Enabling Technologies for Ultra-Reliable and Low Latency Communications: From PHY and MAC Layer Perspectives

Abstract

Future 5th generation (5G) networks are expected to enable three key services -enhanced mobile broadband (eMBB), massive machine type communications (mMTC) and ultra-reliable and low latency communications (URLLC). As per the 3rd generation partnership project (3GPP) URLLC requirements, it is expected that the reliability of one transmission of a 32 byte packet will be at least 99.999% and the latency will be at most 1 ms. This unprecedented level of reliability and latency will yield various new applications such as smart grids, industrial automation and intelligent transport systems. In this survey we present potential future URLLC applications, and summarize the corresponding reliability and latency requirements. We provide a comprehensive discussion on physical (PHY) and medium access control (MAC) layer techniques that enable URLLC, addressing both licensed and unlicensed bands. The paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency. We identify that enabling long-term evolution (LTE) to coexist in the unlicensed spectrum is also a potential enabler of URLLC in the unlicensed band, and provide numerical evaluations. Lastly, the paper discusses the potential future research directions and challenges in achieving the URLLC requirements.

Survey of Radio Resource Management in 5G Heterogeneous Networks

“…Fulfillment of these user requirements must provide seamless services and real-time response; hence, high latency cannot be tolerated. It is crucial to maintain the induced latency at a very minimum level (less than 1 ms) [14,87,88] and thus resource management techniques must address the implementational and computational complexities at the best possible level. The complexities of radio resource management are summarized in Table V.…”

“…The existing ultrahigh frequency (UHF) wireless network design will not be able to cater to 5G needs since the spectra available in 300 MHz to 3 GHz are almost fully occupied and have nearly reached the Shannon limit [12][13][14]. One way of solving spectrum unavailability is to explore the utilization of higher frequency spectra from 3 GHz to 300 GHz.…”

“…RNs are deployed by MNOs at the edge of a cell network or at deadzone areas, where the signal strength from a macrocell network is weak or not available. Through deployment of RNs, the coverage and throughput can be enhanced, and a balanced traffic load between users at the cell edge and cell center can be achieved [14,26]. This mixture of network operations between an existing macrocell network together with the dense deployment of small cells is known as a HetNet.…”

“…It will also isolate the indoor and outdoor technologies; indoor small-cell networks will use mmWave technology whereas the outdoor environment will make use of massive MIMO [27] technology. The 3rd Generation Partnership Project (3GPP) Release 12 specified some potential technologies in the 5G HetNet, such as the dual connectivity (DC) feature that allows for users to connect to both macrocell and small-cell networks at the same time using the same or different carrier frequencies [14,28,29]. The DC feature is expected to enhance the considerable data rate for the overall HetNet.…”

A Survey of End-to-End Solutions for Reliable Low-Latency Communications in 5G Networks

“…We detect a large focus on lowerlayer solutions and a lack of analysis of the reliability and latency conjointly when the focus is set on transport protocols and solutions. Some surveys of the evolution of protocols and techniques for 5G critical communications are those of Sutton et al [27], Pocovi et al [8], Zhang et al [28] and Morgado et al [29], which present a variety of enabling technologies to enhance communication in terms of latency or reliability but mostly focus on the lower layers. Furthermore, Mitra et al [30], Agiwal et al [31], Gupta et al [32] and Olwal et al [33] provide surveys aimed at the study of emergent technologies, paradigms and applications for 5G networks.…”