Xin Fei

A Voronoi Approach for Coverage Protocols in Wireless Sensor Networks

The Voronoi Diagram(VD) is a fundamental algorithm for resolving the coverage problems of wireless sensor networks. Most VD based coverage algorithms collect global location information and construct a VD using a centralized construction algorithm. However, the collection process of global location information is expensive and can not be guaranteed in all scenarios. Based on a localized VD construction algorithm this paper proposes a region coverage algorithm and a fully sponsored coverage algorithm where the GPS requirement for global location awareness is removed. The performance of such algorithms is evaluated by the complexity and message cost through a set of simulation experiments. The results show that our algorithms are better in both aspects when they are compared to the centralized region coverage algorithms and central angle algorithm. The performance and flexibility of our algorithms make them a potential solution for regional coverage and off- duty applications.

An optimal coverage-preserving scheme for wireless sensor networks based on local information exchange

Coverage-preserving and energy-saving solutions have been reported in the literature and are generally based upon both quality coverage and off-duty scheme. Off-duty scheme based solutions present at least three challenging problems: (1) keeping coverage and connectivity of the network while optimizing the number of active sensor nodes; (2) resolving conflicts when determining which nodes should be turned off in order to save energy; and (3) finding optimal wake-up strategies that avoid waking up more nodes than necessary. This paper presents a novel distributed solution, the optimal coverage-preserving scheme (OCoPS), that extends the well-known Central Angle Method in order to identify fully sponsored nodes. OCoPS comprises an extended Central Angle Method, new decision algorithms devised to resolve the off-duty conflict problem under different network densities, and an energy-aware wake-up scheme that solves coverage hole problems in off-duty schemes. Compared to the widely used node scheduling scheme, our solution is based on local information exchange without the uncertainty of self-schedule algorithms. OCoPS is implemented as an extension of LEACH. A set of simulation experiments is carried out to evaluate its performance compared to other well-known schemes which are based on the Central Angle Method and self-scheduling. Our results indicate that on network lifetime OCoPS outperforms other schemes by over 20% and by over 25% when the coverage rate is higher than 80%. The experimental results also show that our coverage scheme effectively limits the number of on-duty node compared to the other schemes.

An energy aware coverage-preserving scheme for wireless sensor networks

How well a large wireless sensor network can be monitored or tracked while keeping long live is a challenging problem known as the energy aware coverage preserving. Several coverage solutions have been introduced based on node scheduling and quality coverage. Node scheduling based solutions usually rely on global clock synchronization and/or time delays to resolve conflicts when determining what nodes should be turned-off to save energy. If these time delays cannot be calculated accurately blind areas might emerge jeopardizing the network coverage quality. Other challenges to node scheduling based solutions include finding optimal wakeup strategies that avoid waking up more nodes than necessary; and keeping connectivity and coverage of the network while optimizing the number of nodes. This paper extends the coverage calculation method proposed by Tian and Georganas, referred here as C-PNSS scheme, and describes a novel distributed solution based on local information exchange without the uncertainty of self-schedule algorithms. A Decision algorithm and a new node wakeup scheme were devised to overcome existing problems in actual schemes. We implement our optimal coverage-preserving scheme (OCoPS) as an extension of LEACH. A set of simulation experiments was performed to evaluate OCoPS performance when compared to LEACH and C-PNSS schemes. The results indicate that our solution outperforms C-PNSS by over 20% on network lifetime and by over 25% on network lifetime when the coverage rate is higher than 80%. LEACH is outperformed by nearly over five times on network lifetime. The experimental results also show that our coverage scheme based on our extended coverage calculation method effectively limits the on-duty node number when compared to both LEACH and C-PNSS.

Irregular Sensing Range Detection Model for Coverage Based Protocols in Wireless Sensor Networks

In order to optimize the performance of wireless sensor networks, based on the boolean sensing model (BSM) many coverage preserving protocols have been proposed; however, BSM model is too idealistic to be maintained in many applications. Sensing range could be changed by environment factors such as the obstacle and weather condition. BSM based protocols can not achieve their design goals because of the errors of coverage measurement. In this paper, we proposed our irregular sensing range detection model (RDM) which solves the range detection problem through estimating the sensing range by a revised α-shape algorithm. A RDM based distributed algorithm for measuring the area coverage is proposed. Its complexity are analyzed and compared to the centralized α-shape based area coverage algorithm. A set of simulation experiments is carried out to evaluate the performance of our algorithm in terms of coverage accuracy, coverage error and complexity. The result shows that the boolean sensing model will lead to errors when obstacles are injected into environment; however, our range detection model can detect the changes of environments and help protocols adapt to it.

A geometry-based coverage strategy over urban VANETs

Vehicular ad hoc networks have emerged as a promising field in wireless networking research. Unlike traditional wireless sensor networks, vehicular networks demand more consideration due to their assorted road topology, the high mobility of vehicles and the irregularly placed feasible region of deployment. As one of the most complex issues in vehicular networks, coverage strategy has been researched extensively, especially in complex urban scenarios. However, most existing coverage approaches are based on an ideal traffic map consisting of straight lines and nodes. These simplifications misrepresent the road networks. In order to provide more realistic vehicular networks deployment, this paper proposes a geometry-based coverage strategy to handle the deployment problem over urban scenarios. By taking the shape and area of road segments into account, our scheme suits different kinds of road topology and effectively solves the maximum coverage problem. To evaluate the effectiveness of our scheme, we compare this coverage strategy with α-coverage algorithm. The simulation result verifies that geometry-based coverage strategy culminates in a higher coverage ratio and a lower drop rate than α-coverage under the same constraints. The results also show that the deployment of Road Side Units (RSUs) in regions with high traffic flow is able to cover the majority of communication, so that less RSUs are able to provide better communication performance.

A Local Information Exchange Based Coverage-Preserving Protocol For Wireless Sensor Networks

Coverage preserving solutions have been reported and are basically based upon node scheduling and quality coverage. Node scheduling based solutions presents at least three challenging problems: 1) resolving conflicts when determining what nodes should be turned-off to save energy; 2) finding optimal wakeup strategies that avoid waking up more nodes than necessary; and 3) keeping connectivity and coverage of the network while optimizing the number of nodes. This paper presents a novel distributed solution that extends the coverage calculation method proposed by Tian and Georganas, referred here as C-PNSS scheme. The solution is based on local information exchange without the uncertainty of self-schedule algorithms. Our Optimal Coverage-Preserving Scheme (OCoPS) comprises a new Decision algorithm, devised to resolve the off-duty conflict problem for different network densities, and an energy aware Wakeup scheme that solves problems, such as coverage holes, that exist in current schemes. We discuss the implementation of OCoPS with the new Decision algorithm as an extension of LEACH. A set of simulation experiments was performed to evaluate OCoPS performance when compared to the C-PNSS scheme. Our results indicate that our solution outperforms C-PNSS by over 20% on network lifetime and by over 25% on network lifetime when the coverage rate is higher than 80%. The experimental results also show that our coverage scheme based on our extended coverage calculation method effectively limits the on-duty node number when compared the original C-PNSS scheme.

Adaptive Data-Gathering Protocols with Mobile Collectors for Vehicular Ad Hoc and Sensor Networks

Energy efficiency and low message delay are the basic QoS requirements for data collection in vehicular ad-hoc and sensor networks. In order to achieve these requirements, many solutions have been developed by attaching collectors/sinks to vehicle or aircraft and moving them either randomly or along a predefined route. This paper presents an adaptive data gathering protocol (ADG) that employs multiple mobile collectors (instead of sinks) to help an existing wireless sensor network achieve such requirements. In the proposed ADG protocol, a virtual elastic-force model is used to help mobile collectors adjust their moving speed and direction while adapting to changes within the network. Because of the irregularity of the information generation rate as well as the cost of mobile collectors, the number of collectors can not be predefined. Mobile collectors are sent out by sink if the information in the network is beyond the capabilities of existing mobile collectors, and are called back when they become redundant. In this paper we discuss our ADG protocol, highlight how its performance can be enhanced using both multi-hop OCOPS and LEACH protocols. We report on the performance evaluation of ADG protocol using an extensive set of simulation experiments. Our simulation results show that the proposed ADG algorithm can be a flexible means of meeting the constraints and different requirements of monitoring applications.

A bio-inspired coverage-aware scheduling scheme for wireless sensor networks

In the densely deployed wireless sensor networks, sensors are scheduled over time in order to maintain the coverage while saving energy of networks. In this article, we investigate the coverage-aware scheduling problem using genetic algorithms. Sensors are optimally scheduled in different time slots to maximize the overall coverage under the given k-cover requirement and lifetime of networks. A set of simulation is carried out. The simulation result shows that, using the optimal schedule generated by genetic algorithm, our algorithm can optimize the coverage performance of wireless sensor network in terms of overall coverage rate and number of active sensors.

Reducing Handoff Latency for NEMO-Based Vehicular Ad Hoc Networks

In a vehicular ad hoc network, vehicles can communicate with their correspondent nodes through the Internet using various wireless technologies. This kind of wireless networks brings a lot of new applications to metropolitan networks, such as online games, VoIP, etc. However, compared with traditional wireless networks, the high speed of vehicles and the limited transmission range of antennas introduce more frequent handoffs. During the handoff, vehicles have to switch their access points to establish new connections and the current wireless communications will be ceased temporarily. Therefore, long handoff latency causes poor throughput and obvious jitter. In this paper, a fast handoff scheme is proposed for vehicular networks. Using this scheme, vehicles are divided into different clusters; and within each cluster, the network mobility solution is used to reduce the total number of handoffs. Moreover, before the mobile routers start actual handoff process, they can receive their new care of addresses through assistant nodes in the same cluster. Simulation results demonstrate that handoff latency can be significantly reduced by our scheme.

A Novel Predictive Handover Protocol for Mobile IP in Vehicular Networks

Vehicular networking is an emerging technology that offers the potential of providing a variety of new services. However, extending vehicular networks to include internet protocol (IP) connections is still problematic, due in part to the incompatibility of mobile IP handovers with the increased mobility of vehicles. The handover process, consisting of discovery, registration, and packet forwarding, has a large overhead and disrupts connectivity. With increased handover frequency and smaller access-point (AP) dwell times in vehicular networks, the handover causes a large degradation in performance. This paper proposes a predictive handover protocol, using a combination of a Kalman filter (KF) and an online hidden Markov model (HMM), to minimize the effects of prediction errors and to capitalize on advanced handover registration. Extensive simulated experiments were carried out in the network simulator ns-2 to study the performance of the proposed protocol within a variety of traffic and network topology scenarios. Results show a significant improvement to both prediction accuracy and network performance when compared with recent proposed approaches.