# Dynamic Packet Duplication for Industrial URLLC
## 1 Introduction  
Wired communications have been widely used in industrial scenarios as new applications of automation and Artificial Intelligence (AI) with high mobility are rolled out. However, wired communications are costly in terms of installation and maintenance and cannot cover new use cases, such as mobility in factories. As a result, the whole industry is shifting towards more flexible and adaptable scenarios, resulting in the Industry 4.0 paradigm. Industry 4.0 is the fourth industrial revolution to improve the flexibility of production and distribution processes where wireless networks have an important part. The advances in the fields of robotics, AI and Machine Learning (ML) converge in Industry 4.0 to adapt production to new customer demands, such as an increased customization, reduced costs and lower environmental impact [1]. Wireless networks are a major enabler of flexibility in Industry 4.0, allowing easy reconfiguration of production lines, mobile appliances, such as robots both within and beyond the bounds of factories. The fifth-generation (5G) radio technology, which has been standardized by the 3 rd Generation Partnership Project (3 GPP) members, aims to provide more flexibility to support new services and applications. Unlike previous technologies, that were focused on traditional mobile broadband, in 5G new services categories have been defined according to their requirements:  
* Enhanced Mobile BroadBand (eMBB): this service category is an evolution of traditional mobile broadband, with higher data rates (up to 20 Gbps) and bandwidth. It is similar to the traditional use of networks by users, such as web browsing or streaming multimedia content. * Massive Machine-Type Communications (mMTC): this service category covers massive connection of devices, with a sporadic and lower volume of data exchange over the network. It is mainly focused on the Internet of Things (IoT). Ultra-Reliable and Low Latency Communications (URLLC): this service category aims to cover critical communications, where short messages are exchanged with requirements of lower latency and higher reliability. The latency requirement varies from 1 to 15 ms, depending on the application itself. However, in 5G, it is expected to reach a maximum latency of 1 ms with a reliability target of \(1-10^{-5}\) for a packet size of 32 bytes at the user plane [2]. URLLC can support use cases, such as closed loop control, hazard sensors, robot automatization, augmented/virtual reality, drone communications and mobile eHealth. The latency requirement varies from 1 to 15 ms, while the reliability targets can range between \(1-10^{-5}\) and \(1-10^{-9}\)[3]. These use cases need advanced radio features and resource cost techniques to fulfill highly demanding latency and reliability targets. There are several approaches to achieve such requirements. One technique is the reduction of the time-slot duration by means of a higher numerology [4; 5] and by changing the radio resource scheduler [6]. Another solution consists of eliminating steps in the connection protocols to reduce the access time--known as Grant-free transmission [7]. Multi-connectivity [8; 9] has been proposed for the sake of achieving high reliability and low latency. In particular, for the sake of achieving high reliability, many solutions have been proposed. The studies in [9; 10] are focused on a static threshold (i.e., Reference Signal Received Power (RSRP) or Channel Quality Indicator (CQI)) that determines the dual connectivity range or Packet Duplication (PD) activation. In [11], eMBB/URLLC multiplexing through preemptive URLLC puncturing was studied, where a Deep Learning Link Adaptation was proposed for eMBB users to maximize the throughput, while ensuring reliability for eMBB users due to corruption of the packets derived from URLLC puncturing. In [12], the PD architecture for carrier aggregation and the dual connectivity approach is presented. The study focuses on how many links are necessary to fulfill reliability and latency requirements for URLLC.