Resource Allocation in Cell-Free Massive MIMO With the Coexistence of eMBB and URLLC

In this paper, we rigorously analyze the non-orthogonal coexistence of enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC) in the downlink of a Cell-Free Massive MIMO (CF-mMIMO) system. We propose an eMBB-URLLC joint resource allocation algorithm based on proactive packet dropping mechanism, maximizing the eMBB users' sum throughput while ensuring the URLLC users' delay and reliability requirements, accounting for both transmission and queueing delays. Specifically, the joint resource allocation scheme is formulated as an NP-hard problem, and is decomposed into two sub-problems. The first sub-problem refers to proactive packet dropping mechanism, we minimize the maximum URLLC required transmission power to meet QoS requirements by optimizing packet loss probabilities. The packet loss probabilities includes transmission error probability, queueing delay violation probability, and proactive packet dropping probability. The second sub-problem consists of two components: eMBB user admission problem and eMBB-URLLC user joint power control problem. We solve the former user admission problem with a dynamic programming approach, and address the later joint power control problem with an iterative algorithm. Numerical results show that our proposed algorithm outperforms the comparable resource allocation algorithm, both in terms of the sum throughput of eMBB users and the overall packet loss probability of URLLC users.