Paired Listen Before Talk for multi-RAT Coexistence in Unlicensed mmWave Bands

For a fair coexistence of multiple Radio Access Technologies (RATs) in unlicensed millimeter-wave (mmWave) bands, where directional transmissions/receptions are needed, two techniques are being considered for channel access: omni-directional Listen-Before-Talk (omniLBT) and directional LBT (dirLBT). Under directional transmissions and receptions, omniLBT is overprotective and depresses spatial reuse, while dirLBT enables spatial reuse but may create hidden node problems. In this regard, this paper proposes a paired LBT (pairLBT) solution, which aims at taking the best of omniLBT and dirLBT. The key idea is to perform directional LBT in paired-directions: the direction of the receiver and the opposite direction(s), so that spatial reuse is permitted while hidden nodes are avoided, hence stimulating a fair multi-RAT coexistence. We derive analytic expressions to properly configure the beamwidth and the energy detection threshold of LBT in the opposite direction(s) in a way such that the impact of hidden node problems is minimized.