# Wireless Sensor Network Aided Assembly Line Monitoring According to Expectations of Industry 4.0
## 1 Introduction  
If a company strives to be a market leader, it must incorporate the newest research results into all its activities. Therefore, the production systems also have to be state of the art. Having in mind the assembling systems, which are part of the production systems, one of the aspects that requires special attention is the control of the assembling process. To be able to control the assembling process successfully, data is required about the status, physical characteristics, and position of the parts being assembled. Additionally, information on the status of the assembling units and tools is needed as well. Localization and tracking of the parts and subassemblies in the assembling system presents the biggest challenge to deal with. The popularity of wireless technology in industrial applications was well predicted in the research of [PERSON] [1]. The relatively low price and easy implementation of wireless technology indicated its use for assembling process supervision. Therefore, extensive research has been done regarding the use of wireless technology in the related technology [2]. One of the possible implementations was the multi agent systems, but this approach did not have adequate success in automation applications [3; 4; 5; 6]. Regarding the control and data acquisition applications in industrial systems, the supervisory control and data acquisition-SCADA systems are used [7]. Additionally, applications for diagnostics, testing, and control are also used, but the communication is usually based on Ethernet TCP/IP, RS-232, RS-485, and RS-422 communication protocols [8]. Distributed automation architecture, as well as IoT systems, require state-of-the-art communication technologies to meet the requirements of Industry 4.0. [9; 10; 11; 12]. Currently, wireless communication is not within the first ten most popular communication protocols. Sensors and actuators are connected to the control unit, which is usually a programmable logic controller-PLC. This use of sensors connected by wires to the control unit carries high installation costs and is highly inflexible if a reconfiguration is needed. A standard method for designing assembling and production systems by using wireless technology already exists [13]. In the case of production systems, the literature review defines \"Wireless Manufacturing\" [14]. In this case, part of the information is transferred by wireless technology. The success of using wireless technology is evident in the case of using radio-frequency identification-RFID technology. RFID technology is commonly used for controlling the material and part flows in production and storing [15; 16]. The literature review also presents the implementation of wireless technology in tracking the material and part flows in assembling systems [17; 18], but the developed solutions are specific for a given assembling task; therefore, an overall solution is yet to be presented. The overall solution in this field of research requires the fusion of research results of different technical fields (electronics, sensor techniques, communication technologies, imbedded systems, etc.). Recent development results in the field of electronics resulted in component miniaturization, low energy consumption, and higher levels of reliability [19; 20]. In the field of sensor techniques, the miniaturization, the level of precision, less noise dependency, low energy consumption, and wider spectrum of measurable non-electric signals is possible. The communication technologies allow new communication protocols [9], which are reliable in high noise-level surroundings, and also low energy consumption in the case of wireless communication. New microcontrollers allow for higher number and quality of A/D and D/A converters, etc. Additionally, the computing speed, energy efficiency as well as the operational memory are higher and bigger, allowing the usage of microcontrollers in several embedded systems [21].