Tzu-Lin Wang

Throughput enhancement by exploiting spatial reuse opportunities with smart antenna systems in wireless ad hoc networks

Smart antenna (or multi-beam antenna) systems can support simultaneous transmissions (or receptions) of multiple packets in different beams using the same channel. However, network performance is highly dependent on transmission scheduling. This study develops two transmission-scheduling schemes for use with smart antenna systems to improve network throughput and reduce transmission delay. The proposed scheduling mechanisms, which are designed to minimize the average latency and maximize network throughput, exploit the opportunities for parallel transmissions and consider communication restrictions and packet sizes. The performance results indicate that the proposed schemes outperform previous schemes in network throughput and transmission delay.

Path Construction and Visit Scheduling for Targets by Using Data Mules

In this paper, the target patrolling problem was considered, in which a set of mobile data collectors, known as data mules (DMs), must efficiently patrol a given set of targets. Because the time interval (or visiting interval) between consecutive visits to each target reflects the degree to which that target is monitored, the goal of this paper was to balance the visiting interval of each target. This paper first presents the basic target points patrolling algorithm, which enables an efficient patrolling route to be constructed for numerous DMs, such that the visiting intervals of all target points are stable. For scenarios containing weighted target points, a weighted target points patrolling (W-TPP) algorithm is presented, which ensures that targets with higher weights have higher data collection frequencies. The energy constraint of each DM was also considered, and this paper presents a W-TPP with recharge (RW-TPP) algorithm, which treats the energy recharge station as a weighted target and arranges for DMs to visit the recharge station before running out of energy. The performance results demonstrated that the proposed algorithms outperformed existing approaches in average visiting frequency, DM movement distance, average quality of monitoring satisfaction rate, and efficiency index.

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.

SRA: A Sensing Radius Adaptation Mechanism for Maximizing Network Lifetime in WSNs

Coverage is an important issue that has been widely discussed in wireless sensor networks (WSNs). However, it is still a big challenge to achieve both purposes of full coverage and energy balance. This paper considers the area coverage problem for a WSN in which each sensor has a variable sensing radius. To prolong the network lifetime, a weighted Voronoi diagram (WVD) is proposed as a tool for determining the responsible sensing region of each sensor according to the remaining energy in a distributed manner. The proposed mechanism, which is called sensing radius adaptation (SRA), mainly consists of three phases. In the first phase, each sensor and its neighboring nodes cooperatively construct the WVD to identify the responsible monitoring area. In the second phase, each sensor adjusts its sensing radius to reduce the overlapping sensing region such that the purpose of energy conservation can be achieved. In the last phase, the sensor with the least remaining energy further adjusts its sensing radius with its neighbor for to maximize the network lifetime. Performance evaluation and analysis reveal that the proposed SRA mechanism outperforms the existing studies in terms of the network lifetime and the degree of energy balance.

TCWTP: Time-Constrained Weighted Targets Patrolling Mechanism in Wireless Mobile Sensor Networks

Target coverage problems have received much attention in recent years. In a large monitoring environment where targets are distributed over an entire monitored region, deploying static sensors leads to high hardware costs because a high number of sensors may be required to achieve network connectivity. This paper considers the target-patrol issue where a set of mobile data mules (DMs) are dispatched to efficiently patrol the given targets under a predefined time constraint. The targets are assigned weights indicating their importance, where more important targets should be visited more frequently by the DMs. Accordingly, this paper proposes a time-constrained weighted targets patrolling (TCWTP) algorithm for locally constructing efficient patrol paths, thereby ensuring globally stable intervals between visits to all target points. A performance analysis revealed that the proposed TCWTP mechanism outperforms existing works in terms of the average interval between visits, quality of monitoring satisfaction ratio, and monitoring fairness ratio.

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 MAC protocol by applying staggered channel model for cognitive radio networks

Cognitive radio (CR) is a novel and promising spectrum management technique, which aims to cope with the spectrum scarcity problem occurring 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 and that the licensed bands can be efficiently utilized by unlicensed users, this paper proposes a cognitive radio MAC protocol called SMC-CR-MAC. When any primary user is detected, the proposed SMC-CR-MAC protocol applies Contiguous Channel Switching and Sender-Receiver Channel Swap rules to cope with the rendezvous, packet collision, and channel congestion problems. Simulation results show that the proposed SMC-CR-MAC protocol can significantly improve the network performance in terms of utilization of licensed bands, standard deviation of traffic load on each channel, and probability of successful rendezvous.

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.

Joint energy-balanced and full-coverage mechanism using sensing range control for maximizing network lifetime in WSNs

Coverage is an important issue that has been widely discussed in wireless sensor networks (WSNs). However, it is still a big challenge to achieve both the purposes of full coverage and energy balancing. This paper considers the area coverage problem for a WSN where each sensor has variable sensing radius. A Weighted Voronoi Diagram (WVD) is proposed as a tool for determining the responsible sensing region of each sensor node according to the remaining energy in a distributed manner. To maximize the network lifetime, techniques for balancing energy consumptions of sensors are further presented. Performance evaluation reveals that the proposed joint energy-balanced and full-coverage mechanism, called EBFC, outperforms the existing studies in terms of network lifetime and degree of energy balancing.

JLR: Joint localization and routing for energy balance and obstacle resistence in WSNs

Recently, many location-aware routing protocols have been proposed to overcome the obstacles and construct the shortest route which minimizes the end-to-end delay and saves overheads for packet forwarding. However, most of them require accurate location information which is difficult to obtain. Another problem of existing location aware routing is that the sensor nodes located on the best route will frequently execute the packet forwarding and result in an energy-unbalanced problem. This phenomenon is especially significant when the WSNs contain obstacle. It is because that the border nodes around the obstacle are always in charge of packet forwarding. Joint consideration of localization and routing mechanism can improve the routing performance since the development of routing mechanism should take into consideration the degree of inaccurate location information which is determined by localization mechanism. This paper proposes a localization algorithm that uses mobile sensor with direction antenna to guarantee a specific accurate level of location information. A novel routing protocol which takes both energy balance and obstacle resistance issues into consideration is proposed to work with the proposed localization mechanism. To the best of our knowledge, this is the pilot study that integrates localization and routing mechanisms and considers both energy balance and obstacle resistance issues based on an environment with inaccurate location information. Performance study shows that the proposed routing protocol outperforms other existing routing protocols in terms of energy balancing and packet delivery ratio.