Abstract
To improve the capacity of cellular systems without additional expenses on licensed frequency bands, the 3GPP consortium has designed cellular technologies that use the unlicensed spectrum. The important peculiarity of the usage models of these technologies, the latest of which is New Radio Unlicensed (NR-U), is the coexistence with Wi-Fi networks deployed in the same frequency band. That is why NR-U uses channel access methods similar to those of Wi-Fi. However, the performance of Wi-Fi networks notably deteriorates in coexistence scenarios. One of the reasons is the slotted structure of transmissions of cellular base stations in the unlicensed spectrum, which may imply the use of a reservation signal. The paper proposes two novel channel access methods for NR-U, in which an NR-U base station randomly stops sending the reservation signal to listen to the channel to detect and resolve collisions. Analytical models are developed to validate the proposed methods and evaluate their efficiency, taking into account important features of NR-U networks, such as flexible numerology and mini-slot transmissions. The obtained numerical results show that the proposed methods significantly improve the performance of the Wi-Fi or NR-U network without degradation of the throughput of the other technology in coexistence scenarios.
Highlights
R APID growth of the amount of mobile traffic makes cellular operators and network developers use more spectrum
We focus on the numerology with θ = 500 μs with allowed mini-slot transmissions (L = θ/14 ≈ 36 μs) or without them (L = θ = 500 μs)
Other configurations of eCR-Listen Before Talk (LBT) are shown as Enhanced CR-LBT (eCR-LBT) with specified values of ξ and φ. gCR-LBT with Nsl CR slots is denoted as gCR-LBT with corresponding values ξ and φ
Summary
R APID growth of the amount of mobile traffic makes cellular operators and network developers use more spectrum. In contrast to EDCA, LTE-LAA has to follow the same slotted structure of the transmissions as the legacy LTE, i.e., a base station can start data transmission only at the licensed spectrum slot boundaries. Waiting for the slot boundary may result in losing channel access if Wi-Fi stations start transmission before the slot boundary Thereby it entails low LTE-LAA performance [6], [7]. For this reason, many research papers [6]–[11] imply that a base station sends a reservation signal until the slot boundary. COMPARISON OF CHANNEL ACCESS METHODS IN UNLICENSED 5 GHZ BAND we discuss channel access methods for the unlicensed spectrum in Wi-Fi and NR-U
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