A statistical method for obtaining the factors inelectronic-component reliability-prediction models

According to US Mil-Hdbk-217, the failure rate of most electronic components can be predicted as λ_p=λ_b×π₁ ×π₂···π_n. A statistical method of obtaining these parameters is presented. The method is based on large quantities of field data, and the more current the data are, the more accurate the values of each level of λ_b and π_i. Using these values, the models in US Mil-Hdbk-217 can be applied to predict the life of electronic products. The method can also be used to verify the present values of each level of λ_b and π_i, and to provide the basis of further amendment     

High-performance adaptive group-of-picture rate control for H.264/AVC

In this paper, an adaptive group-of-picture (AGOP) control is proposed to improve the coding performance for the H.264/AVC system. The efficient algorithm is developed to find the quantized parameter with temporal correlation between inter-frames. According to the estimated parameters, the GOP coding type can be adaptively selected as AGOP or BGOP (basic GOP). The rate control with some decision functions is proposed to modify the quantization parameter (QP). The coding rate can accurately meet the target rate with adjusting QP value dynamically, while keeping low computational overhead. Simulation results show that the proposed algorithm can improve PSNR by about 1 dB in average compared with the original H.264/AVC reference software (JM12.4), from various sequences testing.     

Throughput analysis of CDMA systems using multiuser receivers

Throughput bounds are attained for random channel access multichannel code-division multiple-access (CDMA) systems and spread slotted Aloha systems employing multiuser receivers. It is shown that the normalized throughput of these two systems reaches 1.0 exponentially fast in the region r/K<1, where, r is the average number of simultaneous users in each channel in the random channel access multichannel CDMA system and the packet arrival rate in the spread slotted Aloha system, respectively, and K is the maximum number of users which the multiuser receiver can handle at the same time. Therefore, both of the random channel access multichannel CDMA system and the spread slotted Aloha system employing multiuser receivers can achieve perfect throughput while being stable in the region r/K=1-δ, δ>0. The maximum throughput of the random channel access multichannel CDMA systems is found as K-√(1-(1/M))KlogK-O(logK), where M is the number of channels in the system. The maximum throughput is reached when the average number of simultaneous users is r_m=K-√((1-(1/M))KlogK))+O(√(K/logK)). The maximum throughput of the spread slotted Aloha systems is K-√(KlogK)-O(log K). The maximum throughput is reached when the packet arrival of Poisson distribution has the arrival rate λ_m=K-√(KlogK)+O(√(K/logK))     

基于FREM的自适应AFREM算法

设计了一种基于模糊控制技术的自适应FREM（AFREM）算法。该方案用平均队列长度和丢包比例的变化速率作为拥塞指示,对FREM算法输出的丢弃概率进行动态调整。仿真分析结果表明在动态环境下AFREM算法也能有效地将队列长度钳制到固定TQL值附近,改善了FREM算法的控制性能。     

Pressure-dependent Sellmeier coefficients and material dispersionsfor silica fiber glass

The pressure-dependent Sellmeier coefficients are essential to characterize the optical design parameters for the optical fiber communication systems under deep sea environmental conditions. These coefficients are calculated for densified silica glass for the first time to compute the pressure dependence of material dispersion at any wavelength from the ultraviolet (UV) to 1.71 μm. The zero dispersion wavelength λ₀ (1.2725 μm at 0.1 10⁶ N m ^-2) varies linearly with pressure, and dλ₀/dP is 0.0027 nm/(10⁶ N m^-2). The calculated value is approximately one-third of the experimental value of 0.0076 nm/(10⁶ N m^-2) for a germanium-doped dispersion shifted fiber having λ₀=1.5484 μm and -0.0070 nm/(10⁶ N m^-2) for a pure silica-core fiber cable having λ₀ =1.2860 μm. Since, the refractive indexes are increased with pressure, the negative value of shift of the zero-dispersion wavelength is erroneous. The explanations are due to Ge-doping in silica glass, a possible temperature fluctuation of 0.16°C in the pressure-dependent measurement system of the zero dispersion wavelength and different experimental conditions of the silica glass and the optical fibers. This anomaly can also be attributed to the internal strain development at the core-cladding and fiber-jacketing boundaries due to pressure, which shows a larger experimental value. It accounts for the experimental values satisfactorily     

基于模糊-PID控制沥青骨料称量系统算法的仿真研究

骨料称量系统称是沥青拌舍设备的重要组成部分,称量过程由于动态落差和给料不均匀等因素的影响,常规的PID已经不能保证系统的称量精度。文中提出了一种基于模糊控制的自适应PID控制方法,并在MATLAB,simulink中建了仿真模型。仿真结果表明,系统采用模糊-PID控制算法具有更好的动态特性,增加了系统适应外界干扰的能力,提高了称量精度。     

Adaptive batching scheme for multicast video-on-demand systems

In this paper, an adaptive algorithm is developed for providing true video on demand (VoD) services in a multicast environment. In conventional batching schemes, the batching time of the system is fixed and the performance of such static schemes is highly dependent on the selection of the batching time. If the batching time is wrongly estimated, the performance of the system will be greatly degraded. Our algorithm tries to dynamically find the optimal batching time by the newly updated arrival rate so as to minimize the bandwidth requirement. The results show that the system performance of the adaptive approach is always better than the static scheme in terms of total bandwidth requirement and customer reneging probability, especially in using long batching time for the high arrival rate     

Toward prediction of physiological state signals in sleep apnea

A recurrent connectionist model is described to predict dynamic respiratory state in the apneic sleeping patient. The time-domain model of nonlinear time-lagged interactions between heart rate, respiration, and oxygen saturation was developed to implicitly embed the dynamics of the respiration and cardiovascular control systems. Multiple future time scales were enforced on the network during training to explore the limits of the prediction horizon and produce a global representation of dynamic state trajectory. Predicted apneic respiration state results are presented in terms of invariant geometric statistics (largest Lyapunov exponent λ_L and correlation dimension D_c). The λ_L prediction error was 13%, while D_c error was within 9% of the true time series value. The magnitude of these errors may fall within experimental noise levels. This methodology may eventually be useful in dynamic control of continuous positive airway pressure (CPAP) therapy devices, and may lead to increased patient compliance with this therapy     

Merged Sagnac-Michelson interferometer for distributed disturbancedetection

An interferometric technique is described to detect and locate perturbations along an optical fiber. This distributed sensor has a position dependent response to time-varying disturbances such as strain or temperature. These disturbances cause a phase shift which is detected and converted to spatial information, The sensor consists of a Sagnac interferometer merged with a Michelson interferometer. This is achieved by a frequency selective mirror in the center of the Sagnac-loop. The sensor is illuminated by two light sources with wavelengths λ₁ and λ₂, respectively. The mirror reflects λ₁ and transmits λ₂, causing the interferometer to operate as a Michelson at wavelength λ₁ and as a Sagnac at wavelength λ₂. Any time-varying perturbation on, the fiber will, result in a signal at λ₂ proportional to the product of the rate of phase change caused by the perturbation and the distance of the perturbation relative to the position of the mirror. The output of the Michelson interferometer at wavelength λ₁ is proportional to the phase change caused by the unknown perturbation. By dividing the output of the Sagnac interferometer by the time rate of change of the Michelson interferometer signal, the position of the disturbance relative to the mirror is located. Results obtained with a 200 m-distributed fiber sensor are discussed     

A cause of self‐similarity in TCP traffic

We analyse the statistical properties of aggregated traffic flows generated by TCP, in order to clarify a possible cause of self‐similarity in Internet traffic. Using ns‐2 simulation, we first show that aggregated traffic flows by TCP can be characterized by phase transition phenomena between non‐congested and congested phases in statistical physics. Interestingly, although the traffic exhibits self‐similarity with the Hurst parameter H ≈ 1.0 at the critical point between them, it is close to Poissonian away from the critical point. This result is consistent with results from real WAN traffic measurement. The main contribution of our work is to show that TCP itself contains a mechanism for generating self‐similarity, without assuming self‐similarity or long‐range dependency (LRD) in the application layer (e.g. packet inter‐arrival, connection arrival, and file size distribution). Moreover, we find that the value of the Hurst parameter at the critical point is determined by the simple feedback control called stop‐and‐wait flow control. Namely, it appears even without any packet retransmission events and is independent of the explicit rate increment algorithm such as slow‐start and congestion avoidance. Additionally, we demonstrate that the value of the Hurst parameter at the critical point depends on the constant bit rate algorithm and topology of network. Finally, we indicate that the time series of the round trip time follow the same statistics at the critical state. Copyright © 2005 John Wiley & Sons, Ltd.     

New converses in the theory of identification via channels

New converses for identification via arbitrary single-user and multiple-access channels, with finite first- and second-type probabilities of error, are developed. For the arbitrary single-user channel, it is shown that (λ₁, λ₂)-identification capacity is upper-bounded by λ-capacity, and optimistic (λ₁,λ₂ )-identification capacity is upper-bounded by optimistic λ-capacity, for any λ>λ₁+λ₂. The bounds become tight at the limit of the vanishing probabilities of error, thus generalizing previous results by Han and Verdu (1992), who showed that the identification capacity is equal to transmission capacity for channels satisfying the strong converse of the channel coding theorem. A by-product of the new identification converses is a general formula for optimistic λ-capacity. An outer bound on the (λ₁, λ₂)-identification capacity region of an arbitrary multiple-access channel is developed. A consequence of this bound is that the identification capacity region is equal to the transmission capacity region for any stationary, finite-memory multiple-access channel. The key tool in proving these bounds is the partial resolvability of a channel, a new notion in resolvability theory, which deals with approximation of the output statistics on a suitably chosen part of the output alphabet. This notion of approximation enables us to get sharp bounds on identification for arbitrary channels, and to extend these bounds to the multiple-access channel     

A curved spiral antenna above a conducting cylinder

A curved spiral antenna above a finite hollow conducting cylinder is analyzed using the method of moments. The effects of cylinder length 2H and cylinder radius r_cy on the radiation characteristics of the spiral are evaluated. As 2H increases, the cross-polarization component of the radiation field in the broadside direction decreases to a constant value (approximately -18 dB). When 2H is greater than one wavelength (λ₀), the input impedance of the spiral above a cylinder of radius r_cy=0.25 λ₀ is almost constant (250-j20 Ω) with a gain of approximately 7 dB. The spiral above a cylinder of (2H, r_cy)=(2.7 λ₀, 0.25 λ₀) shows a 3-dB axial ratio bandwidth of approximately 23%, which is wider than a flat spiral antenna above a flat ground plane of infinite extent     

Distributed slot synchronization (DSS): a network-wide slotsynchronization technique for packet-switched optical networks

Distributed slot synchronization (DSS) is a network-wide packet synchronization technique which coordinates node transmissions so that packets arrive aligned to one another at a reference point in the network, independent of propagation delays. DSS was developed for use in the contention resolution with delay-lines (CORD) project, a DARPA-funded 2.5 Gb/s/λ, wavelength division multiplexer (WDM) optical packet-switched network testbed. In this implementation, it was experimentally demonstrated that the DSS system, operating with 80 MHz control logic, achieves a packet arrival jitter of less than 13 ns with 12 km node spacings. DSS was also shown to be robust against noise and node failure or fiber breaks. The technique is data rate and format independent and can be used in other star, extended ring, or tree-and-branch network architectures for metropolitan area network (MAN) and access applications     

Self-phase modulation and dispersion in high data rate fiber-optictransmission systems

The theoretical transmission limits imposed by the interaction of first- and second-order group velocity dispersion and intensity-dependent self-phase modulation (SPM) effects for a range of wavelengths around the zero dispersion wavelength (λ₀) for fibers in which polarization dispersion is negligible are investigated. It is found that increasing the peak input power to 30 mW reduces the transmission distance for data rates greater than 50 Gb/s, if operating at wavelengths shorter than λ₀. Operating at wavelengths longer than λ₀ improves the performance due to the cancellation of first-order dispersion by self-phase modulation. For example, at 50 Gb/s and 30 mW peak input power, the maximum transmission distance is 255 and 162 km, if operating at wavelengths 1 nm longer or shorter than λ₀, respectively. Above 100 Gb/s, higher-order dispersion limits the transmission distance even at wavelengths equal to, or longer than, λ₀. Linear dispersion compensation using a grating-telescope combination can significantly improve system performance for wavelengths where first-order dispersion dominates     

Dependence of Ti-diffused Er:LiNbO3 laser efficiency onwaveguide fabrication parameters and pump wavelength

The mode size, effective pump area, and coupling efficiency as function of initial Ti-stripe width W, diffusion temperature T, and initial Ti-stripe thickness H in c-cut Ti-diffused Er:LiNbO₃ waveguide laser have been studied theoretically, taking into account optical pumping λ_p=1.477 μm and 0.98 μm. The main features of the mode sizes in terms of these diffusion parameters were collected and, as compared with the experimental results, a qualitative agreement has been achieved. The effective pump areas exhibit both significant initial Ti-stripe width and diffusion temperature dependence, especially for W>9 μm and T>1050°C, whereas the initial Ti-stripe thickness can hardly give influence when pumping with λ_p=0.98 μm radiation. On the other hand, coupling efficiency is approximately unchanged with values 0.76-0.78 for λ_p=1.477 μm and 0.8-0.85 for λ _p=0.98 μm, indicating that there are no optimized values of these parameters to increase slope efficiency through coupling efficiency. Moreover, the 0.98 μm pumping reveal lower threshold and higher coupling efficiency than 1.477-μm pumping. Finally, the appropriate waveguide fabrication parameters were proposed for the fabrication of a more efficient laser     

Design of a special family of optical CDMA address codes for fullyasynchronous data communications

A special family of optical address codes, called strict optical orthogonal codes (OOCs), is proposed for fiber-optic code-division multiple access (FO-CDMA) networks. Such codes can strictly guarantee both crosscorrelation and autocorrelation constraints (i.e., λ _c and λ_a) to be one in fully asynchronous data communications and ultrafast switching. Theory of strict OOCs is presented and the code design is described by using the concepts of slot distances. Moreover, the use of strict OOCs can support variable-rate and multirate data communications in an FO-CDMA network with no violation of λ_c=λ_a=1 and no increase of system complexity compared to using conventional OOCs     

Optimal probability-of-error thresholds and performance for twoversions of the sign detector

Expressions are obtained for specifying the optimal error probability (minimum P_e) thresholds λ₀₁ and λ₀₂ for the traditional and modified sign detectors, respectively. These thresholds are shown to depend on the parameters p, P₁, and M where: M is the number of observations z_i used in the test statistic; P₁=P(H₁ ) is the prior probability for hypothesis H₁ that signal s₁ is present and 1-P₁ =P(H₀) corresponds to the hypothesis H₀ that signal s₀ is present; and p=Pr{z_i⩾0|H₁} with s₀=0 for the traditional sign detector and p=Pr{z_i⩾λ|H₁ }=Pr{z_i<λ|H₀} with λ =(s₀+s₁)/2 for the modified sign detector. The expressions for λ₀₁ and λ₀₂, are given explicitly, and shown to be independent of P₁ for sufficiently large M. Optimal P_e versus M performance curves, corresponding to both versions of the sign detector, are obtained for a representative range of values for p and P₁     

Proposal for a novel wiggler

A magnetostatic-field configuration that is independent of the axial (z) coordinate is presented. The motion of an electron in the xz plane in this magnetostatic field is determined. The velocities and the orbit of the electron are identical to those in the ordinary FEL (free electron laser) but with other expressions for the parameters ω₀ and a_ω. An expression for the wavelength of the radiation of the fundamental harmonic (λ_s) is derived. Some numeric examples of λ_s and a_ω are given, and it is concluded that the method presented is promising for obtaining high values of a_ω     

Temperature-dependent Sellmeier coefficients and chromaticdispersions for some optical fiber glasses

Temperature-dependent Sellmeier coefficients are necessary to optimize optical design parameters of the optical fiber transmission system. These coefficients are calculated for fused silica (SiO₂ ), aluminosilicate, and Vycor glasses for the first time to find the temperature dependence of chromatic dispersion at any wavelength from UV to 1.7 μm. The zero dispersion wavelength λ₀ (1.273 μm for SiO₂, 1.393 μm for aluminosilicate, and 1.265 μm for Vycor glasses at 26°C) varies linearly with temperature, and dλ₀/dT is 0.03 nm/K for aluminosilicate and Vycor glasses, whereas for SiO₂ it is 0.025 nm/K. This study interprets the recently observed experimental value of dλ₀/dT for two dispersion shifted optical fibers; and the dominantly material origin of dλ₀/dT is confirmed here as a fundamental property of the optical fiber glasses