Design And Implementation Of GSM Station Receiver On SDR

With the rapid development of mobile communications,communication technology has developed into the time of 4G represented by LTE/LTE-A.Even so,GSM still accounts for a considerable proportion for its good coverage and voice communication quality.Mobile monitor is an important branch in the field of mobile security technology,relating to national and social security,whose importance can't be ingored.Software Defined Radio is very popular among researchers for its adaptability.The use of software-defined radio platform for GSM monitor detection has important practical significance.This thesis focuses on the receiving process of open source project OpenBTS based on USRP platform,algorithms of GSM physical layer processing and cell layer signaling traffic flow.This thesis proposes the scheme of receiver for GSM multi-frequency system based on double USRP,which can monitor the GSM basestation.Work and innovations of this thesis include:First,this thesis proposes a solution of broadband multi-frequency GSM receiver system with double USRP based on the original OpenBTS single frequency receive scheme.Original OpenBTS implements the processing of single frequency signals,the thesis uses double USRP to receive downlink and uplink channel broadband signal,and separates multi-frequency channel using software.This solution makes full use of USRP N210 RF broadband receiving ability.The system can monitor the commercial GSM station.Second,this thesis proposes the design of multi-task with full real-time parallel processing software framework which can realize digital filtering multi-frequency channel separation and processing.In the physical layer,this thesis designs a solution of memory resource sharing,complicated process scheduling,and through CPU binding,computing optimization,to ensure multi-frequency channel tracking process to achieve real-time requirements.The system can process 16 channels of GSM signal.Third,this thesis designs and implements a high robustness and effective of GSM signaling tracing program,and completes commercial scene debugging.Due to time-varying attenuation characteristics of mobile and wireless environment,the receiver can not guarantee that all signaling all received correctly,the thesis optimizes the tracking of signaling.The proposed GSM signaling tracing program,can guarantee even after losing part of the signaling,users can also be monitored.