This document provides an overview of multi-carrier GRFU (GSM Radio Filter Unit) hardware, functions, and configuration for Huawei's BTS3900 base station. It describes the GRFU's hardware structure and principles, typical configuration scenarios, and data configuration process using MML commands. The key aspects covered include the GRFU's modulation/demodulation functions, ports, LED indicators, antenna configuration principles when using one or two GRFUs, and transmit/receive modes.