The Muti-service Digital Distributed Access System digitizes the Feed-in 2G, 3G, 4G, 5G RF signals and converts them into optical signals, and transmits and distributes them through optical fibers for indoor and outdoor coverage. The system consists of Main Unit (MU), Extended Unit (EU), and Remote Unit (RU), which are used for deep coverage of 2G, 3G, 4G, and 5G wireless communication signals.

        The networking structure of the Muti-service Digital Distributed Access System is shown in the following figure:

* Fiber distribution, reducing the RF coaxial cable loss and reduce the difficulty of construction project
* Fiber Optic Cable feeding, and solve concentrated supply problems of active equipment
* Remote Unit (RU) with a small size, light weight which is easy to beautify and reduce user conflict

The MU unit couples the 2G\3G\4G MIMO downlink radio frequency signal provided by the RRU into the optical fiber distribution system, converts it into a digital signal, and then performs framing. After photoelectric conversion into an optical signal, it is transmitted to the extended unit through optical fiber. At the same time, the optical signal uploaded by the extended unit is converted into a digital signal, then deframed, and then converted into an uplink radio frequency signal and transmitted to the signal source. The MU unit supports the remote monitoring and management function of the EU and RU units that it belongs.

        The EU unit forwards the digital signals sent by the MU unit to multiple remote units; at the same time, the signals uploaded by the multiple remote units are combined and then transmitted to the MU unit. The EU unit supports chain cascading networking, and also supports remote power supply to the RU unit. The extended unit supports the remote monitoring and management function of the remote unit to which it belongs.