Mauri Kuorilehto

A survey of application distribution in wireless sensor networks

Wireless sensor networks (WSNs) are deployed to an area of interest to sense phenomena, process sensed data, and take actions accordingly. Due to the limited WSN node resources, distributed processing is required for completing application tasks. Proposals implementing distribution services for WSNs are evolving on different levels of generality. In this paper, these solutions are reviewed in order to determine the current status. According to the review, existing distribution technologies for computer networks are not applicable for WSNs. Operating systems (OSs) and middleware architectures for WSNs implement separate services for distribution within the existing constraints but an approach providing a complete distributed environment for applications is absent. In order to implement an efficient and adaptive environment, a middleware should be tightly integrated in the underlying OS. We recommend a framework in which a middleware distributes the application processing to a WSN so that the application lifetime is maximized. OS implements services for application tasks and information gathering as well as control interfaces for the middleware.

Performance analysis of IEEE 802.15.4 and ZigBee for large-scale wireless sensor network applications

This paper analyses the performance of IEEE 802.15.4 Low-Rate Wireless Personal Area Network (LR-WPAN) in a large-scale Wireless Sensor Network (WSN) application. To minimize the energy consumption of the entire network and to allow adequate network coverage, IEEE 802.15.4 peer-to-peer topology is selected, and configured to a beacon-enabled cluster-tree structure. The analysis consists of models for CSMA-CA mechanism and MAC operations specified by IEEE 802.15.4. Network layer operations in a cluster-tree network specified by ZigBee are included in the analysis. For realistic results, power consumption measurements on an IEEE 802.15.4 evaluation board are also included. The performances of a device and a coordinator are analyzed in terms of power consumption and goodput. The results are verified with simulations using WIreless SEnsor NEtwork Simulator (WISENES). The results depict that the minimum device power consumption is as low as 73 μW, when beacon interval is 3.93 s, and data are transmitted at 4 min intervals. Coordinator power consumption and goodput with 15.36 ms CAP duration and 3.93 s beacon interval are around 370 μW and 34 bits/s

Energy-efficient neighbor discovery protocol for mobile wireless sensor networks

Low energy consumption is a critical design requirement for most wireless sensor network (WSN) applications. Due to minimal transmission power levels, time-varying environmental factors and mobility of nodes, network neighborhood changes frequently. In these conditions, the most critical issue for energy is to minimize the transactions and time consumed for neighbor discovery operations. In this paper, we present an energy-efficient neighbor discovery protocol targeted at synchronized low duty-cycle medium access control (MAC) schemes such as IEEE 802.15.4 and S-MAC. The protocol effectively reduces the need for costly network scans by proactively distributing node schedule information in MAC protocol beacons and by using this information for establishing new communication links. Energy consumption is further reduced by optimizing the beacon transmission rate. The protocol is validated by performance analysis and experimental measurements with physical WSN prototypes. Experimental results show that the protocol can reduce node energy consumption up to 80% at 1-3m/s node mobility.

Cost-Aware Dynamic Routing Protocol for Wireless Sensor Networks - Design and Prototype Experiments

This paper presents an energy-efficient multi-hop routing protocol for wireless sensor networks. The protocol uses cost metrics to create gradients from a source to a destination node. The cost metrics consist of energy, node load, delay, and link reliability information that provide a trade-off between performance and energy usage. A node can query routes from its neighbors, which allows efficient recovery from route losses. The protocol is the first cost-field based WSN routing protocol suitable for low processing and memory capacity nodes that is tested in a practical real-world environment. The protocol performance is evaluated on full scale prototype implementation consisting of 38 ultra-low power nodes in indoor environment. Compared to traditional flooding, the protocol requires only 25% of the bandwidth, while having smaller end-to-end delays

A Wireless Sensor Network for RF-Based Indoor Localization

An RF-based indoor localization design targeted for wireless sensor networks (WSNs) is presented. The energy-efficiency of mobile location nodes is maximized by a localization medium access control (LocMAC) protocol. For location estimation, a location resolver algorithm is introduced. It enables localization with very scarce energy and processing resources, and the utilization of simple and low-cost radio transceiver HardWare (HW) without received signal strength indicator (RSSI) support. For achieving high energy-efficiency and minimizing resource usage, LocMAC is tightly cross-layer designed with the location resolver algorithm. The presented solution is fully calibration-free and can cope with coarse grained and unreliable ranging measurements. We analyze LocMAC power consumption and show that it outperforms current state-of-the-art WSN medium access control (MAC) protocols in location node energy-efficiency. The feasibility of the proposed localization scheme is validated by experimental measurements using real resource constrained WSN node prototypes. The prototype network reaches accuracies ranging from 1 m to 7 m.With one anchor node per a typical office room, the current room of the localized node is determined with 89.7% precision.

Rapid design and evaluation framework for wireless sensor networks

The diversity of applications and typically scarce node resources set very tight constraints to Wireless Sensor Networks (WSN). It is not possible to fulfill all requirements with a general purpose WSN, for which reason the rapid development of application specific WSNs is preferred. We present a new framework called WIreless SEnsor NEtwork Simulator (WISENES) for the design, simulation, and evaluation of WSNs. The target WSN is designed in Specification and Description Language (SDL), simulated in WISENES, and implemented on target platform either through automatic code generation or manually. The high-level WSN model is back-annotated with the measured values from a real platform. In this way, very accurate WSN simulations can be performed with a rapid design cycle. WISENES itself has been verified with TUTWSN (Tampere University of Technology Wireless Sensor Network) and ZigBee protocols. The MAC protocol of ZigBee was designed in two weeks from scratch by one designer, which shows the effectiveness of WISENES. For accuracy comparison, the results show 6.7% difference between the modeled and measured TUTWSN prototype power consumption. WISENES hastens the evaluation of new protocol and application configurations, especially for the large scale and long-term WSN deployments.

WSN API: Application Programming Interface for Wireless Sensor Networks

In this paper, an application programming interface for wireless sensor networks (WSN API) is presented. The WSN API consists of a client-side API (gateway API) and a sensor-side API (node API). The WSN API conceals the complexities of WSN communication protocols and architectures, and provides a well-defined and easy-to-use way to collect data from sensors. Also, easy expandability for new sensor components and applications is provided. The WSN API is implemented practically in TUTWSN prototype platforms

SensorOS: a new operating system for time critical WSN applications

This paper presents design and implementation of a multithreading Operating System (OS), SensorOS, for resource constrainedWireless Sensor Network (WSN) nodes. Compared to event-handler kernels, such as TinyOS, SensorOS enables coexistence of multiple time critical application tasks. SensorOS supports preemptive priority-based scheduling, very fine-granularity timing, and message passing inter-process communication. SensorOS has been implemented for resource constrained Tampere University of Technology WSN (TUTWSN) nodes. In TUTWSN node platform with 2MIPS PIC micro-controller unit, SensorOS kernel uses 6964 B code and 115 B data memory. The context swap time is 92 µs and the variance of timing accuracy for a high priority thread less than 5 µs. The results show that the realtime coordination of WSN applications and protocols can be managed by a versatile OS even on resource constrained nodes.

Security in wireless sensor networks: considerations and experiments

Wireless Sensor Networks (WSN) are seen as attractive solutions for various monitoring and controlling applications, a large part of which require protection. Due to the special characteristics of WSNs, e.g. low processing and energy resources and ad hoc networking, developing a reliable security solution becomes a challenging task. In this paper we survey various security aspects of WSNs, consisting of threats, attacks, and proposed solutions. We also present experiments with our own WSN technology (TUTWSN), concentrating on a centralized key distribution and authentication service. Our experiments suggest that a centralized scheme can be a feasible solution in certain WSN configurations.

Experimenting TCP/IP for Low-Power Wireless Sensor Networks

This paper presents the analysis and real experiments on TCP/IP communication in a low-power monitoring wireless sensor network (WSN). TCP/IP flow control, addressing, and packet fragmentation are adapted in a gateway that relays TCP/IP communication to WSN. The performance of TCP/IP is evaluated between endpoint PCs communicating over TUTWSN (Tampere University of Technology WSN), which is used as a transparent communication medium for TCP/IP data. The evaluation results show that the window-based flow control algorithms of TCP perform too aggressively in WSNs, where random bit errors and topology changes are main reasons for errors instead of congestion. Further, a frequent duty cycle is needed in WSN to compensate the TCP/IP overhead. In TUTWSN, compared to an environmental monitoring application with two second activity cycle and native WSN transport, the enabling of TCP/IP consumes five times more power