This document describes the principles for configuring hardware in 3900 series base stations. It provides definitions for base station components like BBUs, RRUs, and RFUs. It explains that 3900 series base stations use a modular design with BBUs and RF modules to support multiple radio access technologies (RATs) and installation scenarios. The BBU and RF modules can support single-mode and multi-mode configurations through software configurations to provide flexibility for network deployment and evolution.