Browsing by Author "Lau, Lee-Chin"

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An IEEE 802.11 Cognitive Radio MAC Protocol with Dynamic Bandwidth Allocation Capabilities
(2012)
Lau, Lee-Chin
;
Lin, Chih-Che
;
Wang, Shie-Yuan
;
資訊工程學系
;
Department of Computer Science
The Cognitive Radio (CR) technology has emerged as a hot research area recently due to its high potential in addressing the spectrum underutilization problem. In this paper, the CR is applied to unauthorized CR users (CRUs) such that these nodes can access the 802.11 spectrum opportunistically to flexibly use the detected "spectrum holes," with the ultimate goal of improving the 802.11 spectrum utilization. In [5], the authors proposed a bi-directional CR MAC protocol such that the CRUs can smartly negotiate and reserve bandwidth either uni-directionally or bi-directionally, to better support both the TCP and UDP flows. However, the protocol design is inadequate in supporting traffic demands in more complicated network cases. To address this problem, we proposed a CR MAC protocol with a dynamic bandwidth allocation capability, which can well support various types of network traffic, particularly asymmetric two-way traffic flows. We used the NCTUns network simulator to conduct the study. Our simulation results show that the proposed protocols can further utilize the "spectrum holes" in a more effective way while guaranteeing QoS support to both the surrounding CRUs and authorized 802.11 nodes.
Bi-directional Cognitive Radio MAC Protocol for Supporting TCP Flows
(2011)
Lau, Lee-Chin
;
Lin, Chih-Che
;
Wang, Shie-Yuan
;
資訊工程學系
;
Department of Computer Science
The Cognitive Radio (CR) technology has emerged as a recent breakthrough radio technology to meet future wireless demands in terms of both spectrum efficiency and performance of new wireless applications. In an 802.11 Cognitive Radio Network (CRN), when the spectrum is not used, unauthorized users with CRs can access the frequencies assigned to authorized users in an opportunistic manner, thus dramatically improving spectrum efficiency of the network. In [5], the authors proposed a CR MAC protocol for 802.11 CRNs such that the unauthorized CR users (CRUs) can flexibly use the "spectrum holes" without affecting the performance of the authorized users. However, the protocol design proposed in [5] can degrade the throughput performance of TCP flows. Since TCP is a primary transport protocol for most of the internet applications today, it is imperative that a proposed CR MAC protocol can well support TCP flows. To address this problem, in this paper we propose a Bi-directional CR MAC (Bi-MAC) protocol such that the CRUs can smartly negotiate and reserve bandwidth based on the anticipated packet exchanges on the data channels. Our simulation results show that the Bi-MAC protocol can effectively improve both the TCP and UDP performance of CRUs and increase the network goodputs.
Design and Implementation of A more Realistic Radio Propagation Model for Wireless Vehicular Networks over the NCTUns Network Simulator
(2011)
Wang, Shie-Yuan
;
Wang, Po-Fan
;
Li, Yu-Wei
;
Lau, Lee-Chin
;
資訊工程學系
Today, Intelligent Transportation System (ITS) applications has made a great impact on improving the quality and efficiency of the transportation system. This achievement has attracted researchers to propose more ITS applications, particularly to improve the transportation safety through Vehicular Ad Hoc Networks (VANETs). The major difficulty faced by these researchers is the verification of their proposals or ideas through field-trials or real-world experiments. Therefore, VANET simulator becomes the best and the most economical alternative to verify the validity and reliability of a proposed ITS application. Among all the VANET simulators, the NCTUns 6.0 appears as one of the most powerful tool due to its integrated platform of network simulation and microscopic traffic simulation. To further enhance the capability of NCTUns 6.0, we design and implement a more realistic radio propagation model, specifically for VANETs simulation. Through extensive simulations, it is shown that the adoption of a more realistic channel model has greatly affected the vehicles' behavior, as compared to the commonly used two-ray ground channel model.
Enhanced MAC Protocol for Cognitive Radios over IEEE 802.11 Networks
(2011)
Wang, Shie-Yuan
;
Huang, Yu-Ming
;
Lau, Lee-Chin
;
Lin, Chih-Che
;
資訊工程學系
The Cognitive Radio (CR) technology is proposed for solving the spectrum underutilization problem and has gained great attention. By allowing unauthorized users to opportunistically access frequencies authorized to specific networks (called primary networks), the CR technology can increase the bandwidth utilization of the radio spectrum in a global perspective. In [1], the authors proposed a MAC protocol for CRs that aims to "borrow" the link bandwidth from IEEE 802.11 networks. This protocol allows CR users to opportunistically exchange data on an idle 802.11 channel. However, the protocol proposed in [1] selects an 802.11 channel for data exchange in a random manner. This random channel selection process is time-consuming for CR users to start a data transmission. In addition, the protocol does not consider the effects of hidden terminals (HTs), which often exist in wireless networks and significantly decrease the goodputs of a network. To address these problems, in this paper we propose enhancements to the protocol proposed in [1]. The proposed protocol is evaluated using extensive simulations. Our simulation results show that our proposed protocol can effectively decrease the time required for finding an idle 802.11 channel to transmit data and therefore increase the network goodputs in networks with and without the existence of HTs.