The future connectivity landscape, and notably, the 5G wireless systems will feature Ultra-Reliable Low Latency Communication (URLLC). The coupling of high reliability and low latency requirements in URLLC use cases makes the wireless access design very challenging, in terms of both the protocol design and of the associated transmission techniques. This paper aims to provide a broad perspective on the fundamental tradeoffs in URLLC, as well as the principles used in building access protocols. Two specific technologies are considered in the context of URLLC: massive MIMO and multi-connectivity, also termed interface diversity . This paper also touches on the importance of the proper statistical methodology for designing and assessing extremely high-reliability levels.
A detailed description of URLLC use cases that are expected to play important roles in future 5G networks can be found in @cite_55 ; these include automotive, Industry 4.0, ITS and ad-hoc disaster and emergency relief. Another take on emerging mission-critical services in cellular networks, such as tele-surgery, ITS and industrial automation, is given in @cite_3 . Live audio production, another potential URLLC use case, is described in @cite_30 ; notably, this use case emphasizes isochronous communication that is not supported by 4G and the article elaborates the ways to achieve it in 5G networks. A common feature of all mentioned all URLLC use cases is that they are described by a single combination of target reliability and latency parameters. In contrast, @cite_72 proposes a more general URLLC service model with reliable-service composition, by which target reliability performance progressively increases with latency.
@cite_30 @cite_55 @cite_72 @cite_3
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The fifth generation of cellular mobile communication networks is on the horizon and aims to integrate new vertical markets. In this article, we discuss professional wireless audio systems used for live productions as a future use case for 5G. Wireless live audio productions require high communication reliability as well as ultra-low signal delay. Furthermore, these services demand strict synchronization of devices to function properly. The need for low latency and for precise time and phase synchronization goes beyond what is currently under discussion in the context of URLLC. We seize on this aspect, discuss how isochronous data transmission can be implemented and integrated into 5G networks, and show similarities with other 5G verticals such as industrial automation. Wireless 5G systems will not only be “4G, but faster”. One of the novel features discussed in relation to 5G is Ultra-Reliable Communication (URC), an operation mode not present in today's wireless systems. URC refers to provision of certain level of communication service almost 100 of the time. Example URC applications include reliable cloud connectivity, critical connections for industrial automation and reliable wireless coordination among vehicles. This paper puts forward a systematic view on URC in 5G wireless systems. It starts by analyzing the fundamental mechanisms that constitute a wireless connection and concludes that one of the key steps towards enabling URC is revision of the methods for encoding control information (metadata) and data. It introduces the key concept of Reliable Service Composition, where a service is designed to adapt its requirements to the level of reliability that can be attained. The problem of URC is analyzed across two different dimensions. The first dimension is the type of URC problem that is defined based on the time frame used to measure the reliability of the packet transmission. Two types of URC problems are identified: long-term URC (URC-L) and short-term URC (URC-S). The second dimension is represented by the type of reliability impairment that can affect the communication reliability in a given scenario. The main objective of this paper is to create the context for defining and solving the new engineering problems posed by URC in 5G. Fifth-generation cellular mobile networks are expected to support mission critical URLLC services in addition to enhanced mobile broadband applications. This article first introduces three emerging mission critical applications of URLLC and identifies their requirements on end-to-end latency and reliability. We then investigate the various sources of end-to-end delay of current wireless networks by taking 4G LTE as an example. Then we propose and evaluate several techniques to reduce the end-to-end latency from the perspectives of error control coding, signal processing, and radio resource management. We also briefly discuss other network design approaches with the potential for further latency reduction.