  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).
