The Research Of GPS Trajectories Reconstruction Based On NMEA 0183 From GPS Navigation Devices

As GPS devices provide practical functionalities such as positioning,navigation service and route planning,they are usually utilized by people when driving in unfamiliar places.In the meanwhile,the data built-in GPS devices are becoming more and more important.For forensic investigators,it is a hot topic that how to recover historical trajectories from GPS devices.Since the traditional recovery method relies on file system metadata,it will fail when metadata is unavailable.In order to resolve this problem,this paper propose a novel recovery algorithm which can successfully recover the removed GPS information without metadata.The main work is as follows:First of all,it is proposed to study the details of NMEA 0183 protocol specification.It analyzes the characteristics of data blocks belonging to NMEA logs,sentence type,sentence structure and meaning of fields,which is the basis of recovery algorithm.Secondly,a path reconstruction technique based on NMEA 0183 protocol is proposed.At first,the data blocks belonging to NMEA logs are pinpointed when scanning the whole image.Then,a discriminator is designed based on the local continuity of time and space and other features of NMEA 0183.And based on the discriminator,a reassembly algorithm is proposed to reorder and merge the obtained data blocks to generate new logs.Finally,by analyzing the recovered log files,the information of track points can be linked and shown as reconstructed trajectories in maps.As the experimental results shows,the proposed recovery algorithm can successfully recover information in such scenarios: system metadata is available/unavailable,log files are fragmented heavily,part of logs are overwritten and different file systems with various cluster sizes.In addition,the accuracy and recall rate can be always kept above 99%.Then,as anti-forensic techniques always interfere the investigations,numerical simulation experiments are designed to explore the feasibility and reliability of trajectory recovery in anti-forensics conditions.Finally,a GPSDroid system is implemented according to the proposed algorithm.The system integrates the data preprocessing,data reassembling,log analysis and anti-forensic detection modules.It is proved to demonstrate the feasibility of our proposed method.In summary,the GPS trajectory recovery technology based on NMEA 0183 can resolve the problem of metadata dependence by utilizing the features of NMEA logs.In addition,since we consider the GPS anti-forensic techniques,our proposed method performs better than the prior arts.