Phase Noise Cancellation Research Articles

Improving FM Radar Dynamic Range Using Target Phase Noise Cancellation

A method for improving the dynamic range of frequency-modulated continuous-wave (FMCW) radar systems is presented. Bright echo signals detected with FMCW radars can carry strong phase noise sidelobes, especially for radars at W-band and higher frequencies where extremely quiet local oscillators do not exist or are not practical. These sidelobes can hide targets that would otherwise be detectable by the radar. Owing to the mathematical symmetry of phase noise with respect to a dominant carrier tone, the phase noise on the negative-frequency side of a bright echo can be used in post-processing to coherently cancel the corresponding phase noise on the positive-frequency side, revealing the presence of any weak target on the positive-frequency side. We show experimentally how this procedure improves the dynamic range of an airborne 167 GHz cloud radar by up to 18 dB, albeit with a detection sensitivity penalty of about 3 dB.

All-passive multiple-place optical phase noise cancellation

We report on the realization of delivering coherent optical frequency to multiple places based on passive phase noise cancellation over a bus topology fiber network. This technique mitigates any active servo controller on the main fiber link and at arbitrary access places as opposed to the conventional technique, in which an active phase compensation circuit has to be adopted to stabilize the main fiber link. Although the residual fiber phase noise power spectral density in the proposed technique turns out to be a factor of seven higher than that of in the conventional multiple-access technique when the access place is close to the end of the fiber link, it could largely suppress the phase noise introduced by the servo bumps, improve the response speed and phase recovery time, and minimize hardware overhead in systems with many stations and connections without the need for active servo circuits including phase discriminators and active compensators. The proposed technique could considerably simplify future efforts to make precise optical frequency signals available to many users, as required by some large-scale science experiments.

High-frequency broadband laser phase noise cancellation using a delay line.

Laser phase noise remains a limiting factor in many experimental settings, including metrology, time-keeping, as well as quantum optics. Hitherto this issue was addressed at low frequencies ranging from well below 1 Hz to maximally 100 kHz. However, a wide range of experiments, such as, e.g., those involving nanomechanical membrane resonators, are highly sensitive to noise at higher frequencies in the range of 100 kHz to 10 MHz, such as nanomechanical membrane resonators. Here we employ a fiber-loop delay line interferometer optimized to cancel laser phase noise at frequencies around 1.5 MHz. We achieve noise reduction in 300 kHz-wide bands with a peak reduction of more than 10 dB at desired frequencies, reaching phase noise of less than -160 dB(rad2/Hz) with a Ti:Al2O3 laser. These results provide a convenient noise reduction technique to achieve deep ground-state cooling of mechanical motion.

Design and analysis of full duplex RoF system with efficient phase noise cancellation from a coherent RoF system

Abstract A energy efficient and high throughput bi directional radio over fiber (RoF) system is designed and analysed. In order to preserve the phase and the magnitude of the transmitted signals, coherent detection (CD) is employed and hence an optical local oscillator (OLO) source is used. A full duplex system is designed by utilising the same OLO. The phase noise in CD system is logically cancelled using digital signal processing techniques. 10 Gb/s 16-QAM at 5.5 GHz, 10 Gb/s 2-QAM at 2.5 GHz , 5 Gb/s QPSK at 5.5 Ghz and 10 Gb/s 4-QAM at 7.5 GHz are transmitted simultaneously over 25 km optical fiber(OF). It is analysed that any coherent RoF system can be designed to a full duplex system with acceptable log(BER) and error vector magnitude(EVM) values. The minimum values of log(BER) values obtained for 16-QAM, QPSK, 2-QAM and 4-QAM are −10, −8, −16 and −22, respectively.

A simplified coherent-detected radio-over-fiber link with intensity and phase modulation and simple digital phase noise cancellation

Reducing the complexity and the cost is the key to introducing high-performance coherent technologies into practical radio-over-fiber (RoF) links. In this paper, we propose a coherent-detected RoF link with low-complexity optical configuration and a light digital signal processing (DSP) unit. Based on a dual-parallel Mach–Zehnder modulator (DP-MZM) at the transmitter, the amplitude and phase of a light wave are modulated to achieve spectral-efficient use of the optical source. After transmission over a single optical fiber, the modulated signals are coherent-detected at the receiver by being interfered with an independent local oscillator laser and then are demodulated digitally. Compared with other two-optical-source coherent-detected RoF links, our proposed scheme can accomplish dual-channel RF signal transmission albeit with halved optical configuration. Additionally, the DSP algorithm to get rid of the laser phase fluctuation between two lasers is simple and efficient. An experimental demonstration is done. Two 16-QAM microwave vector signals at the same symbol rate of 50 Msymbol/s are transmitted over 25-km single mode fiber (SMF) and the error vector magnitudes (EVMs) of 3.15% and 3.53% are obtained respectively. To explore its potential, two 64-QAM microwave vector signals are transported with similar conditions and the measured EVMs are 4.05% and 5.88%, respectively.

Joint Cancellation of Phase Noise and NB-IoT Interference in OFDM System

In the scenario of the coexistence of long term evolution (LTE) system using orthogonal frequency division multiplexing (OFDM) and narrowband Internet-of-Things (NB-IoT), when the in-band model is used, the narrowband interference caused by NB-IoT will seriously degrade the performance of OFDM. Meanwhile, the phase noise (PHN) generated by the local oscillators also reduce the reliability of OFDM transmission. In this letter, an algorithm of jointly eliminating NB-IoT interference and PHN is proposed within the sparse Bayesian learning framework for OFDM system, when the channel noise follows non-Gaussian distribution. An iterative solution is derived after the optimization structure is constructed. Simulation results demonstrate that the gain of proposed method over the conventional methods is approximately 1.5-3.5 dB when the bit error rate is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .

Experimental demonstration of time-delay interferometry with optical frequency comb

Heterodyne laser phase measurements in the Laser Interferometer Space Antenna (LISA) are degraded by the phase fluctuations of the onboard clocks, resulting in unacceptable sensitivity performance levels of the interferometric data. The current scheme for cancellation of the clock phase noise requires 1 GHz modulation of the ranging laser beams and additional interspacecraft clock recovery heterodyne phase measurements. Here, we report experimental results for an alternative approach to clock noise cancellation based on modified second generation time-delay interferometry (TDI) with optical frequency combs (OFCs). The use of OFCs in the LISA scheme allows simultaneous cancellation of both laser and clock noises, and would eliminate the need for 1 GHz laser modulations and associated demodulation detections. Two Mach-Zehnder interferometers with acousto-optic modulators were used to simulate two LISA arms with Doppler shifts and time delays. With a self-referenced OFC locked to the laser providing the clock signal, we achieve simultaneous suppression of laser and clock noises by 7 and 1.5 orders of magnitudes, respectively, down to the setup noise floor. Based on a numerical analysis, we further show that the noise suppression performance of the OFC-based TDI scheme can meet the LISA mission requirements with an ample margin.

A Calibration-Free Ring-Oscillator PLL With Gain Tracking Achieving 9% Jitter Variation Over PVT

This paper presents a calibration-free and low-jitter phase-locked loop (PLL) with small performance degradation over PVT. We introduce an open-loop discrete-time phase noise cancellation (OPDTPNC) technique to achieve a wideband filtering and circuit inner-gain-tracking for PVT stabilization. The OPDTPNC is an effective phase realignment that enables a filtering bandwidth ~1/4 of the reference clock frequency. Besides, with the common structures and PVT tracking bias for sampler and corrector of the OPDTPNC, the prototype PLL maintains its low jitter under a wide range of PVT variations. Eventually, by cascading a Type-II PLL with the OPDTPNC, the proposed hybrid PLL attains the benefits of both Type-II PLL and injection-locked clock multiplier (ILCM). Fabricated in 28-nm CMOS with an active area of 0.023mm2 it consumes 4.1 mV from a 1 V supply with a reference spur of -63 dBc. The measured rms jitter of the 2.4 GHz PLL is 248 fs and 686 fs with and without OPDTPNC, respectively. When the temperature, supply and loop gain vary from 0 to 100°C, ±5%, and 6dB, respectively, the jitter performance only degrades less than 9%.

Passive optical phase noise cancellation.

We report on the realization of an optical phase noise cancellation technique by passively embedding the optical phase noise information into a radio frequency signal and creating a copy of the optical frequency signal, which is pre-corrected by the amount of phase noise introduced by optical phase perturbations. Neither phase discrimination nor an active servo controller is required due to the open-loop design, mitigating some technical problems, such as the limited compensation speed and finite phase/timing jitter, in conventional phase noise cancellation. We experimentally demonstrate that this technique maintains the same delay-limited bandwidth and phase noise suppression capability as in conventional techniques, but significantly shortens the response speed and phase recovery time. Passive decoupling optical phase perturbation represents a powerful technique in the domains of optical frequency standard comparisons and tools for future optical atomic clocks, which are now under investigation for a potential redefinition of the International Time Scale.

Passive Optical Phase Stabilization on a Ring Fiber Network

Optical frequency transfer provides the means for high-fidelity frequency transfer across thousands of kilometers. A critical step in the further developing optical frequency transfer is its capability to transfer a high spectral purity feature from ultrastable lasers or optical clocks to any remote locations and, at the same time, its adaptability to incorporate the optical frequency transfer technique into any existing communication networks with different topologies. Here we for the first time report a technique that delivers optical-frequency signals to multiple independent remote hubs along a ring optical-fiber network with passive phase stabilization. The technique automatically corrects optical-fiber length fluctuations of arbitrary hubs along the loop by mixing and shifting optical signals. Without the help of an active phase tracker and a compensator, it could significantly mitigate some technical problems such as the limited compensation speed and phase recovery time, the phase jitter contamination caused by the servo bump in conventional phase noise cancellation. Moreover, by transmitting optical signals along both directions using the same optical source, it can improve the signal-to-noise ratio at each hub. This technique maintains the same delay-limited phase noise correction capability as in conventional techniques and, furthermore, improves the phase jitter by a factor of 3, opening a way to a broad distribution of an ultrastable frequency reference with high spectral purity and enabling a wide range of applications beyond metrology over a ring fiber network with the naturally impressive reliability and scalability.

Performance Analysis of Phase Noise Cancellation by Asymmetric CMA for Realizing Affordable Coherent PON Transceivers

We investigate the performance of a phase noise cancellation proposal to overcome the inherent laser linewidth limitation that acts as a key limiting factor in realizing digital signal processing (DSP)-based optical coherent access systems. The proposed cancellation algorithm is evaluated and analyzed through both extensive simulations and experimental studies on coherent 20-Gbit/s quadrature phase-shift keying (QPSK) signals. The use of polarization control based on the constant modulus algorithm (CMA) eliminates the polarization interference, which is a primary factor impacting the cancellation of random phase noise. A unique polarization control scheme with asymmetric CMA is proposed in order to remove the singularity issue created by the standard CMA. Its performance is verified in simulations and experiments. Through experiments that emulate laser linewidth by a phase modulator, it is confirmed that the cancellation algorithm overcomes the inherent limitation on laser linewidth.

Multi-node optical frequency dissemination with post automatic phase correction

We report a technique for coherence transfer of laser light through a fiber link, where the optical phase noise induced by environmental perturbation via the fiber link is compensated by remote users with passive phase noise correction, rather than at the input as is conventional. Neither phase discrimination nor active phase tracking is required due to the open-loop design, mitigating some technical problems such as the limited compensation speed and the finite compensation precision as conventional active phase noise cancellation. We theoretically analyze and experimentally demonstrate that the delay effect introduced residual fiber phase noise after noise compensation is a factor of 7 higher than the conventional techniques. Using this technique, we demonstrate the transfer laser light through a 145-km-long, lab-based spooled fiber. After being compensated, the relative frequency instability in terms of overlapping Allan deviation is 1.9E-15 at 1s averaging time and scales down 5.3E-19 at 10,000 s averaging time. The frequency uncertainty of the light after transferring through the fiber relative to that of the input light is -0.36+-2.6E-18. As the transmitted optical signal remains unaltered until it reaches the remote sites, it can be transmitted simultaneously to multiple remote sites on an arbitrarily complex fiber network, paving a way to develop a multi-node optical frequency dissemination system with post automatic phase noise correction for a number of end users.

Phase Noise Cancellation in Coherent Communication Systems Using a Radio Frequency Pilot Tone

Long-haul optical fiber communication employing digital signal processing (DSP)-based dispersion compensation can be distorted by the phenomenon of equalization-enhanced phase noise (EEPN), due to the reciprocities between the dispersion compensation unit and the local oscillator (LO) laser phase noise (LPN). The impact of EEPN scales increases with the increase of the fiber dispersion, laser linewidths, symbol rates, signal bandwidths, and the order of modulation formats. In this work, the phase noise cancellation (PNC) employing a radio frequency (RF) pilot tone in coherent optical transmission systems has been investigated. A 28-Gsym/s QPSK optical transmission system with a significant EEPN has been implemented, where the carrier phase recovery (CPR) was realized using the one-tap normalized least-mean-square (NLMS) estimation and the differential phase detection (DPD), respectively. It is shown that the RF pilot tone can entirely eliminate the LPN and efficiently suppress the EEPN when it is applied prior to the CPR.

RF pilot tone phase noise cancellation based on DD-MZM SSB modulation for optical heterodyne RoF link

The optical heterodyne radio over fiber (RoF) link using single-sideband (SSB) modulation has advantage in system scalability, tunability, as well as resistance to chromatic dispersion induced frequency selective fading. However, the phase noise which seriously degrades system performance, is a major obstacle to employ low-cost free-running lasers in the aforementioned link. In this paper, the RF pilot tone (RFP) phase noise cancellation (PNC) based on dual drive Mach–Zehnder modulator SSB modulation for optical heterodyne RoF link is investigated and demonstrated. Two kinds of RFP PNC schemes, carrier whole multiplication (CWM) and carrier signal multiplication (CSM), are both derived theoretically and verified experimentally. The impacts of carrier signal power ratio, carrier filter bandwidth and guard band on system performance are studied in detail. The results show that, the RFP-CSM scheme can improve the spectral efficiency by 62.5% and receiver sensitivity of 1.2 dB for 1.25 Gbps quadrature phase shift keying signal at a BER of 3.8 ×10−3, as compared with the RFP-CWM scheme and power detection scheme, mainly attributed to the absence of the second-order nonlinear intermodulation distortion. Furthermore, the RFP-CSM scheme demonstrates good phase noise robustness with different high-order modulation formats under two kinds of linewidth local oscillator lasers.

A Compact X-Band Vector Network Analyzer for Microwave Image Sensing

This paper develops a compact and portable X-band vector network analyzer (VNA) for the low-cost microwave image sensing applications. Since significant local oscillator (LO) injection pulling and poor LO phase noise performance may reduce the accuracy of measurement, the developed VNA uses the single-conversion technique and the phase noise cancellation technique to suppress the injection pulling effect and the LO phase noise, respectively. A hybrid phase detection algorithm that includes arctangent, arcsine, and arccosine functions is proposed to overcome the bottleneck of the distortion of conventional quadrature phase detection in some phase regions. The experimental results demonstrate that the X-band microwave image sensing system that uses the developed VNA, which is highly compact and portable, can effectively yield a contour image of bones in a chicken wing and pork ribs.

Phase Noise Cancelation Based on Polarization Modulation for Massive MIMO-OFDM Systems

In massive multiple-input multiple-output (MIMO) systems, phase noise introduced by oscillators can cause severe performance loss. It leads to common phase error and intercarrier interference in massive MIMO-OFDM uplink. To solve the issue, a novel phase noise cancelation scheme based on polarization modulation for the massive MIMO-OFDM system is proposed. We first introduce the polarization modulation (PM) exploited in massive MIMO-OFDM uplink. Then, by exploiting the zero-forcing detection, we analyze the asymptotically ICI and the distribution of the transformed noise under different XPD values. Furthermore, we demonstrate that phase noise can be asymptotically canceled and only the transformed additive white Gaussian noise exists as the number of antennas at the base station is very large. Moreover, we derive the instantaneous signal-to-noise ratio (SNR) on each subcarrier and analyze the ergodic capacity. To increase the ergodic capacity performance further, a joint modulation scheme combining the PM and 2PSK is proposed and the ergodic capacity performance of the joint modulation is discussed. The simulation results show that the proposed scheme can effectively mitigate phase noise and achieve a higher ergodic capacity.

SPM and phase-noise cancellation using time-division-multiplexed and intensity-modulated pilot symbols

SPM and phase-noise cancellation using time-division-multiplexed and intensity-modulated pilot symbols

A constant loop bandwidth in delta sigma fractional-N PLL frequency synthesizer with phase noise cancellation

This work presents the design of a new and unique design technique of constant loop bandwidth and phase-noise cancellation in a wideband ΔΣ fractional-N PLL frequency synthesizer. Phase noise performance of the proposed ΔΣ fractional-N PLL frequency synthesizer has been verified using CppSim simulator with the help of transistor level simulation results in Cadence SpecctreRF. Transient response of the proposed ΔΣ fractional-N PLL has been verified in transistor level simulation using Cadence SpectreRF in 0.13 μm standard CMOS process. The proposed phase-noise cancellation and constant loop bandwidth in wideband ΔΣ fractional-N PLL reduces the out of band phase noise by 18 dBc/Hz at 2 MHz offset frequency for a closed loop bandwidth of 1 MHz, when ICP,max is equal to 2.6 mA. PLL locking time has been reduced with phase-noise cancellation and a constant loop bandwidth calibration circuits using the proposed CP unit current cell for the mismatch compensated PFD/DAC in wideband ΔΣ fractional-N PLL frequency synthesizer. Optimum phase noise performance can be achieved with the help of proposed design technique. Proposed ΔΣ fractional-N PLL frequency synthesizer is locked within 14.0 μs with an automatic frequency control circuit of the LC VCO and a constant loop bandwidth calibration circuit through the use of proposed CP unit current cell for the mismatch compensated PFD/DAC for the phase-noise cancellation in worst case condition of KVFC = 10 and KLBC = 150. Our new design technique can be extensively integrated for wideband fractional-N PLL for new type of wireless communication paradigm using the thinnest channel subharmonic transistor and low power devices, and it has the potential to open a new era of fractional-N PLLs for wideband application.

Coherent full duplex radio over fiber system with multiple signal transmission

AbstractIn this paper, a cost‐effective and simple full duplex RoF (radio over fiber) system is developed from a simplex coherent RoF. At the transmitter, utilizing the magnitude and phase of the vector carrier, four different information are encoded simultaneously on the carrier light wave. Dividing the total carrier power into two branches, enable the transmitter to modulate two distinct information on each branch. The working of the system is described in two main sections namely uplink section and downlink section. In the first section, encoding of uplink transmitting information and decoding downlink information at the central office (CO) is described. In the second section, modulating downlink transmitting information and demodulating coherently the uplink receiving information at the base station (BS) are described. An algorithm based on fast Fourier transform is described for effectively canceling the phase noise (PN) at the BS. Considering the cost of optical components, the source used to coherently detect the uplinked transmitted information, is again used as the carrier for downlink. Altogether, this system enables to transmit three different information on uplink and are faithfully received at the BS with an average of log(BER) value −23 dB. And for downlink, one information is transmitted and is successfully received at the CO with log(BER) of −9 dB. About 10 dB decrease in log(BER) values was found after the cancellation of PN.

Coherent phase transfer via fiber using heterodyne optical phase locking as optical amplification.

We demonstrate a coherent phase transfer via a 224km cascaded fiber link comprising two 112km links stabilized by two phase-locking loops, respectively. The optical signal is regenerated employing heterodyne optical phase locking (HOPL) after the first 112km transfer. With a gain of more than 50dB, the HOPL is capable of tracking the frequency of the incoming carrier with a fluctuation of 0.48mHz and preserving the instability of the incoming laser to 6×10-20 at 1000s. The phase noise cancellation of each span is investigated, and the out-loop transfer instability of the 224km link reaches 7.7×10-19 at 10,000s. The relation between the transfer instability of each span and that of the whole link is also deduced in the paper, in agreement with experimental results of the 224km link.