Specific emitter identification for GSM cellular telephones

Abstract

GSM cellular telephones are identified by a 15-digit number that resides in the memory of the cellular telephone. This number, or international mobile equipment identity (IMEI), is also used when granting network access to a cellular telephone. The caveat with the usage of IMEI is that it is easy to access and manipulate. This allows for a malicious user to masquerade as another user on a Global System for Mobile Communications (GSM) network and thereby gain illegitimate access to the network. Therefore, there is a need to identify cellular telephones in a manner that is difficult to manipulate and spoof. This study investigates specific emitter identification (SEI) as a way of identifying GSM cellular telephones using the analogue radio frequency (RF) transmissions of the cellular telephone. Second to that the research investigates the sensitivity of SEI to changes in the transmission characterisitcs of the cellular telephone, signal degradation and the usage of different receivers. This research found that it is possible to identify GSM cellular telephones with a peak accuracy of 88.26%. Futhermore, it is shown that SEI is sensitive to the transmission power of a GSM cellular telephone. Classification accuracy of cellular telephones drops with an increase in transmission power of the cellular telephone. Furthermore, it is shown that GSM cellular telephones cannot be accurately identified when multiple receivers are used, even if the receivers are nominally identical. However, the receivers used for this experiment were low cost and low quality receivers. Hence, the result may not generalise to higher quality receivers. Lastly, it is shown that the SEI technique renders poor accuracy (below 60%) when the signal-to-noise ratio (SNR) is below 9 dB.