The master communicates with the relay unit by serial communication interface and the relay unit communicates with module unit by wireless communication network.

上位机和中继单元之间采用串行口通信，中继单元和模块单元之间采用无线网路进行通信。

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Network interface unit (NIU) is an interface device between the control computer and the communication network.

网络接口单元（NIU）是控制计算机与通信网络进行交互的一种接口设备。

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Method for transmitting background noise information in data transmission in data frame, communication system, mobile station and network unit.

在以数据帧形式的数据传输中用于发送背景噪声信息的方法，通信系统，移动台和网络单元。

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