In-phase Quadrature Research Articles

Joint estimation of transmitter and receiver IQ imbalances based on GSOP and GCM for optical coherent systems

In this paper, we propose an in-phase/quadrature (IQ) imbalance estimation scheme for mixed transmitter (Tx) and receiver (Rx) IQ imbalance in the optical coherent transmission system. The proposed scheme is based on traditional IQ imbalance compensation algorithm Gram-Schmidt orthogonalization procedure (GSOP) and the proposed geometric construction method (GCM). In the actual transmission system, frequency offset (FO) and phase noise (PN) are recognized as part of received signal, which has an effect on the estimation of IQ imbalance. At the beginning of the proposed scheme, the GSOP algorithm is used to estimate and compensate Rx IQ imbalance according to the statistical characteristics of the received signal, then standard frequency offset compensation algorithm and k-means clustering aided blind phase search (BPS) algorithm are used to compensate FO and PN respectively. Finally, the proposed method GCM is used to estimate Tx IQ imbalance. 34 Gbaud QPSK and 16QAM signals are experimentally performed to demonstrate the proposed IQ imbalance estimation scheme, the results show the proposed scheme has accurate estimation capability with low estimation algorithm complexity.

A Novel Digital IQ Demodulation for Interferometric Radiometers

In the frame of an SMOS follow-on operational mission, a new instrument design is being developed based on the lessons learned from MIRAS, the SMOS payload. To reduce hardware complexity and mass, digital In-phase Quadrature (IQ) demodulation is considered. In this schema, Q components are obtained by delaying one clock of the digitized IF signals instead of using phase quadrature analog mixers. The purpose of this article is to formulate this concept for application to interferometric radiometry, establish the required data processing methods, and provide experimental results.

Energy-Efficient Index Modulation With In-Phase/Quadrature Format in the Generalized Fading Channel

Dual-mode (DM) or multi-mode (MM) index modulation (IM) techniques with the in-phase/quadrature (IQ) format have been investigated for improving the performance of the orthogonal frequency division multiplexing with IM (OFDM-IM) system in the frequency-selective Rayleigh fading channel. However, all subcarriers in these schemes must be activated so that the energy efficiency (EE) of the system inevitably decreases. In this paper, we propose a novel modulation scheme named quadrature tri-mode index modulation (QTM-IM) technique to achieve a trade-off between the spectral efficiency (SE) and EE. The proposed QTM-IM can also be flexibly extended into multi-mode form called MM with enhanced IQ (MM-EIQ). The multi-mode $M$ -ary pulse amplitude modulation (PAM) constellations containing the origin point are designed to map the information bits into the active subcarriers. On the other hand, the theoretical analysis of IM-based schemes over the Rician fading channel has been conducted since most previous papers only considered the Rayleigh fading channel. At the receiver, three kinds of detectors with different algorithm complexities are employed for signal demodulation. Finally, the computer simulation results demonstrate the enhancement of the proposed schemes. More specially, (i) QTM-IM achieves 4dB signal-to-noise ratio (SNR) gain at the BER level of 10−5 compared with quadrature DM (QDM) scheme with the same SE in the Rician fading channel and (ii) MM-EIQ harvests 0.89 bits/s/Hz SE gain and almost doubles the EE compared with MM-IQ scheme without any SNR loss over the Rayleigh fading channel.

C band 112 Gb/s PAM4 signal transmission over 320 km with a quasi-linear double-side electro-absorption modulated laser (DS-EML)

The growing traffic demand in data center interconnections (DCIs) requires high-speed and low-cost transceivers that can flexibly adapt to different transmission distances up to 80 km or further. In this paper, based on the double-side electro-absorption modulated laser (DS-EML), we propose a transmitter with a fixed 90-degree phase rotation on one side of the DS-EML that can realize quasi-linear complex modulation. We verify the application of the quasi-linear DS-EML for a 112 Gb/s CD pre-compensation 4-level pulse amplitude modulation (PAM4) signal transmission over 320 km by simulation. Compared with the LiNbO3 in-phase quadrature (IQ) modulator and the dual-drive Mach-Zehnder modulator (DDMZM), our proposed transmitter has several obvious advantages, such as low cost, small footprint, ease of integration and reduced power consumption.

Multi-Dimensional, Wide-Range, and Modulation-Format-Transparent Transceiver Imbalance Monitoring

We propose and experimentally demonstrate a dual-polarization (DP) transceiver imbalance monitoring scheme, which is applicable for the coherent system using square QAM signals. The scheme can separate/monitor various kinds of transceiver imbalances and has technical advantages of multi-dimension, wide monitoring range, and modulation-format-transparency. In the proposed scheme, a polarization scrambler is configured between transmitter (Tx) and receiver (Rx). After coherent detection, the proposed digital signal processing (DSP) modules are implemented to monitor transceiver imbalance based on the received signals. To simplify the DSP modules, the implementation sequence of DSP modules is in reverse order compared to the order in which the sequence of impairments is introduced. Firstly, Godard timing error detection (TED) and Gram-Schmidt orthogonalization procedure (GSOP) is used to monitor and compensate Rx imbalances. After compensating the Rx imbalances, Tx imbalance monitoring is implemented. Complex/real maximum likelihood independent component analysis (ML-ICA) and Godard-TED are used to monitor Tx imbalance. Finally, the amplitude ratios of the final output signal and Tx in-phase/quadrature (IQ) amplitude imbalance are fed back to mitigate the interaction of Tx imbalances on the signal power and improve monitoring accuracy. The transceiver IQ and x-polarization/y-polarization (XY) imbalances are separated for the first time by using the frequency offset (FO) naturally existing in the system and the continuous polarization rotation induced by a polarization scrambler. The separation method combined with the reverse algorithm design and amplitude ratio feedback mechanism makes the proposed scheme achieve the most multi-dimensional imbalance monitoring by far. The simulation and experimental results verify that the proposed scheme is modulation-format-transparent and can separate/monitor multi-dimensional transceiver imbalances within a wide range.

BER analysis of IQ imbalance compensation for GFDM systems

As one of the 5G waveform candidates, generalised frequency division multiplexing (GFDM) systems have been proposed to achieve lower out of band radiation and stronger robustness against synchronisation errors. However, theoretical BER performances of GFDM systems with in-phase/quadrature (IQ) imbalance, as well as compensation strategies, have not been widely investigated. In this Letter, the authors evaluate theoretical BER performances of GFDM systems with transmitter IQ imbalance (IQI) before and after a proposed compensation method. Basically, they give approximated BER expressions for different modulations through considering introduced IQI completely as useless interference, and then derive a more precise BER expression for QPSK modulation. Additionally, they put forward a compensation method to remove IQI interference in GFDM systems at the cost of enlarged noise. Furthermore, analytical BER expressions with IQI compensation are derived, and then the effectiveness of the proposed compensation strategy is proven by theoretical and simulation results.

Three-dimensional super-resolution ultrasound imaging of chicken embryos - A validation framework for analysis of microvascular morphology.

The purpose of this present study was to improve the quantification of microvascular networks depicted in three-dimensional (3D) super-resolution ultrasound (SR-US) images and compare results with matched brightfield microscopy and B-mode ultrasound (US) images. Standard contrast-enhanced US (CEUS) images were collected using a high-frequency US scanner (Vevo 3100, FUJIFILM VisualSonics Inc) equipped with an MX250 linear array transducer. Using a developing chicken embryo as our model system, US imaging was performed after administration of a custom microbubble (MB) contrast agent. Guided by stereo microscopy, MBs were introduced into a perfused blood vessel by microinjection with a glass capillary needle. Volume data was collected by mechanically scanning the US transducer throughout a tissue volume-of-interest (VOI) in 90 μm step increments. CEUS images were collected at each increment and stored as in-phase/quadrature (IQ) data (N = 2000 at 152 frames per sec). SR-US images were created for each cross-sectional plane using established data processing methods, and all were then used to form a final 3D volume for subsequent quantification of morphological features. Vessel diameter quantifications from 3D SR-US data exhibited an average error of 1.9% when compared with microscopy images, whereas measures from B-mode US images had an average error of 75.3%. Overall, 3D SR-US images clearly depicted the microvascular network of the developing chicken embryo and measurements of microvascular morphology achieved better accuracy compared to traditional B-mode US.

In-phase/quadrature modulation using directly reflectivity-modulated laser

In the last decade, coherent optical transmission technology has dominated the provision of high-capacity communications in metro and long-haul networks and is expected to expand to short-reach networks such as data center and passive optical networks. Capacities of more than 1.5 Tb/s have been demonstrated for a single wavelength. In-phase/quadrature (IQ) modulation allows information to be encoded in both the phase and amplitude of light (or in-phase and quadrature components) and is typically achieved by nested multiple Mach–Zehnder modulators (MZMs). MZMs have advantages including low chirp, broadband operation, and easy to achieve high-order quadrature amplitude modulation (QAM), but they are typically large and have high RF power consumption and excess losses. A small IQ transmitter with low RF power consumption is therefore in demand for low-cost and highly integrated coherent modules. In this paper, we experimentally demonstrate a directly reflectivity-modulated laser that can potentially achieve this goal. We demonstrate the device on a hybrid silicon/III-V platform, where silicon photonics offers compact components for filters, modulators, and reflectors, and the III-V material provides gain. In principle, the device could inherit the benefits of conventional directly modulated lasers while overcoming their speed limits. We demonstrate 32/50 Gbaud quadrature phase-shifted keying with low bit error ratios and experimentally prove the feasibility of 30 Gbaud 16-QAM.

Silicon Photonics for 100Gbaud

We reviewed recent breakthroughs on silicon photonic for 100Gbaud operation. Recent progress on high-speed Ge photodetector and carrier depletion modulator promises 100Gbaud optical transceivers with all-silicon material platform for commercial applications. We achieved high performance high-speed all-silicon photonics carrier-depletion Mach–Zehnder modulation by co-optimization of doping and device design assisted with an accurate electro-optical (EO) model. We reported all-silicon Mach–Zehnder modulator with a measured 6 dB EO bandwidth of >60 GHz by using a medium doping and 2 mm long phase shifter. We experimentally demonstrated 120Gbaud QPSK and 100Gbaud 32QAM operations using a high performance all-silicon in-phase/quadrature (IQ) modulator with extinction ratio of >25 dB, moderate ${{\boldsymbol{V}}_{\boldsymbol{\pi }}}$ of 6.3 V, and 6 dB electro-optic bandwidth of 50 GHz employing practical Nyquist filter and linear compensation in commercial arbitrary wave generator (AWG) and optical modulation analyzer (OMA). We studied both performance optimization and limitation. Our results show that BER performance can be optimized by pre-equalization (Pre-EQ) method for bandwidth-limited silicon photonic modulators. However, the performance on BER and modulation loss is strongly affected by the equalization bandwidth due to peak-to-average-power-ratio (PAPR). The frequency at fast roll-off of transmitter response is more critical than 3 dB electro-optic bandwidth when Pre-EQ is used for bandwidth compensation.

A Beyond-1-Tb/s Coherent Optical Transmitter Front-End Based on 110-GHz-Bandwidth 2:1 Analog Multiplexer in 250-nm InP DHBT

This article presents an optical transmitter front-end based on 2:1 analog multiplexer (AMUX) for beyond-1-Tb/s/carrier coherent optical communications systems. An AMUX is monolithically integrated with an optical modulator driver to realize an AMUX-Driver IC that can directly drive an optical modulator. The AMUX-Driver IC fabricated by using our in-house 250-nm InP double heterojunction bipolar transistors (DHBTs), which have a peak cutoff frequency ( $f_{\mathrm {T}}$ ) and maximum oscillation frequency ( $f_{\mathrm {max}}$ ) of 460 and 480 GHz, respectively, achieves a record bandwidth of 110 GHz and a 1.5- $\text{V}_{\mathrm {ppd}}$ linear differential output range with a <3% total harmonic distortion (THD). A coherent optical transmitter front-end module compactly integrating two AMUX-Driver ICs and an InP-based optical in-phase quadrature (IQ) modulator achieves an electro-optic (EO) bandwidth higher than 80 GHz at the 6-dB point. Beyond-1-Tb/s/carrier optical modulation based on 168-GBaud polarization-division-multiplexed (PDM) 16-ary quadrature-amplitude-modulation (16QAM) was successfully demonstrated by using this integrated module.

Automatic Modulation Classification Based on In-Phase Quadrature Diagram Constellation Combined with a Deep Learning Model

Objectives: This study aims to present a framework for Automatic Modulation recognition using Deep learning without feature extraction. Methods: We study seven modulations using the In-Phase Quadrature constellation polluted by Additive White Gaussian Noise. We apply the K-means algorithm to normalize data transmitted and polluted by noise; the new diagram obtained is considered as an image and coded in pixel before entering in a Deep Neural Network where we apply 20% dropout on hidden layers to avoid overfitting. The simulation is carried out in Matlab. Findings: Experiment performed on selected modulations following the proposed framework gives a good percentage of recognition equal to 96.12%. Our algorithm Deep Neural Network imaGe gives the best performance results at epoch equal to 2,000,000. Applications: The outcome will be beneficial for researchers in Software-Defined Radio for civilian and military applications like electronic attacks and electronic protection. Keywords: Modulations, I–Q Diagram Constellation, Clustering, Deep Neural Network, Dropout.

IQ imbalance compensation based on simplified GSOP and FPGA implementation in optical coherent QPSK receiver

Abstract In this paper, a simplified Gram-Schmidt orthogonalization procedure (SG) method was proposed for in-phase/quadrature (IQ) imbalance compensation based on the Gram-Schmidt orthogonalization procedure (GSOP) algorithm. The proposed method can compensate IQ imbalance in the optical coherent system by two steps of phase orthogonalization and amplitude balance. In addition, this method avoids square root operation compared to the GSOP in the field programmable gate array (FPGA) hardware implementation, therefore it is easier to implement in terms of resources and complexity. Two steady states are achieved by accumulating scale factor to reduce resource consumption in FPGA hardware implementation of the proposed scheme. Finally, a FPGA design with 32 parallel units is performed to demonstrate the proposed method in a polarization multiplexed quadrature phase shift keying (PM-QPSK) system, the results show the proposed algorithm simplifies FPGA implementation complexity and maintains compensation performance comparable to GSOP algorithms.

FPGA‐based system for effective IQ imbalance mitigation of RF power amplifiers

SummaryTo provide an adequate signal integrity to a power amplifier (PA), we propose a digital system for the degradation at the transmitter path, and it is implemented on a field‐programmable gate array (FPGA) board. The proposed system offers the following features: A ‐ary quadrature amplitude modulation (QAM) digital signal generation and in‐phase/quadrature (IQ) imbalance mitigation, and by default, it performs as a predistortion model extraction from PA‐measured data. The simulations and tests provided are performed to effectively verify the PA linearity by using 256‐QAM signals. The nonlinearities are predicted as a reliable solution for linearizing the PA from measurements of AM/AM and AM/PM conversion curves. The performance is evaluated in terms of linearity, computation complexity, and FPGA hardware synthesis according to a dependability compliance of digital signal processing. Finally, the model is validated with input/output data observations to linearize the model with a fitting normalized mean squared error (NMSE) of around dB, a spurious free dynamic range of 40 dBm, and an adjacent channel power ratio reduction by dBm, for a class‐AB broadband radio frequency PA GaN HEMT of 10 W working at 2.34 GHz.

A 5.8 GHz fully integrated BiCMOS SiGe:C injection-locked-oscillator-based active phase shifter for energy beamforming

This paper presents the design and the implementation of a fully integrated active phase shifter for beamforming at 5.8 GHz. The proposed circuit, implemented in a 0.25 µm BiCMOS SiGe:C process, is based on an original architecture using an injection-locked oscillator (ILO) associated with an in-phase/quadrature (IQ) modulator. The dynamic behaviour of an ILO is first analysed theoretically and important characteristics are deduced. At 2.5 V power supply voltage and total power dissipation of only 92.5 mW, the proposed circuit allows to obtain a 360° phase shift range and occupies 1.43 mm2. This phase shift is synthesised using the ILO for fine-tuning and the IQ modulator for coarse tuning.

Millimeter-wave SFCW SAR imaging system based on in-phase signal measurement with simplified transceiver

A conventional millimeter-wave stepped frequency continuous wave (SFCW) synthetic aperture radar (SAR) imaging system generally utilizes IQ modulation technique to acquire the amplitude and phase of the waves scattered from a target object. Due to measure both in-phase signal and quadrature signal, the transceiver of the conventional system is complicate and costly, and the IQ imbalance problem makes the system difficult to calibrate. To reduce hardware complexity and enhance efficiency-cost ratio, a novel SFCW SAR imaging system only measuring in-phase signal is proposed and demonstrated. For lack of quadrature signal measurement, an algorithm based on Fourier transform is proposed to estimate the amplitude and phase. The ultimate images are obtained through an image-reconstruction algorithm, which uses the estimated amplitude and phase as input parameters. The proposed system is verified by both simulation and experiment, where the frequencies are set from 24GHz to 30GHz. The imaging results with high resolution and low noise are demonstrated. Compared to the conventional system, the image quality of the proposed system is almost identical, but the transceiver of the proposed system is greatly simplified.

Demonstration of modulating retro‐reflection free‐space optical transmission using 80 Gb/s Pol‐MUX QPSK signal in simulated atmosphere environment

The authors experimentally demonstrate a modulating retro-reflector based on electro-optical in-phase quadrature modulator and test it in an atmospheric cell simulated atmosphere environment by using 80 Gb/s polarisation-multiplexing quadrature phase-shift keying (Pol-MUX QPSK) signals. At the BER of 1 × 10 -3 , the power penalties of the x - and y -polarisation signals are both <;1.1 dB when the temperature difference in the atmospheric cell is <;250°C.

Differential drive I/Q modulator based on silicon photonic electro-absorption modulators

We demonstrate up to 100 Gbaud quadrature-amplitude modulated (QAM) signal generation with monolithic silicon in-phase quadrature (I/Q)-modulator based on silicon-germanium (SiGe) electro-absorption modulators (EAM). The modulator is in a differentially driven Mach–Zehnder (MZ) interferometric configuration similar to the conventional MZ modulator (MZM) based (I/Q) modulators. In particular, single-polarization quadrature phase-shift keying (SP-QPSK) signaling at symbol rates of 100 Gbaud with BERs below the hard-decision forward error correction (FEC) limit is shown. SP-QPSK optical signal generation and transmission over 80 km single-mode fiber (SMF) are demonstrated at symbol rates of 50 Gbaud with BER of less than $\mathbf {10^{-5}}$ . The effect of the frequency roll-off used for Nyquist pulse shaping with raised cosine frequency response is studied for SP-QPSK 50 Gbaud signals. Furthermore, 16QAM signals at symbol rates of 50 Gbaud are generated.

Numerical simulation and experimental demonstration of accurate machine learning aided IQ time-skew and power-imbalance identification for coherent transmitters.

A novel method assisted by feed-forward artificial neural network model for joint identification of in-phase/quadrature (IQ) time-skews and power-imbalances for coherent optical transmitters is proposed in this paper. This method not only reduces the complexity of hardware design but also significantly improves the accuracy of time-skew/power-imbalance estimation, therefore largely enhances the efficiency of coherent transmitter offline calibration. The proposed method works in the heterodyne detection manner to detect both the time- and power- imperfections. A modified 2 × 2 real-valued channel equalizer for QPSK and 16-QAM signals is applied to extract the channel coefficients, which can fully reconstruct the signals. A key tool using artificial neural networks is used to establish the explicit numerical relationships between the values of IQ time-skew/power-imbalance and the channel coefficients. Both simulation and experimental tests are carried out to verify the capability of the proposed method. Simulation results show that the mean square errors (MSE) of IQ time-skew and power-imbalance estimation can reach below 0.03% of the symbol period and 5.72 × 10-5 at the optical signal-to-noise ratio value of 20 dB. Experiment tests based on 100-Gb/s and 200-Gb/s coherent optical modules show that the mean absolute errors (MAEs) of estimated IQ time-skew and power-imbalance are 0.145 ps and 0.01 for 32-GBaud QPSK signal and 0.162ps and 0.006 for 32-GBaud 16-QAM signal. A demonstrative calibration process is applied to a coherent optical module with pre-set IQ time-skew and power-imbalance by improving the Q2 factor of 32-Gbaud 16-QAM signals from 12.9 dB to 20.3 dB in a coherent optical transmission link at back-to-back case.

Multi-Scale Induction Machine Model in the Phase Domain With Constant Inner Impedance

An efficient and accurate multi-scale induction machine model for simulating diverse transients in power systems is developed and validated. Voltages, currents, and flux linkages are described through analytic signals that consist of real in-phase and imaginary quadrature components, covering only positive frequencies of the Fourier spectrum. The stator is modeled in the abc phase coordinates of an arbitrary reference frame whose rotating speed is adjusted by a simulation parameter called shift frequency. When the reference frame is stationary at a zero shift frequency, then the model processes instantaneous signals to yield natural waveforms. When the reference frame is set to rotate at the synchronous frequency of the electric network, then the Fourier spectra of the analytic signals are shifted by this synchronous frequency to become dynamic phasors that allow for efficient envelope tracking. The shift frequency can be adapted during simulation. For any rotor position and independent of the variation of the magnetizing inductances with saturation, the induction machine model appears as a Norton current source with constant inner admittance in the abc phase domain to support the integration with simulators that represent the electric network in the abc phase domain. The analysis of test cases covering diverse transients substantiates the claims made in terms of accuracy and efficiency across different time scales.

Performance of grey‐coded IQM‐based optical modulation formats on high‐speed long‐haul optical communication link

In this article the performance of grey-coded advanced optical modulation formats is evaluated on a single-channel high-speed long-haul optical communication link and are compared to the respective differential-coded modulation formats. Polarisation division multiplexed optical in-phase quadrature modulator (IQM) structure and homodyne detection scheme are used to realise 100 Gbps quadrature phase-shift keying (QPSK), 120 Gbps 16-ary quadrature amplitude modulation (16-QAM), 360 Gbps 32-QAM and 480 Gbps 64-QAM modulation formats. Advanced digital signal processing unit with various pre-processing and recovery stages such as direct current blocking, normalisation, low-pass Bessel filter, resampling, quadrature imbalance compensation, chromatic dispersion compensation, non-linear compensation, timing recovery, adaptive equalisation, down-sampling, frequency offset estimation, and carrier phase estimation is used at the receiving end to compensate for signal impairments during propagation. Maximum transmission distances of 7200, 1050, 560, and 360 km have been achieved at an acceptable bit error rate for QPSK, 16-QAM, 32-QAM, and 64-QAM, respectively. The grey-coded systems outperformed the differential-coded systems regarding optical signal-to-noise ratio requirement, receiver sensitivity, and transmission distance.