A Novel User Association and Power Control Algorithm for Cell-free Massive MIMO

The vision of Industry 4.0 relies on advancements in wireless solutions; cell-free Massive Multiple Input Multiple Output (cf-mMIMO) is emerging as a promising physical layer technology for fifth-generation (5G) and beyond 5G technologies. However, industrial applications often demand varied and conflicting Quality-of-Service (QoS) requirements, and finding an optimal and scalable resource allocation strategy is challenging. This paper proposes a novel user association and power control algorithm to minimize the overall uplink (UL) transmit power while ensuring a given spectral efficiency (SE) requirement. The proposed solution identifies the best schedulable users to maximize the number of satisfied users without relying on instantaneous channel state information. Moreover, it adopts a game theory-based power control algorithm to minimize the total uplink power while ensuring the spectral efficiency requirement. Numerical results have shown significant gains in the number of satisfied users. A maximum gain of up to $15 \%$ is observed for a low SE requirement ($0.25 \mathrm{bits} / \mathrm{s} / \mathrm{Hz}$), increasing to $50 \%$ for a SE requirement of $0.75 \mathrm{bits} / \mathrm{s} / \mathrm{Hz}$. Furthermore, the proposed solution has shown great adaptability to varying requirements with respect to state-of-the-art schemes.