Browsing by Author "Wei, David S. L."

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A random graph-based model to analyze packet interference between frequency hopping systems with an application to Bluetooth
(2008-09-05)
Naik, Kshirasagar
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Wei, David S. L.
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Su, Yu T.
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Shiratori, N.
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電信工程研究所
In this paper, we present a graph-based model for analyzing interference between two frequency hopping systems for wireless communication. Informally, frequency hopping means that successive packets are transmitted on different frequencies from a pseudo-random sequence. The frequency band occupied by a packet may be narrow or wide. Our model is based on the concept of probabilistic graphs, where a node represents a "channel" and an edge denotes the probability of interference between two packets belonging to two different channels. Two packets on two channels are said to be mutually interfering if the two packets overlap in time and are transmitted on the same frequency. Thus, from the viewpoint of probabilistic graphs, the expected number of nodes with at least one incident edge is a measure of packet interference in a collection of wireless channels. We apply this model of packet interference to a heterogeneous cluster of Bluetooth piconets, where a piconet could be either of 79-hop type or of 23-hop type. Though the 23-hop type has been phased out, we use it as an example in this paper. (C) 2008 Elsevier B.V. All rights reserved.
Enhanced adaptive frequency hopping for wireless personal area networks in a coexistence environment
(2007)
Hsu, Alex Chia-Chun
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Wei, David S. L.
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Kuo, C. -C. Jay
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Shiratori, Norio
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Chang, Chung-Ju
In this paper, we present an enhanced adaptive frequency hopping (EAFH) mechanism for improving the performance of frequency hopping-based wireless personal area networks (WPANs) under frequency-static and frequency-dynamic interference. The proposed mechanism monitors the overall packet error rate (PER) of the system to determine the right number of channels to be excluded from the hopset. Then based on the PER of individual channel, it decides whether to exclude a certain channel or not. Finally, proper packet length is associated with those channels remaining in the hopset. These decisions, which pertain to hopset size and packet length, are made so as to optimize the performance of the hopping system in a coexistence environment. We developed an analytical model to justify the behavior and performance of the proposed mechanism. Simulations are conducted under an environment of some collocated Bluetooth (BT) piconets and a Wi-Fi network to validate the developed model and show the superiority of EAFH. Simulation results show that, compared with those existing mechanisms including orthogonal hopset-based mechanisms, EAFH could provide much higher throughput while still maintaining reasonably good channel occupancy.
Guest Editorial: Networking Challenges in Cloud Computing Systems and Applications
(2013-12-01)
Wei, David S. L.
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Mukherjee, Sarit
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Naik, Kshirasagar
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Nayak, Amiya
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Tseng, Yu-Chee
Latency analysis for dynamic spectrum access in cognitive radio: Dedicated or embedded control channel?
(2007)
Wang, Li-Chun
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Lu, Yin-Chih
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Wang, Chung-Wei
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Wei, David S. L.
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交大名義發表
Dynamic spectrum access (DSA) is the key feature of cognitive radio (CR) networks, but it also poses many new challenges on the medium access control (MAC) design. One of key challenges is the fact that the secondary CR users can only borrow the licensed spectrum from the primary users for a short period of time. Hence, unlike many available multi-channel MAC protocols for ad hoc networks where throughput is the main performance issue, the DSA protocols in CR networks shall place more emphases on the access latency. Hence, one fundamental issue arises: how can the spectrum be dimensioned for control channels in order to minimize the access delay of DSA protocol in CR networks? In this paper, we provide a comparative study in an analytical manner on the latency performance of two DSA protocols: 1) dedicated control channel, and 2) embedded dedicated control channel approaches. Our results show that an optimal ratio of the control channel bandwidth over the total channel bandwidth can be found to minimize the latency of DSA with dedicated control channels. However, the delay performance of DSA with dedicated control channels is more sensitive to the variations of the data lengths than that of DSA with embedded control channels. Hence, we conclude that the way of dimensioning the spectrum for control frames for DSA in CR networks should be adaptive to the variations of the traffic characteristics and the number of users.