# Emerging Trends in Hybrid Wireless Communication and Data Management for the Industry 4.0
## 3 Challenges  
The identified use cases of the factory of the future and their requirements impose new challenges to the underlying communication system that will need to be addressed in the next years to make possible the fourth industrial revolution. The major general challenges and particularities of the factories of the future include the following aspects.  
Radio propagation. The radio propagation environment in a factory is typically characterized by very rich multipath, caused by a large number of metallic objects in the immediate surroundings of transmitter and receiver, as well as potentially high interference caused by electric machines, arc welding, etc. [19]. The radio propagation environment therefore can challenge the PHY mechanisms of any communication system that is deployed in a factory.  
Industrial-grade quality of service. Many use cases impose stringent requirements in terms of end-to-end latency and communication service availability. The latency levels required are, in some cases, below the levels that can be achieved with current communication technologies, given their time resolution, channel access time, and the need to ask for radio resources to transmit, in many cases. Achieving the communication service availability levels demanded will also require an evolution of the PHY and MAC solutions that are currently available to reliably handle the harsh radio propagation and efficiently manage the interferences [20].  
Scalability. Some of the use cases identified require a large number of devices to be effective, such as condition monitoring through the massive deployment of WSN. Scalable solutions will be needed to efficiently and reliably support a high number of connections in the factory. Data management methods [21] and D2D (Device-to-Device) solutions [22] could be used to address this challenge thanks to their benefits in terms of spectral efficiency and reduced redundancy.  
Heterogeneous use cases and requirements. There is not only a single class of use cases, but there are many different use cases with a wide variety of different requirements. This results in the need for flexible and adaptable solutions for the communication system, especially considering the adaptability of the future factory.  
Mixed traffic. Different use cases require the simultaneous transmission of non-critical and highly-critical data over the same link and to the same device. Different use cases can also coexist in the same factory, thus also requiring the simultaneous transmission of data with different requirements in the same area. This requires that the communication system reliably handles connections with low and high requirements in terms of latency and communication service availability. Their performance should always be guaranteed, independently of each other, which also imposes strong requirements to the design of the underlying communications system and its architecture.  
Seamless integration into the existing infrastructure. The communication system has to support a seamless integration into the existing connectivity infrastructure, such as with (Industrial) Ethernet systems. The communication system should be flexible enough to be able to be combined with other (wire-bound) technologies in the same machine or production line. This can be partly addressed with the adoption of certain mechanisms of the IEEE 802.1 protocol family, including IEEE 802.1 Qbv (time-aware scheduling) and IEEE 802.1Q (VLANs).  
Private network deployments. Due to security, liability, availability, and business reasons, many factory/plant owners require deployment of private networks. This is an inherent characteristic of wired networks deployed today, that becomes more relevant when providing wireless connectivity using a cellular network.