Wireless sensor networks system consists of multiple sensor nodes that are capable of communicating with each other and collaborating on a common sensing goal. Wireless sensor networks system resources of inexpensive, small size and low-power motes in wireless sensor network are extremely limited. While various efforts for developing power efficient softwares including networking protocols,module control software, and operating system and hardwares are made, the lifetime of motes is still limited. Thus, new circuit design methodologies and operating technologies are studied to improve the sensor network capabilities in High Speed IC Laboratory.
Wireless sensor networks can be applied to a wide range of uses. These can be roughly categorized three different area; 1) monitoring spaces, 2) monitoring things, and 3) monitoring the interactions of things with each other and the encompassing space [3]. The first category includes environmental and habitat monitoring, precision agriculture, indoor climate control, surveillance, treaty verification, and intelligent alarms. The second category includes structural monitoring, ecophysiology, condition-based equipment maintenance, medical diagnostics, and urban terrain mapping. The third category, which is the most complex applications, includes wildlife habitats, disaster management, emergency response, ubiquitous computing environments, asset tracking, healthcare, and manufacturing process flow. Fig. 1 shows its application and system architecture. The target application of wireless sensor network in High Speed IC Lab. is livestock disease monitoring focused on CSFV (Classical Swine Fever Virus), Foot and Mouth Disease and so on. The reason for selecting the target application is that these diseases damage the stock farming and infect farmers every year in Korea. The research is on going project of the Center for Distributed Sensor Network in GIST.
The sensor network systems are typically made up of several nodes which are usually called motes. Each node (mote) has one or many different types of sensors. The node is physically small and thus has limited resources and capabilities mainly due to limited battery lifetime. The capabilities of wireless communications are also limited to low bandwidth and low power levels. A wireless sensor network test-bed was implemented to study system architecture and operation technology and for environmental monitoring applications.
Several research centers are interested in developing micro-sized wireless sensor network mote, including sensor, hardware platform, networking protocols, and operating system software. But, it is not easy to implement all the functions on a micro-sized single chip. The cubic-inch sized mote is implemented as a prototype with all functions for wireless sensor network test-bed. Mote collects various types of information from sensors such as temperature, humidity, luminance, vibration, pressure, and so on. A lot of components which are mainly sensor, signal conditioner, ADC(analog to digital converter), processor, RF transceiver, and battery are required to collect the plain information. Fig. 2 shows the fabricated mote (56x26 mm2) for wireless sensor networks.
Base station receives data transmitted from motes. It converts received data to the data suitable for a computer that contains Intel x86 compatible CPU(s). It sends converted data to a server via RS-232C or Ethernet. It also supports JTAG interfaces to debug and to store an executable program code into the mote. Fig.3 shows the 76x55 mm2 size fabricated base station for wireless sensor networks.
An operating system is a program that acts as an intermediary between a user of a computer and the computer hardware. The purpose of an operating system is to provide an environment in which users can execute programs. The primary goal of an operating system is thus to make the computer system convenient to use. A secondary goal is to use the computer hardware in an efficient manner.
Server stores sensed data into DBMS (database management system). The DBMS is a system that is usually automated and computerized for the management of any collection of compatible and ideally normalized data. The performance of the server depends on database scheme. So, well-designed database scheme is necessary for a massively distributed sensor network.
Client interface supports an interface for an authorized user to access stored data. The authorized user can get information such as mote information, sensor information, collected data, and so on. The user can search, modify, and delete data in the database allowed by his privilege. Also, the user can trace the data changes graphically. Fig.4 shows the client interface that is tracing the sensed data.
The High Speed IC Lab. participates in wireless sensor network researches carried out in the Center for Distributed Sensor Networks. Wireless sensor networks technology including system architecture, operation, and low-power A/D mixed IC design technologies for wireless sensor networks are covered by the The High Speed IC Lab.
The sensor network systems are typically made up of several nodes which are usually called motes. Each node (mote) has one or many different types of sensors. The node is physically small and thus has limited resources and capabilities mainly due to limited battery lifetime. The capabilities of wireless communications are also limited to low bandwidth and low power levels. A wireless sensor network test-bed was implemented to study system architecture and operation technology and for environmental monitoring applications.
The low-voltage and low-power techniques are the key design factors for sensor network applications. Many researchers have tried to reduce the power consumption by using the several capacitor-based circuits and by halting power or clock signals in an unused sub-block. Fig.5 shows layout image and microscope image of the designed ADC. Research to further reduce the power consumption by using novel low-power circuit techniques is under way.
The LNA/ADC block interfacing between the CPU and sensors shown in Fig. 5-a was implemented. The detected analog signals from sensors are amplified by the LNA. Then, the amplified analog signals are converted by the ADC into digital signals for signal processing. Since power for the MDSN motes will be derived from solar cells, the LNA/ADC was designed to operate at 1 V to 1.2 V-approximately the potential of two solar cells in series. In RF transceiver, DAC and ADC components are required for modulation/demodulation. Thus, ADC and DAC are implemented for the emerging IEEE 802.15.4 (ZigBee) protocol which is a set of applications that require simple wireless connectivity, relaxed throughput, very low power consumption, and lower module cost. Since the transceiver has the O-QPSK carrier modulation format and direct conversion architecture, it is possible to design the MODEM even if ADC and DAC have a low bit number (4~6).
