Numerology-Aware MCOT Selection for Improving Fairness in 5G NR-U Networks

NR-U enables 5G to access the unlicensed bands. However, a 5G NR-U transmitter has to follow the Listen Before Talk (LBT) procedure, where the transmitter has to sense the channel for a while prior to its transmission. Since NR-U is a scheduled technology, the transmission begins only at slot boundaries. But the LBT procedure may end before reaching the slot boundary, and then the transmitter has to wait for a gap period to align with the slot boundary. 5G has different numerologies, and the slot duration of each numerology is different. When nodes with different numerologies are contending for channel access, the node with a lower slot duration has a high probability of winning the channel since, after the LBT procedure, its next slot mostly comes sooner, which leads to fairness issues. In this letter, we propose an algorithm to improve the fairness in multinumerology contention by adaptively changing the Maximum Channel Occupation Time (MCOT) of each numerology according to the slot duration and the number of nodes in each numerology.