Li-Ling Hung

A novel multi-channel MAC protocol with directional antenna for enhancing spatial reuse and bandwidth utilization in WLANs

This paper aims at developing an efficient MAC protocol for wireless LAN by considering multi-channel and directional antennae. Extending IEEE 802.11 to a multi-channel environment not only exploits the bandwidth utilization but also reduces the degree of contentions. Involving directional antennae in designing multi-channel MAC protocol additionally increases the spatial reuse, allowing more parallel communications. This study proposes an efficient Multi-Channel MAC protocol with a Directional Antenna (MCDA) for WLAN. Since each station is only equipped with a single antenna, communicating pairs that progress their communications on data channels cannot maintain the channel usage information which is only obtained from the control channel, raising the channel collision problem. The proposed protocol adopts the channel switch sequence (CSS) mechanism to cope with the channel collision problem and to reduce message exchange overhead for switching channels. According to the state management, MCDA then controls directional antenna transmitting data on a selected channel to exploit the opportunities of spatial reuse, and to maintain fairness among communicating pairs. Simulation results show that the proposed MCDA protocol maintains the fairness and significantly improves bandwidth utilization and throughput.

BUFE-MAC: A Protocol With Bandwidth Utilization and Fairness Enhancements for Mesh-Backbone-Based VANETs

Vehicular ad hoc network technologies can improve traffic safety for drivers and provide comfort services for passengers. Because the hardware of a roadside unit (RSU) is costly, in most previous research, vehicles might exchange data with an RSU through multihop transmissions. However, the vehicle with a larger number of hops to the RSU has fewer opportunities and longer time to exchange its data with the RSU because the contentions and collisions increase with the number of hops. This paper proposes the bandwidth utilization and fairness enhancements medium access control (BUFE MAC) protocol, which considers a vehicular ad hoc network that accesses the Internet through fixed Internet Gateways along the road. BUFE-MAC aims at increasing bandwidth utilization, maintaining fairness, and avoiding collision. The performance study reveals that the proposed MAC protocol not only avoids the collision problem but improves the performance in terms of end-to-end throughput and fairness as well.

On-supporting energy balanced k-barrier coverage in wireless sensor networks

The k-barrier coverage problem is known as the problem of detecting the intruders by at least k sensors when the intruders moving along the crossing paths from one boundary to another. This paper proposes decentralized algorithms to cope with the k-barrier coverage problem. For a given value k, the proposed algorithms find out the maximum disjoint sets of sensors such that each set of sensors meets the requirement of k-barrier coverage for users. Three mechanisms, called Basic, Backtracking, and Branch, are proposed for constructing as more as possible the disjoint sets of sensors that satisfy the requirement of k-barrier coverage. Performance study reveals that the proposed algorithms achieve near-optimal performance.

Cooperative MAC Protocol for Multi-Channel Wireless Networks

The existing channel variation (or fading) is one of the big challenges that affects the capacity of wireless networks. Recently, cooperative communication has been considered as an effective way to improve the communication reliability. In this paper, a novel medium access control (MAC) protocol, called CMMI, has been proposed for exploiting the opportunities of cooperative transmissions to improve link reliability in wireless networks. Based on the new proposed multi-channel model, the proposed CMMI fully utilizes the wireless spectrum for finding the cooperative nodes and then collaboratively recover the failure transmissions. Simulation results show that the proposed CMMI can obviously improve the network performance in terms of network throughput, average packet delay and packet delivery ratio.

Decentralized and energy-balanced algorithms for maintaining temporal full-coverage in mobile WSNs

Coverage is one of the most important issues in Wireless Sensor Networks (WSNs). However, full coverage only can be achieved when surplus mobile sensors contribute a coverage area larger than the hole size. When there is no surplus mobile sensor to cover a big hole, previous studies have utilized mobile sensors by moving the hole from one location to another, therefore achieving temporal full-coverage, where each location on the monitoring region has been ever covered by mobile sensors during a fixed time interval. However, with only some mobile sensors participating in the hole-movement task, this results in an energy-imbalance WSN. This paper considers a mobile WSN that contains a big hole where there exists no redundant mobile sensor to heal the hole. Three distributed algorithms, called Basic, Forward-Only, and Any-Direction movement mechanisms, are proposed to achieve the purpose of temporal full-coverage in a way that the total energy consumption is minimized or that the energy consumption of all mobile sensors that participate in the hole-movement task are balanced. Simulation results reveal that the proposed hole-movement mechanisms enhance the coverage of WSNs and balance the energy consumption of mobile sensor nodes. Copyright

A Cognitive Radio MAC protocol for exploiting bandwidth utilization in wireless networks

Cognitive Radio (CR) is a novel and promising spectrum management technique which aims to cope with the spectrum scarcity problem occurred in unlicensed bands and alleviate the inefficient spectrum utilization of licensed bands. To ensure that the operation of licensed users will not be adversely affected but the licensed bands can be fully utilized by the unlicensed users, this paper proposes a cognitive radio MAC protocol, called SMC-CR-MAC. When any Primary User (PU) is detected, the proposed SMC-CR-MAC applies Contiguous Channel Switching and Sender-Receiver Channel Swap approaches to cope with the rendezvous, packet collision, and channel congestion problems. Simulation results show that the proposed SMC-CR-MAC can significantly improve the network performance in terms of the utilization of licensed bands and network throughput.

A cooperative mechanism for monitoring in rechargeable wireless mobile sensor networks

The mobile wireless sensor network has much more popular applications in recent years. In the meanwhile, wireless rechargeable sensor networks emerge some technological breakthroughs. However, employing the rechargeable ability to improve the efficiency and lifetime of environment monitoring is a great challenge without cooperation when the rechargeable area is partial of the environment. In this paper, a distributed cooperative algorithm for partial rechargeable mobile wireless sensor network is proposed. The algorithm considers both energy consumption for movement and the resident energy of mobile sensors to cooperate with neighbors for expending the lifetime of environment monitoring. Furthermore, we provide analytical result for obtaining the factors achieving monitoring the environment eternally under some arbitrary parameter settings. The simulations results represent that the efficiency of proposed algorithm.

On Distinguishing Relative Locations with Busy Tones for Wireless Sensor Networks

Bounding-box mechanism is a well known low-cost localization approach for wireless sensor networks. However, the bounding-box location information can not distinguish the relative locations of neighboring sensors, hence leading to a poor performance for some applications such as location-aware routing. This paper proposes a Distinguishing Relative Locations (DRL) mechanism which uses a mobile anchor to broadcast tones and beacons aiming at distinguishing the relative locations of any two neighboring nodes. Experimental study reveals that the proposed DRL mechanism effectively distinguishes relative locations of any two neighboring nodes and hence significantly improves the performance of location-aware routing in wireless sensor networks (WSNs).

ORZBP: An Obstacle-Resistant Zone-based Broadcasting Protocol for Wireless Sensor Networks

Wireless Sensor Networks (WSNs) comprise a few sink nodes and a large number of sensor nodes. The WSN environment contains unpredictable obstacles, such as mountains, lakes, buildings, or regions without any sensor node, impeding or blocking message relay. Broadcasting is an essential operation broadly used in WSNs. However, the blind flooding results in the large-scale waste of energy and bandwidth resources even though it is the simplest way to overcome obstacle-resistant problems. On the other hand, the blind flooding also raises the amount of packet collisions and contentions. This paper proposes a distributed obstacle resistant broadcasting protocol, called as ORZBP, to reduce the number of forwarding nodes and to overcome the obstacle problem. Experimental results reveal that ORZBP reduces the redundant bandwidth and power consumptions, avoids the possible packet collision as well as achieves the high success rate.

Location-aware power saving mechanism based on adaptive Quorum systems for mobile Ad hoc networks

IEEE 802.11 specifies a Power Saving Mode (PSM) in order to save the energy consumptions of mobile hosts. Following the standard of PSM, a number of studies [1–4] further discussed the wakeup/sleep scheduling of beacon intervals based on Quorum systems so that any communication pair of hosts has common awake intervals for data exchange. However, most of them did not take into consideration the fact that non-neighbor stations do not require to have a common wake up intervals since they are unable to communicate with each other. Hence the energy conservation and the transmission delay can be not significantly improved. This paper utilizes the location information and proposes a location-aware power saving mechanism. Experiment results reveal that the proposed scheme outperforms existing approaches in terms of energy conservation and transmission delay.