Novel LAA Waiting and Transmission Time Configuration Methods for Improved LTE-LAA/Wi-Fi Coexistence Over Unlicensed Bands

Abstract

Long Term Evolution-Licensed Assisted Access (LTE-LAA) has been pointed out as a key solution to cope with the increasing amounts of data traffic and the scarcity of the licensed spectrum. The 3rd Generation Partnership Project (3GPP) has standardised LAA to operate over the 5 GHz unlicensed spectrum which is mainly occupied by Wi-Fi. It is a challenging problem to ensure a fair coexistence between these technologies. Several studies have been proposed in the literature to allow a fair LAA/Wi-Fi coexistence. In this work, various methods are proposed to adapt/select the waiting times for LAA based on the activity statistics of the existing Wi-Fi network. The main novelty is that the knowledge of the existing Wi-Fi activities is exploited to tune the boundaries of the Contention Window (CW) for LAA and to select fixed waiting times for LAA. Moreover, a dynamic method is proposed to adapt the Transmission Opportunity (TxOP) times for LAA based on the Hybrid Automatic Repeat Request (HARQ) feedbacks. The methods are evaluated using ns-3 network simulator based on the 3GPP fairness definition. We show that selecting fixed waiting times for LAA based on the existing Wi-Fi activities is more friendly to the existing Wi-Fi and provides better total aggregated throughputs for both coexisting networks compared to the 3GPP Category 4 Listen Before Talk (Cat 4 LBT) algorithm. Moreover, the proposed dynamic TxOP method is more friendly to the existing Wi-Fi and provides better total aggregated throughputs compared to the fixed TxOP period approach of the 3GPP Cat 4 LBT scheme. INDEX TERMS Licensed assisted access, LTE/Wi-Fi coexistence, ns-3, Unlicensed spectrum, Wi-Fi.

Resolving 5G NR-U Contention for Gap-Based Channel Access in Shared Sub-7 GHz Bands

“…The requirement of transmissions having to be synchronized to slot boundaries was acknowledged and resolved with RS. This LAA module was also used by the research community to evaluate novel coexistence solutions [49]- [51]. It was developed, however, as a standalone module and is not integrated with the latest ns-3 releases.…”

Performance-Fairness Trade-off for Wi-Fi and LTE-LAA Coexistence

“…A fairness evaluation for Wi-Fi and LTE in unlicensed spectrum for three different coexistence procedures: continuous transmission, discontinuous transmission and LBT was addressed in [42]. The work in [43] presented a dynamic transmission time and a fixed waiting time configuration for LTE-LAA and Wi-Fi coexistence.…”

Enhanced Collision Resolution Methods With Mini-Slot Support for 5G NR-U

“…A set of papers [23]- [26] considers modifications of LBT in which the adjusting of the contention window is not exponential. In [23], machine learning is used to predict the optimal size of the contention window of LTE-LAA based on the number of negative acknowledgments.…”

“…According to the results, both approaches [23], [24] improve fairness in coexistence scenarios. Moreover, in [25], [26], the authors propose several schemes of adjusting contention window bounds for LTE-LAA based on the real-time estimation of Wi-Fi activity.…”