Yeong-Sheng Chen

Efficient localization scheme with ring overlapping by utilizing mobile anchors in wireless sensor networks

In this study, we propose an efficient localization scheme in wireless sensor networks. The proposed scheme utilizes mobile anchors and is based on ring overlapping. In a wireless sensor network, there are some nodes knowing their locations, which are called the reference nodes, and the other nodes without the knowledge of their locations are called the blind nodes. Based on the relative RSSI (Received Signal Strength Indicator) values, we utilize mobile beacons to find out the rings that are centered with a certain reference node and contain the blind node. These rings are called B-Rings. Since the mobile anchor and the reference node know their own locations, the B-rings can be precisely derived. By utilizing the mobile beacons, the widths of the B-Rings can be further minimized; and then by overlapping them, the location of the blind nodes can be efficiently estimated. Besides, most existing location schemes that utilize mobile anchors let the mobile anchor move randomly. In contrast, we propose a regular and simple movement scheme for the mobile anchor. Thus, the mobile anchor consumes less energy than other schemes in which the mobile anchor move randomly. Simulations of the proposed scheme show that the proposed localization mechanism has better accuracy than other existing related approaches

Efficient uplink scheduling policy for variable bit rate traffic in IEEE 802.16 BWA systems

One of the major challenges in the context of transmitting real-time multimedia data in broadband wireless access (BWA) systems is that the varied bit rate of traffic causes low bandwidth utilization. The conventional uplink scheduling algorithms for variable bit rate (VBR) video traffic transmission in IEEE 802.16 BWA systems have some disadvantages, including waste of uplink bandwidth, MAC overhead, and access delay. To cope with these difficulties, we propose an uplink scheduling algorithm for VBR traffic transmission for IEEE 802.16 BWA systems. In the proposed algorithm, the base station (BS) assigns uplink bandwidth to the video user by considering the traffic state transitions. The uplink bandwidth is equally divided into several intervals where each interval represents a traffic state. Only when the traffic state is changed, the bandwidth request process is incurred. Also, by using two reserved bits in the generic MAC header of IEEE 802.16 BWA systems as piggyback bits, the information about traffic state transition can be sent to the BS without extra overhead. Simulations conducted with QualNet 4.0 show that the bandwidth waste ratio of our proposed algorithm is less than that of the conventional algorithms. That is, the proposed algorithm outperforms the conventional algorithms for VBR traffic transmission in IEEE 802.16 BWA systems in terms of bandwidth utilization. Copyright

Efficient pseudonym changing schemes for location privacy protection in VANETs

To achieve location privacy for Location-Based Services (LBS) in the Vehicular Ad-hoc Network (VANET) environment, many pseudonym changing mechanisms have been proposed in the literature. Although some exiting mechanisms, such as AGE, SLOW, SPOT and can achieve high security level, yet much overhead is incurred due to a large number of pseudonym changes. While performing pseudonym changes, the services from the location server will be interrupted and the routing has to be reestablished, causing communication overheads. In light of this observation, this study proposes efficient pseudonym changing schemes to minimize the number of pseudonym changes while still achieving high location privacy protection level. Criteria for performing pseudonym changing are proposed by considering the age of pseudonyms, the speed, and the moving direction of the vehicles. Thus, four mechanisms AS, AD, SD and ADS are developed by using the combination of these three factors. Simulations have been carried out with the SUMO simulator. Compared with other existing pseudonym changing approaches, simulation results show that the proposed mechanisms have better performance in the sense of achieving high protection rate with less number of pseudonym changes, and, in particular, ADS always has the best performance.

Adaptive Traffic-Aware Power-Saving Protocol for IEEE 802.11 Ad Hoc Networks

Due to rapid advances in wireless network technologies, and the maturity of portable communication devices, ubiquitous wireless computing has become increasingly popular. One of the most important issues in ubiquitous wireless computing is the reduction of power consumption of the portable devices. In this study, we propose a traffic-aware power-saving protocol for IEEE 802.11 multi-hop ad hoc networks. In the proposed protocol, the mobile stations determine their sleep-awake patterns based on a quorum approach. In general, the length of the quorum cycle is an important factor in the sleep-awake ratio, and will determine the power consumption ratio. In light of this observation, the proposed protocol dynamically adjusts the length of the quorum cycle by considering the network utilization during its previous quorum cycle. Simulation results show that our proposed protocol can effectively reduce power consumption in mobile Ad Hoc networks.

Enhanced HCCA mechanism for multimedia traffics with QoS support in IEEE 802.11e networks

In broadband wireless networks, providing Quality of Service (QoS) support for multimedia traffics is no doubt crucial to many application requirements such as real-time audio and video streaming communications. IEEE 802.11e Medium Access Control (MAC) standard proposes Hybrid Coordination Function (HCF), which is composed of HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA) mechanisms for QoS support. HCCA performs a polling procedure with parameterized channel. However, a station may not always have pending data to transmit. That is, polling all the stations may waste time and therefore deteriorate the transmission performance. In this paper, we propose a modified HCCA mechanism using the beacon frame broadcasted by the AP to determine which station can transmit its pending data so as to improve the transmission performance. The simulation results show that the performance improvement of our proposed mechanism is significant for QoS support particularly under light load condition.

Context-aware services based on OSGi for smart homes

Recently, context aware service has become one of the most promising topics for ubiquitous computing. In this study, we focus on developing a context aware framework based on the OSGi model to automatically provide appropriate information and services for users in a smart home environment. A middleware for integrating home services through a reasoning system is developed. By using JESS Markup Language (JessML), the semantic information of contexts can be easily described, shared and reused. Also, Java expert system shell (JESS) is used for automatically reasoning adaptive services for users. Experiments performed with the developed prototype system show that the proposed framework can automatically provide appropriate context aware services for users in a smart home environment.

Efficient localization algorithm in wireless ad hoc sensor networks by utilizing radical centers

This study proposes an analytic localization algorithm by utilizing radical centers. Assume that a target node (blind node) can measure its distances to three or more anchor nodes (reference nodes). By picking three distance measurements to three anchor nodes, a radical center is computed. Through analytic formulation, the radical center is shown to be able to be treated as an estimation of the target node location. Since every three distance measurements generates one radical center, to further improve and fuse these estimations, effective filtering mechanisms are then proposed to filter out the improper estimations. Afterwards, the remaining radical centers are averaged, and the solution is the final estimation of the target node location. The location errors of the proposed method and the conventional MMSE (Minimum Mean Square Error method) are analytically compared. It is shown that the proposed algorithm outperforms the conventional MMSE method both in accuracy and efficiency. Extensive computer simulations were carried out and the results verify the advantage of the proposed location algorithm over the MMSE approach.

High Performance Distributed Coordination Function with QoS support in IEEE 802.11e networks

IEEE 802.11e standard is specified to support QoS (Quality of Service) in wireless local area networks for multimedia traffic such as real-time audio and video streaming. It proposes two wireless network access mechanisms to support QoS: HCF Controlled Channel Access (HCCA) and Enhanced Distributed Channel Access (EDCA). EDCA is a contention-based scheme. When the network size is increased, there will be more collisions and idle slots. Therefore, the performance will degrade a lot. To cope with this problem, this study proposed a High Performance Distributed Coordination Function with QoS support (QHDCF) protocol to enhance the performance. In QHDCF, the transmitting station determines the next transmitter according a selection rule from a probability formulation perspective based on the priorities and numbers of stations in different traffic classes. Since, in the proposed QHDCF, stations do not contend for channel access, transmission collisions are reduced a lot, and hence the network throughput is enhanced. Moreover, in EDCA, the high-priority traffic will always get the transmission opportunity and therefore low-priority traffic will suffer starvation. In contrast, in QHDCF, the high-priority traffic has better transmission opportunity on a probability base and hence does not starve the low-priority traffic. Simulation results show that the proposed QHDCF protocol outperform EDCA protocol in different packet sizes and number of stations.

An Efficient Localization Scheme with Ring Overlapping by Utilizing Mobile Anchors in Wireless Sensor Networks

In this study, we propose an efficient localization scheme in wireless sensor networks. The proposed scheme utilizes mobile anchors and is based on ring overlapping. In a wireless sensor network, there are some nodes knowing their locations, which are called the reference nodes, and the other nodes without the knowledge of their locations are called the blind nodes. Based on the relative RSSI (Received Signal Strength Indicator) values, we utilize mobile beacons to find out the rings that are centered with a certain reference node and contain the blind node. These rings are called B-Rings. Since the mobile anchor and the reference node know their own locations, the B-rings can be precisely derived. By utilizing the mobile beacons, the widths of the B-Rings can be further minimized; and then by overlapping them, the location of the blind nodes can be efficiently estimated. Besides, most existing location schemes that utilize mobile anchors let the mobile anchor move randomly. In contrast, we propose a regular and simple movement scheme for the mobile anchor. Thus, the mobile anchor consumes less energy than other schemes in which the mobile anchor move randomly. Simulations of the proposed scheme show that the proposed localization mechanism has better accuracy than other existing related approaches

An Efficient Quorum-Based Fault-Tolerant Approach for Mobility Agents in Wireless Mobile Networks

In this paper, we propose an efficient quorum-based mechanism to the fault-tolerance problem in mobile IP protocol. In a network with N HAs, all the HAs are grouped into N quorums with logical circular structure. Every HA has lceilradic(N)rceil backup quorums and divides the network that it manages into lceilradic(N)rceil equal parts. According to the home address of the MN, each HA finds out the backup quorum in the network segment and stores the mobility bindings of the MN in lceilradic(N)rceil-1 backup HAs. When a HA crashes, the system will select the HA with minimum load from each backup quorum to take over the bindings of the faulty HA. In comparison with previous related works, our experimental results show that the proposed fault-tolerant protocol has many advantages: better system load balance, less latency for registration process, less system resource requirements, and no extra hardware cost.