In communication system, the noise process must be known, in order to compute the system performance. The nonlinear effects act as strong perturbation in long- haul system. This perturbation effects the signal, when interact with amplitude noise, and results in random motion of the phase of the signal. Based on the perturbation theory, the variance of nonlinearphasenoise contaminated by both self- and cross-phase modulation, is derived analytically for phase-shift-keying system. Through this work, it is investigated that for longer transmission distance, 40-Gb/s systems are more sensitive to nonlinearphasenoise as compared to 50-Gb/s systems. Also, when transmitting the data through the fiber optic link, bit errors are produced due to various effects such as noise from optical amplifiers and nonlinearity occurring in fiber. On the basis of the simulation results , we have compared the bit error rate based on 8-PSK with theoretical results, and result shows that in real time approach, the bit error rate is high for the same signal to noise ratio. MATLAB software is used to validate the analytical expressions for the variance of nonlinearphasenoise.
In this paper, we proposed a novel monitoring and compensation method for joint phasenoise which included LPN and NL phase disturbance. In transmitter, a RF pilot was inserted into monitored channel, due to that it was affected by LPN and NL as same as in-band signals during transmitting. So we can extract the phase deviation of the received RF pilot in receiver and compensate the receiving signal’s phase error based on phase rotation. The theoretical analysis and experimental results were presented. It shows that the proposed method has a sig- nificant effect on compensation of joint phasenoise in 112 Gb/s PDM-4QAM system.
In optical transmission systems a great part of the research is focused on increasing the system reach and robustness . All-optical signal regeneration is auspicious techniques to achieve this extension, which can be performing with fiber nonlinearity. Optical nonlinear material is specially used for ultra-high speed performance. Power launched inside the optical fiber interacts with fiber material and due to refractive index several transmission impairments for example linear, nonlinear, scattering and etc. are produced . These interactions depend on the noise evolution of signals transmitted inside the fiber[3-4]. Practically nonlinearphasenoise is much more dominant than amplitude noise. During system design nonlinearphasenoise is dealt separately [5, 6]. Regeneration signals are based on (electronic or all-optical signal) processing both are significantly in use depends upon application. Electronic-based regeneration requires conversion of data by mean of optical-to-electrical- ]optical [7, 8]. All optical regeneration do not require any conversion O-E-O . An ideal regenerator would suppress noise in both the signal’s amplitude and phase [9, 10]. However, use of the complex optical-field gives rise to a new dominant limitation to system performance, namely nonlinearphasenoise [13-14].
In this paper, we investigate the phase-conjugated twin waves (PCTWs) technique in spatially division multiplexing (SDM) system for suppressing the nonlinearphasenoise. Furthermore, the analytical model that describes the phasenoise suppression is developed. In the proposed system, the 20 Gsymbol/s quadrature phase shift keying (QPSK) signal and its phase-conjugated copy are spatially multiplexed through two identical optical fiber channels. At receiver, they are coherently superimposed to suppress the nonlinearphasenoise and maximize the signal-to-noise ratio (SNR). The analytical results show that the phasenoise variance is extremely decreased when PCTWs technique is employed. In addition, the numerical results reveal that the proposed scheme improves SNR of received signal by more than 4.5 dB and extends the achievable transmission distance by 77.8% at bit error rate (BER) of 10 -5 .
We propose a procedure to estimate the model parameters of presented nonlinear Resistance-Capacitance (RC) and the widely used linear Resistance-Inductance-Capacitance (RIC) models of the respiratory system by Maximum Likelihood Estimator (MLE). The measurement noise is assumed to be Generalized Gaussian Distributed (GGD), and the variance and the shape factor of the measurement noise are estimated by MLE and Kurtosis method, respectively. The performance of the MLE algorithm is also demonstrated by the Cramer-Rao Lower Bound (CRLB) with artificially produced respiratory signals. Airway flow, mask pressure, and lung volume are measured from patients with Chronic Obstructive Pulmonary Disease (COPD) under the noninvasive ventilation and from healthy subjects. Simulations show that respiratory signals from healthy subjects are better represented by the RIC model compared to the nonlinear RC model. On the other hand, the Patient group respiratory signals are fitted to the nonlinear RC model with lower measurement noise variance, better converged measurement noise shape factor, and model parameter tracks. Also, it is observed that for the Patient group the shape factor of the measurement noise converges to values between 1 and 2 whereas for the Control group shape factor values are estimated in the super-Gaussian area.
The optical phase-lock demodulation technique has been utilized with the implementation of additional feedback to reference signal by phase modulation to LO signal. In this system, the receiver sensitivity is highly dependent on the costly optical sources and photo-detectors. Also, these components are responsible for the predominant noise sources i.e., phasenoise and shot noise. The input reference signals after long distance travel through optical fibre is very weak in strength and for good reception, relatively high power LO signal is modulated with it. The inevitable quantum detection shot noise and random phase generation to the phase part of Laser broadens the spectral
papers cited belong to the class of nonlinear oscillators with two or more stable steady states. In the absence of #uctuations, the system, being in one of these states, cannot pass to one of the other states without external action of some kind. In the presence of weak noise, however, the system executes small random oscillations in the vicinity of one of the steady states and, from time to time, undergoes a transition to a di!erent state. If the noise is su$ciently weak, such transitions occur only very rarely. Thus that the system remains in the vicinity of the corresponding stable state over a long period, and the probability distribution consequently has a chance to reach its stationary value. First we consider systems for which one can obtain, exactly or approximately, a single "rst-order di!erential equation with a random source describing the behavior of a certain variable z characterizing the motion of the system.
The R divider allows the input reference frequency to be divided down to produce the reference clock (CLK) for the PFD. It has a wide range of division ratio from 1 to 16383. The N divider is a 13-bit counter and has division ratios from 1 to 8191 . The PFD compares the phase and frequency of the signal from R and N divider. It produces an output control signal proportional to the phase and frequency difference between them. The on-chip registers of the synthesizer can be programmed externally by using serial peripheral interface (SPI) through writing to CLK, DATA and latch enable (LE) control of the device. The maximum allowable CLK rate of the device is 20MHz. The system is interfaced to personnel computer (PC) through 8085 µP via RS232 for writing data to the device. The synthesizer includes a 24-bit shift register where the data is clocked down on each rising edge of the signal. Initially, the data is clocked with most significant bit (MSB) and transferred from the shift register to one of the four latches available in the device on the rising edge of latch enable (LE). The destination latch is determined by the state of the two least significant bits (LSB) in the shift register. An external parallel tank circuit consisting of an inductor and a capacitor is used with the VCO to adjust the frequency. The varactor diode (MMBV609) with a parallel inductor is connected into the tank circuit to provide a voltage variable capacitance for the input of the VCO. These components have direct impact on the tuning sensitivity and PN. The quality factor (Q) of the tank circuit has direct impact on the resulting PN of the oscillator . Therefore, the Q is kept high for lower PN in the oscillator. The typical operating frequency of the VCO is 1100MHz.
Impulse noise reduction or removal is a very active research area of image processing. This paper presented a constrained optimization type of numerical algorithm for removing noise from images. The complete variation of the digital image is reduced subject to constraints involving the measurements of the noise. The parameters are imposed using Lagrange multipliers. The solution is secured using the gradient-projection method. This method uses a time dependent partial differential equation on a manifold determined by the boundary conditions. At time of zero the solution converges to a steady state condition results the de-noised image. It is very difficult to get image with normal methods this is over come by the numerical algorithm as it is simple and relatively fast. The results appear to be state-of-the-art for very noisy images. The method is asymptomatic, gives sharp edges in the image. The technique elucidate as a first step of moving each level set of the image normal to itself with velocity equal to the curvature of the level set divided by the magnitude of the direction of the image, and a second step which projects the image back onto the curtailment set.
tion impedance is required in matching the junction to the external high-frequency current so as to achieve maximum power transfer. The calculation of the impedance Z( ) of a point Josephson junction ignoring thermal noise effects has been given in many papers 共 see, e.g., Refs. 16 and 23 and references cited therein 兲 . Accounts of noise effects based on a numerical solution of the Fokker-Planck equation have been given in Ref. 24 共 see also the discussion of these results in Ref. 25 兲 . Another method of solution of this equation for a similar problem 共 a ring-laser gyroscope 兲 has been sug- gested by Cresser et al. 26 in terms of infinite continued frac- tions. Further development of this continued fraction ap- proach for the calculation of Z( ) has been given in Refs. 27 and 28. However, all the above solutions are valid only for a weak ac signal and so pertain to the linear response. The calculation of the nonlinear impedance of a Josephson junc- tion requires the evaluation of the time-dependent nonlinear response to a strong ac current, which is a much more com- plicated problem than calculating, for example, the dc current-voltage characteristics, where it is sufficient to find only a time-independent stationary solution of the Langevin 共 or the corresponding Fokker-Planck 兲 equation. The calcula- tion of the time-dependent portion of the nonlinear ac re- sponse requires therefore the application of the nonlinear- response theory, which has not yet been developed up to now 共 in contrast to well-documented linear-response theory 兲 . At- tempts to calculate the nonlinear ac response 共 mainly, the microwave resistance and reactance 兲 to the strong probing ac current have been made by many authors, mainly, by us- ing the perturbation theory, which is valid for low ac current amplitudes only, or in the noiseless limit, where the under- lying nonlinear equation of motion can be solved numeri- cally 共 see, e.g., Refs. 23, 29 and 30 and references cited therein 兲 . To our knowledge, the nonlinear ac response has PRB 62
It is important to note that in the procedure of decompo- sition, the attenuation of reflection data also is a factor of causing the mode mixing problem. The weak later part of a given attenuated signal becomes significant after the prior IMF is subtracted from the original data. Therefore, the at- tenuated signal may allocate in pieces in more than one IMF. In order to provide a certain solution for signal/noise separa- tion techniques based on the EMD method, we performed the logarithmic transform technique in this study to balance the display of data values and to increase the sensitivity of the de- composition. The advantage of doing this is that the logarith- mic transform allows displaying data of large dynamic range without introducing any artificial distortion. Conventionally, some approaches are used to deal with the data attenuation. Among them, the AGC (auto gain control) correction and the energy compensation by using a gain function are two com- mon techniques. The AGC correction is easy to apply, but the original attributes of the data will be distorted after the amplitude adjustment, and further signal analysis could be irrelevant. As for the gain correction, the true inverse Q (at- tenuating factor) filter for the data cannot be obtained without the help of a precise laboratory measurement or other joint estimates (Irving and Knight, 2003).
In , a median-based switching filter, called progressive switching median (PSM) filter, is proposed where both the impulse detector and the noise filter are applied progressively in iterative manners. But due to its iterative manner the execution time will be noticeable and it can not be used in real-time applications. In , an algorithm based on long-range correlation (LRC) is introduced. This method aims to increase the range seen by conventional methods to enhance image restoration rate. Due to the fact it looks for the most similar pixel in a long range around noisy pixel, it will be necessary that the image have the property like texture. So this method will not be able to restore all kinds of images specially where there is no similar pixel to the noise disturbed one. The simulations show that this method takes a long time to finish the filtering process together with producing a poor filtered image. In  an adaptive rank-ordered mean (AROM) filter is proposed that employs the switching scheme based on the two-stage impulse detection mechanism. The objective is to utilize the rank-conditioned median (RCM) filter [14, 15] and CWM filter  to define more general operators. In the first stage of impulse detection scheme, the RCM mechanism sees if the central sample lies outside the trimming range and how much small or big the central pixel is in comparison with other pixels that lie within the trimming range in the window. In the second stage of impulse detection scheme, the CWM mechanism with variable center weights is used to decide the values of local thresholds in the sliding window. The ultimate output is switched between the current pixel itself and the rank-ordered mean of two central ranks of the surrounding pixels in the window.
The 9.6 GHz signal from VCDRO has two same signals via the power splitter. A 9.6 GHz signal is connected to the LO terminal of mixer 3. Another 9.6 GHz signal forms a 407.3 MHz signal, then that is linked with the RF terminal of the mixer 3. The 407.3 MHz signal is generated by mixing 300 MHz signal obtained by dividing by 8-divider and 4-divider with a 107.3MHz frequency signal. The 107.3MHz filter has better performance, especially the out-of-band suppression ratio. The 107.3 MHz output of the mixer 1 is synthesized using 100 MHz and 7.3 MHz produced that 100 MHz is up-converted. The 100 MHz signals are obtained using 9.6 GHz signal via 8-divider, 3-divider and 4-divider. Figure 2 shows measurement results for the phasenoise of this 4-divider used inside the frequency synthesizer.
Furthermore, some conditions are satisﬁed in the practical MMIC VCO design in order to reduce the white frequency noise and ﬂicker frequency noise. The ﬁrst step is to put the transistor at the operating point where it provides the maximum added power. Second, one should dissipate the maximum of the power in the resonator, which is the main storage element of the circuit, to maximize its stored energy. Third, one must transfer this stored energy to the transistor controlling voltage port and output port where the Flicker frequency noise conversion into phasenoise takes place by adjusting the phase diﬀerence between the resonator voltage, on one hand, and the transistor controlling voltage and output voltage on the other hand. According to the above design condition, the MMIC VCO has been designed and fabricated, the power spectrum of which is measured by Spectrum analyzer Anritsu MS2668C and is shown in Figure 5. The phasenoise of the MMIC VCO is − 77 dBc/Hz@100 KHz.
where U(x) is an arbitrary potential that we will assume to have more than one minimum. For weak noise f(t), the system mostly performs small uctuations about one of the potential minima but, occasionally, a large uctuation occurs in which the system switches from one potential well to another. The probability P nm of a transition n ! m, where n and m are two minima, can be obtained 1]
Voltage Controlled Oscillator (VCO) employing LC-resonators plays the most crucial role in the phase-lock-loops (PLLs), clock recovery circuits, frequency synthesizers, and communication systems, and many efforts in the past have been spent to understand the design of differential VCOs. However, multiphase VCOs are also essential parts of many electronic systems. Among the multiphase VCOs, the quadrature VCO has received a lot of attention because we are used to the binary system and the QVCO is used in a homodyne transceiver and can be easily derived from two differential VCOs with a coupling network. In contrast, three-phase VCOs have received rarely attention, and they are used to study the operation principle and physical mechanism of oscillator including the phasenoise. A 3-phase VCO can be realized with 3-stage ring oscillators [1, 2] with wide tuning
In this paper, we deal with a class of neutral random nonlinear systems. The existence and uniqueness of the solution to neutral random functional nonlinear systems (NRFSs) are established. Furthermore, the criteria on noise-to-state stability in the moment of a special class of NRFSs, named neutral random delay nonlinear systems, are derived. An example is given for illustration.
There are different concepts for the generation of linear fre- quency ramps. Automatic frequency control (AFC) schemes are fully analogue ways of linearising a non-linear VCO but with a low precision. In the field of digitally assisted con- cepts the PLL linearisation is an effective method to linearise and stabilise a VCO. Especially fractional-N phase-locked- loops are excellent means to generate highly linear frequency ramps. Basically a fractional PLL is well suited to achieve both, a very good ramp linearity and a phase-noise reduction of the VCO. Unfortunately this requires a very high refer- ence frequency and a complex high-speed digital circuit that would result in a costly design.