The output current of a standard USB interface is max.500mA, which does not meet the peak current demand of GPRS modules. If you need to supply a module with power via USB, you can operate as follows:

1) Use AT+QGPCLASS to set the GPRS level to 8. This command will take effect after the module’s next restart. There is only one uplink slot when the GPRS level is 8.

2) Connect two low-ESR 2200uF capacitors to the VBAT pin and keep them close to the module.

3) Adjusting the VBAT voltage to between 4.2V and 4.5V is recommended, as this can prevent the module from functioning abnormally due to the voltage drop of VBAT.

4) Test the module with a weak signal (e.g. a CSQ value of less than 14). If the module works properly this indicates that the module can be powered via USB interface.