RF Signal Frequency Research Articles

Duobinary modulation/predistortion techniques effects on high bit rate radio over fiber systems

<span>The work has presented duobinary modulation and predistortion techniques for the radio over fiber system enhancement for achieving security level. Duobinary modulation technique has more compact modulated spectral linewidth with standard non return to zero modulation code. Different NRZ/RZ rectangle shape employed that are namely exponential rectangle shape (ERS), and Gaussian rectangle shape (GRS) for different transmission bit rates. Switching bias voltage, and switching RF voltage based LiNbO<sub>3</sub> modulator are changed to measure the performance parameters of the radio over fiber (RoF) system. Predistortion technique improves the linearity of transmitter amplifiers and it is considered as a power efficiency technique. The optimum values of the Q-factor, data error rate (BER), electrical power, signal gain, noise figure, and light signal/noise ratio are achieved with 8 Volt for both switching biases/switching RF signal at 100 GHz. Signal quality/BER and electrical power after the receiver enhancement ratio by using this technique at different RF signal frequencies. </span>

Performance Analysis of Modulation Formats for Next Generation RoF Systems

Radio over fiber (RoF) has found to be one of the most effective communication techniques. It has the tendency to incorporate both optical fiber and free space radio paths. In this research article, importance, benefits, and applications of RoF system are discussed in detail for futuristic networks. The performance of RoF system is visualized by modulating the data with the RF signal having same frequency at both transmitter and receiver ends. Initially, the performance is checked using non-return to zero (NRZ) format and later compared with duobinary (DB) and carrier suppressed return to zero (CSRZ). Various simulations are performed which directly affect the system performance. Important parameters such as RoF link distance, data rate, transmitter power, amplifier gain, and RF signal frequency are tested. The operation is carried out at 1550 nm wavelength and 30 GHz RF frequency. System is optimized to receive the transmitted waveforms successfully. Simulations are performed in Optisystem 17.0 and MATLAB. For the analysis, the results are plotted using Q-factor and BER values.

Effects of different mobile phone UMTS signals on DNA, apoptosis and oxidative stress in human lymphocytes

Different scientific reports suggested link between exposure to radiofrequency radiation (RF) from mobile communications and induction of reactive oxygen species (ROS) and DNA damage while other studies have not found such a link. However, the available studies are not directly comparable because they were performed at different parameters of exposure, including carrier frequency of RF signal, which was shown to be a critical for appearance of the RF effects. For the first time, we comparatively analyzed genotoxic effects of UMTS signals at different frequency channels used by 3G mobile phones (1923, 1947.47, and 1977 MHz). Genotoxicity was examined in human lymphocytes exposed to RF for 1 h and 3 h using complimentary endpoints such as induction of ROS by imaging flow cytometry, DNA damage by alkaline comet assay, mutations in TP53 gene by RSM assay, preleukemic fusion genes (PFG) by RT-qPCR, and apoptosis by flow cytometry. No effects of RF exposure on ROS, apoptosis, PFG, and mutations in TP53 gene were revealed regardless the UMTS frequency while inhibition of a bulk RNA expression was found. On the other hand, we found relatively small but statistically significant induction of DNA damage in dependence on UMTS frequency channel with maximal effect at 1977.0 MHz. Our data support a notion that each specific signal used in mobile communication should be tested in specially designed experiments to rule out that prolonged exposure to RF from mobile communication would induce genotoxic effects and affect the health of human population.

Real-Time RF Multi-Dimensional Signal Switching Using Polarization-Dependent Optical Mixing

Real-time switching of RF signal properties, including phase, frequency, and amplitude, is essential for emerging high-speed RF systems to improve security, signal fidelity, and enhance data capacity. While it is easy to switch the amplitude of an RF signal at GHz speed, unfortunately, it is extremely challenging to perform phase or frequency switching of an RF signal with a fast switching time in the picosecond range. In this paper, a real-time RF signal switching technique is proposed and demonstrated based on polarization dependent four-wave mixing in a highly-nonlinear optical fiber. Due to the amplitude, phase, and frequency transparent property of four-wave mixing, the proposed scheme is capable of manipulating multidimensional RF signal of over tens of GHz frequency, and achieve frequency hopping and phase switching of a GHz RF signal. The switching time is not limited by the proposed temporal switching technique; instead, it is solely depending on the rise/fall time of the control signal itself. Furthermore, the generation of frequency hopping signal with a switching time of 50 ps, as well as simultaneously frequency and phase switching of a GHz RF signal have been experimentally demonstrated based on the proposed RF signal switching scheme.

Cooperative communications with optimal harvesting duration for Nakagamifading channels

In this paper, we analyze the throughput of cooperative communications with wireless energy harvesting. Relay nodes harvest energy from Radio Frequency RF signal transmitted by the source. We derive the packet error probability as well as the throughput for Nakagami fading channels. We also suggest to enhance the throughput by choosing the value of harvesting duration. Our results are valid for both Amplify and Forward AF and Decode and Forward DF relaying.

Linearized microwave photonic link based on dual-driven Mach–Zehnder modulator

A highly linearized microwave photonic link (MPL) based on a dual-drive Mach–Zehnder modulator (DDMZM) is proposed. Eliminating or suppressing these nonlinear distortions is achieved by adjusting the polarization of the light and the frequency of the radio frequency (rf) signal as well as controlling the dc bias voltage of DDMZMs. The proposed technique is verified by the simulation test of two-tone and three-tone. Theoretical analysis and simulation experiments show that under the two-tone condition, when the modulation depth is

Microwave photonic RF front-end for co-frequency co-time full duplex 5G communication with integrated RF signal self-interference cancellation, optoelectronic oscillator and frequency down-conversion.

A novel RF front-end, which could simultaneously realize wideband RF signal self-interference cancellation (SIC), local oscillator (LO) generator based on optoelectronic oscillator (OEO) and frequency down-conversion has been proposed and experimentally demonstrated. In our microwave photonic RF front-end, only one single-polarization optical in-phase and quadrature-phase (IQ) modulator are required. The upper Mach-Zehnder modulator (MZM) of this optical IQ modulator works as a mixer; the lower MZM works as a reference arm; the parent Mach-Zehnder interferometer (MZI) is used to combine two output optical signals of these two child MZMs. In this way, not only self-interference signal is cancelled in optical domain but also frequency down-conversion is realized at the same time. On the other hand, the upper MZM is also shared to form an OEO by using a self-polarization-stabilization technique. By this means, no external LO signal for frequency down-conversion and electrical attenuator for SIC are needed in our scheme, contributing to compact structure and cost reduction. In our proof-of-concept experiment, a LO signal with central frequency of 10 GHz and phase noise of -108.66 dBc/Hz@10kHz is generated. By optimizing the bias points of the used optical IQ modulator, a 5×20MHz 64-ary quadrature amplitude modulation-orthogonal frequency division multiplexing (64QAM-OFDM) LTE-A signal with central frequency of 12.6 GHz is down-converted to 2.6 GHz, and about 28 dB cancellation ratio is achieved. The proposed scheme is suitable for wideband, integrated co-frequency co-time full duplex 5G communication.

Longitudinal phase-space diagnostics using a stripline-type beam-timing monitor at the KEKB injector linac

Abstract A new beam-timing monitor (BTM) has been developed to analyze the longitudinal beam dynamics and bunching characteristics at the pre-injector of the KEKB injector linear accelerator (linac). The BTM is a conventional stripline-type beam monitor with two pickup electrodes. It measures the relative time delay between the arrival time of the beam signal and 1st-zero-cross time of the fundamental accelerating radio frequency (rf) signal (2856 MHz) immediately after the detection of the beam signal. The beam tests were performed to evaluate the performance and characteristics of the BTM for primary single-bunched electron beams with high bunch charges of ∼ 8 nC for positron production. It was found that the results show that the resolution in the delay-time measurement is σ ∼ 1.2 ps in one standard deviation. This report describes the basic design of the BTM system, the beam tests, and results in detail, to investigate the sensitivity and stability of the beam timing based on the longitudinal phase-space parameters at the pre-injector and location A1 of the injector linac, along with the calibration method in the pulse-height variation of the BTM signal.

Brillouin-Assisted Notch Filtering Based All-Optical Image Rejection Mixer

A novel approach for realizing a microwave photonic image rejection mixer is presented in this paper. It is based on using a widely tunable narrow-band optical notch filter implemented by stimulated Brillouin scattering (SBS) to remove the image signal. The image rejection mixer has a simple structure as it only requires a single integrated dual-polarization modulator for both frequency conversion and pump wave generation for the SBS process. The absence of electrical components enables the image rejection mixer to be operated over a wide frequency range with a high image rejection ratio. A technique is also proposed to suppress the noise generated by the SBS process in the image rejection mixer. Experimental results demonstrate a high and constant image rejection ratio of over 32 dB for the image rejection mixer operating over an RF signal frequency range of 11.8–19.6 GHz, and around −5 dB conversion efficiency.

Cascaded modulator topology for frequency conversion in antenna remoting applications.

A new cascaded modulator structure that has the ability to realize high conversion efficiency microwave frequency downconversion, while at the same time able to overcome two fundamental limitations in the dual-parallel modulator approach, is presented. It is based on utilizing the polarization-dependent modulation efficiency property in LiNbO3 electro-optic modulators. The new structure allows the modulators for the RF signal and local oscillator (LO) modulation to be placed in different locations suitable for antenna remoting applications, and it has infinite isolation between the LO and RF signal ports. We present experimental results demonstrating that the proposed structure can be used to realize high conversion efficiency frequency downconversion over wide RF and intermediate frequency (IF) signal frequency ranges as the reported dual-parallel-modulator-based microwave photonic frequency downconverter. Very high isolation of more than 70dB between the LO and RF signal ports is also demonstrated.

Broadband high dynamic range fiber optic link based on a dual-polarization modulator.

This paper presents a simple, linearized fiber-optic link that is capable of realizing a high spurious free dynamic range (SFDR) at different input RF signal frequencies without the need of readjusting system parameters. The link is based on a commercial dual-polarization modulator followed by a linear polarizer. The third-order nonlinearity at the third-order intermodulation distortion frequency can be cancelled by designing the angle of the linear polarizer. No electrical component is involved in the linearization process. The high SFDR performance is theoretically analyzed, simulated using photonic simulation software, and experimentally verified. Experimental verification of the dual-polarization modulator-based linearized fiber-optic link shows that a high SFDR of more than 124 dB⋅Hz4/5 is obtained at different input RF signal frequencies over a 2-18 GHz bandwidth. An SFDR of 127.3 dB⋅Hz4/5 is also demonstrated with the use of an optical amplifier to increase the link output average optical power, which is among the highest reported SFDRs measured in a fiber-optic link.

Instantaneous microwave frequency measurement with high-resolution based on stimulated Brillouin scattering

A novel photonic method of instantaneous microwave frequency measurement (IMFM) based on Stimulated Brillouin scattering (SBS) is proposed. The principle of the technique is the employment of SBS effect to amplify/attenuate two adjacent frequency components, which result in a definite amplitude comparison function (ACF). Using this technique, the frequency of an unknown RF signal can be precisely obtained. Experimental results show the measurement capability of the proposed method over a frequency range of 0.47–23 GHz with a higher resolution of 8 MHz.

A single electron transistor charge sensor in strong rf fields

We measure the charge sensitivity, Se, of a single electron transistor (SET) in the presence of strong (Vrf ∼ e/Cg) spurious radio frequency (rf) signals at frequencies up to 50 MHz, where Cg is the gate capacitance. Although Se appears to degrade when exposed to Vrf, we find that broadening of conduction peaks is largely due to the measurement technique and show that Se is maintained even with strong Vrf present. We show cancellation of a known Vrf signal at 1 MHz, demonstrating that a stable bias point in the presence of rf signals is possible.

Optical Single Sideband Modulator Without Second-Order Sidebands

An optical single sideband modulator without generating both the −2nd- and +2nd-order sidebands is presented. It is based on a parallel operation of two dual-drive Mach–Zehnder modulators (DDMZMs) where one is operated as a conventional single sideband (SSB) modulator and the other is operated as a single-drive Mach–Zehnder modulator (MZM) biased at the maximum transmission point. The 2nd-order sidebands generated by the SSB modulator and the maximum-biased MZM can be cancelled by controlling the sideband amplitude and phase. Canceling the 2nd-order sidebands eliminates the second-order harmonic component presented at the output of a long-reach fiber optic link. The new SSB modulator can be implemented using standard off-the-shelf components and has a wide bandwidth. Experimental results show >20 dB 2nd-order sidebands suppression for different modulation indexes and 22.6 dB reduction in the fiber optic link output second-order harmonic component, compared to using a conventional SSB modulator formed by a DDMZM and a 90° hybrid coupler. Results also demonstrate that the performance of the new SSB modulator is insensitive to the optical carrier frequency and the input RF signal frequency.

COMPLEX ASSESSMENT OF ARTERIES STIFFNESS PARAMETERS AND TRADITIONAL RISK FACTORS AS THE PREDICTORS OF EARLY VASCULAR AGEING SYNDROME

Aim . Evaluation of structural and functional properties of arteries in healthy persons and in coronary heart disease (CHD) patients with various severity of coronary lesion, in different age groups. Material and methods . To the study, 135 patients included, with various CHD types, and 56 healthy persons at the age 35 to 65 y. o. All participants underwent laboratory testing for glucose level and lipid profile in blood. Applanation tonometry was done, and volumetric sphygmography, ultrasound scanning of common carotid arteries with the technology of high frequency RF signal. Results. All participants were selected into two cohorts: younger and older than 50 y. o., which included patients with no hemodynamically significant stenoses of coronary arteries, with significant stenosis of one artery and healthy persons. According to the results of traditional risk factors analysis, CHD patients more prevalently had tobacco addiction, arterial hypertension, as well as family anamnesis of lipid disorders. By ultrasound scanning data of common carotid arteries, the parameters of arterial stiffness predominated in patients with coronary lesions. Applanation tonometry showed that CHD patients and healthy persons had comparable levels of central arterial pressure in both age groups. In all healthy persons the carotid-femoral pulse wave velocity was within normal range, and in CHD it was higher by 10 m/s. Volumetric sphygmography showed that severity of coronary lesion correlated with the increase of vascular rigidity parameters. Conclusion. The results of current study confirm the necessity for development of novel criteria of risk assessment and prevention of cardiovascular diseases early development. Screening for predictors of early vascular ageing syndrome will make it to identify persons with low relative but high absolute risk of coronary events.

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Photonic Generation of Triangular-shaped Waveform Based on External Modulation

We present a novel approach for triangular-shaped waveform generation by applying optical single sideband (OSSB) modulation and optical carrier suppression (OCS) modulation to an input signal. Firstly, an OSSB modulated signal consists of an optical carrier and +1st-order sideband, is initially generated with a dual-drive Mach-Zehnder modulator (DD-MZM1) driven by a quadruple frequency RF signal. By tuning the amplitude of the RF signal and the bias of the DD-MZM1, the power ratio between the carrier and the +1st-order sideband is controlled as 19 dB. These two components are then transmitted to a DD-MZM2 which is driven by a fundamental frequency. After OCS modulation, four sidebands are existed in optical spectra of the modulated signal. By utilizing a fiber Bragg grating (FBG) to remove the undesired sideband, an output signal that features a triangular-shaped waveform is finally achieved.

A Novel Hybrid-Channel Attenuation Measurement System at 50–110 GHz

A novel hybrid-channel attenuation measurement system has been built for the measurement of $V$ - and $W$ -band waveguide attenuators from 50 to 110 GHz. The measurement system combines two single channels of the $V$ and $W$ bands together into one system. The $V$ -band channel is used as the measurement channel and the $W$ -band channel is used as the synchronization channel when the $V$ -band attenuator is measured and vice versa. The measurement system is free of cross talk between the two channels and removes the need for isolators between the local oscillator and the mixer since the RF signal frequencies in the two channels are different. In addition, a compensation module was designed to cancel the self-mixing produced by the $W$ -band mixer at frequencies above 102 GHz. The expanded uncertainty of the system is evaluated to be 0.004–0.08 dB at frequencies $\le 102$ GHz and 0.005–0.11 dB at frequencies $>102$ GHz for an attenuation range from 0 to 80 dB.

Beam-induced wakefield observation inX-band choke-mode cavities

The $X$-band choke-mode structure is currently being studied as an alternative design for the accelerating structure of the compact linear collider (CLIC) main linac. The geometry of the choke-mode structure is designed to ensure the strong suppression of the beam-induced long-range transverse wakefield and therefore maintain the stability and quality of the beam in the CLIC main linac. Experiments conducted at the Argonne Wakefield Accelerator Facility are presented in this study to verify the design of the wakefield suppressor. The beam-induced radio frequency (rf) signals in a three-cell choke-mode structure were measured, and measured results show good agreement with the simulation results. The measured results also show strong damping in high-order dipolar modes with a quality factor $Q$ of 10 to 20. The difference between the frequencies of the first and second dipole modes is about 3 GHz, which validates the special design of the cancelling dipole modes at the time of the succeeding bunch (0.5 ns).

Improving Radio Energy Harvesting in Robots Using Mobility Diversity

In this paper, we propose a new technique that exploits a robot's (intelligently) controlled mobility to maximize stored radio energy. In particular, we examine a scenario where the mobile robot takes a break from its normal activity for a duration of T s. This “dead time” consists of three phases-searching, positioning, and resting-which ensure that the robot can optimize its energy harvesting from a base station transmitting a narrowband RF signal over a flat-fading wireless channel. We utilize the mobility diversity principle, which arises due to the spatial wireless channel diversity experienced by motion of the robot. By optimal exploitation of the small scale fading, we maximize the net amount of energy (i.e., the energy harvested by the robot minus the mechanical energy used for motion) that the robot stores over the “dead time”. To the best of the authors' knowledge, this paper is the first use of the mobility diversity principle to optimize energy harvesting from an RF signal. We demonstrate that mobility, if intelligently controlled, is actually not a foe but is indeed a friend that can provide significant benefits under wireless fading channels. Through simulations, we verify the analytical results and illustrate the improvement in the energy stored compared with not using intelligent mobility. Finally, we show that the efficiency of our approach is clearly coupled with various design parameters, including the center frequency of the narrowband RF signal and the duration of the “dead time”.