Investigating GSM Control Channels with RTL-SDR and GNU Radio

This paper focuses on the compliance of publicly available specifications of Global System for Mobile communication (GSM) with the extremely closed GSM industry with the help of RTL-SDR, GNU Radio and Wireshark. GNU Radio is a free and open software which enables the translation of real-world systems to programmable flow graphs. GSM, together with other technologies, is part of the evolution of wireless mobile telecommunications. Hence, verification of GSM working is of crucial importance. During this paper, Control channel information like the bandwidth for specific network providers was reckoned, along with the IMSI number and ARFCN channel in use by mobile device of the respective network. It was also noted that observed cell towers used both frequency hopping and encryption. The channel information thus obtained provides efficient techniques for the detection of spectrum holes providing high spectral resolution capability.