Interference mitigation strategy design and applications for wireless sensor networks

The Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 standard presents a very useful technology for implementing low-cost, low-power, wireless sensor networks. Its main focus, which is to applications requiring simple wireless connectivity with relaxed throughout and latency requirements, makes it suitable for connecting devices that have not been networked, such as industrial and control instrumentation equipments, agricultural equipments, vehicular equipments, and home appliances. Its usage of the license-free 2.4 GHz frequency band makes the technique successful for fast and worldwide market deployments. However, concerns about interference have arisen due to the presence of other wireless technologies using the same spectrum. Although the IEEE 802.15.4 standard has provided some mechanisms, to enhance capability to coexist with other wireless devices operating on the same frequency band, including Carrier Sensor Multiple Access (CSMA), Clear Channel Assessment (CCA), channel alignment, and low duty cycle, it is essential to design and implement adjustable mechanisms for an IEEE 802.15.4 based system integrated into a practical application to deal with interference which changes randomly over time. Among the potential interfering systems (Wi-Fi, Bluetooth, cordless phones, microwave ovens, wireless headsets, etc) which work on the same Industrial, Scientific, and Medical (ISM) frequency band, Wi-Fi systems (IEEE 802.11 technique) have attracted most concerns because of their high transmission power and large deployment in both residential and office environments. This thesis aims to propose a methodology for IEEE 802.15.4 wireless systems to adopt proper adjustment in order to mitigate the effect of interference caused by IEEE 802.11 systems through energy detection, channel agility and data recovery. The contribution of this thesis consists of five parts. Firstly, a strategy is proposed to enable IEEE 802.15.4 systems to maintain normal communications using the means of consecutive transmissions, when the system s default mechanism of retransmission is insufficient to ensure successful rate due to the occurrence of Wi-Fi interference. Secondly, a novel strategy is proposed to use a feasible way for IEEE 802.15.4 systems to estimate the interference pattern, and accordingly adjust system parameters for the purpose of achieving optimized communication effectiveness during time of interference without relying on hardware changes and IEEE 802.15.4 protocol modifications. Thirdly, a data recovery mechanism is proposed for transport control to be applied for recovering lost data by associating with the proposed strategies to ensure the data integrity when IEEE 802.15.4 systems are suffering from interference. Fourthly, a practical case is studied to discuss how to design a sustainable system for home automation application constructed on the basis of IEEE 802.15.4 technique. Finally, a comprehensive design is proposed to enable the implementation of an interference mitigation strategy for IEEE 802.15.4 based ad hoc WSNs within a structure of building fire safety monitoring system. The proposed strategies and system designs are demonstrated mainly through theoretical analysis and experimental tests. The results obtained from the experimental tests have verified that the interference caused by an IEEE 802.11 system on an IEEE 802.15.4 system can be effectively mitigated through adjusting IEEE 802.15.4 system s parameters cooperating with interference pattern estimation. The proposed methods are suitable to be integrated into a system-level solution for an IEEE 802.15.4 system to deal with interference, which is also applicable to those wireless systems facing similar interference issues to enable the development of efficient mitigation strategies

A self-organizing routing algorithm for wireless sensor networks

Wireless sensor networks (WSN) are designed to collect and process sensory data from environments. Some environments are dangerous or un-reachable to human beings and it is difficult to replace sensor nodes when they are out of battery or even destroyed, i.e. wireless sensor nodes are in general prone to failure. This kind of characteristics require WSN to detect whether or not its next destination is still available (alive) and to maintain a transferring path if the next destination in the route does not exist (dead). In the normal state, nodes are in power-saving 'sleep' state. When a route is created for some purpose, all nodes in this route will be active and be ready to respond requests from its neighbors. Our approach is to maintain the routing table up-to-date by sending message from a last node to its next node and judging whether the next node is alive according to the response. If problems happen, node will self-organize and try to maintain transferring

Safety and security of remote monitoring and control of intelligent home environments

Intelligent home environments are one of the major application areas of pervasive computing. Safety and security are two most important issues in the remote monitoring and control of intelligent home environments. This article takes safety and security into consideration together and proposes a phone-out-only policy for ensuring security and virtual home environments for safety. A remote monitoring and control system for a security camera is used to illustrate the new methodologies for safety and security. By using the demonstration system people are able to easily monitor and control a security camera, central heating, microwave oven and washer from anywhere by using mobile phones. Our system distinguishes from the existing DTI (Department of Trade and Industry in the UK) next wave technologies and a few of on-going EU projects in the ways of dealing with safety and security and its simplicity. Remote monitoring and control of intelligent home environments can be of great benefits to the working families and holiday makers and has a great commercial potential

Zigbee enabled radio frequency identification system

The Radio Frequency Identification (RFID) system is a widely used Auto-ID technology today to identify and track objects and people in manufacturing, inventory management, retailing, and security applications. The Zigbee technology, which is a recently emerged network communication protocol based on the IEEE 802.15.4 standard, provides a self-organized mesh network topology with a power-effective, low data rate and multi-hop data transmission. The RFID system could profit some of its features by introducing the Zigbee technology into the existing RFID architectures, such as having extended effective range, improving network flexibility and having compatibility with other Zigbee enabled environment systems. In this paper we first discuss the possible benefits and applications while applying Zigbee to the different parts of the RFID system. Then an integrated Zigbee RFID system architecture is discussed and a demo system is described at the end of the paper

A ZigBee-based home automation system

In recent years, the home environment has seen a rapid introduction of network enabled digital technology. This technology offers new and exciting opportunities to increase the connectivity of devices within the home for the purpose of home automation. Moreover, with the rapid expansion of the Internet, there is the added potential for the remote control and monitoring of such network enabled devices. However, the adoption of home automation systems has been slow. This paper identifies the reasons for this slow adoption and evaluates the potential of ZigBee for addressing these problems through the design and implementation of a flexible home automation architecture. A ZigBee based home automation system and Wi-Fi network are integrated through a common home gateway. The home gateway provides network interoperability, a simple and flexible user interface, and remote access to the system. A dedicated virtual home is implemented to cater for the system’s security and safety needs. To demonstrate the feasibility and effectiveness of the proposed system, four devices, a light switch, radiator valve, safety sensor and ZigBee remote control have been developed and evaluated with the home automation system

Safety and Security of Remote Monitoring and Control of intelligent Home Environments

Intelligent home environments are one of the major application areas of pervasive computing. Safety and security are two most important issues in the remote monitoring and control of intelligent home environments. This article takes safety and security into consideration together and proposes a phone-out-only policy for ensuring security and virtual home environments for safety. A remote monitoring and control system for a security camera is used to illustrate the new methodologies for safety and security. By using the demonstration system people are able to easily monitor and control a security camera, central heating, microwave oven and washer from anywhere by using mobile phones. Our system distinguishes from the existing DTI (Department of Trade and Industry in the UK) next wave technologies and a few of on-going EU projects in the ways of dealing with safety and security and its simplicity. Remote monitoring and control of intelligent home environments can be of great benefits to the working families and holiday makers and has a great commercial potential

Charge Carrier Dynamics of Organic Cation-Treated Perovskites Probed with Time-Resolved Microwave Conductivity

Metal halide perovskites have emerged as a set of promising optoelectronic materials benefiting from their outstanding optoelectronic properties and unprecedented success in photovoltaics. Recent studies have suggested that mixing lower-dimensional A-site cations within perovskites helps mitigate this environmental and phase instability for 3D perovskites. However, the charge carrier transport properties in mixed 2D/3D perovskites are still not fully understood. In this work, charge carrier mobilities and recombination rate constants in perovskite thin films were analyzed with transient time-resolved microwave conductivity and time-resolved photoluminescence. It was found that upon large-cation treatment of 3D perovskites, charge carrier transport and radiative recombination efficiency were enhanced by the passivation of surface defects, which is evidenced by the decay dynamics of charge carriers

A Self-Organizing Routing Algorithm for Wireless Sensor Networks

Wireless sensor networks (WSN) are designed to collect and process sensory data from environments. Some environments are dangerous or un-reachable to human beings and it is difficult to replace sensor nodes when they are out of battery or even destroyed, i.e. wireless sensor nodes are in general prone to failure. This kind of characteristics require WSN to detect whether or not its next destination is still available (alive) and to maintain a transferring path if the next destination in the route does not exist (dead). In the normal state, nodes are in power-saving 'sleep' state. When a route is created for some purpose, all nodes in this route will be active and be ready to respond requests from its neighbors. Our approach is to maintain the routing table up-to-date by sending message from a last node to its next node and judging whether the next node is alive according to the response. If problems happen, node will self-organize and try to maintain transferring

Transparent Heterogeneous Networks for Remote Control of Home Environments

Home environment has seen a rapid introduction of network technologies. The types of home networks introduced, include home automation, multimedia entertainment, and security networks. These networks are often developed by different organisations and consist of varying network technologies. Consequently, little attention has been given to the coexistence and interoperability of these networks. This naturally developing heterogeneous network architecture introduces new and significant usability and safety concerns. This paper addresses these concerns, through the design and implementation of a home gateway. A case study is implemented showing the application of the home gateway, to facilitate interoperability, between a home automation and a video surveillance network

Robust Estimation for Generalized Additive Models

<div><p>This article studies <i>M</i>-type estimators for fitting robust generalized additive models in the presence of anomalous data. A new theoretical construct is developed to connect the costly <i>M</i>-type estimation with least-squares type calculations. Its asymptotic properties are studied and used to motivate a computational algorithm. The main idea is to decompose the overall <i>M</i>-type estimation problem into a sequence of well-studied conventional additive model fittings. The resulting algorithm is fast and stable, can be paired with different nonparametric smoothers, and can also be applied to cases with multiple covariates. As another contribution of this article, automatic methods for smoothing parameter selection are proposed. These methods are designed to be resistant to outliers. The empirical performance of the proposed methodology is illustrated via both simulation experiments and real data analysis. Supplementary materials are available online.</p></div