4G module is the SIM7250 wireless communication
module which i s produced by the Simcom Company, and it
is based on the 4G-LTE network wireless data transmission
module. This is embedded within a complete TCP/IP
protocol stack. SIM725 provides an USIM card interface
that has four pins, the voltage VCC as a power source,
SIM_Rs is a reset signal for USIM card. SIM_CLK work
can provide SIM card with the work clock. USIM DATA is
the data I/O ports. Its working principle is shown in figure
3.