Deyun Gao

Improving WLAN VoIP Capacity Through Service Differentiation

Voice over Internet protocol (VoIP) is one of the most important applications for IEEE 802.11 wireless local area networks (WLANs). For network planners who deploy VoIP over WLANs, one of the important issues is the VoIP capacity. Directly implementing VoIP over infrastructure WLANs will create the bottleneck problem at the access point (AP). In this paper, we propose the use of the service differentiation provided by the new IEEE 802.11e standard to solve the bottleneck problem and improve voice capacity. In particular, we propose the allocation of a higher priority access category (AC) to the AP while allocating lower priority AC to mobile stations. We develop a simple Markov chain model, which considers the important enhanced distributed channel access (EDCA) parameters and the channel errors under saturation and nonsaturation conditions. Based on the developed analytical model, we analyze the performance of VoIP over EDCA. By appropriately selecting the EDCA parameters, we are able to differentiate the services for the downlink and uplink. The experimental results are very promising. With the adjustment of only one EDCA parameter, we improve the VoIP capacity by 20%-30%.

Admission Control Based on Rate-Variance Envelop for VBR Traffic Over IEEE 802.11e HCCA WLANs

With the increasing popularity of using wireless local area networks (WLANs) for Internet access, the controlled channel access mechanism in IEEE 802.11e WLANs, i.e., HCF controlled channel access (HCCA), has received much more attention since its inherent centralized mechanism is more efficient in handling time-bounded multimedia traffic. So far, only a few research studies address the admission control problem of variable bit rate (VBR) traffic over HCCA. These existing studies consider each traffic flow individually and, thus, cannot exploit the statistical multiplexing gain among multiple VBR traffic flows. In this paper, we apply the existing statistical multiplexing framework to the studied admission control problem, with all the features of IEEE 802.11e HCCA being taken into consideration. Experimental results show that our proposed admission control scheme achieves significant improvement in network utilization while still satisfying all the quality-of-service (QoS) requirements.

TC-BAC: A trust and centrality degree based access control model in wireless sensor networks

Access control is one of the major security concerns for wireless sensor networks. However, applying conventional access control models that rely on the central Certificate Authority and sophisticated cryptographic algorithms to wireless sensor networks poses new challenges as wireless sensor networks are highly distributed and resource-constrained. In this paper, a distributed and fine-grained access control model based on the trust and centrality degree is proposed (TC-BAC). Our design uses the combination of trust and risk to grant access control. To meet the security requirements of an access control system with the absence of Certificate Authority, a distributed trust mechanism is developed to allow access of a trusted node to a network. Then, centrality degree is used to assess the risk factor of a node and award the access, which can reduce the risk ratio of the access control scheme and provide a certain protection level. Finally, our design also takes multi-domain access control into account and solves this problem by utilizing a mapping mechanism and group access policies. We show with simulation that TC-BAC can achieve both the intended level of security and high efficiency suitable for wireless sensor networks.

A multilevel information fusion approach for road congestion detection in VANETs

Abstract As city road congestion problems become more serious, many researchers have started to use the technique of vehicle ad hoc networks (VANETs) for road congestion detection. However, various on-board sensors equipped in vehicles may generate lots of atomic messages, which usually cause serious channel competition problems. In this paper, we propose a multilevel information fusion approach by combining the fuzzy clustering-based feature level information fusion (FCMA) and the modified Dempster–Shafer evidence reasoning-based decision level information fusion (D-SEMA). The FCMA can extract the key features from atomic messages, thereby greatly reducing the network traffic load. Furthermore, the D-SEMA mechanism is used to judge whether the road congestion event occurs. Performance analysis and simulation results under ONE simulator show that the proposed multilevel information fusion approach can detect road congestion efficiently with low bandwidth consumption.

A hybrid localization and tracking system in camera sensor networks

Position information is of vital importance in the various applications in energy-constrained wireless sensor networks. It has to design a localization mechanism considering both precision and energy consumption factors. In this paper, we propose a hybrid localization system in wireless sensor networks, which is composed of coarse-grained localization system and fine-grained localization system. The coarse-grained localization system takes the wireless signal strength as the reference for distance and gets the rough region as the unknown node. The fine-grained localization system is in charge of location refinement that takes image to localize the unknown node with camera sensor nodes. On the basis of the hybrid localization system, we furthermore design a hybrid tracking system for localizing a moving object. Finally, we build up a test bed to conduct experiments with our developed sensor network. The experiment results show that the proposed hybrid localization and tracking system can achieve high position precision and low energy consumption. Copyright

A practical deployment of Intelligent Building Wireless Sensor Network for environmental monitoring and air-conditioning control

Wireless sensor network is the core support technology in the framework of the Internet of Things. Environmental monitoring and devices control of intelligent building based on wireless sensor network is considered as one of the most crucial applications. It can perceive several environmental parameters and feedback control information to devices to provide more comfortable environment for people. However, it is difficult to ensure performance of wireless sensor network deployed in the buildings, because there usually are several serious disturbances from coexistence wireless systems and human actions. In this paper, we deploy a practical Intelligent Building Wireless Sensor Network (IBWSN) based on the analysis of actual spectrum, Link Quality Indicator, Received Signal Strength Indicator and Package Loss Rate. Performance evaluation proves that the presented system can satisfy the needs of the proposed applications for environmental monitoring and air-conditioning control.

Hop-distance relationship analysis with quasi-UDG model for node localization in wireless sensor networks

In wireless sensor networks (WSNs), location information plays an important role in many fundamental services which includes geographic routing, target tracking, location-based coverage, topology control, and others. One promising approach in sensor network localization is the determination of location based on hop counts. A critical priori of this approach that directly influences the accuracy of location estimation is the hop-distance relationship. However, most of the related works on the hop-distance relationship assume the unit-disk graph (UDG) model that is unrealistic in a practical scenario. In this paper, we formulate the hop-distance relationship for quasi-UDG model in WSNs where sensor nodes are randomly and independently deployed in a circular region based on a Poisson point process. Different from the UDG model, quasi-UDG model has the non-uniformity property for connectivity. We derive an approximated recursive expression for the probability of the hop count with a given geographic distance. The border effect and dependence problem are also taken into consideration. Furthermore, we give the expressions describing the distribution of distance with known hop counts for inner nodes and those suffered from the border effect where we discover the insignificance of the border effect. The analytical results are validated by simulations showing the accuracy of the employed approximation. Besides, we demonstrate the localization application of the formulated relationship and show the accuracy improvement in the WSN localization.

Defending Against New-Flow Attack in SDN-Based Internet of Things

Recently, the Internet of Things (IoT) is attracting significant attention from both academia and industry. To connect the huge amount of IoT devices effectively, software-defined networking (SDN) is considered as a promising way because of its centralized network management and programmable routing logic. However, due to the limited resources in both the data plane and the control plane, SDN is vulnerable to the new-flow attack, which can disable the SDN-based IoT by exhausting the switches or the controller. Therefore, in this paper, we propose a smart security mechanism (SSM) to defend against the new-flow attack. The SSM uses the standard southbound and northbound interfaces of SDN, and it includes a low-cost method that monitors the new-flow attack by reusing the asynchronous messages on the control link. The monitor method can differentiate the new-flow attack from the normal flow burst by checking the hit rate of the flow entries. Based on the monitoring result, the SSM uses a dynamic access control method to mitigate the new-flow attack by perceiving the behavior of the security middleware in the IoT. The dynamic access control method can intercept the attack flows at their access switch. Extensive simulations and testbed-based experiments are conducted and the corresponding results verify the feasibility of our claims.

LBMA: A novel Locator Based Mobility support Approach in Named Data Networking

To enhance seamless source mobility support in the mobile NDN (Named Data Networking) environment, we propose a novel Locator Based Mobility support Approach, dubbed LBMA. In this approach, we assign a unique topologically layered locator to each AR (Access Route) in NDN network, and extend the AR with additional functionalities, such as caching and forwarding Interest packets on behalf of the source. Meanwhile, we add an optional field to the original NDN packet, and modify the Outgoing Interface(s) field in the ARs original FIB (Forwarding Information Base) entries, to record the mobility status and the current locator of the source. Specifically, the consumer in LBMA can continue the interrupted communication, without delivering Interest packets towards the old location of the source, nor waiting for all relevant devices completing the FIB entries updating. The performance analysis result indicates that LBMA has lower handoff cost and shorter handoff latency, compared with other existing source mobility support approaches.

A Novel Reliable Transmission Protocol for Urgent Information in Wireless Sensor Networks

In monitoring wireless sensor networks (WSNs), the occurrence of an emergency will generate a large amount of data in a very short time. Among them, some urgent information is more critical and needs to be transmitted out reliably as soon as possible. In this scenario, congestion is inevitable due to the limited resources, especially near the sink. To address this problem, we propose a novel reliable transmission protocol for urgent information (RETP-UI) in WSNs. In RETP-UI, not only the current queue length but also the ratio of queue lengths fluctuation is adopted as indication of congestion. Each sensor node evaluates its congestion level locally and determines its congestion state with a state machine. Furthermore, we use a multistage rate adjustment mechanism to adjust each nodes sending rate cooperatively according to different congestion states. Finally, with extensive simulation results we illustrate that the performance of RETP-UI is significantly improved over traditional protocols.