ConPA: A Contention-free Mechanism with Power Adaptation for Beyond Listen-Before-Talk

In view of the need to find novel means to utilize the unlicensed spectrum to meet the rising latency and reliability requirements of new applications, we propose a novel mechanism that allows devices to transmit anytime that a packet has to be delivered. The proposed mechanism, Contention-free with Power Adaptation (ConPA), aims to bypass the contention periods of current Listen-Before-Talk (LBT) approaches, which are the main source of unreliability in unlicensed technologies like Wi-Fi. To assess the feasibility of ConPA, we provide an analytical method based on Markov chains, which allows deriving relevant performance metrics, including throughput, airtime, and quality of transmissions. Using such a model, we study the performance of ConPA in various scenarios, and compare it to baseline channel access approaches like the Distributed Coordination Function (DCF) and the IEEE 802.11ax Overlapping Basic Service Set (OBSS) Packet Detect (PD)-based Spatial Reuse (SR). Our results prove the effectiveness of ConPA in reusing the space to offer substantial throughput gains with respect to the baselines (up to 76% improvement).

I. Introduction

Future wireless communications systems will have to support the extreme performance requirements of next-generation applications like industrial digital twinning or immersive telepresence [1], which emphasize latency and reliability atop of throughput, capacity, and coverage [2]. A significant portion of these systems is expected to operate in the unlicensed spectrum, which is regarded as an appealing option for easy deployment of private solutions and free access to a vast chunk of frequency bands (e.g., up to 1.2 GHz of spectrum in the 6 GHz band). However, most of the operations in unlicensed bands below 7 GHz are regulated by Listen-Before-Talk (LBT), a mechanism based on Carrier Sense Multiple Access (CSMA) with Collision Avoidance (CA) that was purposed to provide fair distributed channel access. The LBT procedure relies on Clear Channel Assessment (CCA), whereby a transmitter device must first perform Energy Detection (ED) to check if the measured power at the intended transmission channel is above a certain threshold (i.e., the channel is busy thus deferring transmission) or not (i.e., the channel is idle thus allowing transmission).