Sumudu Wijetunge

Wireless Sensor Networks for Structural Health Monitoring: Considerations for communication protocol design

Structural Health Monitoring (SHM) systems have been used with many important structures to enhance the public safety and to reduce the economical losses. Wireless Sensor Networks (WSN) is an emerging technology which can be deployed with SHM applications. However, some system requirements have been overlooked in the current WSN designs for SHM applications. Therefore a complete analysis in system requirements is needed for WSN for SHM. In this paper, the system requirements posed by SHM applications are considered to assess potential candidates for the protocols in WSN for SHM. Based on that, we show that none of the commonly available protocols satisfy all the requirements associated with SHM systems. Hence, it is necessary to modify the existing protocols or design an entirely new protocol to completely satisfy the requirements of WSN for SHM application.

Performance Analysis of IEEE 802.15.4 MAC Protocol with ACK Frame Transmission

A common way of achieving reliable data transmission in wireless sensor network applications is by using a retransmission mechanism with medium access control (MAC) level acknowledgements. The IEEE 802.15.4 standard, which is widely acknowledged as the state-of-the-art PHY/MAC standard for wireless sensor networks, supports MAC-level acknowledgements and retransmissions. In this paper, based on a three-dimensional discrete-time Markov chain, we propose a new analytical model to analyse the performance of the IEEE 802.15.4 MAC protocol with retransmission and MAC level acknowledgements under unsaturated traffic conditions. Further, we present a simplified version of the proposed analytical model with some approximations. Using the proposed analytical models, we evaluate the network performance in terms of the aggregate channel throughput, average power consumption of a node, frame discard ratio, and frame delivery ratio. The analytical results are substantiated through ns−2 simulations. The effects of the frame arrival rate, number of nodes, frame length and various MAC parameters, on the performance of the network are discussed. The results of both analytical models are compared and it is shown that the simplified model provides an acceptable accuracy with less computational complexity.

Throughput analysis of IEEE 802.15.4 MAC protocol in the presence of hidden nodes

The IEEE 802.15.4 medium access control (MAC) protocol, which is widely used in current WSN deployments, does not provide any hidden node avoidance mechanisms. This leads to severe performance degradation in IEEE 802.15.4 MAC protocol in the presence of hidden nodes. In this paper, we apply a discrete-time Markov Chain model to analyse the throughput of IEEE 802.15.4 MAC protocol in the presence of hidden nodes. Based on the proposed model, the effects of network size, network topology, frame length and frame arrival rate on the throughput of the system are investigated.

IEEE 802.15.4 based hybrid MAC protocol for hybrid monitoring WSNs

This paper presents an improved wireless MAC protocol that enables IEEE 802.15.4 based WSNs to provide an energy-efficient, reliable, and delay-limited data transmission for hybrid monitoring applications. The proposed protocol is implemented in ns-2, and its performance is evaluated in terms of energy consumption, delay, and reliability in data transmission. Extensive simulations verify the improved performance of the proposed protocol in hybrid monitoring applications.

Throughput analysis of IEEE 802.15.4 beacon-enabled MAC protocol in the presence of hidden nodes

The presence of hidden nodes degrades the performance of wireless networks due to an excessive amount of data frame collisions. The IEEE 802.15.4 medium access control (MAC) protocol, which is widely used in current wireless sensor networks, does not provide any hidden node avoidance mechanisms and consequently could lead to severe performance degradation in networks with hidden nodes. This paper presents a simple technique based on discrete-time Markov chain analysis to approximate the throughput of IEEE 802.15.4 MAC protocol in the presence of hidden nodes. Using different network configurations, we validate the applicability of the proposed analysis for generic star-topology networks. Based on the analysis, the effects of network size, topology, frame length and frame arrival rate on the throughput of the system are investigated.

Impact of MAC parameters on the performance of IEEE 802.15.4 MAC protocol with ACK frame transmission

IEEE 802.15.4 medium access control (MAC) specifications support an optional feature of MAC-level acknowledgements and frame retransmissions to ensure reliability in data transmission. In this paper, we propose a generalised analytical model, which is based on a three-dimensional, discrete-time Markov chain, to analyse the performance of the IEEE 802.15.4 MAC protocol with retransmission and MAC-level acknowledgements under unsaturated traffic conditions. The network performance is evaluated in terms of aggregate throughput, average power consumption of a node, frame discard ratio and frame delivery ratio. Based on our results, we discuss the impact of different MAC parameters on the performance of the network.

Performance analysis of IEEE 802.15.4 MAC Protocol for WSNs with ACK frame transmission under unsaturated traffic conditions

In this paper, we apply a discrete-time Markov Chain model to analyse the performance of IEEE 802.15.4 MAC Protocol with acknowledgement (ACK) frame transmission under unsaturated traffic conditions. We evaluate the system performance in terms of aggregate throughput and average power consumption of a node. Analytical results are substantiated through ns2 simulations. The effects of frame arriving rate, number of nodes and frame length, on the performance of the system are also discussed.

Throughput analysis of non-beacon enabled IEEE 802.15.4 networks with unsaturated traffic

In this paper, we propose a Markov chain based analysis to model the unslotted CSMA/CA medium access control protocol used in non-beacon enabled IEEE 802.15.4 networks that operate under unsaturated traffic conditions. The proposed analysis is then used to evaluate the performance of the protocol in terms of the aggregate network throughput. Based on our results, we discuss the impact of different network parameters including the number of nodes and data frame length on the unsaturated throughput of the protocol.

Social Impact of SMS in Sri Lanka

Though Sri Lanka has a relatively low penetration of fixed (landline) phones, mobile phones have made a significant penetration during last six years. The number of mobile subscribers within the island by the end of 2007 was almost 70 times of the customers reported a decade back. A large number of supplementary services have been introduced with the booming increase in the mobile customer base. Short Message Service (SMS) is one such service that has made a significant penetration in Sri Lankan society. Nowadays, SMS has become the major non verbal communication channel among the general public. The cost effectiveness of the service has lead to its popularity within the country. From simple person to person communication to achieving a confidential bank transaction, a vast range of applications have emerged based on SMS. In this paper, we present how Sri Lanka has adopted to SMS. In particular, we investigate the factors causing the popularity of this service in Sri Lanka and its social impact on the island nation.

Performance analysis of IEEE 802.15.4 MAC protocol for WSNs in burst error channels

A three-dimensional discrete-time Markov Chain model is applied to analyse the performance of the IEEE 802.15.4 MAC protocol under burst channel errors. Real world wireless sensor network conditions including unsaturated traffic, frame retransmission and acknowledgement (ACK) frame transmission are considered for the analysis. The system performance is evaluated in terms of aggregate network throughput, average power consumption per node, frame delivery ratio, and bytes-per-Joule capacity per node. Analytical results are validated through ns − 2 simulations. The effects of varying channel conditions and frame arrival rate on the performance of the system are also discussed.