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from several seconds to several minutes.(3) Mature stage: wireless communication is further applied to much faster control purposes (allowed time delay window: from several hundred milliseconds to sev-eral seconds). Such applications include in-line inspection and control of moving vehicles in the factory. In this stage, optimization of wireless communication is considered to progress in two dierent directions.(4) Reconguration/Total management stage: leading-edge applications are introduced into the factory including: wireless in-house network, in-house IP telephone, regular data exchange for remote control, and real-time image data trac.Summarizing the descriptions above, the process to-ward widespread use of wireless communication can be conceived to advance in the following four stages (“Unwire” stages), which are classied using two parameters: band occupation rate per system, and communication anomaly degree of the communication (See Fig.5).(1) Initial Stage(2) Growing Stage(3) Mature Stage(3) -1 Communication Quality Specic Optimization Stage(3) -2 Application Specic Optimization Stage(4) Reconguration/Total Management StageMachines in the factory are designed individually rather than systematically. e wireless communication function is selected and implemented accordingly.Each wireless communication system is selected from the following two viewpoints. One of them is the stage characterized by a communication quality-oriented system that places special focus on the avoidance of data loss in specic data packets (③ -1 Quality Specic Optimization Stage), and the other is characterized by the existence of a system that provides leading-edge additional value to manufacturing machines (③ -2 Application Specic Optimization Stage). e following are concrete examples:③ -1 Communication Quality Specic Optimization Stageis stage is characterized by the introduction of com-munication quality-oriented systems typically used to control AGV. ey place special focus on loss in particular packets. Design strategy tends to be single-system centric and place focus on the avoidance of data loss and optimi-zation of delay time. e techniques oen employed to maintain communication quality include multiple genera-tion and transmission of the same packet.e following is a concrete example from an on-site experiment. Figure 6 shows the overall manufacturing ow in the factory where our experiment was carried out.It is a typical “one-by-one production” line, where the line accepts a large part, processes it, and outputs it se-quentially on a one-by-one basis. In the gure, two parts (part ① and part ②) are transferred from two separate previous processes into the line by means of automatic guided vehicles. When they are put into the line, they are rst joined together into a larger part ③ for subsequent processing. In this particular example, part ② is a large semi-assembly, on which part ① is to be mounted. Aer undergoing subsequent assembly with other parts, the nished product (part ④) is transferred to the next process.e devices (a pair of transmitter and receiver) used in the experiment were mounted on racks (height 150 cm) which were arranged in two dierent arrangements for comparison: line-of-sight (LOS) and non-line-of-sight (NLOS) arrangements. e communication distance for the LOS and NLOS arrangements were approximately 15 m and 25 m, respectively. Wi-Fi used in the experiment was an OpenWRT 4.1.1-based wireless mesh router RMR9000 [9] driven by an ath5 k-based Wi-Fi driver.e experiment was carried out by sending limited-time broadcast communication from the transmitter to the receiver. e receiver returned the broadcast messages to the transmitter by way of LAN cable to evaluate delay time (both ends used a common terminal clock). e maximum round trip time (RTT) by way of LAN cable amounts to several hundreds of microseconds, which can be ignored in this experiment. Data to control AGVs was sent/received FiF7Data delay observed in automatic conveying machine control channel2 Terrestrial Communication Technology Research and Development40　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 2 (2017)