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

## TL;DR

This paper develops a theoretical framework and models to quantify and optimize the effective capacity of License-assisted Access (LAA) in unlicensed spectrum for 5G, addressing QoS and coexistence challenges.

## Contribution

It introduces a novel four-state semi-Markovian model for LAA, derives a closed-form effective capacity expression, and demonstrates capacity and energy efficiency improvements through optimization.

## Key findings

- Effective capacity is concave in transmit rate.
- Maximizing effective capacity yields 62.7% improvement.
- Energy efficiency increases by 171.4% with optimization.

## 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 WiFi) 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.