Ranjith Liyanapathirana

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.

Selective sub-carrier relaying and power allocation for multi-relay-assisted cooperative OFDM systems

We investigate the relay selection, sub-carrier pairing and power allocation problems in a two-hop, multi-relay-assisted cooperative OFDM system with amplify-and-forward (AF) relays. We propose a sub optimal but more feasible approach to solve the power allocation problem with relay selection and sub-carrier pairing. The proposed method is based on selective sub-carrier relaying concept where the relays forward only a selected set of sub-carriers of the received OFDM symbol. Transmit power allocation is performed such that the end-to-end system capacity is maximized under individual power constraints at each node. The proposed technique outperforms the all sub-carrier relaying scheme when the relays are distributed between the source and the destination.

Outage probability analysis of two-hop MIMO relay networks with interference at the relay

In this paper, the outage probability analysis of two-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay networks is presented. The source and the destination are equipped with multiple antennas and communicate with each other, with the help of a single antenna relay which is subject to interference. Two systems are considered; transmit antenna selection with maximal ratio combining (TAS/MRC) and transmit antenna selection with selection combining (TAS/SC). We derive closed form expressions for the cumulative distribution function (CDF) for an arbitrary number of interferences under flat Rayleigh fading channels. Analytical and Monte Carlo simulation results are presented to validate the analysis and to demonstrate the effect of interference.

Efficient simulation of OFDM and OSTBC-OFDM systems over multipath Rayleigh fading channels

We present an importance sampling (IS) based approach for efficient simulation of Orthogonal Frequency Division Multiplexing Systems (OFDM) operating over multipath fading channels. We derive the optimal biasing parameters for Rayleigh fading multipath channels considering an OFDM system and an OFDM system with Orthogonal Space-Time Block Coded (OSTBC) transmission. The numerical results prove significant computational efficiency gains in the order of 108 in estimating probabilities of the order 10−11.

Measurement System With Accelerometer Integrated RFID Tag for Infrastructure Health Monitoring

This paper presents a measurement system for measuring dynamic acceleration of infrastructure remotely using semipassive radio-frequency identification (RFID) tag. This measurement is critical to the vibration-based method for infrastructure health monitoring. Design considerations of accelerometer integrated ultrahigh-frequency RFID tag and dynamic acceleration measurements through an RFID wireless link are discussed. Measurement results of the system for a structural specimen have shown that it is capable of acquiring data which provides the information of natural frequency of the structural specimen. Moreover, the system can distinctively identify the state changes of the structural specimen by natural frequency shifts. These results are benchmarked against the results obtained with two commercial systems. It is shown that the standard deviation of the measurement of the natural frequency is ±0.01 Hz which is very close to the standard deviation of the commercial measurement systems.

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.

Fast simulation of turbo codes over AWGN channels

In this paper, we illustrate the use of importance sampling (IS) for efficient simulation of Turbo Codes over additive white Gaussian noise (AWGN) channels. In particular, we show how to bias the probability density function (pdf) of the AWGN process using the most probable error path (MPEP) method in order to maximize the computational efficiency gain. The new noise pdf is designed based on the optimal biased distribution where zero variance estimator can be achieved. It is demonstrated that the proposed method requires much smaller sample sizes to achieve the same accuracy required by a conventional MC estimator.

Power allocation in OFDM cognitive radio relay networks with outdated channel state information

In this paper, we study power allocation in OFDM cognitive radio CR relay networks. The objective of power allocation is to maximize the instantaneous capacity of the CR network. It is assumed that the available channel state information between the secondary and primary users is an outdated but correlated version of the actual instantaneous channel state information. Optimal power allocation schemes are developed for both decode-and-forward and amplify-and-forward relay assisted CR transmission, assuming that the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. In addition, suboptimal power allocation schemes with reduced complexity are also proposed. Performance of the proposed schemes is compared with uniform power allocation and numerical results confirm that the proposed power allocation schemes achieve significant capacity improvement in comparison to uniform power loading. Furthermore, the proposed suboptimal power allocation schemes can be used as less complex alternatives for optimal power allocation with some capacity degradation. Copyright

Power allocation in DF relay assisted OFDM cognitive radio networks with outdated CSI

In this paper, we investigate power allocation in decode-and-forward (DF) relay assisted OFDM cognitive radio (CR) networks. The objective is to maximize the instantaneous capacity of the CR system. Due to channel feedback delay, the available channel state information (CSI) between the secondary and primary users is considered as an outdated but correlated version of the actual instantaneous CSI. An optimal power allocation scheme is presented assuming that the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. In addition, a suboptimal scheme with reduced complexity is also proposed. Numerical results confirm that the proposed suboptimal power allocation scheme can be used as a less complex alternative for optimal power allocation with some degradation in capacity.