This paper proposes a reliable wildfire monitoring system based on a wireless sensor network (WSN) sparsely deployed in adverse conditions. The physical environment under consideration is characterized by asymmetric, irregular, and unreliable wireless links, inadequate Fresnel zone clearance, and routing problems, to name a few. We use reliable communication schemes on a fault-tolerant network topology, where sensory data are guaranteed to reach the base station with organized data storage and real-time visualization. Our approach has been validated experimentally for the case of peat-forest wildfire in southern Borneo where the fire breaks out frequently.

Abstract Recently, solar energy emerged as a feasible supplement to battery power for wireless sensor networks (WSNs) which are expected to operate for long periods. Since solar energy can be harvested periodically and permanently, solar‐powered WSNs can use the energy more efficiently for various network‐wide performances than traditional battery‐based WSNs of which aim is mostly to minimize the energy consumption for extending the network lifetime. However, using solar power in WSNs requires a different energy management from battery‐based WSNs since solar power is a highly varying energy supply. Therefore, firstly we describe a time‐slot‐based energy allocation scheme to use the solar energy optimally, based on expectation model for harvested solar energy. Then, we propose a flow‐control algorithm to maximize the amount of data collected by the network, which cooperates with our energy allocation scheme. Our algorithms run on each node in a distributed manner using only local information of its neighbors, which is a suitable approach for scalable WSNs. We implement indoor and outdoor testbeds of solar‐powered WSN and demonstrate the efficiency of our approaches on them. Copyright © 2010 John Wiley & Sons, Ltd.

We explore the use of IEEE 802.11 wireless technology to support health monitoring application, by providing ubiquitous connectivity while allowing patients greater mobility. The acquisition of electrocardiogram (ECG) is used as an example to highlight the engineering choices, such as packetization and access control rules, that must be made in designing a wireless transport. The error-prone nature of wireless channels, together with the unpredictable delay and jitter caused by the non-deterministic nature of access to the wireless medium, need to be considered. We discuss how our design choice with respect to each issue affects the performance of the network in a high-quality ECG monitoring service with bounded delay. We evaluate our schemes using simulations with non-compressed 2-lead ECG data from the MIT-BIH arrhythmia database.

Some of the most challenging issues in data outsourcing scenario are the enforcement of authorization policies and the support of policy updates. Ciphertext-policy attribute-based encryption is a promising cryptographic solution to these issues for enforcing access control policies defined by a data owner on outsourced data. However, the problem of applying the attribute-based encryption in an outsourced architecture introduces several challenges with regard to the attribute and user revocation. In this paper, we propose an access control mechanism using ciphertext-policy attribute-based encryption to enforce access control policies with efficient attribute and user revocation capability. The fine-grained access control can be achieved by dual encryption mechanism which takes advantage of the attribute-based encryption and selective group key distribution in each attribute group. We demonstrate how to apply the proposed mechanism to securely manage the outsourced data. The analysis results indicate that the proposed scheme is efficient and secure in the data outsourcing systems.

Troubleshooting unresponsive sensor nodes is a significant challenge in remote sensor network deployments. This paper introduces the tele-diagnostic powertracer, an in-situ troubleshooting tool that uses external power measurements to determine the internal health condition of an unresponsive host and the most likely cause of its failure. We developed our own low-cost power meter with low-bandwidth radio to report power measurements and findings, hence allowing remote (i.e., tele-) diagnosis. The tool was deployed and tested in a remote solar-powered sensing network for acoustic and visual environmental monitoring. It was shown to successfully distinguish between several categories of failures that cause unresponsive behavior including energy depletion, antenna damage, radio disconnection, system crashes, and anomalous reboots. It was also able to determine the internal health conditions of an unresponsive node, such as the presence or absence of sensing and data storage activities (for each of multiple sensors). The paper explores the feasibility of building such a remote diagnostic tool from the standpoint of economy, scale and diagnostic accuracy. To the authors' knowledge, this is the first paper that presents a remote diagnostic tool that uses power measurements to diagnose sensor system failures.

Broadcast and multicast services (BCMCS) in CDMA2000 wireless telecommunications networks restrict high- quality multimedia services to their intended recipients by encrypting content. The air specification of BCMCS includes the advance encryption standard (AES) block cipher in the security layer of the broadcast protocol suite. We surveyed the AES block cipher algorithm and characterized the time it requires. We also profiled the execution time of each transformation that comprises the AES cipher. Drawing on these results, we proposed a analytic model that can predict the time required to decrypt encrypted contents at a mobile by considering cross-layer information, such as the characteristics of error control using Reed-Solomon coding in the MAC layer and varying conditions of the fading channel in the physical layer. This model will enable us to estimate the buffer size required to ensure seamless multimedia services.

Using solar power in wireless sensor networks (WSNs) requires a different approach to energy consumption from networks with battery-based nodes. Since solar energy can be harvested periodically, our aim is to use this harvested energy efficiently for specific network-wide performance goals, not just to minimize the energy consumption to sustain the network lifetime. Therefore, we propose a flow control algorithm to maximize the amount of data collected by the network while cooperating with our energy allocation scheme in order to efficiently use the available solar energy which varies from time to time. Our algorithm runs on each node in a distributed manner using only information about its neighbors. We demonstrate the efficacy of our approach on a real solar-powered WSN.

In this paper, we present a reliable storage service, called SolarStore, that adaptively trades-off storage reliability versus energy consumption in solar-powered sensor networks. SolarStore adopts a predominantly disconnected network model, where long-running data-collection experiments are conducted in the absence of a continuous connection to the outside world. SolarStore (i) replicates data in the network until the next upload opportunity, and (ii) adapts the degree of data replication dynamically depending on solar energy and storage availability. The goal is to maximize the amount of data that can eventually be retrieved from the network subject to energy and storage constraints. Maximization of retrievable data implies minimizing sensing blackouts due to energy depletion as well as minimizing loss due to node damage in harsh environmental conditions. We have deployed an outdoor solar-powered sensor network, on which SolarStore is implemented and tested. An indoor testbed is also set up for performance evaluation under environmental conditions not attained locally. Experiments show that SolarStore is successful in dynamically responding to variations in the environment in a manner that increases retrievable data under different node failure scenarios.

In this paper, we present AdaptSens: a reliable data collection and storage system for solar-powered sensor networks. Unlike battery-operated devices, solar-powered systems have a less predictable energy supply and their ability to harvest energy depends on past spending, thereby creating incentives for adaptive matching of energy supply and demand. Our storage system is novel in its layered architecture and its incremental layer activation mechanism. AdaptSens provides a set of functions, in separate layers, such as sensory data collection, replication (to prevent failure-induced data loss), and storage balancing (to prevent depletion-induced data loss). The mechanism utilizes surplus energy when available by activating more layers, and resorts to progressively more energy-efficient (partial hibernation) modes when energy is scarce. Best reliability is achieved when all layers are active but meaningful intermediate modes allow different degrees of energy conservation. The efficacy of AdaptSens in trading off reliability for energy is tested on both an outdoor system and an indoor testbed. Evaluation results show that AdaptSens minimizes the sum of all data losses when combining the energy, storage and node failure factors.

BCMCS (broadcast and multicast services) greatly increase the capacity of CDMA2000 mobile networks for multimedia broadcasting, but only require minor changes to existing radio and core network protocols. To provide high-quality multimedia services over error-prone wireless networks, we need to control delay, because it is one of the most important QoS parameters for multimedia applications. We identified error control using Reed-Solomon (RS) forward error correction (FEC) in the medium access control (MAC) layer as a significant cause of delay variation, and have proposed a novel analytic model that can predict the time required for RS decoding at a mobile, under different levels of block interleaving and for varying conditions of the Rayleigh fading channel at that mobile. This model enables us to estimate the buffer size required to ensure seamless multimedia services.