LBT-Based Adaptive Channel Access for LTE-U Systems

TLDR

Mobile operators seek to use unlicensed spectrum to meet growing demand, and LTE‑U extends LTE into this band, but its coexistence with Wi‑Fi remains the main challenge. The paper proposes a listen‑before‑talk access mechanism with an adaptive backoff window that adjusts to licensed bandwidth and Wi‑Fi load to meet small‑cell QoS while reducing Wi‑Fi collisions. The approach jointly allocates licensed and unlicensed bands for spectrum efficiency and incorporates an admission control scheme to limit Wi‑Fi interference. Simulations demonstrate that the proposed scheme achieves fair coexistence with Wi‑Fi and outperforms non‑adaptive baseline access methods.

Abstract

Driven by the demand for more radio spectrum resources, mobile operators are looking to exploit the unlicensed spectrum as a complement to the licensed spectrum. LTE-unlicensed (LTE-U), also referred to as licensed-assisted access by the third generation partnership project, is an extension of the LTE standard operating on the unlicensed spectrum. To realize LTE-U, its coexistence with Wi-Fi systems is the main challenge and must be addressed. In this paper, a listen-before-talk access mechanism featuring an adaptive distributed control function protocol is adopted for the small base stations (SBSs), whereby the backoff window size is adaptively adjusted according to the available licensed spectrum bandwidth and the Wi-Fi traffic load to satisfy the quality-of-service requirements of small cell users and minimize the collision probability of Wi-Fi users. Meanwhile, both licensed and unlicensed spectrum bands are jointly allocated to optimize spectrum efficiency. An admission control mechanism is further developed for the SBS to limit collision with Wi-Fi traffic. Extensive simulation results show that the proposed schemes achieve fair and harmonious coexistence between LTE-U small cells and the surrounding Wi-Fi service sets and substantially outperform baseline non-adaptive channel access mechanisms in the unlicensed spectrum.