Browsing by Author "Lai, WR"

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A new random walk model for PCS networks
(2000-07-01)
Akyildiz, IF
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Lin, YB
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Lai, WR
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Chen, RJ
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資訊工程學系
This paper proposes a new approach to simplify the two-dimensional random walk models capturing the movement of mobile users in Personal Communications Services (PCS) networks. Analytical models are proposed for the new random walks. For a PCS network with hexagonal configuration, our approach reduces the states of the two-dimensional random walk from (3n(2) + 3n - 5) to n(n + 1)/2, where n is the layers of a cluster. For a mesh configuration, our approach reduces the states from (2n(2) - 2n + 1) to (n(2) + 2n + 4)/4 if n is even and to (n(2) + 2n + 5)/4 if n is odd. Simulation experiments are conducted to validate the analytical models. The results indicate that the errors between the analytical and simulation models are within 1%, Three applications (i.e., microcell/macrocell configuration, distance-based location update, and GPRS mobility management for data routing) are used to show how our new model can be used to investigate the performance of PCS networks.
Effects of cache mechanism on wireless data access
(2003-11-01)
Lin, YB
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Lai, WR
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Chen, JJ
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資訊工程學系
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Department of Computer Science
In wireless data transmission, the capacity of wireless links is typically limited. Since many applications exhibit temporal locality for data access, the cache mechanism can be built in a wireless terminal to effectively reduce the data access time. This paper studies the cache performance of the wireless terminal by considering a business-card application. We investigate the least-recently used replacement policy and two strongly consistent data access algorithms called poll-each-read and callback. An analytic model is proposed to derive the effective hit ratio of data access, which is used to validate against simulation experiments. Our study reports how the data access rate and the data update distribution affect the cache performance in a wireless terminal.
Performance analysis for dual band PCS networks
(2000-02-01)
Lin, YB
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Lai, WR
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Chen, RJ
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資訊工程學系
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Department of Computer Science
In a dual band personal communications services (PCS) network, heavy traffic areas are covered by microcells which overlay macrocells. In such a network, microcells and macrocells utilize different frequency bands. We propose an analytic model to study the performance of a dual band PCS architecture. Our model assumes that a PCS subscriber has a general residence time distribution in a microcell and the macrocell residence time distribution is derived from the microcell residence time distribution. An iterative algorithm is used to compute the overflow traffic from a microcell to its overlaid macrocell. Then, the call incompletion probability is computed by a macrocell model based on the overflow traffic. Our study indicates that the variance of the microcell residence time distribution and the number of microcells covered by a macrocell have significant effects on the call incompletion probability.
Performance modeling of wireless PBX systems
(1999)
Lai, WR
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Lin, YB
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資訊工程學系
;
Department of Computer Science
This paper studies the effects of cell residence times on wireless private branch exchange (WPBX) systems. In a WPBX, several base stations are connected to a PBX, and the PBX is connected to the Public Switched Telephone Network. It is important to determine the external line capacity and the radio channel capacities of a WPBX to optimize its system performance. Our previous study utilized an analytic model to study WPBX without user mobility. This paper proposes both the analytic and the simulation models to investigate the performance for WPBX with user mobility. Specifically, we study the effects of handoff and the variance of the cell residence times on resource planning. Based on the workload to the WPBX, our study provides several guidelines to determine the capacities for the PBX and the base stations.