Queue-based performance optimization under latency constraints in multi-user cellular environments

Abstract

In next-generation wireless networks, it is expected that communication services seeking low latency will be increasing exceedingly. Especially, ultra-reliable low latency communication (URLLC) has been considered as one of main use cases in fifth-generation networks. This thesis proposes techniques which optimize diverse performance metrics while satisfying the low queueing delay constraint for a variety of low latency communication services. The proposed techniques achieve both low queueing latency and performance optimization by dynamically determining transmission/reception schemes to adjust queue backlogs, depending on time-varying stochastic networks. Chapter 3 presents the probabilistic caching policy for video files of varying quality levels in the stochastic wireless caching network. In addition, the thesis proposes an algorithm for streaming users which dynamically selects video quality level and associates with a caching node to download the high-quality video file with nearly no playback delay. In Chapter 4, the adaptive detector selection algorithm is proposed for roadside units to rapidly respond to safety information sent from a large number of vehicles and pedestrians in vehicle-to-everything communications. The roadside unit adaptively selects an optimal detector scheme which minimizes word error rates while limiting the queueing delay to a certain level. Chapter 5 considers environments where small battery-powered devices communicate with many other devices, e.g., Internet-of-things (IoT) networks. In these environments, the thesis proposes dynamic algorithms of user scheduling and power allocation to maximize power efficiency while satisfying the low-latency constraint and quality-of-service (QoS) requirements in hybrid multiple access systems. For the proposed algorithm, the time-average data rate is considered as a QoS requirement for the users. In addition, user scheduling determines whether the link is activated or not as well as whether the transmitter serves users by orthogonal multiple access or non-orthogonal multiple access.