A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. NEXT GENERATION WIRELESS NETWORKS FOR I-IOT <s> What will 5G be? What it will not be is an incremental advance on 4G. The previous four generations of cellular technology have each been a major paradigm shift that has broken backward compatibility. Indeed, 5G will need to be a paradigm shift that includes very high carrier frequencies with massive bandwidths, extreme base station and device densities, and unprecedented numbers of antennas. However, unlike the previous four generations, it will also be highly integrative: tying any new 5G air interface and spectrum together with LTE and WiFi to provide universal high-rate coverage and a seamless user experience. To support this, the core network will also have to reach unprecedented levels of flexibility and intelligence, spectrum regulation will need to be rethought and improved, and energy and cost efficiencies will become even more critical considerations. This paper discusses all of these topics, identifying key challenges for future research and preliminary 5G standardization activities, while providing a comprehensive overview of the current literature, and in particular of the papers appearing in this special issue. <s> BIB001 </s> A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. NEXT GENERATION WIRELESS NETWORKS FOR I-IOT <s> Within the foreseeable future, the growing number of mobile devices, and their diversity, will challenge the current network architecture. Furthermore, users will expect greater data rates, lower latency, lower packet drop rates, etc. in future wireless networks. Ultra Dense Networks (UDN), considered to be one of the best ways to meet user expectations and support future wireless network deployment, will face multiple significant hurdles, including interference, mobility, and cost. In this paper, we review existing research efforts toward addressing those challenges and present future avenues for research. We first develop a taxonomy to review and describe existing research efforts. Next, we focus on inter-cell interference, handover performance, and energy efficiency as the key techniques to addressing the most pressing challenges. Finally, we present several future research directions, including emergent Internet-of-Things (IoT) applications, security and privacy, modeling and realistic simulations, and relevant techniques. <s> BIB002 </s> A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. NEXT GENERATION WIRELESS NETWORKS FOR I-IOT <s> Industrial applications aimed at real-time control and monitoring of cyber-physical systems pose significant challenges to the underlying communication networks in terms of determinism, low latency, and high reliability. The migration of these networks from wired to wireless could bring several benefits in terms of cost reduction and simplification of design, but currently available wireless techniques cannot cope with the stringent requirements of the most critical applications. In this paper, we consider the problem of designing a high-performance wireless network for industrial control, targeting at Gbps data rates and 10- ${\mu }$ s-level cycle time. To this aim, we start from analyzing the required performance and deployment scenarios, then we take a look at the most advanced standards and emerging trends that may be applicable. Building on this investigation, we outline the main directions for the development of a wireless high-performance system. <s> BIB003 </s> A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. NEXT GENERATION WIRELESS NETWORKS FOR I-IOT <s> Industrial automation deployments constitute challenging environments where moving IoT machines may produce high-definition video and other heavy sensor data during surveying and inspection operations. Transporting massive contents to the edge network infrastructure and then eventually to the remote human operator requires reliable and high-rate radio links supported by intelligent data caching and delivery mechanisms. In this work, we address the challenges of contents dissemination in characteristic factory automation scenarios by proposing to engage moving industrial machines as device-to-device (D2D) caching helpers. With the goal to improve reliability of high-rate millimeter-wave (mmWave) data connections, we introduce the alternative contents dissemination modes and then construct a novel mobility-aware methodology that helps develop predictive mode selection strategies based on the anticipated radio link conditions. We also conduct a thorough system-level evaluation of representative data dissemination strategies to confirm the benefits of predictive solutions that employ D2D-enabled collaborative caching at the wireless edge to lower contents delivery latency and improve data acquisition reliability. <s> BIB004 </s> A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. NEXT GENERATION WIRELESS NETWORKS FOR I-IOT <s> To apply cyber-physical system (CPS) technique in industrial internet, a wireless technology that is able to robustly maintain hyperconnectivity between a data center and distributed user entities and/or industrial Internet of Things devices is required. We investigate the feasibility of utilizing massive multiple-input multiple-output (MIMO) as such a wireless technology. We analyze the performance of a massive MIMO base station deployed at a data center to provide massive connectivity to a large number of devices. In addition, we discuss related research challenges for deploying massive MIMO in industrial internet applications of CPS, such as device scheduling and power control, energy efficient design and radio frequency energy transfer/harvesting, signaling techniques for drones and mobile robots, and applications of underwater industrial internet. <s> BIB005
5G, as the next generation wireless network, leverages various techniques (ultra-dense network (UDN), massive multiple-input and multiple-output (MIMO) and mmWave, etc.) to engender a 1,000-fold improvement in network capacity, a 100-fold increase in user data rate, and a 10-fold improvement in end-to-end delay BIB002 - BIB001 . It is worth noting that 5G is designed to satisfy the requirements of a variety of diverse applications that may require high network capacity, high throughput, low latency, and many others. Recall that typical requirements of I-IoT from the communication network perspective include low latency (milliseconds level) and high reliability for short packets (less than 10 2 Bits) BIB003 . Here, 5G has the potential to assist I-IoT applications, as it is able to provide the desired high network capacity and throughput, and low latency. Thus, it is necessary to investigate the existing research efforts that adapt and integrate the 5G techniques in I-IoT. UDN, which leverages the dense deployment of small-cell Base Stations (BSs) to improve network capacity, is one of the key enablers of 5G BIB002 . UDN aims to connect a massive number of mobile devices, which can potentially fit the industrial application scenarios (i.e., the massively deployed sensors and actuators of I-IoT). Relevant to this aspect, Ding and Pérez  investigated the network performance of uplinks in UDN for IoT and pointed out several caveats (excessive inter-cell interference, among others). Massive MIMO systems are equipped with an immense number of transmitter antennas at base stations, which could even exceed the number of receiver antennas of the massive number of served devices. In addition, mmWave, another important technique in 5G, offers much higher bandwidth to improve the communication performance for high throughput I-IoT applications (e.g., surveying and inspection). Nonetheless, in I-IoT scenarios, blockage is a critical issue that affects data transmission links. Thus, towards resolving this issue, Orsino et al. BIB004 investigated the possibilities of device-to-device (D2D) communication in industrial environments. Specifically, they leveraged D2D on mmWave links to improve reliability and reduce latency. This work can be mapped to <Monitoring, FA, Latency> in Figure. 7. Given the huge performance gain supported by massive MIMO (diversity gain, array gain, etc.), it can clearly provide connectivity to I-IoT devices. For example, Lee and Yang BIB005 illustrated the feasibility of using massive MIMO in I-IoT scenarios and further defined several research problems and challenges. Moreover, their analysis and simulation results showed the capability of massive MIMO to support a large number of connections from I-IoT devices with moderate data rate at low cost. Nonetheless, a number of issues (device scheduling, power control, etc.) may be raised when the massive MIMO is used in I-IoT. In summary, 5G has the potential to satisfy the communication requirements for numerous industrial applications. Taking the power grid as an example, Bag et al.  adopted 5G to improve the performance of protection, control, monitoring, and diagnostics. In their study, 5G was leveraged to provide high-speed communications between relays of distribution lines, which support fault current detection in a cost-efficient manner. This work can be mapped to the cube in <Controlling/Monitoring, PA, Latency/Reliability> in Figure. 7.