Markov-Based OVSF Code Assignment Scheme and Call Admission Control for Wideband-CDMA Communication Systems |
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Authors: | Email author" target="_blank">Ben-Jye?ChangEmail author Min-Xiou?Chen Ren-Hung?Hwang Chun-Huan?Chuang |
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Institution: | (1) Department of Computer Science & Information Engineering, Chaoyang University of Technology, Taichung, Taiwan, ROC;(2) Department of Computer Science & Information Engineering, National Chungcheng University, Chiayi, Taiwan, ROC |
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Abstract: | For the reason of the orthogonal characteristic of the Orthogonal Variable Spreading Factor (OVSF) code tree in Wideband CDMA
(WCDMA) systems, code blocking increases as traffic load (i.e. Erlang load) or the required rate increases. This causes inefficient
utilization of channelization codes. Hence, how to efficiently manage the resource of channelization codes of the OVSF code
tree in WCDMA systems is an important issue and has been studied extensively. There are two aspects to achieve efficiency
including code assignment and code reassignment. In the aspect of code assignment, an efficient code assignment scheme reduces
code blocking probability significantly. In the aspect of code reassignment, code reassignment results in several drawbacks,
such as large overhead of computation, high complexity of codes moving, and long call setup time for a new request call, etc.
Therefore, in this paper we focus on the first aspect of how to efficiently assign the channelization codes. Additionally,
most researches did not consider the analysis of tree state with dynamic traffic load and their analysis lack of systematic
call admission control (CAC) mechanism. Therefore, in this paper, we first propose the Markov decision process (MDP) based
analysis to assign channelization codes efficiently. Next, we extend the MDP-based approach as the call admission control
mechanism to maximize the system revenue while reducing blocking probability. Furthermore, a bit string masking algorithm
is proposed to reduce the time complexity of tree managing and searching for available channelization codes. Numerical results
indicate that the proposed MDP approach yields the best fractional reward loss, code blocking reward loss, and code blocking
ratio as compared to that of other schemes, including the random, left most, and crowded first schemes.
Ben-Jye Chang received his M.S. degree in computer engineering from University of Massachusetts, Lowell, in 1991 and the Ph.D. degree in
computer science and information engineering from National Chung-Cheng University, Taiwan, in 2001. He joined the Department
of Computer Science and Information Engineering faculty at Chaoyang University of Technology, Taiwan, in 2002, where he is
currently an associate professor. His research interests include QoS-based networks, QoS wireless networking, resource management
for wireless networks and mobile cellular networks, and performance evaluation of networks.
Min-Xiou Chen received the B.S. and M.S. degrees in computer science and information engineering from Tung Hai University and National
Chung Cheng University in 1996, and 1998, respectively. He is currently a Ph.D. candidate in the Department of Computer Science
and Information Engineering, National Chung Cheng University. His research interests include wireless communication, SIP,
and resource management in WCDMA systems.
Ren-Hung Hwang received his M.S. and Ph.D. degrees in computer science from University of Massachusetts, Amherst, Massachusetts, USA, in
1989 and 1993, respectively. He joined the Department of Computer Science and Information Engineering, National Chung Cheng
University, Chia-Yi, Taiwan, in 1993, where he is now a full professor and the Chair of the Department of Communication Engineering.
His research interests include Internet QoS, peer-to-peer infrastructure design, and 3G QoS.
Chun-Huan Chuang received the B.S. and M.S. degrees in computer science and information engineering from National Chung Cheng University,
Taiwan, in 2001 and 2003, respectively. His research interests include wireless communication and resource management in WCDMA
systems. |
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Keywords: | MDP OVSF code assignment CAC WCDMA 3G networks |
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