Network access device and system

A network access system, comprising a network access device, the network access device comprising:

• a first signal transceiver port, configured to transmit and receive a first radio frequency signal in a multiple-input-multiple-output manner;
• a second signal transceiver port, configured to transmit and receive a second radio frequency signal in a single-input-single-output manner;
• a signal processing unit, configured to filter the first radio frequency signal and the second radio frequency signal, and to combine and/or split the first radio frequency signal and the second radio frequency signal, the signal processing unit being respectively connected to the first signal transceiver port and the second signal transceiver port;
• a synchronization unit, configured to demodulate, analyze and modulate the first radio frequency signal and a Time Division Duplex (TDD) switch signal in the second radio frequency signal, the synchronization unit being respectively connected to the first signal transceiver port, the second signal transceiver port, and the signal processing unit.