link for polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK) signals is proposed and experimentally demonstrated in an atmospheric chamber with the optical phase conjugation (OPC) compensating the turbulence-induced signal distortions. The phase fluctuations can be effectively reduced by the OPC, as the error vector magnitudes are 10.03% and 8.28% decreased for x- and y-polarization. At the bit error rate of 1 × 10–3, the power penalty of the dual-hop link with OPC is 2.85 or 2.34 dB lower than that of each polarization without OPC.

ML based modulation format identifier using K-NN algorithm

This paper uses Machine Learning (ML) to detect PSK (Phase-shift keying) signals using a supervised learning model based on K-Nearest Neighbor (K-NN) algorithm. The incoming signal constellation created has been compared to the training data by the K-NN algorithm to determine the modulation format of the received information. By calculating the Euclidean distance over the whole training set for K occurrences of the nearest data points, four PSK signals: BPSK, QPSK, 8PSK, and 16PSK, have been correctly predicted with a very high accuracy level.

Coherent Combining and Long Coherent Integration for BOC Signal Acquisition under Strong Interference

<h3>Abstract</h3> A coherent combining and long coherent integration (CCLCI) scheme is presented for standalone direct acquisition of binary offset carrier (BOC) signals under strong radio frequency interference (RFI). To mitigate the ambiguity of BOC signals, a split-spectrum method extracts the upper and lower sidebands of a BOC signal, treats them separately as two binary phase shift keying (BPSK) signals, and finally combines the results to recover the loss due to splitting. The CCLCI scheme burns through strong interference by building up the desired weak signal while averaging out noise and interference. It exploits all information available (L1 and L2, upper and lower sidebands, odd and even chips, and I- and Q-components) by applying coherent combining across signal components and long coherent integration over time, followed by noncoherent accumulation if necessary. Issues and enabling techniques are described. The results of an embedded implementation in demonstration with a GPS RF simulator are analyzed.

All-optical phase-preserving amplitude-regeneration technology based on bidirectional orthogonal-pumped semiconductor optical amplifier configuration

The phase-preserving amplitude regeneration scheme based on the bidirectional orthogonal-pumped semiconductor optical amplifier (SOA) is proposed in this work. Experimental investigation into the multiple four-wave mixing (FWM) process from the pump, the signal and their corresponding reflective fields is carried out in detail. The regeneration performance obtained from the product between co-propagating fields is also discussed, including its dependence on the signal launch power and the signal quality, to quantify the amplitude regeneration and the phase preserving behaviors. The amplitude distortion is suppressed by 2.2 dB experimentally, confirming the regeneration capability of the proposed scheme. Moreover, the regeneration performance is further investigated for multiple phase shift keying (MPSK) signals through the simulation. According to the numerical results, the operational parameters of the regenerator are the same for advanced modulation formats, proving the robust operation of the proposed bidirectional orthogonal-pumped SOA configuration.

Blind Separation for Wireless Communication Convolutive Mixtures Based on Denoising IVA

In wireless communication systems, signal transmission through a channel can not avoid the influence of noise. When it reaches the receiver, it is accompanied by time delay and attenuation. Therefore, the observed mixture signals at the receiver are convolutional mixed signals with noise contamination. To solve the problem of traditional frequency-domain based convolutive blind signal separation methods have poor separation performance for convolutional mixed signals with noise, this paper propose a denoise-FastIVA method to separate convolutional mixed signals with noise. The basic principle is to use a wavelet transform to denoise the observation signal, reduce the effect of noise on the separation effect of the algorithm, and enhance the robustness of the fast fixed-point independent vector analysis (FastIVA) separation algorithm to noise. Simulation experiments show the effectiveness of a denoise-FastIVA, under the condition that the baseband signal of binary phase shift keying (BPSK) and binary frequency shift keying (2FSK) signal modulation signal is 10 bits respectively,the separation accuracy of linear frequency modulization (LFM) has increased from 87% to more than 94%; BPSK has risen from 83% to over 97%; 2FSK has improved from 81% to over 95%. When the SNR is greater than 10 dB, the separation similarity of denoise-FastIVA for the communication mixed signals is more than 90%, and the demixing signal can demodulate the baseband signal completely and correctly. Baseband signals of experimental BPSK and 2FSK signal modulation signals are 100 bits respectively. When the signal-to-noise ratio is greater than 5dB, the signal separated by denoise-FastIVA method has the highest similarity coefficient with the source signal, and the bit error rate (BER) of the separated BPSK signal and the separated 2FSK signal are the lowest, compared with the traditional frequency domain demixing method and FastIVA algorithm.

Accurate OSNR monitoring based on data-augmentation-assisted DNN with a small-scale dataset.

Deep neural networks (DNNs) have been successfully applied for accurate optical signal-to-noise ratio (OSNR) monitoring. However, the performance of OSNR monitoring substantially degrades when a mega dataset is inaccessible. Here, we demonstrate an accurate OSNR monitoring scheme based on a data-augmentation (DA)-assisted DNN with a small-scale dataset. When a 20 GBaud quadrature phase shift keying (QPSK) signal is transmitted over 400 to 2600 km standard single-mode fiber (SSMF) with an OSNR range from 8 to 14 dB, we experimentally evaluate the minimum dataset size to secure a mean absolute error (MAE) of OSNR monitoring less than 1 dB. The DA-assisted scheme only requires 50% of the raw data, in comparison with the traditional DNN scheme. Thus, the DA-assisted DNN scheme is promising for field-trial accurate OSNR monitoring, especially when the collection of mega datasets is inconvenient.

Sub-sampling generation of ultra-high baud rate PAM/QAM signals via high-order partial response narrowing

Ultra-high baud rate signal generation and detection is of great importance for future intra-data-center interconnect (intra-DCI). In this work, based on a single digital-to-analog convertor (DAC) with 120GSa/s sampling rate, we experimentally demonstrate sub-sampling generation of pulse amplitude modulation (PAM) signals by using high-order partial response narrowing (HPRN) scheme. High-order partial response is utilized to concentrate most of the signal energy into the Nyquist region of DAC sampling rate. A digital brick-wall filter is then employed to avoid spectral overlap by removing the out-of-band components in the frequency domain. The manually induced inter-symbol interference (ISI) can be eliminated by maximum likelihood sequence detection (MLSD) at the receiver. In the experiment, 210Gbaud on-off keying (OOK) signal can be successfully generated and transmitted over 500m standard single-mode fiber (SSMF) with bit-error rate (BER) below the 20% hard-decision forward error correction (HD-FEC) threshold of 1.5×10−2, achieving sub-sampling rate of 0.571. For high-order modulation formats, 217.5Gb/s (145Gbaud) PAM-3 BTB generation and 256Gb/s (128Gbaud) PAM-4 500m transmission are also realized, respectively. Furthermore, for coherent detection systems, 160Gbaud quadrature phase shift keying (QPSK) signal generation is demonstrated by applying HPRN on the in-phase and quadrature components separately, and using carrier phase recovery including pilot symbol group-based coarse estimation and shaped constellation-based blind phase search (BPS) algorithm. The results reveal that the HPRN scheme can extend the usage of DAC at the expense of higher optical signal-to-noise ratio (OSNR) for 200G high-speed optical links and beyond.

Hybrid FSK-PSK Waveform Optimization for Radar Based on Alternating Direction Method of Multiplier (ADMM).

In this paper, a new radar signal modulated with a hybrid of the frequency shift keying (FSK) and the phase shift keying (PSK) signal—i.e., the FSK-PSK signal—is studied. Different phase encoding sequences are used to modulate the sub-pulses to obtain lower sidelobe levels and ensure signal orthogonality. In addition, to counter intra-pulse slice repeater jamming of specific length generated by the enemy jammer, an orthogonal waveform made of sub-pulses of equal length based on the FSK-PSK modulation scheme is designed. The simulation results show that the optimized discrete phase encoding sequence can significantly enhance the orthogonality of the sub-pulse in the FSK-PSK signal and effectively suppress the slice repeater jamming. Two algorithms are proposed: (1) the low sidelobe waveform optimization algorithm based on ADMM (LSW-ADMM); and (2) the anti-slice-repeater-jamming algorithm based on ADMM (ASRJ-ADMM). Both algorithms exhibit fast convergence speed and low computational complexity.

High-speed modulating retro-reflectors with optical phase conjugation compensation

A modulating retro-reflector (MRR) with optical phase conjugation (OPC) compensation is presented and demonstrated to mitigate the turbulence-induced channel distortion for high-speed coherent free-space optical (FSO) communications. The impact of the turbulence on the beam spot, the phase fluctuation and the bit error rate (BER) is analyzed for the MRR FSO link carrying quadrature phase-shift keying (QPSK) signals with spatial or single-mode fiber (SMF)-based OPC. The mitigation of the atmospheric turbulence is verified by comparing the transmission performance of the MRR FSO links with and without OPC. The compensation using SMF-based OPC is experimentally demonstrated in a turbulence-tunable atmospheric chamber. The BER is improved by two orders of magnitude in the turbulent channel with the temperature difference of 250 °C, and the power penalty is reduced by about 2.0 dB, which agree well with the simulation results. A larger receiving aperture size will improve the compensation effect