An investigation into the accuracy of follow-on GPRS/mobile data CDRs

This study investigated the accuracy of 3G and 4G follow-on GPRS (General Packet Radio Service)/mobile data CDRs (Call Detail Records) from three UK mobile network operators (EE, Vodafone and Three). Follow-on GPRS/mobile data CDRs are currently considered to be more open to misinterpretation than voice/SMS CDRs as uncertainties exist regarding the correspondence between the timestamp and the Cell ID presented within the CDRs. Consequently, follow-on GPRS/mobile CDRs may be disregarded during criminal investigations, potentially losing valuable intelligence and evidence. To assess the accuracy of follow-on GPRS/mobile data CDRs, connected mode RF (Radio Frequency) surveys were conducted while simultaneously producing follow-on GPRS/mobile data CDRs in a travelling vehicle. This allowed a comparison of the start Cell ID presented in the CDR and the Cell ID that provided coverage to the device at the start time of the CDR to assess the correspondence between the timestamp and the Cell ID presented within the CDRs, and to consider the validity of the terminology used by experts. It was found that individual follow-on GPRS/mobile data CDRs cannot consistently place a device within the coverage area of the start Cell ID at the start time of the CDR. Instead, the results indicate that a terminology which places the device within the coverage area of the start Cell ID 'at or before' the start time of the CDR is appropriate. It is crucial that follow-on GPRS/mobile data CDRs are analysed with this consideration in mind so to interpret the evidence correctly.