This paper analyzes the impact of stakeholder priorities and causal relationships between decision criteria when determining the most suitable renewable natural gas (RNG) and hydrogen gaseous fuels production path. The criteria indicators were defined to reflect the life cycle of environmental desirability and economic feasibility . The study introduces a framework-based approach using fuzzy multi-objective optimization by ratio analysis (FMOORA) with an integrated causality and importance weighting system. The core novelty of this study is the novel criterion weighting system that simultaneously considers the impacts of the internal and external causal relationships and the criteria importance arising from stakeholder priorities to derive a more realistic weighting scheme. Weighting schemes using fuzzy cognitive maps and the best-worst method were provided to consider the decision-maker’s priorities in highlighting each causality or importance weighting concept. Accordingly, the highest importance values of 0.152 and 0.267 were obtained for levelized cost of energy with fuzzy cognitive maps and the best-worst method, respectively. The profitability index scored the least importance values in both methods (fuzzy cognitive map – 0.071 and best-worst method – 0.038). Accordingly, RNG from livestock with pressure swing adsorption was ranked first under all weighting schemes. Hydrogen from steam methane reforming achieved the best spot under hydrogen production routes, with ranks varying from 8 to 12 when both RNG and hydrogen production scenarios are considered. The findings indicate that the proposed framework is useful for conducting preliminary feasibility assessments of gaseous fuel investment strategies. Additionally, the integrated weighting system can be considered in conjunction with other multi-criteria decision-making techniques to make more reliable decisions in different problems.

Analog backscatter enables sensing and communication at lower power consumption than digital backscatter. In analog tags, a sensor typically changes the resistance or capacitance value that then translates into a frequency change that is backscattered on top of a carrier. However, to read the sensor data with high resolution, a powerful receiver is required. The resolution of sensor data is limited by the FFT size and computation at the receiver. This limits the use of low-cost radio receivers, like RTL-SDR, that are gaining popularity in the RF community. We propose to use higher order harmonic frequencies, that are inherently generated by square wave backscattering at no extra cost, to derive sensor data using such low-cost radio receivers. We present experimental results that demonstrate the viability of our approach.

High-speed visible light communication (VLC) is a complementary technology to conventional radio frequency communication in wireless networks. One of the essential traits of VLC systems is the ability to provide wireless communication and illumination seamlessly. High-speed VLC systems use high-power LEDs as transmitters in their access points (APs). In real-world deployments, overlapping light beams from multiple APs are necessary to avoid unlit areas. However, overlapping light beams could cause interference in each other's communication at the receiver; hence APs must synchronise their communication. This paper presents Harmony, a time synchronisation system for VLC APs to synchronise their transmissions. Internally, Harmony uses synchronous transmissions in the infrared frequency spectrum to reach nodes over multiple hops. The evaluation of a prototype implementation of Harmony on a small-scale testbed shows that it can synchronise nodes up to nine hops with a maximum error of a few 100s of nanoseconds. While the enduring work on high-speed VLC systems primarily focuses on improving the performance of individual APs, Harmony provides an infrastructure for enhancing system-wide performance.

Z-number is a new framework of fuzzy sets that combines with constraint and reliability. Managing the uncertainty of Z-number is an important issue in the fuzzy decision making of Z-number based. In this paper, we first develop a new uncertainty measure of fuzzy set considering the influence of fuzziness measure and the range (or cardinality) of the fuzzy set. Some properties of the developed uncertainty measure of the fuzzy set are presented. We then propose and discuss method of measuring the uncertainty of Z-number. Examples are used to illustrate the effectiveness of the proposed methodologies.

In the application of Z-number, how to generate Z-number is a significant and open issue. In this paper, we proposed a method of generating Z-number based on the OWA weights using maximum entropy considering the attitude (preference) of the decision maker. Some numerical examples are used to illustrate the effectiveness of the proposed method. Results show that the attitude (preference) of the decision maker can give an optimal possibility distribution of the reliability for Z-number using maximum entropy.

A significant number of human and elephant lives have been lost due to the human-elephant conflict in Sri Lanka. To save lives of humans and elephants, it is therefore important to minimize encounters between them. In this paper, we present Eloc, a system that detects the presence of elephants using their infrasonic emissions near human habitats and then localize their positions. The high cost of infrasonic detectors is an important challenge to the real-world deployment of such localization systems, in particular in developing countries where the human-elephant conflict occurs. In order to address this problem, we design a low cost infrasonic detector that can be easily built using commodity off-the-shelf hardware. We present promising results in localizing an artificial infrasonic source and real-world experiments that suggest that we can localize free ranging elephants in the wild using this low cost infrasonic detector with an accuracy of around 10 m at distances of several hundred meters.

Glossy is a flooding-based communication primitive for low-power wireless networks that leverages constructive interference to achieve high reliability. The Low-power Wireless Bus (LWB) uses Glossy to abstract an entire wireless network into a shared bus like topology. As Glossy is not designed as a secure communication protocol, Glossy and hence LWB are vulnerable to unauthorised eavesdropping and packet injection attacks. In this paper, we propose several security mechanisms to protect Glossy and LWB communication and evaluate their effectiveness in real-world settings. The evaluation of the proposed security mechanisms shows that we can confine the effect of the packet injection attacks on Glossy networks into single hop nodes from the attacker.

The human-elephant conflict is causing significant damages to the life of human and elephants in Sri Lanka. Minimizing encounters between humans and elephants is hence crucial in alleviating the human-elephant conflict. We have earlier introduced Eloc, a cost-effective localization system that is based on infrasonic emissions from wild elephants. One of the remaining challenges is a resource-efficient method to detect the elephants' infrasonic emissions. We present our efforts on devising a support vector machine (SVM) that is able to detect elephant rumbles on Eloc nodes.

Visible Light Communication (VLC) is an emerging communication channel serving as a complement to traditional wireless communication. Visible light has many advantages over other communication channels like its inability to penetrate opaque objects. Securely sharing secret keys is a known problem in computer security. Sharing security keys using Radio Frequency (RF) communication is prone to sniffing attacks. In this paper, we introduce a system called BouKey which uses visible light to share keys. This makes BouKey immune to through the wall sniffing attacks. BouKey divides the key and shares it using multiple transmission bulbs allowing the key to be received in a specific area only. Our initial results show that the characteristics and height of the receiver, as well as the transmission angle play a key role in determining the shape and size of this area.

Glossy networks make use of concurrent ransmissions to achieve rapid network flooding in wireless networks with high reliability. They are robust against jamming and header injection attacks. We find that Glossy floods can be hijacked by a packet injection attacker to penetrate into the network and cause severe loss. We demonstrate the design of such an attacker by evaluating its effectiveness in a 30-node testbed.

Cyber-physical systems consist of several wirelessly connected components such as sensors that monitor physical phenomena, computational entities that make decisions based on sensed information and actuators that interact with physical processes. Connecting cyber-physical systems to the Internet using IP protocols increases interoperability by avoiding the need for protocol translation gateways. Unfortunately, in this context TCP has been disregarded since it is known to perform poorly in wireless scenarios as it treats packet loss as an indicator for network congestion rather than poor link quality. In this paper, we use the Low-power Wireless Bus (LWB) as a link layer for TCP/IP, taking advantage of its reliability and its routing-free communication. We design a system that integrates LWB with a low-power IP stack and includes TCP-aware schedulers for LWB. We evaluate our system with experiments on real hardware using uIP, a popular embedded Internet protocol stack. Our results demonstrate high TCP throughput in mobile and static scenarios and, furthermore, show that mobility does not decrease TCP performance.

The poor performance of TCP over wireless and lossy links has hindered its use in low power networks. The Low Power Wireless Bus (LWB) offers high reliable and low latency communication in IEEE 802.15.4 networks. In this paper, we argue that TCP can be used to provide reliable connectivity between sensor nodes in an LWB-based sensor network and external Internet hosts.