Statistical analysis of fiber-optic CDMA communication systems. I. Device modeling

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs).     

On optimal nonlinear feedback regulation of linear plants

A design technique for optimal nonlinear regulation of linear plants, based on a homogeneous feedback law of degree2p - 1 (p > frac{1}{2}), is developed.     

A new and accurate fault location algorithm for combined transmission lines using Adaptive Network-Based Fuzzy Inference System

This paper presents a new and accurate algorithm for locating faults in a combined overhead transmission line with underground power cable using Adaptive Network-Based Fuzzy Inference System (ANFIS). The proposed method uses 10 ANFIS networks and consists of 3 stages, including fault type classification, faulty section detection and exact fault location. In the first part, an ANFIS is used to determine the fault type, applying four inputs, i.e., fundamental component of three phase currents and zero sequence current. Another ANFIS network is used to detect the faulty section, whether the fault is on the overhead line or on the underground cable. Other eight ANFIS networks are utilized to pinpoint the faults (two for each fault type). Four inputs, i.e., the dc component of the current, fundamental frequency of the voltage and current and the angle between them, are used to train the neuro-fuzzy inference systems in order to accurately locate the faults on each part of the combined line. The proposed method is evaluated under different fault conditions such as different fault locations, different fault inception angles and different fault resistances. Simulation results confirm that the proposed method can be used as an efficient means for accurate fault location on the combined transmission lines.     

A novel low voltage very low power CMOS class AB current output stage with ultra high output current drive capability

In this paper a novel low voltage (LV) very low power (VLP) class AB current output stage (COS) with extremely high linearity and high output impedance is presented. A novel current splitting method is used to minimize the transistors gate–source voltages providing LV operation and ultra high current drive capability. High linearity and very high output impedance are achieved employing a novel resistor based current mirror avoiding conventional cascode structures to be used. The operation of the proposed COS has been verified through HSPICE simulations based on TSMC 0.18 μm CMOS technology parameters. Under supply voltage of ±0.7 V and bias current of 5 μA, it can deliver output currents as high as 14 mA with THD better than ?53 dB and extremely high output impedance of 320 MΩ while consuming only 29 μW. This makes the proposed COS to have ultra large current drive ratio (I_outmax/I_bias or the ratio of peak output current to the bias current of output branch transistors) of 2800. By increasing supply voltage to ±0.9 V, it can deliver extremely large output current of ±24 mA corresponding to 3200 current drive ratio while consuming only 42.9 μW and exhibiting high output impedance of 350 MΩ. Interestingly, the proposed COS is the first yet reported one with such extremely high output current and a THD even less than ?45 dB. Such ultra high current drive capability, high linearity and high output impedance make the proposed COS an outstanding choice for LV, VLP and high drive current mode circuits. The superiority of the proposed COS gets more significance by showing in this work that conventional COS can deliver only ±3.29 mA in equal condition. The proposed COS also exhibits high positive and negative power supply rejection ratio (PSRR+/PSRR?) of 125 dB and 130 dB, respectively. That makes it very suitable for LV, VLP mixed mode applications. The Monte Carlo simulation results are provided, which prove the outstanding robust performance of the proposed block versus process tolerances. Favorably the proposed COS resolves the major limitation of current output stages that so far has prevented designing high drive current mode circuits under low supply voltages. In brief, the deliberate combination of so many effective novel methods presents a wonderful phenomenal COS block to the world of science and engineering.     

High Gain Modified Dual-Band and Dual-Circularly Polarized Array Antenna

Wireless Personal Communications - A novel design of double-layer dual-band circularly polarized array antennas (DDCPAAs) is presented in this paper. First, a DDCP single antenna is introduced as...     

The S-transform using a new window to improve frequency and time resolutions

The S-transform presents arbitrary time series as localized invertible time–frequency spectra. This transformation improves the short-time Fourier transform and the wavelet transform by merging the multiresolution and frequency-dependent analysis properties of wavelet transform with the absolute phase retaining of Fourier transform. The generalized S-transform utilizes a combination of a Fourier transform kernel and a scalable-sliding window. The common S-transform applies a Gaussian window to provide appropriate time and frequency resolution and minimizes the product of these resolutions. However, the Gaussian S-transform is unable to obtain uniform time and frequency resolution for all frequency components. In this paper, a novel window based on the $t$ student distribution is proposed for the S-transform to achieve a more uniform resolution. Simulation results show that the S-transform with the proposed window provides in comparison with the Gaussian window a more uniform resolution for the entire time and frequency range. The result is suitable for applications such as spectrum sensing.     

Moisture susceptibility of warm mixed-reclaimed asphalt pavement containing Sasobit and Zycotherm additives

In this research, the influence of Sasobit and Zycotherm on the properties of reclaimed asphalt pavement (RAP)-warm mix asphalt (WMA) was investigated. Moisture susceptibility was evaluated applying the resilient modulus ratio, the indirect tensile strength ratio, and the fracture energy ratio. Laboratory testing results indicated that Zycotherm mixtures had more resistance to moisture damage than Sasobit WMA and hot mix asphalt (HMA) mixtures. The stiffness of mixtures increased dramatically by increasing the amount of RAP and using Sasobit exacerbated this problem.     

Prediction of hydrate equilibrium conditions using k-nearest neighbor algorithm to CO2 capture

Gas or clathrate hydrates are an important issue when they form in the oil and gas pipelines. Since the determination of the hydrate formation temperature and pressure is very difficult experimentally for every gas system and it is impossible in terms of cost and time approximately, mathematical models can be useful tools to overcome these difficulties. In this study, k-nearest neighbor model was used to predict the equilibrium conditions of hydrate formation in absorption and separation of carbon dioxide from flue gas mixture, containing carbon dioxide and nitrogen. At the training phase, temperature and composition data of nitrogen and carbon dioxide in the flue gas mixture at equilibrium conditions and the equilibrium pressures of hydrate formation were used as input and output, respectively. The error percentage less than 0.38% indicates the high accuracy of the proposed model. In this study, 80%, 85%, and 90% of the training data are examined for three numbers of nearest. For three numbers of used nearest (k = 1, k = 2 and k = 3), the value of k = 1 leads to the lowest error; so, it is selected as the best nearest in the presented model.     

Generalized carrier to interference ratio analysis for shotgun cellular systems in multiple dimensions over composite Rayleigh–Lognormal (Suzuki) fading

Telecommunication Systems - This paper analyzes the carrier-to-interference ratio (CIR) of the so-called shotgun cellular systems (SCSs) in $$\tau $$ dimensions ( $$\tau =1, 2,$$ and 3). SCSs are...