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Performance Analysis (performance + analysis)
Selected AbstractsPERFORMANCE ANALYSIS FOR A SAMPLE OF MICROFINANCE INSTITUTIONS IN INDIAANNALS OF PUBLIC AND COOPERATIVE ECONOMICS, Issue 2 2008Alain De CROMBRUGGHE ABSTRACT,:,We use regression analysis to study the determinants of self-sustainability of a sample of microfinance institutions in India. These institutions stand out by their ability and willingness to report financial and operational data to Sa Dhan, a know-how sharing organization. We investigate particularly three aspects of sustainability: cost coverage by revenue, repayment of loans and cost-control. Our results suggest that the challenge of covering costs on small and partly unsecured loans can indeed be met, without necessarily increasing the size of the loans or raising the monitoring cost. The analysis suggests other ways to improve the financial results, like a better targeting of the interest rate policy or increasing the number of borrowers per field officer especially in collective delivery models. [source] Effect of augmented visual feedback from a virtual reality simulation system on manual dexterity trainingEUROPEAN JOURNAL OF DENTAL EDUCATION, Issue 1 2005E. Wierinck Little research has been published about the impact of simulation technology on the learning process of novel motor skills. Especially the role of augmented feedback (FB) on the quality of performance and the transfer of the acquired behaviour to a no-augmented FB condition require further investigation. Therefore, novice dental students were randomly assigned to one of three groups and given the task of drilling a geometrical class 1 cavity. The FB group trained under augmented visual FB conditions, provided by the virtual reality (VR) system (DentSimTM). The no-FB group practised under normal vision conditions, in the absence of augmented FB. A control group performed the test sessions without participating in any training programme. All preparations were evaluated by the VR grading system according to four traditional (outline shape, floor depth, floor smoothness and wall inclination), and two critical, criteria (pulp exposure and damage to adjacent teeth). Performance analyses revealed an overall trend towards significant improvement with training for the experimental groups. The FB group obtained the highest scores. It scored better for floor depth (P < 0.001), whilst the no-FB group was best for floor smoothness (P < 0.005). However, at the retention tests, the FB group demonstrated inferior performance in comparison with the no-FB group. The transfer test on a traditional unit revealed no significant differences between the training groups. Consequently, drilling experience on a VR system under the condition of frequently provided FB and lack of any tutorial input was considered to be not beneficial to learning. The present data are discussed in view of the guidance hypothesis of FB, which refers to the apprentice's dependence on FB. [source] Performance analysis of a semantics-enabled service registryCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 3 2008W. Fang Abstract Service discovery is a critical task in service-oriented architectures. In this paper, we study GRIMOIRES, the semantics-enabled service registry of the OMII software distribution, from a performance perspective. We study the scalability of GRIMOIRES against the amount of information that has been published into it. The methodology we use and the data we present are helpful for researchers to understand the performance characteristics of the registry and, more generally, of semantics-enabled service discovery. Based on this experimentation, we claim that GRIMOIRES is an efficient semantics-aware service discovery engine. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance analysis and improvement for BitTorrent-like file sharing systemsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 13 2007Ye Tian Abstract In this paper, we present a simple mathematical model for studying the performance of the BitTorrent (http://www.bittorrent.com) file sharing system. We are especially interested in the distribution of peers in different states of the download job progress. With the model we find that the distribution of the download peers follows an asymmetric U-shaped curve under the stable state, due to BitTorrent's unchoking strategies. In addition, we find that the seeds' departure rate and the download peers' abort rate will influence the peer distribution in different ways notably. We also analyze the content availability under the dying process of the BitTorrent file sharing system. We find that the system's stability deteriorates with decreasing and unevenly distributed online peers, and BitTorrent's built-in ,tit-for-tat' unchoking strategy could not help to preserve the integrity of the file among the download peers. We propose an innovative ,tit-for-tat' unchoking strategy which enables more peers to finish the download job and prolongs the system's lifetime. By playing our innovative strategy, download peers could cooperate to improve the stability of the system by making a trade-off between the current downloading rate and the future service availability. Finally, experimental results are presented to validate our analytical results and support our proposals. Copyright © 2007 John Wiley & Sons, Ltd. [source] Specification and detection of performance problems with ASLCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 11 2007Michael Gerndt Abstract Performance analysis is an important step in tuning performance-critical applications. It is a cyclic process of measuring and analyzing performance data, driven by the programmer's hypotheses on potential performance problems. Currently this process is controlled manually by the programmer. The goal of the work described in this article is to automate the performance analysis process based on a formal specification of performance properties. One result of the APART project is the APART Specification Language (ASL) for the formal specification of performance properties. Performance bottlenecks can then be identified based on the specification, since bottlenecks are viewed as performance properties with a large negative impact. We also present the overall design and an initial evaluation of the Periscope system which utilizes ASL specifications to automatically search for performance bottlenecks in a distributed manner. Copyright © 2006 John Wiley & Sons, Ltd. [source] Performance analysis of high-performance file-transfer systems for Grid applicationsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 8 2006Cosimo Anglano Abstract Data-intensive Grid applications require the availability of tools able to transfer very large files in the shortest amount of time. Many file-transfer tools, based on solutions aimed at overcoming the limitations imposed by the TCP protocol, have recently been developed. In this paper we experimentally compare the performance of some of these tools in various network scenarios by running experiments on PlanetLab, an open platform for the development, deployment, and access of planetary-scale services, that comprises hundreds of hosts scattered across the globe. Our results show that solutions based on UDP and adopting rate-based algorithms result in better performance than other alternatives in most cases, while solutions based on TCP achieve similar performance only under specific circumstances. Copyright © 2005 John Wiley & Sons, Ltd. [source] SCALEA: a performance analysis tool for parallel programsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 11-12 2003Hong-Linh Truong Abstract Many existing performance analysis tools lack the flexibility to control instrumentation and performance measurement for code regions and performance metrics of interest. Performance analysis is commonly restricted to single experiments. In this paper we present SCALEA, which is a performance instrumentation, measurement, analysis, and visualization tool for parallel programs that supports post-mortem performance analysis. SCALEA currently focuses on performance analysis for OpenMP, MPI, HPF, and mixed parallel programs. It computes a variety of performance metrics based on a novel classification of overhead. SCALEA also supports multi-experiment performance analysis that allows one to compare and to evaluate the performance outcome of several experiments. A highly flexible instrumentation and measurement system is provided which can be controlled by command-line options and program directives. SCALEA can be interfaced by external tools through the provision of a full Fortran90 OpenMP/MPI/HPF frontend that allows one to instrument an abstract syntax tree at a very high-level with C-function calls and to generate source code. A graphical user interface is provided to view a large variety of performance metrics at the level of arbitrary code regions, threads, processes, and computational nodes for single- and multi-experiment performance analysis. Copyright © 2003 John Wiley & Sons, Ltd. [source] Performance analysis of optical code switching routerEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2010F. R. Durand In this work we study and evaluate the performance of an optical code switching router (OCSR), intended to be utilised in hybrid wavelength-division multiplexing/optical code-division multiplexing (WDM/OCDM) networks. This OCSR can transport and route efficiently user data over optical code paths without departing from the optical domain. Limitations of the proposed OCSR are investigated and its superior performance demonstrated based on non-coherent prime codes. Our results indicate that our solution is useful in showing the effects of the optimum threshold level on the OCSR performance. We propose a continuous adjustment of the optimum threshold level based on the measurement of the mean optical power before the decoder. The influence of various parameters of the optical codes on the OCSR performance are also considered and evaluated. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance analysis of a cellular mobile network with retrials and guard channels using waiting and first passage time measuresEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2009A. Economou Most studies of modern cellular mobile networks concern performance measures directly computable from the stationary state probabilities such as the blocking probability and the mean traffic rates of the various kinds of calls. In this paper, we consider a cellular mobile system with retrials and guard channels for the handover calls, but we concentrate on performance measures related to the waiting and first passage times of the system. More concretely, we first build a Markovian model representing a station of the network and then we study the waiting time of a customer, the idle times of the guard channels and the time between successive lost calls. These measures shed light on the behaviour of the system and quantify the quality of service from both points of view of the customer and the administrator. Several numerical results illustrate the effect of the system parameters in its performance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of optically preamplified DC-coupled burst mode receiversEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2009T. J. Zuo Bit error rate and threshold acquisition penalty evaluation is performed for an optically preamplified DC-coupled burst mode receiver using a moment generating function (MGF) description of the signal plus noise. The threshold itself is a random variable and is also described using an appropriate MGF. Chernoff bound (CB), modified Chernoff bound (MCB) and the saddle-point approximation (SPA) techniques make use of the MGF to provide the performance analyses. This represents the first time that these widely used approaches to receiver performance evaluation have been applied to an optically preamplified burst mode receiver and it is shown that they give threshold acquisition penalty results in good agreement with a prior existing approach, whilst having the facility to incorporate arbitrary receiver filtering, receiver thermal noise and non-ideal extinction ratio. A traditional Gaussian approximation (GA) is also calculated and comparison shows that it is clearly less accurate (it exceeds the upper bounds provided by CB and MCB) in the realistic cases examined. It is deduced, in common with the equivalent continuous mode analysis, that the MCB is the most sensible approach. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance analysis of a generic system model for uncoded IDMA using serial and parallel interference cancellation,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2008Oliver Nagy This paper shows how to accurately describe a fully synchronised interleave division multiple access (IDMA) scheme without channel coding by a matrix model. This model allows the derivation of the optimal detector and provides additional insights into the IDMA principle, and we show that the matrices are structured and sparse. We use BER and EXIT charts to study the performance of parallel and serial interference cancellation schemes and demonstrate that the latter converges faster and is independent of the scrambling code. Any bit interleaved DS-CDMA system can be viewed as a special case of IDMA, and an IDMA receiver can therefore be used to detect DS-CDMA signals. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of nonlinearly amplified M-QAM signals in MIMO channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2008Ahmed Iyanda Sulyman In this paper, we investigate the effect of nonlinearity in multiple input multiple output (MIMO) channels. New results on the error rate performance of several M-QAM constellations in linear and nonlinear MIMO channels are presented. The results show that for any MIMO configuration, performance degradation due to nonlinearity reduces as the fading gets more severe, and for a particular fading channel, the degradation increases as the MIMO dimension is increased. Optimum operating points for nonlinear amplifiers in MIMO channels are then reported. At these points, highly efficient utilisation of the amplifiers are achieved at minimal performance loss. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance analysis of TH-UWB radio systems using proper waveform design in the presence of narrow-band interferenceEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2006Hassan Khani Ultra-wide band (UWB) radio systems, because of their huge bandwidth, must coexist with many narrow-band systems in their frequency band. This coexistence may cause significant degradation in the performance of both kinds of systems. Currently, several methods exist for narrow-band interference (NBI) suppression in UWB radio systems. One of them is based on mitigating the effects of NBI through proper waveform design. In Reference 1, it has been shown that using properly designed doublet waveform can significantly reduce the effects of NBI on an important kind of UWB radio systems, i.e. BPSK time-hopping UWB (TH-UWB) systems. In this paper, the proper waveform design technique is extended to BPPM TH-UWB systems. It is shown that this method can properly suppress the effects of NBI on the performance of BPPM TH-UWB systems. Copyright © 2005 AEIT. [source] Performance analysis of different meteorological data and resolutions using MaScOD hydrological modelHYDROLOGICAL PROCESSES, Issue 16 2004Roshan Shrestha Abstract Distributed meteorological data collected from different sources are rarely identical within the same domain of space and time. Discrepancies of these data in magnitude, pattern, and resolution play an important role in hydrological simulation. Using four different sets of distributed meteorological data (from the HUBEX-Intense Observation Period and GAME experimental products at different resolutions), hydrological simulations are conducted through a distributed hydrological model called MaScOD (macro-scale OHyMoS assisted distributed) hydrological model. The model's performance is measured using 12 different indexes. Based on these indexes, a relative normalized score is calculated to evaluate the overall performance of the result from each data set. Three sub-basins of the Huaihe River basin in China, taking the cases at Bengbu (132 350 km2), Wangjiaba (29 844 km2) and Suiping (2093 km2), are used for numerical experiments. This study shows the competence of coarse-resolution meteorological data, the GAME reanalysis 1·25° data, to apply in hydrological simulations of large catchments. However, that data failed to simulate the hydrograph in smaller catchments. The results are significantly improved by including spatial variability at finer resolution in that data. Copyright © 2004 John Wiley & Sons, Ltd. [source] Performance analysis of IDEAL algorithm for three-dimensional incompressible fluid flow and heat transfer problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2009Dong-Liang Sun Abstract Recently, an efficient segregated algorithm for incompressible fluid flow and heat transfer problems, called inner doubly iterative efficient algorithm for linked equations (IDEAL), has been proposed by the present authors. In the algorithm there exist inner doubly iterative processes for pressure equation at each iteration level, which almost completely overcome two approximations in SIMPLE algorithm. Thus, the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate and stability of solution process. However, validations have only been conducted for two-dimensional cases. In the present paper the performance of the IDEAL algorithm for three-dimensional incompressible fluid flow and heat transfer problems is analyzed and a systemic comparison is made between the algorithm and three other most widely used algorithms (SIMPLER, SIMPLEC and PISO). By the comparison of five application examples, it is found that the IDEAL algorithm is the most robust and the most efficient one among the four algorithms compared. For the five three-dimensional cases studied, when each algorithm works at its own optimal under-relaxation factor, the IDEAL algorithm can reduce the computation time by 12.9,52.7% over SIMPLER algorithm, by 45.3,73.4% over SIMPLEC algorithm and by 10.7,53.1% over PISO algorithm. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance analysis of velocity,pressure smoothing for direction-of-arrival estimation of coherent signalsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 1 2010Yougen Xu Abstract In this paper, we consider the problem of direction-of-arrival (DOA) estimation of coherent signals by using a number of identically oriented acoustic vector-sensors, wherein source decorrelation can be achieved by velocity,pressure smoothing. We examine the effect of velocity,pressure smoothing on the performance of MUSIC-type methods in terms of the overall root mean-square errors (RMSE) of DOA estimates. The closed-form expression for the overall RMSE is derived and analyzed. We also compare velocity,pressure smoothing with the conventional spatial smoothing technique. Simulation results are given to confirm the analyses. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance analysis of data scheduling algorithms for multi-item requests in multi-channel broadcast environmentsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2010Kai Liu Abstract Nowadays querying multiple-dependent data items in a request is common in many advanced mobile applications, such as traffic information enquiry services. In addition, multi-channel architectures are widely deployed in many data dissemination systems. In this paper, we extend a number of data productivity-based scheduling algorithms and evaluate their performance in scheduling multi-item requests in multi-channel broadcast environments. We observe from the experimental results two performance problems that render these algorithms ineffective. Lastly, we discuss possible causes of these problems to give insights in the design of a better solution. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance analysis of system with L-branch selection combining over correlated Weibull fading channels in the presence of cochannel interferenceINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2010. Stefanovi, Mihajlo Abstract In this paper, the performance of L-branch selection combining receiver over correlated Weibull fading channels in the presence of correlated Weibull-distributed cochannel interference is analyzed. Closed-form expressions for probability density function and cumulative distribution function of the signal-to-interference ratio at the output of the selection combining receiver present main contribution of this paper. Numerical results are also presented to show the effects of various parameters as the fading severity, correlation and number of branches on outage probability. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance analysis of relative service using TCP-aware marking and dynamic WREDINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2009Christos Bouras Abstract The implementation of successful assured forwarding (AF) services according to the DiffServ framework remains a challenging problem today, despite the numerous proposals for assured forwarding per-hop-behaviour (AF PHB) mechanisms and AF-based service implementations. The interaction of the TCP and UDP traffic under an AF-based service and a number of relative issues such as fairness among flows, achievable bandwidth guarantees and qualitative performance have been taken into consideration in this work in order to address the existing limitations. We propose two modules, the TCP-window aware marker (TWAM) and the dynamic WRED (WRED) mechanism for implementing the differentiated services (DiffServ) AF PHB. We provide analytical models and an experimental evaluation in order to demonstrate how they succeed in enhancing the quality, improving the performance and easing the deployment of a production level AF-based service. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of a reuse partitioning technique for multi-channel cellular systems supporting elastic services,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2009Gábor Fodor Abstract For multi-cell systems employing intra-cell orthogonal communication channels, inter-cell interference mitigation techniques are expected to be one of the key radio resource management functions. In this paper we propose and analyze a simple reuse partitioning technique (with random and coordinated resource block allocation in neighbor cells) that is able to reduce inter-cell interference. We propose a model that is able to take into account that sessions dynamically enter and leave the system. Rigid sessions require a class-specific fixed number of resource blocks, while elastic sessions can enter the system if a minimum number of resources are allocated to them. In this rather general setting (and using the example of a system employing frequency division for multiple access) we analyze the system performance in terms of the expected number of channel collisions, the session-blocking probabilities, the signal-to-interference-and-noise ratio (SINR) and packet error rate performance. We present numerical results on the various trade-offs between these measures (including the trade-off between the reuse factor and the SINR performance) that provide insight into the behavior of multi-channel cellular systems and help dimensionalize the parameters of a reuse partitioned system. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of adaptive receivers for DS/CDMA communication systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2008Fang-Biau Ueng Abstract Both intersymbol interference (ISI) and multiple-access interference (MAI) are the important issues in code division multiple access (CDMA) multiuser communication systems. The step size of the traditional least-mean-square (LMS) adaptive receivers must be substantially adjusted to overcome the effect due to different channel responses or different numbers of active users. The normalized-LMS (NLMS) algorithm can automatically manipulate the adjustment to avoid the problem just discussed. This paper proposes the symbol-based interference rejection filter with NLMS algorithm and derives both finite impulse response (FIR)- and infinite impulse response (IIR)-type algorithms. We also derive the optimal step sizes and minimum mean-square errors (MSEs) for both the FIR and IIR symbol-based receivers. The complexity of our proposed FIR receiver is lower than that of the conventional chip-based receivers. In addition, it is shown that the bit error rate performance of our proposed symbol-based receivers is superior to conventional one in the simulations. Simulations also show the correctness of our theoretical analysis of minimum MSE. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of microcell/macrocell with reuse partitioning in TDMA-based cellular systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2008Jane Y. Yu Abstract System capacity and grade of service (GoS) are both important for the rapid growth of cellular communication services. In this paper, we propose a two-tier TDMA-based cellular system with macrocell overlaid on microcell clusters by implementing fixed channel assignment (FCA) scheme and fixed reuse partitioning (FRP) scheme in microcell layer and macrocell layer, respectively, named FCA,FRP overlay scheme. Improvement can be achieved in both system capacity and GoS. Theoretical analysis based on the overlay scheme without overflow and with overflow is first presented. It shows that the simulation results are agreed with the analytical results. Then, simulation results, obtained from the overlay scheme with and without overflow, show that the performance in terms of the call blocking probability, the call dropping probability and system capacity of such a system can be greatly improved compared with a conventional one-tier cellular system deployed with FCA or FRP scheme. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance analysis of wireless multihop diversity systemsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2008Diomidis S. Michalopoulos Abstract We study the performance of multihop diversity systems with non-regenerative relays over independent and non-identical Rayleigh fading channels. The analysis is based on the evaluation of the instantaneous end-to-end signal-to-noise ratio (SNR), depending on the type of the relay and the diversity scheme used. A closed-form expression is derived for the average end-to-end SNR, when fixed-gain relays and a maximal ratio combiner are used; also, an analytical expression formula for the average symbol-error rate (ASER) for the above case is presented. The results show that, as expected, multihop diversity systems outperform conventional telecommunication systems in terms of ASER when the same amount of energy is assumed to be consumed in both cases. Copyright © 2008 John Wiley & Sons, Ltd. [source] Online end-to-end quality of service monitoring for service level agreement managementINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2008Xiaoyuan Ta Abstract A major challenge in network and service level agreement (SLA) management is to provide Quality of Service (QoS) demanded by heterogeneous network applications. Online QoS monitoring plays an important role in the process by providing objective measurements that can be used for improving network design, troubleshooting and management. Online QoS monitoring becomes increasingly difficult and complex due to the rapid expansion of the Internet and the dramatic increase in the speed of network. Sampling techniques have been explored as a means to reduce the difficulty and complexity of measurement. In this paper, we investigate several major sampling techniques, i.e. systematic sampling, simple random sampling and stratified sampling. Performance analysis is conducted on these techniques. It is shown that stratified sampling with optimum allocation has the best performance. However, stratified sampling with optimum allocation requires additional statistics usually not available for real-time applications. An adaptive stratified sampling algorithm is proposed to solve the problem. Both theoretical analysis and simulation show that the proposed adaptive stratified sampling algorithm outperforms other sampling techniques and achieves a performance comparable to stratified sampling with optimum allocation. A QoS monitoring software using the aforementioned sampling techniques is designed and tested in various real networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance analysis of IEEE 802.11 DCF with stochastic reward nets,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2007R. Jayaparvathy Abstract In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11-based wireless local area networks (WLANs). We consider the distributed co-ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN-based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on,off traffic model and taking into account the freezing of the back-off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd. [source] Performance analysis of a channel allocation scheme for multi-service mobile cellular networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2007Shensheng Tang Abstract This paper presents a new channel allocation scheme, namely the dynamic partition with pre-emptive priority (DPPP) scheme, for multi-service mobile cellular networks. The system is modelled by a two-dimensional Markov process and analysed by the matrix-analytic method. A pre-emptive priority (PP) mechanism is employed to guarantee the quality of service (QoS) requirement of the real-time (RT) traffic at the expense of some degradation of non-real-time (NRT) traffic, while the victim buffer compensates the degradation and has no negative impact on the RT traffic. The complete service differentiation between new calls and handoff calls from different traffic classes is achieved by using the dynamic partition (DP) concept with the help of related design parameters. The performance analysis and numerical results show that the DPPP scheme, compared with the existing schemes, is effective and practical in multi-service environments. Copyright © 2006 John Wiley & Sons, Ltd. [source] Performance analysis of the IEEE 802.11 MAC protocol for wireless LANsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2005P. Chatzimisios Abstract Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co-ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd. [source] Performance analysis of an improved multi-carrier CDMA system under frequency-selective Rayleigh fading channelsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2003Hsiao-Hwa Chen Abstract In this article, an analytical method is proposed to study an improved orthogonal multi-carrier DS/CDMA system, which uses QPSK for both spreading and carrier modulations without redundant sub-carriers and time interleavers in each sub-channel. The article concerns in particular such a system and its performance under frequency-selective Rayleigh fading channels with various delay-power profiles. The bit error probabilities under varying multipath-diversity orders (using maximal ratio combing RAKE reception) and different numbers of resolvable multipaths are derived. It has been shown that the system, despite of its structural simplicity, performs well in mitigating frequency-selective fading. The performance is also evaluated taking into account various other parameter sets, such as numbers of users and sub-carriers, lengths of PN codes and the number of fingers in an RAKE receiver, etc. Copyright © 2003 John Wiley & Sons, Ltd. [source] Performance analysis of dynamic channel assignment algorithms in cellular mobile systems with hand-offINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2002L. Cong Abstract In this paper, the traffic performance of dynamic channel assignment (DCA) in cellular mobile system with hand-off is investigated. A traffic model for cellular system incorporating hand-off is established first. Under the framework of the model, a hand-off priority scheme is developed to reduce the forced termination of calls in progress. This paper analyses and derives the traffic performance bound for DCA strategies with hand-off by extending the maximum packing (MP) scheme to include the hand-off procedure. For practical implementation, a distributed DCA algorithm (DDCA) is also proposed. A non-priority scheme and the proposed priority scheme can be combined with either MP or DDCA. It is shown that the simulation results of DDCA scheme are comparable with the analytical bounds given by MP for both the non-prioritized case and prioritized case. A reasonable trade-off between the new call blocking probability and forced termination probability can be achieved by using the proposed prioritized scheme in DCA. Copyright © 2002 John Wiley & Sons, Ltd. [source] Performance analysis of integrating voice and data services over PACS systems in a multicarrier environmentINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2002Jyh-Horng Wen Abstract The purpose of this paper is to study the performance of integrating voice and data services over PACS systems in a multicarrier environment. Several time-slot allocation schemes are proposed. With continuous-time Markov model, the performance can be evaluated. The results show that while using one system broadcast channel (SBC), the blocking rate of circuit mode services and system throughput are improved, at the sacrifice of increasing the blocking probability of packet mode services. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||