Mikko Kohvakka

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.

Wireless sensor prototype platform

This paper presents the design and performance measurements of a wireless sensor prototype platform (UbiSensor). UbiSensor combines techniques used in wireless microsensors and radio frequency identification (RFID) resulting a wireless sensor having sensing, data processing, network protocol execution, and energy scavenging capabilities. The platform design is driven by energy consumption minimization of given tasks. A commercially available microcontroller, low power RF transceiver, and power generator circuits are used. The measurements indicate 430 /spl mu/W power consumption in typical operating conditions, using 1 Hz sample and transmit rate, which can be scavenged by a 29 mm/sup 2/ sized solar cell or using a transponder interface circuit in a near proximity to a RFID reader. UbiSensor performance results are promising, but further research is required.

Ultra low energy wireless temperature sensor network implementation

Condition monitoring in buildings is one of the most potential and foreseen applications for wireless sensor networks (WSN). This paper presents the design and full scale prototype implementation of WSN for temperature monitoring. The prototypes are implemented using low power commercial of-the-shelf components including a 2.4 GHz radio, microcontrollers, and a custom TUTWSN communication protocol. A user application provides a graphical data analysis. Measurements indicate 183 muW to 390 muW average node power consumptions, as temperature is measured at 5 s intervals and data is multi-hop routed to a gateway. Predicted lifetime with two AA batteries is up to 4.9 years. In addition, experiments indicate that time accuracy is extremely important in hardware prototypes

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.

Transmission Power Based Path Loss Metering for Wireless Sensor Networks

The metering of path loss to neighbouring nodes is vital in multi-hop wireless sensor networks (WSN) for managing network self-configuration, robust data routing, and node localization. Conventionally, path loss is measured by a received signal strength indicator (RSSI) mechanism of a transceiver. Yet, the lowest hardware complexity, energy consumption and cost are reached by transceivers without RSSI. We present a new simple transmission power based path loss metering method for WSNs without RSSI mechanism. The method determines path loss from frames transmitted at different power levels. Performance measurements with physical WSN prototypes indicate sufficient accuracy for network management. According to performance analysis, the power consumption of the proposed method is below 10 mu. An energy analysis in a large IEEE 802.15.4 network indicates 51% to 69% energy saving compared to RSSI-equipped transceivers by using the path loss metering method together with a simple and low power transceiver

High-performance multi-radio WSN platform

This paper presents the design and implementation of a unique multi-radio Wireless Sensor Network (WSN) platform compared to current WSN nodes that have only one radio interface. Four independent, low energy radio transceivers allow simultaneous reception and transmission to either another multi-radio WSN node or up to four different WSN nodes. This also enables high interference tolerance, low latency, and high mesh-networking performance. The platform is based on synthesizable multi-processor System-on-Chip implementation on FPGA. The radios are compatible with ultra-low energy microcontroller based WSN nodes, which can be freely mixed in the network. The platform applicability is demonstrated by an ultra low latency WSN router and high data rate file transfer applications. Theoretical hop delay is as low as 106 µs, while 3.3 Mbps network throughput is achievable. Performance measurements for up to four parallel Nios II softcore processors are also presented.

Design, implementation, and experiments on outdoor deployment of wireless sensor network for environmental monitoring

This paper presents the design, implementation, and practical real world experiments of an energy optimized multi-hop wireless sensor network (WSN) targeted at environmental monitoring. The WSN is fully autonomous and consists of energy-efficient and scalable communication protocols and low-power hardware platform. Software tools are developed for configuring and analyzing large scale networks. The network has been deployed in outdoor environment consisting of 20 nodes covering over 2 km2 area. The results show that the multi-hop network works autonomously, reacts to environmental changes, and is able to operate temperatures down to -30 °C. The hardware nodes operating on 433 MHz frequency provide over 1 km communication distances, while still having sufficient throughput and low energy consumption. The deployed nodes had a lifetime of 6 months with a 1600 mAh battery, while generating 4 packets per minute.

Energy-efficient reservation-based medium access control protocol for wireless sensor networks

In Wireless Sensor Networks (WSNs), a robust and energy-efficient Medium Access Control (MAC) protocol is required for high energy efficiency in harsh operating conditions, where node and link failures are common. This paper presents the design of a novel MAC protocol for low-power WSNs. The developed MAC protocol minimizes the energy overhead of idle time and collisions by strict frame synchronization and slot reservation. It combines a dynamic bandwidth adjustment mechanism, multi-cluster-tree network topology, and a network channel allowing rapid and low-energy neighbor discoveries. The protocol achieves high scalability by employing frequency and time division between clusters. Performance analysis shows that the MAC protocol outperforms current state-of-the-art protocols in energy efficiency, and the energy overhead compared to an ideal MAC protocol is only 2.85% to 27.1%. The high energy efficiency is achieved in both leaf and router nodes. The models and the feasibility of the protocol were verified by simulations and with a full-scale prototype implementation.

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