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.
Highlights
Unlicensed spectrum bands have inspired researchers as a promising solution for the licensed spectrum shortage given the current exponential increase in demand for wireless data and services
If the channel is sensed to be busy by the LAA evolved Node B (eNB), the upper bound of the Contention Window (CW) is doubled, which in many cases may lead to longer waiting times than the actual occupancy times of the Wi-Fi transmissions, LAA would wait a long time before re-accessing a channel that could be empty since a long time ago
It is worth noting that the DYNAMIC CW (DynCW)-2 method in general outperforms DynCW-3; this suggests that the two-point adaptation process of the CW performed by DynCW-2 allows a faster convergence to an appropriate CW size when this is required by the Wi-Fi traffic conditions
Summary
Unlicensed spectrum bands have inspired researchers as a promising solution for the licensed spectrum shortage given the current exponential increase in demand for wireless data and services. A significant amount of spectrum of approximately 600 MHz is available for various purposes over the unlicensed 5 GHz band [1], [2] This unlicensed available spectrum has recently attracted the industry and researchers to be utilised for Long Term Evolution (LTE). LTE has been recently deployed to operate over unlicensed bands providing enhanced mobile networks capacities [3], [4]. This same concept is likely to be introduced as well in the future 3GPP specification for 5G New Radio Unlicensed (5G NR-U) and still constitutes a research topic of recent interest [5], [6]
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