Sensor Network Technology is important basic technology in the so-called "context-awareness (understanding the situation)" concept of ubiquitous computing. In order to collect information by arranging various sensors to observe factors such as temperature, humidity, and vibrations in key locations, small wireless sensor networks have been attracting attention. Advanced data collection that could not be achieved with isolated units of conventional sensors is now possible. By placing sensor nodes in many locations, changes in the environment can be known in real time, and a distribution chart can be created from data collected by sensors dispersed over a wide area connected as part of a sensor network. In addition, the situation can be assessed by relating different types of sensor data. Wireless sensor networks are used in a wide range of applications including maintenance and energy management of facilities and equipment, quality control of agricultural produce and industrial products, customer service in commercial facilities, as well as security and health management. Wireless sensor networks play an active role in all situations of people's daily
lives.

 

 

■UWB Active Tag II

UWB (Ultra-Wideband) is a next-generation wireless system that transmits signals in a wide bandwidth of 500 MHz or wider with very low output power and has been attracting attention due to its many advantages. There are two major UWB approaches. One is a short-distance and high-speed UWB (110 Mbps at 10 m) and the other is an impulse-type UWB with low power consumption and positioning capability with high accuracy. YRP Ubiquitous Networking Laboratory has focused on the latter impulse-type UWB for wireless system for sensor networks and developed it.
"UWB Active Tag II" (Photo 1): The antenna, RF circuit, a microcomputer, and a temperature sensor are all mounted on a single board. It realizes very low-power consumption (battery life of more than 10 years), highly accurate positioning (margin of error: 15 cm) and the communication capability of 10 Mbps at 10 m and 250 kbps at 30 m. A compact base station (Photo 2) built on T-Engine incorporates all control functions of a UWB base station.
"UWB Active Tag II" realizes the following functions by utilizing the positioning function, a feature of the impulse-type UWB.

 

●Distance Measuring Function
Measuring the distance between two terminals with high accuracy is possible. This function has been attracting attention as a means of detecting approaching vehicles since the appearance of hybrid vehicles and electric vehicles.

 

●Two Dimensional Positioning Function
The positions of tags in an area where compact base stations are placed in four corners can be detected with high accuracy. This function can be applied to locating items stocked in a flat warehouse automatically and identifying the location of box pallet in the market, etc. If the space is large, this function can be applied by extending and arranging the base stations in cellular grids.

 

●Three Dimensional Positioning Function
The three-dimensional position of a terminal in a space can be identified with high accuracy by placing the base station in vertical direction as well. In addition to two-dimensional positioning, this function can locate on which row on a shelf an item has been placed.

 

 

 

■Specified Low-Power Station Active Tag

"Specified Low-Power Station Active Tag" (Photo 3) is a node for building wireless sensor networks using 400-MHz radio wave. An antenna, RF circuit, a microcomputer, and various types of sensors (temperature, humidity, luminance, acceleration, descent) are mounted on a single board. The radio signal used by the "specified low-power station active tag" has communication distance of 100 m within a line of sight communication path, and its wavelength is relatively long, so it is not easily blocked by a barrier. It goes around shelves which are as large as a person and can circumvent such obstacles. In addition, μT-Kernel is installed in specified low-power station active tags and advanced communication protocols such as multi-hop communication are available.

 

Photo 3: Specified Low-Power Station Active Tag