A Comparative Study on Multi-Channel Access Methods in 5G NR-U Networks

To satisfy the increasing demands for high throughput of 5G networks, 3GPP has designed the NR-U technology allowing a cellular base station (gNB) to utilize unlicensed frequency bands. In particular, with NR-U, a gNB can operate in the 5 GHz frequency bands already used by widely deployed Wi-Fi networks. Obviously, to achieve the best performance, a gNB must use a part of the spectrum as wide as possible. However, a gNB usually cannot simultaneously transmit in one channel and receive data or perform channel access procedure in another channel because of the RF power leakage problem. To cope with this problem and fully exploit all the benefits of the unlicensed spectrum, the NR-U specification defines several multi-channel access methods. However, the specification does not provide any guidelines about the selection of the appropriate method depending on network conditions or other factors. In this paper, we survey and compare all the multi-channel access methods defined in the NR-U specification and also several proposals from the literature. We evaluate the efficiency of each method in dense network scenarios and determine in which scenarios one methods outperform the others.