Phase Noise In Systems Research Articles

Single-step phase identification and phase locking for coherent beam combination using deep learning

Coherent beam combination offers a solution to the challenges associated with the power handling capacity of individual fibres, however, the combined intensity profile strongly depends on the relative phase of each fibre. Optimal combination necessitates precise control over the phase of each fibre channel, however, determining the required phase compensations is challenging because phase information is typically not available. Additionally, the presence of continuously varying phase noise in fibre laser systems means that a single-step and high-speed correction process is required. In this work, we use a spatial light modulator to demonstrate coherent combination in a seven-beam system. Deep learning is used to identify the relative phase offsets for each beam directly from the combined intensity pattern, allowing real-time correction. Furthermore, we demonstrate that the deep learning agent can calculate the phase corrections needed to achieve user-specified target intensity profiles thus simultaneously achieving both beam combination and beam shaping.

Analysis of phase noise for DFT-spread OFDM systems in coherent optical communication

Previous studies have revealed the similarity between phase noise in the symbol domain of discrete Fourier transform spread (DFT-Spread) coherent orthogonal frequency division multiplexing (CO-OFDM) systems and that in the time domain. This paper further details this characteristic through both formulas and simulation results, while also analyzing and summarizing its formation conditions and influencing factors. Based on this, a phase noise compensation (PNC) scheme based on DFT-Spread OFDM is proposed for high-order quadrature amplitude modulation (QAM) transmission with large fast Fourier transform (FFT) sizes. The proposed scheme effectively suppresses inter-carrier interference (ICI) introduced by phase noise in OFDM systems, as verified through simulations of dual-polarization (DP) 64-QAM CO-OFDM transmission over 80 km single-mode fiber (SMF). This work suggests that proposed PNC scheme enhance the tolerance for laser linewidth in OFDM systems, and may offer a possible solution for short distance high-baud-rate high-order QAM coherent transmission.

Low-noise microwave generation with an air-gap optical reference cavity

We demonstrate a high finesse, microfabricated mirror-based, air-gap cavity with volume less than 1 ml, constructed in an array, that can support low-noise microwave generation through optical frequency division. We use the air-gap cavity in conjunction with a 10 nm bandwidth mode-locked laser to generate low phase noise 10 GHz microwaves, exhibiting a phase noise of −95 and −142 dBc/Hz at 100 Hz and 10 kHz offset frequencies, respectively. This is accomplished using the 2-point lock optical frequency division method, where we exploit 40 dB common-mode rejection of two lasers separated by 1.29 THz and locked to the same air-gap cavity. If used with an octave spanning comb, the air-gap cavity is capable of supporting 10 GHz phase noise below −160 dBc/Hz at 10 kHz offset, a level significantly lower than electronic synthesizers. These results show how extremely small optical reference cavities, operated without the benefit of vacuum enclosures or thermal insulation, can, nonetheless, support state-of-the-art microwave phase noise in compact and portable systems.

Phase noise analysis of mutually synchronized spin Hall nano-oscillators

The reduction in phase noise in electronic systems is of utmost importance in modern communication and signal processing applications and requires an understanding of the underlying physical processes. Here, we systematically study the phase noise in mutually synchronized chains of nano-constriction spin Hall nano-oscillators (SHNOs). We find that longer chains have improved phase noise figures at low offset frequencies (1/f noise), where chains of two and ten mutually synchronized SHNOs have 2.8 and 6.2 dB lower phase noise than single SHNOs. This is close to the theoretical values of 3 and 10 dB, and the deviation is ascribed to process variations between nano-constrictions. However, at higher offset frequencies (thermal noise), the phase noise unexpectedly increases with chain length, which we ascribe to process variations, a higher operating temperature in the long chains at the same drive current and phase delays in the coupling between nano-constrictions.

Pattern search and compressed sensing based phase noise and channel estimation for mmWave massive MIMO-OFDM systems

Phase noise (PN) can seriously affect the performance of millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems, especially when orthogonal frequency division multiplexing (OFDM) is employed. This paper studies the PN effect on mmWave massive MIMO-OFDM systems, and proposes a time variant training mode to save training time. In addition, an iterative channel and PN estimation method is proposed, which can estimate the PN with pattern search and estimate the channel with compressed sensing, and can converge according to the residual of the received signal. Moreover, the error vector magnitude and the computational complexity are analyzed. Finally, our simulation results demonstrate that by employing the proposed method, the performance of the mmWave massive MIMO-OFDM system can be improved.

Optical phase-locked loop phase noise in 5G mm-wave OFDM ARoF systems

The use of millimeter-wave (mm-wave) frequencies is required in order to support the increasing number of connected devices expected from the fifth generation (5G) of mobile communications. Subsequently, the generation of radio-frequency (RF) carriers ranging from 10GHz to 300GHz and their transport through optical distribution network (ODN) is a key element of the future 5G fronthaul. Optically assisted RF carrier generation is one of the most promising solutions to tackle this issue, allowing a wide use of analog radio-over-fiber (ARoF) architectures. However the main limitation of these optical methods is related to the finite coherence of lasers sources, which can dramatically degrade data transmission in analog formats. To mitigate its impact, the use of orthogonal frequency-division multiplexing (OFDM) as the 5G standard allows employing efficient phase noise compensation algorithms. Therefore, in this study, we present an experimental demonstration of a mm-wave generation technique based on an optical phase-locked loop (OPLL) that fulfills the frequency specifications for 5G. Then, an algorithm is introduced that improves data recovery at reception and reduces the impact of a possible high phase noise carrier. Finally, a back-to-back data transmission experiment is performed, demonstrating the efficiency of the algorithm to reach the 5G requirements. These results emphasize the use of OPLLs as a viable solution to generate mm-wave carriers for 5G and beyond.

Enhancement of Accuracy of mm-Wave Vital Sign Radar Using Polar Cross Correlation and Low-Noise mm-Wave Frequency Synthesizer

The accuracy of a radar for sensing vital signs is generally affected by system noise, including the phase noise of the frequency synthesizer and the intermodulation of the vital sign signals. System noise becomes particularly serious when vital sign radars operate in the millimeter wave (mm-wave) band because the phase noise performance of mm-wave frequency synthesizers is generally inferior to that of microwave frequency synthesizers. To address the problem of system noise, a polar cross-correlation function (CCF) and a low-noise mm-wave frequency synthesizer were developed. The polar CCF can suppress both the intermodulation of vital sign signals and the phase noise of the radar system. The low-noise mm-wave frequency synthesizer further reduces the system phase noise by injection- and frequency-locked loop (IFLL) and loop bandwidth (BW) optimization. Experiments demonstrated that the proposed IFLL and loop BW optimization reduce the phase noise of a 24 GHz vital sign radar by more than 28 dB within the loop BW. The proposed polar CCF can further reduce the noise floor and intermodulation of the detected vital sign signals by 24 dB and 17 dB, respectively. These noise reductions reduced the standard deviation (SD) of the sensed respiration rate (RR) and heart rate (HR) by more than half, making the implemented 24 GHz vital signs radar system more reliable and accurate.

A high sensitivity and strong stability miniaturized optically-pumped magnetometer

In this paper, we focus on the phase noise in optically-pumped magnetometer systems and investigate its sources, and use dual-phase lock-in technique to solve the problem. The results show that the phase noise is maximum when the system operates under zero-magnetic-field condition, and the main source comes from the environment stray magnetic field. The dual-phase lock-in technique improves the phase noise rejection by a factor of 10 compared to the single-phase lock-in technique. The sensitivity of the system is 22 fT Hz−1/2 and the bandwidth is 158 Hz, which offers a favorable outlook for use in clinical settings.

Effect of erbium-doped fiber amplifier loss compensation on 5G new radio millimeter-wave seamless transmission over analog fiber and free space optical fronthaul at 60 GHz

We demonstrate a fifth generation (5G) new radio (NR) signal transmitted by an analog optical and seamless antenna wireless connection at the frequency band of 60 GHz to exploit a high-frequency unlicensed frequency range. An optical frequency doubling technique, using two Mach–Zehnder modulators operating in a carrier suppressed and linear regime, respectively, was adopted to obtain the desired millimeter wave frequency at the photodetector’s output. The proposed system was tested with the 5G NR signals with a maximum bandwidth of 200 MHz and 64 quadrature amplitude modulation format. It was shown that the signal transmitted through the optical fiber and free space optical link with 1 m long seamless antenna transmission at 62 GHz was capable of meeting the signal quality requirements in terms of error vector magnitude. Moreover, the system phase noise performance showed an almost negligible difference between the various system configurations.

Compensation of The Nonlinear Impairments in All-Optical OFDM Systems Based on The Optical Phase Conjugation (OPC) Module

This study presents a nonlinearity mitigation technique for achieving high performance in the All-Optical Orthogonal Frequency Division Multiplexing (AO-OFDM) transmission systems. Therefore, the Optical Phase Conjugation (OPC) technique has been employed for mitigating the Nonlinear Phase Noise (NLPN) in the AO-OFDM transmission systems. The NLPN has been mitigated in the AO-OFDM transmission system by utilizing the proposed OPC at the middle point of the transmission link. The proposed system is numerically simulated by Virtual Photonics Integrated (VPI) Transmission Maker 9.0 at a symbol rate of 25 Gsymbol/s. During the simulation, 29 subcarriers were generated by Optical Frequency Comb Generator (OFCG) and modulated by 4-array Quadrature Amplitude Modulator (4-QAM). The generated signals are transmitted over 580 km fiber link and received by the coherent receiver. The transmission link contains 4 spans before and 4 spans after OPC module. Each span comprises the Standard Single-Mode Fiber (SSMF) and an EDFA (noise figure = 6 dB) to compensate for the fiber loss. The length of each span is fixed at 70 km in the system simulation. In addition, a 20 km Dispersion Compensation Fiber (DCF) has been used just before the OPC module to compensate for accumulated fiber dispersion. The Signal-to-Noise Ratio (SNR) and Error Vector Magnitude (EVM) have been used to certify the feasibility of the proposed technique. The results reveal that by employing the proposed OPC module, the SNR is improved by ~3.4 dB, and the EVMs are substantially reduced.

Mitigation of nonlinear phase noise in single-channel coherent 16-QAM systems employing logistic regression

We propose and analyze a classifier based on logistic regression (LR) to mitigate the impact of nonlinear phase noise (NPN) caused by Kerr-induced self-phase-modulation in digital coherent systems with single-channel unrepeated links. Simulation results reveal that the proposed approach reduces the bit error ratio (BER) in a 100-km-long 16 quadrature amplitude modulation (16-QAM) system operating at 56-Gbps. Thus, the BER is reduced from 6.88 × 10−4 when using maximum likelihood to 4.27 × 10−4 after applying the LR-based classification, representing an increase of 0.36 dB in the effective Q-factor. This performance enhancement is achieved with only 624 operations per symbol, which can be easily parallelized into 16 lines of 39 operations.

A System Phase Noise Model for Frequency-Modulated MEMS Gyroscopes

A system phase noise model is proposed in this paper for frequency-modulated (FM) gyroscopes, which gives us a clearly guidance for different noise and how to improve the final performance. The author here introduces a mathematical calculation method to deal with the time domain noise and transforms the time-varying noise into phase modulation paths to analyze the frequency noise effect. Meanwhile, the proposed model reveals the relationships about mechanical vibration noise mechanical additional loop noise and performance indicators. In this way, combing frequency spectrum and Allan variance curves, the weight of each noise can be determined. Here, we get different physical noise sources from actual circuit chip by the proposed phase noise decomposition method and analyze the whole noise contribution. After that, we can clearly understand the performance indicators required to design the circuit. Finally, this work offers a whole theory instructions to quantitate different frequency noise for FM gyroscopes.

Mitigating Channel Aging and Phase Noise in Millimeter Wave MIMO Systems

We consider non-stationary and time-varying millimeter wave (mmWave) communication systems subjected to phase noise at both transmitter and receiver. Our aim is to compensate for practical imperfections in high-mobility scenarios, such as vehicle-to-everything (V2X). To this end, an analytical expression of the mean square error (MSE) performance of the data transmission in mmWave communication systems is derived, taking into account both phase noise disturbance and time-varying effects modeled via a first-order auto-regressive (AR) model. Building on the latter result, a convergent minimum mean square error (MMSE) beamforming algorithm is then proposed, which is shown via simulations to outperform state-of-the-art beamforming methods designed to optimize MMSE as well as rate-maximization design criteria.

Joint Channel and Phase Noise Estimation and Data Detection for GFDM

Generalized frequency division multiplexing (GFDM), an enabler of beyond-5G wireless networks, can be critically impaired due to radio frequency (RF) phase noise. However, joint channel estimation and phase noise compensation for GFDM systems have not been addressed before. Hence, we tackle this problem. To this end, we propose an iterative algorithm for joint channel and phase noise estimation and two algorithms for joint data detection and phase noise compensation. These algorithms use linear and non-linear least-squares (NLS) methods and employ block-type and comb-type pilots. The complexity of these algorithms is also analyzed. Moreover, to reduce their complexity, interpolation techniques are deployed to decrease the number of unknowns. We also analyze the signal-to-interference-plus noise ratio (SINR) and sum-rate of GFDM contaminated with phase noise. Furthermore, the accuracy of the channel and phase noise estimates is established via Cramer-Rao lower bounds (CRLBs). The simulation results illustrate that the mean-squared error (MSE) performance of the proposed joint channel and phase noise estimator reaches the CRLB. Moreover, the proposed joint data symbol detection and phase noise compensation algorithms nearly eliminate the impacts of phase noise in GFDM systems.

Analysis and Compensation of Phase Noise in Mm-Wave OFDM ARoF Systems for Beyond 5G

Fifth-generation mobile networks (5G) are the solution for the demanding mobile traffic requirements, providing technologies that fulfill the requisites of different type of services. The utilization of the millimeter-wave (mm-wave) band is the straightforward technique to achieve high bit rates. Moreover, analog radio-over-fiber (ARoF) brings outstanding benefits such as low cost, low power consumption, and high spectral efficiency, among others. Thereby, mm-wave ARoF is a strong candidate to pave the way for common public radio interface (CPRI) in the fronthaul for the future 5G architecture. As orthogonal frequency-division multiplexing (OFDM) is the adopted waveform in the 5G standard, it should be also utilized in mm-wave ARoF systems for 5G. However, phase noise is one of the most degrading factors in mm-wave OFDM ARoF systems. Therefore, in this work, an analysis of the phase noise is carried out through an experimental setup up. The configuration of this setup enables to gradually modify the final phase noise level of the system. Furthermore, an original and novel algorithm to compensate the phase noise in OFDM receivers is proposed. The performance of this algorithm is experimentally evaluated through the setup for different phase noise levels and different subcarrier spacings. The obtained results show the effectiveness of the proposed algorithm under those conditions, highlighting the viability of mm-wave OFDM ARoF for 5G and beyond.

28 GHz balanced pHEMT VCO with low phase noise and high output power performance for 5G mm-Wave systems

This paper presents the study and design of a balanced voltage controlled oscillator VCO for 5G wireless communication systems. This circuit is designed in monolithic microwave integrated circuit (MMIC) technology using PH15 process from UMS foundry. The VCO ensures an adequate tuning range by a single-ended pHEMT varactors configuration. The simulation results show that this circuit delivers a sinusoidal signal of output power around 9 dBm with a second harmonic rejection between 25.87 and 33.83 dB, the oscillation frequency varies between 26.46 and 28.90 GHz, the phase noise is -113.155 and -133.167 dBc/Hz respectively at 1 MHz and 10 MHz offset and the Figure of Merit is -181.06 dBc/Hz. The power consumed by the VCO is 122 mW. The oscillator layout with bias and RF output pads occupies an area of 0.515 mm2.

Downlink Compressive Channel Estimation With Phase Noise in Massive MIMO Systems

Phase noise (PN) introduced by the oscillator at the base station and user side severely degrades the channel estimation performance. This paper investigates the impact of PN on downlink compressive channel estimation in massive multiple-input multiple-output (MIMO) systems. Particularly, the downlink compressive channel estimation with PN is modeled as a sparse signal recovery problem with additive correlated perturbation on the pilot matrix, which is a general formulation for both non-synchronous and synchronous PN. Based on this signal model, the performance of the equivalent sensing matrix is analyzed by invoking restricted isometry property (RIP) in compressive sensing. In addition, the upper bound for $l_{1}$ -minimization based channel estimation method and tight channel estimation bound are derived in the framework of RIP and Oracle least square methodology, respectively. Finally, we propose a PN-aware sparse Bayesian learning (PNA-SBL) algorithm to improve the channel estimation performance in the presence of synchronous PN. Simulation results demonstrate our analysis and superiority of the proposed PNA-SBL algorithm.

A low-jitter clock multiplier using a simple low-power ECDLL with extra settled delays in VCDL

This paper investigated the improved voltage-controlled delay line (VCDL) suitable for edge-combining delay-locked loops and multiplying delay-locked loops (MDLLs). One of the most important factors in jitter production is to increase the number of delay cells. By generating more delays in each stage of VCDL, further delays with a certain coefficient are produced in each delay cell stage, which are suitable for MDLLs. This can reduce the output jitter and power consumption of the proposed structure. An improved frequency multiplication is used to multiply the generated frequencies, which reduces the occupied area and power consumption in comparison to conventional ECDLL. Since the phase-noise of VCDL is affected by the noise of control voltage, the noise transfer functions of control voltage will be transferred to the ECDLL output. Reducing noise from the delay cell can help reduce the overall system phase noise. Post-layout simulations with TSMC 0.13 μm technology are performed using CMOS technology in the frequency range of 8 MHz to 1 GHz, and the RMS jitter is 1.06 ps at a frequency of 1 GHz. Reduction in the number of delay cells and use of low-power 50% duty cycle corrector can cause low output jitter and reduce power consumption. The overall power consumption of the system is 3.01 mW at a frequency of 1 GHz in the fast-locking situation with 1.2 V power supply, which demonstrates improvement in the results compared to previous related works.

Photonic-assisted single system for microwave frequency and phase noise measurement

We propose a photonic-assisted single system for measuring the frequency and phase noise of microwave signals in a large spectral range. Both the frequency and phase noise to be measured are extracted from the phase difference between the signal under testing and its replica delayed by a span of fiber and a variable optical delay line (VODL). The system calibration, frequency measurement, and phase noise measurement are performed by adjusting the VODL at different working modes. Accurate frequency and phase noise measurement for microwave signals in a large frequency range from 5 to 50 GHz is experimentally demonstrated.

Simplified ML-Based Carrier Frequency Offset and Phase Noise Estimation for CO-OFDM Systems

The coherent optical orthogonal frequency division multiplexing (CO-OFDM) has become prominent among emerging telecommunication techniques and applications. However, carrier frequency offset (CFO) and laser phase noise adversely impact and degrade the performance of the CO-OFDM systems. In this paper, a simplified maximum-likelihood (ML) approach, which eliminates the need for the exhaustive search associated with traditional ML methods, is derived and utilized for the estimation of CFO and laser phase noise in CO-OFDM systems. Furthermore, to obtain an improved performance, the proposed simplified low-complexity ML estimator is uniquely combined with an efficient data-dependent pilot-aided (DD-PA) technique, for the acquisition of both the CFO and the laser phase noise. The performance of the simplified ML-based estimators is compared with existing methods and verified in a 16-ary quadrature amplitude modulation (16-QAM) CO-OFDM system with polarization mode dispersion (PMD), chromatic dispersion (CD) and other polarization dependent losses (PDLs) along the fiber link.