System bandwidth and the existence of generalized shift-invariant frames

We consider the question whether, given a countable family of lattices ${({\mathrm{\Gamma }}_j)}_{j\in J}$ in a locally compact abelian group G, there exist functions ${(g_j)}_{j\in J}$ such that the resulting generalized shift-invariant system ${(g_j(??\gamma ))}_{j\in J,\gamma \in {\mathrm{\Gamma }}_j}$ is a tight frame of $L^2(G)$. This paper develops a new approach to the study of generalized shift-invariant system via almost periodic functions, based on a novel unconditional convergence property. From this theory, we derive characterizing relations for tight and dual frame generators, we introduce the system bandwidth as a measure of the total bandwidth a generalized shift-invariant system can carry, and we show that the so-called Calderón sum is uniformly bounded from below for generalized shift-invariant frames. Without the unconditional convergence property, we show, counter intuitively, that even orthonormal bases can have arbitrary small system bandwidth. Our results show that the question of existence of frame generators for a general lattice system is rather subtle and depends on analytical and algebraic properties of the lattice system.     

Calculation of the frequency response in step-index plastic optical fibers using the time-dependent power flow equation

The time-dependent power flow equation, which is reduced to its time-independent counterpart is employed to calculate frequency response and bandwidth in addition to mode coupling and mode-dependent attenuation in a step-index plastic optical fiber. The frequency response is specified as a function of distance from the input fiber end. This is compared to reported measurements. Mode-dependent attenuation and mode dispersion and coupling are known to be strong in plastic optical fibers, leading to major implications for their frequency response in data transmission systems.     

Study on some aspects of the “singer's formant” in north indian classical singing

This article deals with a spectrographic analysis of the singer's formant as occurred during singing of the vowels /a/, /i/, and /o/ in North Indian classical vocal music. The resonance balance, center frequency, and band-width are shown as a function of fundamental frequency for eight singers.Two new parameters have been defined viz. asymmetry parameter (A) and spectral energy balance (W). Their variation with fundamental frequency is shown.     

Analysis of cyclic queueing networks with parallelism and vacation

The aim of this paper is to improve the machine interference model with vacation to deal with more recent problems of the communication area. To this scope the model is extended to include parallelism in the vacation station. The underlying Markov process is analyzed and a state arrangement is found that yields an efficient matrix-analytic technique that substantially lowers down the time- and space-complexity of standard methods. A numerical example of the method effectiveness is presented, and an example of resource allocation is introduced that finds applications in the QoS management of wireless networks. The author is thankful to the anonymous referees for the improvements their comments have earned to the quality of the presentation and to the completeness of the paper. The author is thankful to Giuseppe Iazeolla, whose careful reading of the original draft of this paper led to significant improvements in its overall quality. This work was partially supported by funds from the FIRB project “Performance Evaluation of Complex Systems: Techniques Methodologies and Tools” and by the University of Roma TorVergata project on High Performance ICT Platforms.     

Generating asymptotically optimal broadcasting schedules to minimize average waiting time

The performance of a Video-on-Demand broadcasting scheme is commonly evaluated by the maximum waiting time encountered by the customer before viewing can start. This paper addresses the issue of minimizing the average waiting time. Recently, we proposed Harmonic Block Windows scheduling to specifically minimize the average waiting time for given bandwidth. Here, we present an efficient heuristic algorithm that generates asymptotically optimal Harmonic Block Windows schedules. Using simulation, we demonstrate that, as we increase the “block size”, the normalized average waiting time of these schedules approaches the theoretical minimum achievable by any “fixed start points” schedule.     

Bandwidth packing with priority classes

The bandwidth packing problem is defined as the selection and routing of messages from a given list of messages with prespecified requirements on demand for bandwidth. The messages have to be routed over a network with given topology so that the generated revenue is maximized. Messages to be routed are classified into two priority classes. An integer programming based formulation of this problem is proposed and a Lagrangean relaxation based methodology is described for solving this problem. A general purpose heuristic is then developed for generating feasible solutions of good quality. Several numerical experiments are conducted using a number of problem parameters such as number of messages, ratio of messages for lower and higher priority classes, capacity of links, and demand distribution of messages belonging to different classes and high quality solutions to the priority bandwidth packing problem are generated under the different situations.     

全光纤模式转换器的设计及优化

提出了一种新型全光纤LP02模宽带模式转换器.基于模式匹配原理采用双芯光纤设计,利用LP11模作为中间过渡模式,实现了宽带模式转换.运用光束传播法和模式耦合理论分析了光纤参量对有效折射率的影响,选择合适的光纤参量实现了模式匹配,分析了纤芯距离等参量对模式转换效率和带宽的影响,对比相同光纤参量下,直接和间接模式转换方法,数值模拟表明,采用间接法能够有效提高模式转换带宽,当要求转换效率大于80%时,这种模式转换器带宽能够达到121nm.     

Accurate analysis for reflection-peak bandwidths of sampled fiber Bragg gratings without chirp based on multiple-phase-shift technique

Dense comb-like reflective spectrum is available for a sampled fiber Bragg grating (SFBG) by using multiple-phase-shift (MPS) technique. The expressions for the reflection-peak bandwidths of a uniform SFBG based on MPS technique are derived through Fourier transform of the index modulation. The new expressions can be used to accurately calculate the reflection-peak bandwidths as taking the parameters into account, such as the duty cycle and the “AC” index change. The simulation spectrum based on the transfer matrix method agrees well with the theoretical analysis.     

Kernel density in the study of the strong stability of the queueing system

We use kernel density with correction of boundary effects to study the strong stability of the M/M/1 system after perturbation of arrival flow (respectively service times), to evaluate the proximity of G/M/1 (respectively M/G/1) and M/M/1 systems when the distribution G is unknown. Simulation studies are performed to support the results.     

A traffic shaping model for optimizing network operations

The management of technology in multi-service computer networks, such as university networks, has become a challenge with the explosive growth of entertainment oriented peer-to-peer (P2P) traffic. Traffic shaping is one of the tools used to manage bandwidth to improve system performance by allocating bandwidth between P2P and non-peer-to-peer (NP2P) traffic. We present a model for traffic shaping and bandwidth management that considers the trade-offs from allocating different amounts of bandwidths for different application categories and use data from a university network. The current policy allocates varying bandwidths over the day to P2P and NP2P traffic to reflect the importance of not letting entertainment based traffic choke the network during the day time at the expense of the more important traffic, such as Web traffic. We highlight the difficulties in obtaining data in the form required for analysis, and the need to estimate demand for allocations not covered by current policy. We present a goal programming model for this estimation task. We also model the traffic shaping problem as a Markov decision process and develop an algorithm for determining the optimal bandwidth allocation to maximize the utility of all users. Finally we use a numerical example to illustrate our approach.