Eric Hsiao-Kuang Wu

JTCP: jitter-based TCP for heterogeneous wireless networks

Transmission control protocol (TCP), a widely used transport protocol performs well over the traditional network which is constructed by purely wired links. As wireless access networks are growing rapidly, the wired/wireless mixed internetwork, a heterogeneous environment will get wide deployment in the next-generation ALL-IP wireless networks. TCP which detects the losses as congestion events could not suit the heterogeneous network in which the losses will be introduced by higher bit-error rates or handoffs. There exist some unsolved challenges for applying TCP over wireless links. End-to-end congestion control and fairness issues are two significant factors. To satisfy these two criteria, we propose a jitter-based scheme to adapt sending rates to the packet losses and jitter ratios. The experiment results show that our jitter-based TCP (JTCP) conducts good performance over the heterogeneous network.

Utilization based duty cycle tuning MAC protocol for wireless sensor networks

In this paper, we propose U-MAC, a medium access control protocol designed for wireless sensor networks. Nowadays, wireless sensor network are formed by a great quantity of sensor nodes, which are generally battery-powered and may not recharge easily. Consequently, how to prolong the lifetime of the nodes is an important issue while designing a MAC protocol. However, lowering the energy consumption may result in higher latency. Addressing on such tradeoff, U-MAC balances the tradeoff by utilization based tuning of duty cycle and selective sleeping after transmission. The experiment results show that our proposed U-MAC saves energy about 43% and reduce latency by 65% from S-MAC in a chain topology. In the cross topology, U-MAC also achieves 32% energy saving and 45% latency reduction from S-MAC

DuRT: Dual RSSI Trend Based Localization for Wireless Sensor Networks

Localization is a key issue in wireless sensor networks. The geographical location of sensors is important information that is required in sensor network operations such as target detection, monitoring, and rescue. These methods are classified into two categories, namely range-based and range-free. Range-based localizations achieve high location accuracy by using specific hardware or using absolute received signal strength indicator (RSSI) values, whereas range-free approaches obtain location estimates with lower accuracy. Because of the hardware and energy constraints in sensor networks, RSSI offers a convenient method to find the position of sensor nodes. However, in the presence of channel noise, fading, and attenuation, it is not possible to estimate the actual location. In this paper, we propose an RSSI-based localization scheme that considers the trend of RSSI values obtained from beacons to estimate the position of sensor nodes. Through applying polynomial modeling on the relationship between received RSSI and distance, we are able to locate the maximum RSSI point on the anchor trajectory. Using two such trajectories, the sensor position can be determined by calculating the intersection point of perpendiculars passing through the maximum RSSI point on each trajectory. In addition, we devised schemes to improve the localization method to perform under a variety of cases such as single trajectory, unavailability of RSSI trends, and so. The advantage of our scheme is that it does not rely on absolute RSSI values and hence, can be applied in dynamic environments. In simulations, we demonstrate that the proposed localization scheme achieves higher location accuracy compared with existing localization approaches.

An Opportunistic Cognitive MAC Protocol for Coexistence with WLAN

In last decades, the demand of wireless spectrum has increased rapidly with the development of mobile communication services. Recent studies recognize that traditional fixed spectrum assignment does not use spectrum efficiently. Such a wasting phenomenon could be amended after the present of cognitive radio. Cognitive radio is a new type of technology that enables secondary usage to unlicensed user. This paper presents an opportunistic cognitive MAC protocol (OC-MAC) for cognitive radios to access unoccupied resource opportunistically and coexist with wireless local area network (WLAN). By a primary traffic predication model and transmission etiquette, OC-MAC avoids producing fatal damage to licensed users. Then a ns2 simulation model is developed to evaluate its performance in scenarios with coexisting WLAN and cognitive network.

Binary-Partition-Assisted MAC-Layer Broadcast for Emergency Message Dissemination in VANETs

Vehicular ad hoc networks (VANETs) have recently been considered as an attractive network architecture to provide various services ranging from road safety to entertainment applications. In this paper, we propose an IEEE-802.11-based multihop broadcast protocol to address the issue of emergency message dissemination in VANETs. The protocol adopts a binary-partition-based approach to repetitively divide the area inside the transmission range to obtain the furthest possible segment. The forwarding duty is then delegated to a vehicle chosen in that segment. Aside from accomplishing directional broadcast for highway scenario, the protocol also exhibits good adaptation to complex road structures. The main focus of the paper lies in reducing broadcast delay, which is an important factor for time-critical safety applications. Most importantly, the contention delay remains almost constant, irrespective of vehicle density. Mathematical analysis is performed to assess the effectiveness of the protocol. Simulation results demonstrate that the proposed protocol imparts greater performance in terms of latency and message progress when compared with contemporary multihop broadcast protocols for VANETs.

Mobility Pattern Aware Routing for Heterogeneous Vehicular Networks

The intelligent transportation system (ITS), a worldwide initiative program utilizes novel information and communication technology for transport infrastructure and vehicles. Among extensive ITS components, efficient communication system is the most important role which connects numerous vehicles with roadside infrastructure and management center in the ITS program. Vehicular ad hoc network (VANET) has been a cornerstone of the envisioned ITS without infrastructure. However, multihop data delivery through VANET is difficult by the fact that vehicular networks are highly mobile and frequently disconnected. Thus, traditional ad hoc routing protocols are not well suited for these high dynamic network. In this paper we propose a new heterogeneous vehicular network (HVN) architecture and a mobility pattern aware routing for HVN. HVN integrates wireless metropolitan area network (WMAN) with VANET technology and reserves advantages of better coverage in WMAN and high data rate in VANET. Vehicles in HVN can communicate with each other and access Internet ubiquitously. We mainly focus on the routing issue for HVN, because the routing protocol for HVN is different from those used in MANET or VANET. With the WMAN infrastructure support in HVN, the mobility pattern aware routing protocol can adopt the whole information of the vehicular network and unique characteristics of vehicle mobility to establish a reliable route path in high dynamic vehicular network.

An admission control strategy for differentiated services in IEEE 802.11

With the provisioning of high-speed wireless LAN (WLAN) environments, traffic classes (e.g., VoIP or video-conference) with different QoS requirements will be introduced in future WLANs. The IEEE 802.11e draft is currently standardizing a distributed access approach, called the enhanced distributed coordination function (EDCF), to support service differentiation in the MAC layer. However, since each mobile station transmits data packets egotistically in a distributed environment, the QoS requirement of each traffic class may not be guaranteed. In this paper, we develop an admission control strategy to guarantee the QoS requirement of each traffic class. In order to provide a criterion for admission decision, we introduce an analytical model for EDCF to evaluate the expected bandwidth and the expected packet delay of each traffic class. The admission control strategy uses the performance measures derived from the analytical model to decide if a new traffic stream is permitted into the system. We validate the accuracy of the analytical model by using the ns-2 simulator. Some performance evaluations are also demonstrated to illustrate the effect of the proposed admission control strategy.

BAHG: Back-Bone-Assisted Hop Greedy Routing for VANET's City Environments

Using advanced wireless local area network technologies, vehicular ad hoc networks (VANETs) have become viable and valuable for their wide variety of novel applications, such as road safety, multimedia content sharing, commerce on wheels, etc. Multihop information dissemination in VANETs is constrained by the high mobility of vehicles and the frequent disconnections. Currently, geographic routing protocols are widely adopted for VANETs as they do not require route construction and route maintenance phases. Again, with connectivity awareness, they perform well in terms of reliable delivery. To obtain destination position, some protocols use flooding, which can be detrimental in city environments. Further, in the case of sparse and void regions, frequent use of the recovery strategy elevates hop count. Some geographic routing protocols adopt the minimum weighted algorithm based on distance or connectivity to select intermediate intersections. However, the shortest path or the path with higher connectivity may include numerous intermediate intersections. As a result, these protocols yield routing paths with higher hop count. In this paper, we propose a hop greedy routing scheme that yields a routing path with the minimum number of intermediate intersection nodes while taking connectivity into consideration. Moreover, we introduce back-bone nodes that play a key role in providing connectivity status around an intersection. Apart from this, by tracking the movement of source as well as destination, the back-bone nodes enable a packet to be forwarded in the changed direction. Simulation results signify the benefits of the proposed routing strategy in terms of high packet delivery ratio and shorter end-to-end delay.

Maximum traffic scheduling and capacity analysis for IEEE 802.15.3 high data rate MAC protocol

IEEE 802.15.3 is designed to provide low complexity, low cost, low power consumption and high data rate wireless connectivity among devices within wireless personal area networks (WPAN). A piconet is a basic topology of WPAN and is defined as a collection of one or more associated devices that share a single piconet coordinator (PNC). One functionality of a PNC is to schedule traffic of a piconet. But the scheduling method of a PNC is out of the scope of IEEE 802.15.3 draft standard. This paper proposes a scheduling method, which is called maximum traffic (MT) scheduling for IEEE 802.153. MT scheduling guarantees that total transmission data is maximum at any point of time and the needed time slots for transmission is minimum. MT scheduling is designed and analyzed by the properties of a graph coloring problem. Furthermore, the reasonable number of devices for a piconet and the durations of contention access period (CAP) and contention free period (CFP) are also investigated by this paper.

BPAB: Binary Partition Assisted Emergency Broadcast Protocol For Vehicular Ad Hoc Networks

Vehicular Ad Hoc Network has recently been considered as attractive network architecture to provide various services ranging from road safety to entertainment applications. In this paper, we propose an IEEE 802.11 based multihop broadcast protocol to address the issue of safety message dissemination in Vehicular Ad Hoc Networks. This position- based protocol adopts a repetitive 2-partition method to divide the area inside transmission range resulting in a furthest narrow segment and delegates the forwarding duty to a vehicle chosen in the furthest segment. The main focus of the paper lies in reducing broadcast delay which is an important factor in time critical safety applications. We attempt to attain consistent performance irrespective of node density and different VANET scenarios. In addition to this, the protocol also solves the hidden terminal problem of multihop broadcasting. Simulation results show that our protocol achieves greater performance in terms of latency and message progress when compared with other well known multihop broadcast protocols for Vehicular Ad Hoc Networks