Distributed MIMO for 6G sub-Networks in the Unlicensed Spectrum

In this paper, we consider the sixth generation (6G) sub-networks, where hyper reliable low latency communications (HRLLC) requirements are expected to be met. We focus on a scenario where multiple sub-networks are active in the service area and assess the feasibility of using the 6 GHz unlicensed spectrum to operate such deployment, evaluating the impact of listen before talk (LBT). Then, we explore the benefits of using distributed multiple input multiple output (MIMO), where the available antennas in every sub-network are distributed over a number of access points (APs). Specifically, we compare different configurations of distributed MIMO with respect to centralized MIMO, where a single AP with all antennas is located at the center of every sub-network.

Power Control in Cell-Free Massive MIMO Networks for UAVs URLLC under the Finite Blocklength Regime

In this paper, we concentrate on the employment of a user-centric (UC) cell-free massive MIMO (CFmMIMO) network for providing ultra reliable low latency communication (URLLC) when traditional ground users (GUs) coexists with unmanned aerial vehicles (UAVs). We study power control in both the downlink and the uplink of such a scenario when partial zero-forcing (PZF) transmit/receive beamforming and maximum ratio transmission/combining are utilized. We consider optimization problems where the objective is either to maximize the total users' sum URLLC rate or to maximize the minimum user's URLLC rate. The considered URLLC rate function is both complicated and nonconvex rendering the considered optimization problems nonconvex. Thus, we present two approximations for the URLLC rate function and resort to successive convex optimization (SCO) to tackle the considered optimization problems. Particularly, we present SCO with iterative concave lower bound approximation (SCO-ICBA) and SCO with iterative interference approximation (SCO-IIA). We provide extensive simulations to evaluate SCO-ICBA and SCO-IIA and compare UC CFmMIMO deployment with traditional colocated massive MIMO (COmMIMO) systems.

Optimal Joint Beamforming and Power Control in Cell-Free Massive MIMO Downlink

In this paper, a novel optimization model for joint beamforming and power control in the downlink (DL) of a cell-free massive MIMO (CFmMIMO) system is presented. The objective of the proposed optimization model is to minimize the maximum user interference while satisfying quality of service (QoS) constraints and power consumption limits. The proposed min-max optimization model is formulated as a mixed-integer nonlinear program, that is directly tractable. Numerical results show that the proposed joint beamforming and power control scheme is effective and outperforms competing schemes in terms of data rate, power consumption, and energy efficiency.