# Ruin Theory for Dynamic Spectrum Allocation in LTE-U Networks

## TL;DR

This paper introduces a ruin theory-based model for fair spectrum sharing between LTE-U and WiFi systems, optimizing duty-cycle allocation to ensure coexistence without degrading WiFi performance.

## Contribution

It proposes a novel application of ruin theory to spectrum sharing, enabling fair duty-cycle allocation between LTE-U and WiFi systems.

## Key findings

- The ruin-based algorithm improves fairness for WiFi compared to equal sharing.
- Simulation results demonstrate better coexistence performance.
- The model effectively maintains WiFi performance while sharing unlicensed spectrum.

## Abstract

LTE in the unlicensed band (LTE-U) is a promising solution to overcome the scarcity of the wireless spectrum. However, to reap the benefits of LTE-U, it is essential to maintain its effective coexistence with WiFi systems. Such a coexistence, hence, constitutes a major challenge for LTE-U deployment. In this paper, the problem of unlicensed spectrum sharing among WiFi and LTE-U system is studied. In particular, a fair time sharing model based on \emph{ruin theory} is proposed to share redundant spectral resources from the unlicensed band with LTE-U without jeopardizing the performance of the WiFi system. Fairness among both WiFi and LTE-U is maintained by applying the concept of the probability of ruin. In particular, the probability of ruin is used to perform efficient duty-cycle allocation in LTE-U, so as to provide fairness to the WiFi system and maintain certain WiFi performance. Simulation results show that the proposed ruin-based algorithm provides better fairness to the WiFi system as compared to equal duty-cycle sharing among WiFi and LTE-U.