Cell-Free Network-Assisted Full-Duplex Enabled Short-Packet Communications Toward Energy Efficiency in IIoT Networks

The Industrial Internet of Things (IIoT) is envisioned as the future paradigm for the next-generation industrial system. To provide low-latency and high-reliable communication for a large number of battery-limited industrial equipments, this paper proposes a cell-free network-assisted full-duplex (NAFD)-enabled short packet communications (SPC) scheme in IIoT networks, where access points (APs) operating in the uplink (UL) mode or downlink (DL) mode simultaneously serve UL sensors and DL actuators on 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, data rates and duplex mode selection. The formulated problem is a mixed-integer fractional programming and decomposed into three subproblems. We develop the optimal and suboptimal algorithms for joint power control and beamforming design. A semi-closed-form solution is derived for the optimal data rates, and an efficient duplex selection algorithm is also proposed to find the computationally optimal duplex mode. Simulation results demonstrate the convergence of proposed algorithms, and the flexible cell-free NAFD scheme can achieve better EE performance than benchmark schemes such co-time co-frequency full duplex (CCFD), frequency division duplex (FDD) and greedy algorithm (GA) schemes.