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tions carrier can be seen on both ends of Fig.2, indicating that the spectrum analyzer received signals stronger than those from the factory’s RFID tag system for a wider fre-quency range. is nding leads to the conclusion that the knowledge of the in-house system does not suce to evaluate the wireless communication environment cor-rectly, especially if the factory is located adjacent to a residential area.Productions systems can also be a noise source that disrupts communications. Figure 3 shows a screen capture of a high temporal resolution spectrum analyzer operated in a large factory remote from residential areas. Because the spectrum analyzer was operated in the vicinity of a large processing machine, the screen is lled with strong noise.As is apparent from these examples, the wireless com-munication environment in the factory is aected by vari-ety of reasons such as: category of industry, scale of factory, existence of radio shielding objects, location (radio wave incident from outside), and noise from in-house equipment. Such complexity poses a challenge to eective utilization of radio waves in the factory.(3) Mixed existence of dissimilar systemsIt is very rare for all the systems in the factory to be replaced at once. Rather, individually optimized facilities in a system are updated/replaced in a staggered fashion, and each process undergoes stepwise revamping, oen resulting in the introduction of dissimilar wireless systems in incremental steps. is situation makes system-wide optimization dicult. It is a general observation that the 2.4 GHz range, thanks to its generic applicability and ease of use, is the rst to become congested.3Current status of wireless communication in the factoryis section describes some of the actual situations found in the factory. Figure 4 shows two screen captures taken on two separate days ((a) July 2015, (b) Dec. 2015) from a 920 MHz-band spectrum analyzer operated in a large factory located remote from residential areas. e horizontal axis represents the observed signal strength.e capture taken in Dec. 2015 shows much higher signal strength than in the capture taken in July 2015, in-dicating signicant growth in the usage of the 920 MHz range. Similarly, usage in the 2.4 GHz range and the 5 GHz range also shows a general increase. Note, however, that these two ranges still have space for additional trac, and no signicant change in the rate of packet loss was ob-served. As is apparent from this example, the radio wave environment undergoes changes with the growth of wire-less uses.Adoption of wireless communication is considered to follow similar steps as did the urban infrastructure with city growth. erefore, the following discussions will be based on the four-stage model of urban development: (1) Initial stage, (2) Growing stage, (3) Mature stage, and (4) Reconguration/Total management stage.(1) Initial Stage: the scope of wireless communication is limited to exchange of small lumps of data (usually ≦50 bytes) under relatively relaxed punctuality requirements. Typical example includes the data exchange between remote controllers and OK/Not-OK signaling for better visualiza-tion of the process status. Stable system operation can be achieved relatively easily by introducing modern manufac-turing equipment with wireless communication capability and a suitable wireless communication scheme.(2) Growing Stage: wireless communication is applied to those devices that exchange data at higher frequency, e.g. sending data and RFID. Allowed time delay ranges FiF5　Four unwire stagesFiF6　 Typical production line configurationProcess APart ①Process BProcess C(①＋②)Process DPart ②Part ③Part ④Automatic guided vehicleAutomatic guided vehicle392-6 Toward Smart Factory using Wireless Communication Technologies