Low Altitude 3-D Coverage Performance Analysis of Cell-Free RAN for 6G Systems
Jiamin Li, Qijun Pan, Ziqian Wan, Pengcheng Zhu, Dongming Wang, Mengting Lou, Jing Jin, Feiyang Liu, Xiaohu You
Abstract
In this article, we propose to utilize a more flexible and scalable cell-free radio access network (CF-RAN) for 6G systems to promote the coverage performance of the low altitude three-dimensional (3-D) scenarios, where unmanned aerial vehicles (UAVs) and ground users (GUEs) are coexisted. User-centric association strategy and scalable receiving schemes such as maximum ratio combing (MRC), partial zero-forcing (P-ZF) and partial minimum-mean-square error (P-MMSE) are adopted to reduce the interference between UAVs and GUEs and improve the scalability of signal processing. Closed-form expressions for uplink spectral efficiency (SE) are derived with considered receivers. Based on the derived closed-form expressions, we propose a power allocation strategy by solving a multi-objective optimization problem between maximizing the average SE of UAVs and GUEs simultaneously with intelligent algorithm——Deep Q-Network (DQN). Numerical results verify the accuracy of the derived closed-form expressions and the effectiveness of the proposed power allocation schemes for low altitude 3-D coverage with coexisted UAVs and GUEs. The coverage performance analysis under various system parameters offers much of flexibilities for the optimization of the low altitude CF-RAN systems.