CPS-Based Smart Warehouse for Industry 4.0: A Survey of the Underlying Technologies <s> Introduction <s> Bluetooth Low Energy (BLE) is an emerging low-power wireless technology developed for short-range control and monitoring applications that is expected to be incorporated into billions of devices in the next few years. This paper describes the main features of BLE, explores its potential applications, and investigates the impact of various critical parameters on its performance. BLE represents a trade-off between energy consumption, latency, piconet size, and throughput that mainly depends on parameters such as connInterval and connSlaveLatency. According to theoretical results, the lifetime of a BLE device powered by a coin cell battery ranges between 2.0 days and 14.1 years. The number of simultaneous slaves per master ranges between 2 and 5,917. The minimum latency for a master to obtain a sensor reading is 676 μs, although simulation results show that, under high bit error rate, average latency increases by up to three orders of magnitude. The paper provides experimental results that complement the theoretical and simulation findings, and indicates implementation constraints that may reduce BLE performance. <s> BIB001 </s> CPS-Based Smart Warehouse for Industry 4.0: A Survey of the Underlying Technologies <s> Introduction <s> Abstract Recent advances in manufacturing industry has paved way for a systematical deployment of Cyber-Physical Systems (CPS), within which information from all related perspectives is closely monitored and synchronized between the physical factory floor and the cyber computational space. Moreover, by utilizing advanced information analytics, networked machines will be able to perform more efficiently, collaboratively and resiliently. Such trend is transforming manufacturing industry to the next generation, namely Industry 4.0. At this early development phase, there is an urgent need for a clear definition of CPS. In this paper, a unified 5-level architecture is proposed as a guideline for implementation of CPS. <s> BIB002 </s> CPS-Based Smart Warehouse for Industry 4.0: A Survey of the Underlying Technologies <s> Introduction <s> A Web-oriented architecture using REST framework is proposed to enable warehouse objects to communicate over the Web. In the proposed mechanism, the smart warehouse consists of a data collection module and an administrative module. The former includes a collection of radio-frequency identification sensors to read RFID tags of the products, wireless sensors for operational data collection, and the actuators. It is responsible for the data collection process of products and goods stored in the warehouse as well as the collection of operational parameters, i.e. temperature, humidity, air quality, and pressure. The latter acts as the brain of the smart warehouse by processing data, organizing data, generating events, and executing actions. The warehouse user is provided with the environment to control the functionality of various sensors, things, appliances, and HAVC system of warehouse through the Web. An event decision system is built on top of the Web architecture to control real-time processing of the sensors, things, etc. In the proposed architecture, the smart gateway consists of two layers, namely transport module (TM) and device service module (DSM). The combination of TM and DSM creates the device controller for embedded devices operating on proprietary protocols. The proposed system is simulated and evaluated in various scenarios in context of discovery time, response time, and transmission failure. Its effect is seen in the form of improved performance of warehouse in quick interaction and in high accuracy as well. <s> BIB003
The human history has witnessed three times industrial revolutions. Nowadays, we come to the fourth industrial revolution, i.e., Industry 4.0. As shown in Figure 1a , the research community has been developing a variety of technologies for Industry 4.0, such as Radio-Frequency IDentification (RFID), NarrowBand IoT (NB-IoT), Wi-Fi, Near-Field Communication (NFC), 5th Generation mobile networks (5G), Global Positioning System (GPS), Wireless Sensor Network (WSN), robotics, etc. In this paper, we focus on the technologies towards building smart warehouses BIB003 . In a traditional warehouse, the operations of pickup, delivery, and bookkeeping are accomplished by storekeepers. There are several drawbacks of conventional warehouses. First, it is time-consuming to store/fetch inventories into/from them. Second, the usage of storekeepers is a waste of human resources. Finally, it is not environmentally friendly to record the stocks using account books. Therefore, it is profoundly essential to make traditional warehouse smart. A smart warehouse is an automated, unmanned, and paperless warehouse when conducting the operations of pickup, delivery, and bookkeeping. The insight to make traditional warehouses smart lies in using Cyber-Physical System (CPS) BIB002 . A CPS can monitor and create a virtual copy of the real-world industry processes, and thus we can know the status of each industry process, control and make proper decisions in a real-time manner. In other words, CPS can bring the virtual and physical worlds together to construct an entirely networked world, where smart objects communicate and interact with each other. At that time, time-efficiency, energy-efficiency, and accuracy will be significantly improved while cost, error rate, and waste will be substantially decreased. Although CPS has the potential to bring revolution to traditional warehouses, it is not easy to integrate CPS techniques into smart warehouses for Industry 4.0. In a CPS-based smart warehouse, each inventory is affixed with one or more low-cost devices such as RFID tags and NFC tags; various CPS devices, such as Wi-Fi APs (Access Points), BLE (Bluetooth Low Energy) beacons, and cameras are deployed in the environment; multiple robots are navigating in the environment for specific purposes; and human beings are only responsible for sending required instructions to the warehouse and monitoring the warehouse if wanted. As stated above, a CPS-based smart warehouse contains four main components: CPS devices, inventories, robots, and human beings. For CPS devices, there can be thousands of CPS devices working together. Thus, we need to schedule the communication among the CPS devices efficiently. For inventories, we want to timely know their status and location context according to the data reported by the attached devices. For robots, they are required to collaboratively accomplish some tasks that are repetitive and harmful to human beings. For human beings, we need to recognize their gestures or other activities to do warehouse operation. The gestures and other activities may be extracted using the CPS devices deployed in the environment. Hence, we survey four issues towards building CPS-based smart warehouses. As shown in Figure 1b , the four research topics are efficient communication scheduling, accurate and robust localization, human activity recognition, and multi-robot collaboration: • Efficient Communication Scheduling: In a CPS-based smart warehouse, there can be thousands of CPS devices, e.g., various sensors, RFID readers and tags, BLE beacons, and Wi-Fi APs. The CPS devices form a dense Local Area Network (LAN). In the LAN, some of the data are required to be collected timely, e.g., the data to recognize human activities. However, the limited wireless communication bandwidth may not support real-time data collection from such large number of CPS devices. Therefore, it is significant to investigate time-efficient communication scheduling mechanisms. In addition, the communication scheduling mechanism is supposed to be energy-efficient for eco-friendly purposes. • Accurate and Robust Localization: For the basic operations of a warehouse such as inventory fetching and tracking, we need to know the location of the concerned objects. Localization is a classical and important problem, and various techniques such as GPS, Wi-Fi, Bluetooth, and RFID have been developed for localization. However, different localization approaches have different drawbacks. For example, GPS suffers from low accuracy for indoor localization; Wi-Fi can only track the objects equipped with smartphones; BLE beacons have a short lifetime due to the limited battery volume BIB001 ; and RFID has relatively short communication range (usually less than 10 m). Hence, we need to make efforts to develop suitable localization techniques for the smart warehouse scenario. By saying suitable, the localization approach should be accurate, robust, fast, and wide-coverage. • Multi-Robot Collaboration: A smart robot consists of various sensors, accurate actuators, and powerful processors. These components enable a robot to sense extensively, to decide intelligently, and to behave precisely. The industries have been using smart robots in tasks which are difficult, time-consuming, or harmful to human beings. Traditional applications are for manufacturing such as forging, die casting, heat treatment, etc. Nowadays, we enter the age of industry 4.0. Smart robots provide great potential for the smart warehouse. For example, in early 2012, Amazon spent $775 million to build Kiva system, in which smart robots are used to carry and arrange goods in the warehouse. We can see the promising future to use multi-robot system (MRS) in Industry 4.0. To better utilize MRSs, the technologies of task scheduling and local coordination for MRS are required. • Human Activity Recognition: In a warehouse, human beings, as the main operators, play a dominating role in managing various kinds of objects, good, tools, etc. Human activity recognition can be applied in human-computer interaction for remote warehouse operations. If the physical and emotional activities could be recognized, we have more comprehensive inputs to control the warehouse. Therefore, to achieve automated and elaborate industrial manufacturing, transportation, and management, human activity recognition can be quite helpful for the realization and development of Industrial 4.0. The contributions of this paper are as follows: • We give a formal definition of smart warehouse. That is, a smart warehouse is an automated, unmanned, and paperless warehouse when conducting the operations of pickup, delivery, and bookkeeping. Furthermore, we analyze the underlying technologies towards building a smart warehouse.