Multi-Tier Caching for Statistical-QoS Driven Digital Twins Over mURLLC-Based 6G Massive-MIMO Mobile Wireless Networks Using FBC

Digital Twin (DT) has been widely envisioned as a major intelligent application of 6 G wireless networks requiring stringent quality-of-service (QoS) for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">massive ultra-reliable and low latency communications</i> (mURLLC) to support efficient interactions between physical and virtual objects. As a 6 G enabler, multi-tier caching, which is one of the key multi-tier computing (MC) techniques, stores the highly-demanded data at different wireless network tiers to efficiently reduce mURLLC streaming delay and data move. However, how to efficiently cache mURLLC data at different caching tiers in wireless networks and how to support <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">both delay</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">error-rate</i> bounded QoS for DT still remain challenging problems. To overcome these difficulties, in this paper we propose to integrate multi-tier caching with inite blocklength coding (FBC) for supporting mURLLC-based DT by developing multi-tier 6 G mobile networks. First, we develop the efficient inter-tier and intra-tier collaborative multi-tier caching mechanisms, where popular DT data is selectively cached at different wireless network caching tiers including: router tier, massive-multiple-input-multiple-output (MIMO) base-station/WiFi-access-point tier, and mobile device tier. Second, our proposed inter-tier collaborative caching mechanisms maximize the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">aggregate caching gain</i> , in terms of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><inline-formula><tex-math notation="LaTeX">$\epsilon$</tex-math></inline-formula>-effective capacity</i> , across three caching tiers to support statistical delay and error-rate bounded QoS provisioning by using FBC. Third, we develop the intra-tier caching algorithm at each caching tier to optimize each caching-tier's QoS performances. Finally, we numerically validate and evaluate our developed multi-tier hierarchical caching schemes using statistical-QoS/FBC over next-generation DT-enabled mobile networks.