Channel-feedback-free transmission for downlink FD-RAN: A radio map based complex-valued precoding network approach

• Published in: China communications Vol. 21; no. 4; pp. 10 - 22
• Main Authors: Jiwei, Zhao, Jiacheng, Chen, Zeyu, Sun, Yuhang, Shi, Haibo, Zhou, Shen, Xuemin Sherman
• Format: Journal Article
• Language: English
• Published: China Institute of Communications 01-04-2024
• Subjects: Array signal processing; Base stations; beamforming; complex neural networks; deep learning; Downlink; FD-RAN; Neural networks; Precoding; Real-time systems; Spectral efficiency
• ISSN: 1673-5447
• DOI: 10.23919/JCC.fa.2023-0393.202404

As the demand for high-quality services proliferates, an innovative network architecture, the fully-decoupled RAN (FD-RAN), has emerged for more flexible spectrum resource utilization and lower network costs. However, with the decoupling of uplink base stations and downlink base stations in FD-RAN, the traditional transmission mechanism, which relies on real-time channel feedback, is not suitable as the receiver is not able to feedback accurate and timely channel state information to the transmitter. This paper proposes a novel transmission scheme without relying on physical layer channel feedback. Specifically, we design a radio map based complex-valued precoding network (RMCPNet) model, which outputs the base station precoding based on user location. RM-CPNet comprises multiple subnets, with each subnet responsible for extracting unique modal features from diverse input modalities. Furthermore, the multimodal embeddings derived from these distinct subnets are integrated within the information fusion layer, culminating in a unified representation. We also develop a specific RMCPNet training algorithm that employs the negative spectral efficiency as the loss function. We evaluate the performance of the proposed scheme on the public DeepMIMO dataset and show that RMCP-Net can achieve 16% and 76% performance improvements over the conventional real-valued neural network and statistical codebook approach, respectively.