Paired Listen before Talk for Multi-RAT Coexistence in Unlicensed mmWave Bands

Abstract

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: omnidirectional Listen-Before-Talk (omniLBT) and directional LBT (dirLBT). Under directional transmissions and receptions, om-niLBT 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.

LBT Switching Procedures for New Radio-Based Access to Unlicensed Spectrum

“…In this regard, our previous results in [12], [11] demonstrate the omniLBT-dirLBT trade-off. In particular, we show that for low network densities, dirLBT already performs significantly better than omniLBT, while for high network density, omniLBT is a good technique.…”

“…To address the omniLBT-dirLBT trade-off, in [11] we proposed a paired LBT solution, in which the physical (PHY) carrier sense at the transmitter is done directionally in paired directions (e.g., the receiver direction and opposite directions) to detect hidden node problems. In [12], we presented a Listen-Before-Receive (LBR) solution, wherein carrier sense at the receiver is triggered and used to complement LBT at the transmitter side.…”

New Radio Beam-Based Access to Unlicensed Spectrum: Design Challenges and Solutions

“…(c) shows how the om-niLBT/dirLBT trade-offs are addressed by pairLBT, for nonaligned (top) and aligned (bottom) transmissions. We show in [56] through simulations that the pairLBT solution allows improving the ability to perform carrier sense by avoiding hidden node problems, which appear under dirLBT, and by stimulating spatial reuse, which is prevented with omniLBT (see Fig. 5).…”

“…5.(a)-bottom. In contrast, dirLBT does not create overprotection because it only senses the spatial direction in which the transmission will be carried out (see [56] we presented a totally distributed solution, coined paired LBT (pairLBT). The key idea of pairLBT is to perform directional sensing in paired directions: the receiver's direction (which is equivalent to perform legacy dirLBT) and its opposite direction(s).…”

“…The opposite directions can denote a single direction or a set of directions depending on whether the beams for carrier sense are either reconfigurable or predefined based on a set of previously configured beams, respectively. In this line, in [56], we derive analytic expressions to optimize the parameters (beam shape and ED threshold) for LBT in the opposite direction(s) with the objective of reducing hidden node problems, and also propose additional extensions to the pairLBT solution that use the sensed power during the sensing in the opposite direction(s) to properly adjust the transmit/receive strategy. Fig.…”