Interaction of call blocking and cell loss in an ATM network

The introduction of broadband ATM networks and services will raise new operational issues. An area of significant challenge to the network operators will be network dimensioning. ATM networks differ from today's STM networks in that they will have to provide acceptable performance with respect to not only call blocking, but also cell loss and cell delay. Consequently, it is important to understand the interaction of call blocking and cell loss/delay in ATM networks. The paper presents a method of exploiting the interaction of call blocking and cell loss performance in order to efficiently operate the ATM networks. Specifically, the paper demonstrates that when the network is dimensioned or engineered to meet an appropriate call blocking objective, the cell loss performance perceived by the accepted calls can be significantly better than the cell loss objective set for the connection admission control (CAC) to admit or deny a call     

The localization of spontaneous brain activity: an efficient way toanalyze large data sets

An efficient solution is presented of the problem to localize the electric generators of spontaneous magnetoencephalography (MEG) and electroencephalography (EEG) data for large data sets. When a data set contains more than 100,000 samples standard methods fail or become impractical. The method presented here is useful, for example, for the localization of (pathological) brain rhythms or the analysis of single-trial data.The problem is defined as finding the good fitting dipoles using the single-dipole model applied on each time sample. First, the data is bandpass filtered to select the rhythm of interest. Next, the empirical relationship between data power and probability of a dipole with a high goodness of fit (g.o.f.) is used to preselect data points. Then a global search algorithm is applied, based on precomputed lead fields on a fixed grid, to obtain a good initial guess for the nonlinear dipole search. Finally, the dipole search is applied on those samples that have a low initial guess error. In a group of five patients, it is found that 50% of the dipoles with a g.o.f. of at least 90% can be found by disregarding 90% of the data samples. Those dipoles can be found efficiently by disregarding all sample points with an initial guess relative residual error of 15% or lower. Finally, a simple empirical expression is found for the optimal mesh size of the global search grid. The method is completely automatic and makes it possible to study simple generators of large MEG and EEG data sets on a routine basis.     

Evaluation of call blocking probabilities in LEO satellite networks

In this paper, we present a new method for calculating call blocking probabilities (CBPs) in a low Earth orbit satellite network that carries voice calls. The calculation of the CBPs uses the Erlang‐B formula, but the traffic intensity has been modified to take into the time and location in which the calls are made. Copyright © 2009 John Wiley & Sons, Ltd.     

Tetrolet变换方块效应改善算法

针对Tetrolet 变换算法对图像去噪后存在方块效应的缺陷,文中对Tetrolet 变换算法进行了扩展和改进,并引入移位（Cycle Spinning）来有效消除Tetrolet 变换算法中的方块效应。仿真结果表明,所提出的算法不仅能有效去除噪声,而且可得到更高的峰值信噪比,提高了图像的主客观质量。去噪后图像保留了原始图像的边缘和细节等局部特征,较为平滑,且方块效应得到了一定的改善和抑制,因而该算法是有效可行的。     

CAC-RD: an UMTS call admission control

The third wireless network generation (3G) aims to provide fast Internet access with quality of service (QoS) guarantees, especially to multimedia applications. UMTS (Universal Mobile Telecommunication System) is a kind of 3G networks. To provide QoS, the network must use an efficient admission control mechanism. This mechanism needs to prioritize network access to critical classes of applications. This work proposes an UMTS admission control mechanism, called CAC-RD (Call Admission Control—based on Reservation and Diagnosis). It is based on network diagnosis and on channel reservation for handovers. These techniques are associated with new calls blocking when the network reaches utilization thresholds. CAC-RD is a tool that prioritises handovers and conversational applications. The main CAC-RD goals are the handovers blocking reduction and the acceptable performance levels guarantee. Simulation results show that the CAC-RD channel reservation and the diagnosis techniques associated with the intrinsic network signal power control effectively reduces blockings while guarantying performance levels. Due to computational resource limits, simulations cannot answer related to admission control in big networks with thousands of users. This work presents a method to extrapolate scientific questions like CAC’s behavior with thousands of users and many antennas. An artificial neural network approach for CAC-RD in UMTS 3G networks is presented as an extension of the work.     

Analysis of call blocking probability in TDM/WDM networks withtransparency constraint

In this letter we devise and validate by simulation an analytical model to study the performance of TDM/WDM networks using a three-stage switching architecture as an abstract model. We consider the transparency property as a constraint: a new incoming call can be accepted only without modifying the routing of previously accepted calls. We concentrate on the analysis of the call blocking probability by varying the traffic pattern and the configuration of the switching architecture. We show that a very good agreement is obtained between simulation and analytical results     

Sequential testing of sorted and transformed data as an efficient way to implement long GLRTs

It is often required to detect a long weak signal in Gaussian noise, and frequently, the exact form of that signal is parameterized but not known. A bank of matched filters provides an appropriate detector. However, in some practical applications, there are very many matched filters, and most are quite long. The consequent computational needs may render the classical bank-of-filters approach infeasibly expensive. One example, and our original motivation, is the detection of chirp gravitational waves by an Earth-based interferometer. In this paper, we provide a computational approach to this problem via sequential testing. Since the sequential tests to be used are not for constant signals, we develop the theory in terms of average sample number (ASN) for this case. Specifically, we propose two easily calculable expressions for the ASN: one a bound and the other an approximation. The sequential approach does yield moderate computational savings, but we find that by preprocessing the data using short/medium fast Fourier transforms (FFTs) and an appropriate sorting of these FFT outputs such that the most informative samples are entered to a sequential test first, quite high numerical efficiency can be realized. The idea is simple but appears to be quite successful: Examples are presented in which the computational load is reduced by several orders of magnitude. The FFT is an example of an energy-agglomerating transform, but of course, there are many others. The point here is that the transform need not match the sought signal exactly in the sense that all energy becomes confined to a single sample; it is enough that the energy becomes concentrated, and the more concentrated the better.     

Efficient estimation of call blocking probabilities in cellularmobile telephony networks with customer retrials

A novel approximate technique is proposed for the estimation of call blocking probabilities in cellular mobile telephony networks where call blocking triggers customer retrials. The approximate analysis technique is based on Markovian models with state spaces whose cardinalities are proportional to the maximum number of calls that can be simultaneously in progress within cells. The accuracy of the approximate technique is assessed by comparison against results of detailed simulation experiments, results of a previously proposed Markovian analysis approach, and upper and lower bounds to the call blocking probability. Numerical results show that the proposed approximate technique is very accurate, in spite of the remarkably small state spaces of the Markovian models     

Connection architecture and protocols to support efficient handoffs over an ATM/B-ISDN personal communications network

The next generation personal communication network will likely internetwork wireless networks via the ATM/B-ISDN to enable ubiquitous broadband personal communication services. Support of user terminal mobility, particularly the capability for fast and seamless handoffs, over the ATM/B-ISDN is an expected requirement that is not currently met. We propose extensions to the ATM/B-ISDN user transport and signaling network architectures and signaling protocols to meet these requirements. The new architecture employs the Mobile Virtual Circuit (MVC), a dynamic connection tree in which routes are predetermined but not set up for potential handoff connections. During a handoff, associated signaling using source-routing with a new robust adaptation feature is employed for fast resource allocation to establish the handoff connection by distributed control. We also address the new problem of packet ordering synchronization to enable a seamless handoff. The connection tree reconfigures after each handoff to enable continuous support of successive handoffs. The proposed scheme optimizes handoff delay over the ATM/B-ISDN while minimizing unnecessary resource allocation, chances of handoff failure, and call processing load in the intelligent network, and the extensions are backward compatible to current ATM/B-ISDN standards and implementations.This paper was presented in part in PIMRC'95 in Toronto, and Globecom'95 in Singapore. This work was supported by the Canadian Institute of Telecommunications Research (CITR), funded under the Canadian Federal Government's Networks of Centres of Excellence Program.     

Analysis of the call blocking rate of two-hop-relay cellular system in the dead spots

In a traditional cellular system, the call requests initiated by mobile stations (MSs) must be carried through a base station (BS) via the cellular interface, but when MSs are located in the dead spots, their call requests will be blocked because the MSs cannot communicate with the BS. It is considered to relay these blocked calls requested using Ad-hoc network, which will improve the performance of the system as a whole. This article first introduces a novel architecture of the two-hop-relay cellular system in the dead spots, and then analyzes and compares the call blocking rate of the traditional cellular and the two-hop-relay cellular system respectively under three different conditions. The first and second conditions are the traditional cellular system without and with taking account of the effect of the dead spots. The third condition is the two-hop-relay cellular system with taking account of the effect of the dead spots. Numerical analytical result shows that the two-hop-relay cellular system can obtain lower call blocking rate than the traditional cellular system when considering the effect of dead spots. Consequently, this novel architecture can resolve the problem of coverage limitation of a traditional cellular system effectively.     

Engineering the photoelectrochemical behaviors of ZnO for efficient solar water splitting

Solar water splitting is a promising strategy for the sustainable production of renewable hydrogen and solving the world’s crisis of energy and environment. The third-generation direct bandgap semiconductor of zinc oxide (ZnO) with properties of environmental friendliness and high efficiency for various photocatalytic reactions, is a suitable material for photoanodes because of its appropriate band structure, fine surface structure, and high electron mobility. However, practical applications of ZnO are usually limited by its high recombination rate of photogenerated electron–hole pairs, lack of surface reaction force, inadequate visible light response, and intrinsic photocorrosion. Given the lack of review on ZnO’s application in photoelectrochemical (PEC) water splitting, this paper reviews ZnO’s research progress in PEC water splitting. It commences with the basic principle of PEC water splitting and the structure and properties of ZnO. Then, we explicitly describe the related strategies to solve the above problems of ZnO as a photoanode, including morphology control, doping modification, construction of heterostructure, and the piezo-photoelectric enhancement of ZnO. This review aims to comprehensively describe recent findings and developments of ZnO in PEC water splitting and to provide a useful reference for the further application and development of ZnO nanomaterials in highly efficient PEC water splitting.     

Performance analysis of several call launching schemes in an outbound call management system

An outbound call management (OCM) system is used in launching calls to customers in a company or service center for the purpose or application of, for example, bill processing. Preliminary study of OCM systems has been done in a few prior studies. This paper conducts performance analysis of several new call launching schemes for an OCM system. An empirical scheme is first proposed and analyzed. The empirical scheme has the advantage of easy implementation. This paper continues to examine the performance of an optimal launching scheme via the technique of linear programming. To reduce the complexity, a suboptimal scheme is next proposed and analyzed. Through numerical examples, the empirical scheme is shown to perform only slightly worse than the optimal scheme, but better than the suboptimal scheme.The work reported in this paper is supported by the National Science Council of the Republic of China under Grant NSC81-0404-E002-010(1992).     

A computationally efficient selected mapping technique for reducing PAPR of OFDM

In orthogonal frequency division multiplexing (OFDM) system, high value of peak-to-average power ratio (PAPR) is an operational problem that may cause non-linear distortion resulting in high bit error rate. Selected mapping (SLM) is a well known technique that shows good PAPR reduction capability but inflicts added computational overhead. In this paper, using Riemann sequence based SLM method, we applied reverse searching technique to find out low PAPR yielding phase sequences with significant reduction in computational complexity. Additionally, we explored side-information free transmission that achieves higher throughput but sacrifices PAPR reduction. Finally, to overcome this loss in PAPR reduction, we proposed application of Square-rooting companding technique over the output OFDM transmitted signal. Simulation results show that the proposed method is able to compensate the sacrifice in PAPR and achieved PAPR reduction of 8.9 dB with very low computational overhead.     

Comparison of call gapping and percent blocking for overloadcontrol in distributed switching systems and telecommunications networks

Two overload control techniques are compared. A percent blocking throttle blocks and rejects an arrival with a given probability. A call gapping throttle closes the gap size for a deterministic time interval; after this interval, the next job to arrive passes through and the throttle again closes for the deterministic time interval. The comparison of the throttle schemes is based on nine criteria, seven of which concern robustness. The key strengths of call gapping are shown to be a greater robustness to changes in total arrival rate, and higher goodput, the throughput times the probability of it being good. For varying arrival rate, where the control setting is fixed, call gapping maintains reasonable goodput over regions where percent blocking has allowed goodput to fall to zero. The strengths of percent blocking are shown to be robustness to changes in number of active sources and robustness to unbalanced loads. The optimal control setting for percent blocking is shown to be a function of the total arrival rate and not a function of the number of active sources or the individual arrival rates     

Effect of mobile terminal heterogeneity on call blocking/dropping probability in cooperative heterogeneous cellular networks

It is envisaged that next generation wireless networks (NGWN) will be heterogeneous, consisting of multiple radio access technologies (RATs) coexisting in the same geographical area. In these heterogeneous wireless networks, mobile terminals of different capabilities (heterogeneous terminals) will be used by subscribers to access network services. We investigate the effect of using heterogeneous mobile terminals (e.g. single-mode, dual-mode, triple-mode, etc.) on call blocking and call dropping probabilities in cooperative heterogeneous wireless networks. We develop analytical models for heterogeneous mobile terminals and joint radio resource management in heterogeneous wireless networks. Using a two-class three-RAT heterogeneous wireless network as an example, the effect of using heterogeneous terminals in the network is evaluated. Results show the overall call blocking/dropping probability experienced by subscribers in heterogeneous wireless networks depends on the capabilities of mobile terminals used by the subscribers. In the worst case scenario, when all subscribers use single-mode mobile terminals, each subscriber is confined to a single RAT and consequently, joint radio resource management in heterogeneous wireless network has no improvement on new call blocking and handoff call dropping probabilities. However, in the best case scenario, when all subscribers use three-mode terminals, new class-1 call blocking probability decreases from 0.37 (for 100% single-mode terminals) to 0.05, at the arrival rate of 6 calls per minute. New class-2 call blocking probability also decreases from 0.8 to 0.52. Similarly, handoff class-1 call dropping probability decreases from 0.14 to 0.003, and handoff class-2 call dropping probability decreases from 0.44 to 0.09.     

Robust pole placement: an efficient method

A newly developed method is used to solve nonsmooth optimisation problems arising in robust pole placement. The method is very efficient owing to its desirable numerical properties such as guaranteed fast rate of convergence and ease of implementation.<>     

Cross-correlated correlative encoding: an efficient modulationmethod

A new cross-correlated correlative baseband encoding scheme is presented as a means of doubling the capacity of a mobile communication systems without the cost of complex baseband filtering. System performance is studied in a non-linear amplified channel for 6 to 9 dB improved power efficiency. The system is analyzed for spectrum efficiency, adjacent channel interference (ACI), co-channel interference (CCI) and bit error rate (BER) performance in a Rayleigh faded cellular network. Computer simulated results and hardware experimentation show that modified correlative encoding achieves up to a 70% improvement in spectrum efficiency and double network capacity when compared to constant envelope GMSK modulation used in GSM, DCS1800, PCS1900 and DECT systems