Reliable Multi-Path Routing Schemes for Real-Time Streaming

In off-line streaming, packet level erasure resilient Forward Error Correction (FEC) codes rely on the unrestricted buffering time at the receiver. In real-time streaming, the extremely short playback buffering time makes FEC inefficient for protecting a single path communication against long link failures. It has been shown that one alternative path added to a single path route makes packet level FEC applicable even when the buffering time is limited. Further path diversity, however, increases the number of underlying links increasing the total link failure rate, requiring from the sender possibly more FEC packets. We introduce a scalar coefficient for rating a multi-path routing topology of any complexity. It is called Redundancy Overall Requirement (ROR) and is proportional to the total number of adaptive FEC packets required for protection of the communication. With the capillary routing algorithm, introduced in this paper we build thousands of multi-path routing patterns. By computing their ROR coefficients, we show that contrary to the expectations the overall requirement in FEC codes is reduced when the further diversity of dual-path routing is achieved by the capillary routing algorithm.Comment: Emin Gabrielyan, "Reliable Multi-Path Routing Schemes for Voice over Packet Networks", ICDT'06, International Conference on Digital Telecommunications, Cote d'Azur, France, 29-31 August 2006, pp. 65-7

Induced polarization of Lambda(1116) in kaon electroproduction

We have measured. the induced polarization of the Lambda(1116) in the reaction ep - \u3e e\u27 K+ Lambda, detecting the scattered e\u27 and K+ in the final state along with the proton from the decay Lambda - \u3e p pi(-). The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy W (1.6 \u3c = W \u3c = 2.7 GeV) and covered the full range of the kaon production angle at an average momentum transfer Q(2) = 1.90 GeV2. In this experiment a 5.50-GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the W and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially Q(2) independent in our kinematic domain, suggesting that somewhere below the Q(2) covered here there must be a strong Q(2) dependence. Along with previously published photo-and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved s-channel resonances

Energy Calibration of the JLab Bremsstrahlung Tagging System

In this report, we present the energy calibration of the Hall B bremsstrahlung tagging system at the Thomas Jefferson National Accelerator Facility. The calibration was performed using a magnetic pair spectrometer. The tagged photon energy spectrum was measured in coincidence with $e^+e^-$ pairs as a function of the pair spectrometer magnetic field. Taking advantage of the internal linearity of the pair spectrometer, the energy of the tagging system was calibrated at the level of $\pm 0.1$. The absolute energy scale was determined using the $e^+e^-$ rate measurements close to the end-point of the photon spectrum. The energy variations across the full tagging range were found to be $<3$ MeV.Comment: 15 pages, 12 figure

Особенности использования статистического метода стабилизации частоты генераторов в распределенных информационно-измерительных системах

The article deals with the problems of frequency stabilization of generators in distributed information-measuring systems on the basis of the static frequency stabilization method. The examples of similar systems are given. The necessity to ensure high stability of signal frequency generated by subscribers to improve the efficiency of the stated systems is noted. Two main features of applying the static frequency stabilization method are stated. The first one is determined with a delay in signal input into the device for estimating the frequency-time signal parameters in relation to the signal phase measurement interval. The second feature involves the entry delay of the formed control signal of generator frequency correction. It is shown that the mentioned features lead to divergence of the current variation of generator frequency and the value under correction, obtained considering the delay. The description of information signals enabling to specify a mathematical model of the process of assessment forming of the information signal frequency variation, taking into account the mentioned factors, is offered. It is shown that the possibility of using a statistical method to stabilize the frequency of generators in distributed informationmeasuring systems is determined not only with the values of nominal frequencies and relative instabilities of generators included into the information-measuring system, but also by the autocorrelation function of a random process describing the change of information signal frequency. In case of small time delays between the evaluation of information signal frequency and frequency stabilization, the use of the method to be considered allows to reduce the relative instability of information signal frequency. When time delays are greater than the correlation interval, the use of the statistical method does not lead to the change of relative instability of information signal frequency. Within the correlation interval, the use of the statistical method of frequency stabilization can cause depending on the autocorrelation function values both decrease and increase of the relative information signal frequency instability.В статье рассмотрены вопросы стабилизации частоты генераторов в распределенных информационно-измерительных системах на основе использования метода статической стабилизации частоты. Приведены примеры таких систем и отмечена необходимость обеспечения высокой стабильности частоты формируемых абонентами сигналов для повышения эффективности функционирования указанных систем. Отмечены две основные особенности применения метода статистической стабилизации частоты. Первая определяется задержкой поступления сигнала в устройство оценивания частотно-временных параметров сигнала по отношению к интервалу измерения фазы сигнала. Вторая особенность связана с задержкой прихода сформированного управляющего сигнала коррекции частоты генератора. Показано, что отмеченные особенности приводят к несовпадению текущего отклонения частоты генератора и корректируемого значения, полученного с учетом задержки. Предложено описание информационных сигналов, позволяющих уточнить математическую модель процесса формирования оценки отклонения частоты информационного сигнала с учетом указанных факторов. Показано, что возможность использования статистического метода стабилизации частоты генераторов в распределенных информационно-измерительных системах определяется не только значениями номинальных частот и относительных нестабильностей генераторов, входящих в состав информационно-измерительной системы, но и автокорреляционной функцией случайного процесса, описывающего изменение частоты информационного сигнала. При малых временных задержках между оцениванием частоты информационного сигнала и стабилизацией частоты использование рассматриваемого метода позволяет уменьшить относительную нестабильность частоты информационного сигнала. При временных задержках больше интервала корреляции использование статистического метода не приводит к изменению относительной нестабильности частоты информационного сигнала. В пределах интервала корреляции использование статистического метода стабилизации частоты может приводить в зависимости от значений автокорреляционной функции как к уменьшению, так и увеличению относительной нестабильности частоты информационного сигнала

Синтез амплитудно-фазового распределения в квазикольцевой антенной решетке

Ring antenna arrays find wide application in radio systems of various purpose. However, in many cases it is necessary to use quasi-ring antenna arrays when the emitters are not located in a circle. Such a transition leads to a change in the radiation pattern, i.e. to a shift in its main maximum, an increase in the level of the side lobes, and appearance of two maxima of the radiation pattern. Therefore, to ensure the formation of a directional pattern with specified parameters, it is necessary to correct the amplitude-phase distribution of the quasi-annular antenna array. In this paper, features are considered and an algorithm for the synthesis of the amplitude-phase distribution of a quasi-annular antenna array is developed. The possibilities of preserving the parameters of the directional pattern during the transition from the ring to the quasi-annular antenna array are analyzed.Разработан алгоритм синтеза амплитудно-фазового распределения квазикольцевой антенной решетки, обеспечивающий минимальное среднеквадратическое отклонение параметров формируемой диаграммы направленности этой решетки от заданных параметров диаграммы направленности кольцевой антенной решетки

Induced polarization of {\Lambda}(1116) in kaon electroproduction

We have measured the induced polarization of the ${\Lambda}(1116)$ in the reaction $ep\rightarrow e'K^+{\Lambda}$, detecting the scattered $e'$ and $K^+$ in the final state along with the proton from the decay $\Lambda\rightarrow p\pi^-$.The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy $W$ ($1.6\leq W \leq 2.7$ GeV) and covered the full range of the kaon production angle at an average momentum transfer $Q^2=1.90$ GeV$^2$.In this experiment a 5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the $W$ and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially $Q^2$ independent in our kinematic domain, suggesting that somewhere below the $Q^2$ covered here there must be a strong $Q^2$ dependence. Along with previously published photo- and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved $s$-channel resonances.Comment: 13 figure