OKI has been developing technologies enabling sensor networks to be applied to the integrity monitoring of structures. As new applications for sensor networks, the company is focusing on the monitoring of AGV (Automated Guided Vehicle) in factories and monitoring human biodata (heart rate, body temperature, etc.). The difference from structure monitoring is that the monitoring target moves. Although the 920MHz wireless sensor network with excellent range and wraparound characteristics is suitable for monitoring moving objects, AGV monitoring requires monitoring the operation of several hundred vehicles, and biodata monitoring faces the problem of dealing with constantly changing network configurations due to unpredictable movement of people. In order to apply sensor networks to these new monitoring systems, OKI is developing sensor network technology that collects data from a large number of mobile terminals.
The terminal's movement conditions vary widely, and it is extremely difficult to develop a method that exhibits the best performance under all conditions. Therefore, in OKI's mobile sensor network technology, fixed-mobile mixed type and fully mobile type methods are being developed. The fixed-mobile mixed type makes terminal movement possible while minimizing the deterioration of conventional throughput and power saving performance by constructing a minimal network that covers the movement range with fixed installation terminals. In the fully mobile type, even when all the hundreds and thousands of terminals in the network are moving, the network connectivity is maintained, and multiple connections through the use of TDMA (Time Division Multiple Access) ensures one communication is made every certain period of time (about 1 to several seconds). In addition, due to their use for mobile terminals, both methods are being developed with emphasis on power saving performance. If these two methods are selected appropriately according to application, it can be applied to monitoring systems with terminals of varying mobile conditions.