说明：  信道模型包括宽带传播模型（链路级仿真需要）和窄带传播模型（系统级仿真需要，包括路径损耗模型和阴影衰落模型）。
(Channel model including broadband propagation model (link level simulation needed) and narrow-band propagation model (system-level simulation needs, including the path loss model and shadow fading model).)