GPRS modem RF testing

I test the receiver signal strenght of the GSM GPRS modem using the AT+CSQ command
How can I test the RF output power of a GPRS modem without sophisticated test equipment. Is there an AT+ command to the nearest GSM base station to return my received signal strenth (loopback test)

Thank you

Normally there will be internal calibration done at the factory for one time, by which you will measure the RSSI