K-Preferential Slotted ALOHA for Ultra Reliable Low Latency Communications

Ultra-reliable low-latency communication (URLLC), one of the key component of 5G, provides a set of features required to support mission-critical applications. Slotted ALOHA is one of the most popular mechanism to share a channel among multiple users. However, slotted ALOHA cannot meet high reliability requirements of URLLC when large number of users are present in the network. In this paper, we propose a preferential medium access control scheme to match the high reliability requirement of URLLC. It is ensured by dedicating every Kth slot exclusively for URLLC transmission. We analytically obtain the packet delay distribution and reliability of both the URLLC and regular packets. An optimization problem is framed to maximize the reliability of regular packets subject to meeting the URLLC reliability constraints. Extensive simulations indicate that our proposed $K$-preferential S-ALOHA protocol can meet the URLLC requirements even when the network traffic is high.