Effective Capacity of Licensed-Assisted Access in Unlicensed Spectrum for 5G: From Theory to Application

TLDR

License‑assisted access (LAA) promises to offload cellular traffic to unlicensed bands, but QoS provisioning and capacity quantification are challenged by the distributed, heterogeneous coexistence with legacy Wi‑Fi systems. This work introduces new effective‑capacity theories to evaluate LAA under statistical QoS constraints. A four‑state semi‑Markovian model that captures collisions, random backoffs, and lossy channels is formulated, yielding a closed‑form effective‑capacity expression and a two‑state abstraction that exposes its concavity in transmit rate. Simulations confirm that exploiting this concavity increases LAA effective capacity and energy efficiency by 62.7 % and 171.4 % over prior methods, offering practical guidance for LAA design and deployment.

Abstract

License-assisted access (LAA) is a promising technology to offload dramatically increasing cellular traffic to unlicensed bands. Challenges arise from the provision of quality-of-service (QoS) and the quantification of capacity, due to the distributed and heterogeneous nature of LAA and legacy systems (such as Wi-Fi) coexisting in the bands. In this paper, we develop new theories of the effective capacity to measure LAA under statistical QoS requirements. A new four-state semi-Markovian model is developed to capture transmission collisions, random backoffs, and lossy wireless channels of LAA in distributed heterogeneous network environments. A closed-form expression for the effective capacity is derived to comprehensively analyze LAA. The four-state model is further abstracted to an insightful two-state equivalent which reveals the concavity of the effective capacity in terms of transmit rate. Validated by simulations, the concavity is exploited to maximize the effective capacity and effective energy efficiency of LAA, and provide significant improvements of 62.7% and 171.4%, respectively, over existing approaches. Our results are of practical value to holistic designs and deployments of LAA systems.