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By merging cloud computing into the RAN, C-RAN has been foreseen as a prospective 5G wireless systems architecture. Due to the innovative move of migrating the baseband processing functionalities to the centralized cloud baseband unit pool, C-RAN is anticipated to reduce energy consumption significantly to be a green RAN. Moreover, with the cloud-based architecture, lots of new functionalities and RAN designs are ready to be incorporated, which redefines the RAN as a flexible RAN. In this article, we review the recent advances of exploiting cloud computing to form a green and flexible C-RAN from two cloud-based properties: centralized processing and the software-defined environment. For the centralized processing property, we include coordinated multipoint and limited fronthaul capacity, multicasting, and CSI issues in C-RAN. For the software-defined environment property, we summarize elastic service scaling, functionality splitting, and functionality extension. We also include some of our recent research results and discuss several open challenges. [ABSTRACT FROM PUBLISHER]

Supporting ultra-reliable and low-latency communications (URLLC) is one of the major goals in 5G communication systems. Previous studies focus on ensuring end-to-end delay requirement by reducing transmission delay and coding delay, and only consider reliability in data transmission. However, the reliability reflected by overall packet loss also includes other components such as queueing delay violation. Moreover, which tools are appropriate to design radio resource allocation under constraints on delay, reliability, and availability is not well understood. As a result, how to optimize resource allocation for URLLC is still unclear. In this article, we first discuss the delay and packet loss components in URLLC and the network availability for supporting the quality of service of users. Then we present tools for resource optimization in URLLC. Last, we summarize the major challenges related to resource management for URLLC, and perform a case study. [ABSTRACT FROM AUTHOR]