Cell-Free NAFD for Energy-Efficient Short Packet Communications in IIoT Networks

To provide low-latency and reliable communication for a large number of battery-limited equipments in industrial Internet of Things (IIoT), this paper proposes a cell-free network-assisted full-duplex (NAFD) enabled short packet communications (SPC) scheme, where access points (APs) operating in the uplink (UL) mode or downlink (DL) mode simultaneously serve UL sensors and DL actuators in the same frequency resource. Considering the UL-to-DL error propagation as well as the dynamic between latency, reliability and energy efficiency (EE), we take the effective EE as the performance metric and investigate the effective EE maximization problem by jointly optimizing UL power, DL beamforming matrices and data rates. The formulated problem belongs to fractional programming. We develop the optimal algorithm for joint power control and beamforming design. A semi-closed-form solution is also derived for the optimal data rates. Simulation results demonstrate the convergence of algorithms, and the proposed scheme can achieve better EE performance than in-band full duplex (FD) and frequency division duplex (FDD) schemes.