Browsing by Author "Peng, NF"

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A minimum-cost strategy for cluster recruitment
(2000)
Chan, WY
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Peng, NF
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統計學研究所
;
Institute of Statistics
It is becoming increasingly common for the design of a clinical study to involve cluster samples. Very few researches investigated the appropriate number of clusters. None of them treat cluster size and the number of clusters as random variables. In reality, the recruitment of clusters can not be reached at one time and the cluster sizes are usually random. The longer the recruitment takes the more expensive the total study costs will be. This paper provides a strategy for sequential recruitment of clusters, which can minimize the total study cost. By treating the number of additional observational subjects required at each time point as a Markov Chain, we derive an iterative procedure for optimal strategy and study the property of this strategy, especially the duration of the cluster recruitment. This strategy is also extended to search for an optimal number of centers in a multi-center clinical trial.
A statistic approach for deriving the short message transmission delay distributions
(2004-11-01)
Hung, HN
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Lin, YB
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Lu, MK
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Peng, NF
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統計學研究所
Short Message Service (SMS) is one of the most popular mobile data services. This paper develops a web-based short message system and analyzes the short message transmission delays based on 40 000 measured data collected from commercial operation. We investigate the distributions of SMS round-trip transmission delays. These distributions are roughly approximated by truncated normal, gamma, log-normal, and Weibull distributions with various parameters, which can be utilized in theoretical analysis. Furthermore, with the nonparametric fitting approach, we use the rejection method to develop random number generators for these delays, which can be used in any simulation models that employ SMS transmission delays.
Connection failure detection mechanism of UMTS charging protocol
(2006-05-01)
Hung, HN
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Lin, YB
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Peng, NF
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Sou, SI
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統計學研究所
In Universal Mobile Telecommunications System (UNITS), the extension of GPRS tunneling protocol called GTP' is utilized to transfer the Charging Data Records (CDRs) from GPRS Support Nodes (GSNs) to Charging Gateways (CGs). To ensure that the mobile operator receives the charging information, availability for the GTP1 transmission is essential. One important issue on GTP' availability is connection failure detection. It is desirable to select appropriate parameter values to avoid false failure detections (e.g., temporary network congestions) while to detect the true failures quickly. We propose an analytic model to compute the false failure detection probability and the expected true failure detection time. Based on our study, the network operator can select the appropriate parameter values for various traffic conditions to reduce the probability of false failure detection and/or true failure detection time.
Continuous time Markov chains observed on an alternating renewal process with exponentially distributed durations
(2006-02-15)
Chan, WY
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Peng, NF
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統計學研究所
;
Institute of Statistics
A continuous time Markov chain observed on a system following the dynamic behavior of an alternating renewal process is studied. This alternating renewal process is assumed to have exponentially distributed durations. The limiting behavior of the process is examined. Examples of applications are given. (c) 2005 Published by Elsevier B.V.
Modeling channel assignment of small-scale cellular networks
(2005-03-01)
Hung, HN
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Lee, PC
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Lin, YB
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Peng, NF
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統計學研究所
In a cellular telecommunications network, the call blocking, forced termination, and call incompletion probabilities are major output measures of system performance. Most previous analytic studies assumed that the handover traffic to a cell is a fixed-rate Poisson process. Such assumption may cause significant inaccuracy in modeling. This paper shows that the handover traffic to a cell depends on the workloads of the neighboring cells. Based on this observation, we derive the exact equation for the handover force-termination probability when the mobile station (MS) cell residence times are exponentially distributed. Then, we propose an approximate model with general MS cell residence time distributions. The results are compared with a previously proposed model. Our comparison study indicates that the new model can capture the handover behavior much better than the old one for small-scale cellular networks.
On weak lumpability of a finite Markov chain
(1996-05-01)
Peng, NF
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統計學研究所
;
Institute of Statistics
An irreducible and homogeneous Markov chain with finite state space is considered. Under a mild condition Gamma on the transition probability matrix, a necessary and sufficient condition for weak lumpability, and the characterization of the set of initial starting vectors which make it lumpable are obtained. A similar result is obtained for those transition probability matrices without the restriction of condition Gamma.
Repacking on demand for two-tier wireless local loop
(2004-05-01)
Hung, HN
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Lin, YB
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Peng, NF
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Tsai, HM
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統計學研究所
This paper proposes a radio channel assignment scheme called repacking on demand (RoD) for two-tier wireless local loop (WLL) networks. A two-tier WLL overlays a macrocell with several microcells. When a new call arrives at a two-tier WLL with RoD, if no idle channel is available in both the microcell and the macrocell, repacking is performed (i.e., a call in the macrocell is moved to its corresponding microcell), and then the reclaimed macrocell channel is used to serve the new call. An analytic model is proposed to compute the call blocking probability of the two-tier WLL with repacking. This analytic model is validated against simulation experiments.We prove that the blocking probability is not affected by the call holding time distributions, but is only dependent on the mean of the call holding times. Compared with some previous proposed schemes, RoD has low blocking probability and significantly reduces repacking rate.
Resolving mobile database overflow with most idle replacement
(2001-10-01)
Hung, HN
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Lin, YB
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Peng, NF
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Yang, SR
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統計學研究所
In a personal communications service (PCS) network, mobility databases called visitor location registers (VLRs) are utilized to temporarily store the subscription data and the location information for the roaming users. Because of user mobility, it is possible that the VLR is full when a mobile user arrives. Under such a circumstance, the incoming user has no VLR record and thus cannot receive PCS services. This issue is called VLR overflow. To resolve the VLR overflow problem, a VLR record can be selected for replacement when the VLR is full and then the reclaimed storage is used to hold the record of the requesting user. This paper considers the most idle replacement policy to provide services to mobile users without VLR records. In this policy, the record with the longest idle time is selected for replacement. We propose an analytic model to investigate the performance of this replacement policy. The analytic results are validated against simulation experiments. The results indicate that our approach effectively resolves the VLR overflow problem.
Spectral representations of the transition probability matrices for continuous time finite Markov chains
(1996-03-01)
Peng, NF
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交大名義發表
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統計學研究所
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National Chiao Tung University
;
Institute of Statistics
Using an easy linear-algebraic method, we obtain spectral representations, without the need for eigenvector determination, of the transition probability matrices for completely general continuous time Markov chains with finite state space. Comparing the proof presented here with that of Brown (1991), who provided a similar result for a special class of finite Markov chains, we observe that ours is more concise.