The Design And Application Of GSM Air Interface Protocol Analysis Software

During nearly three decades, mobile communication technology has made rapid development. As the main representative of the second generation of mobile communication system, GSM is still very important, and GSM users still account for a large proportion. Air interface is a communication interface between the mobile station and base station, and network monitoring and optimization basing on air interface has advantages of low cost and high flexibility. So we studied GSM air interface protocol and designed this GSM protocol analysis software.This GSM protocol analysis system is designed on SDR composed of FPGA and PC and software on PC is studied in this paper. In order to finish this system, we studied standardized GSM air interface protocol of 3 layers. According to protocol, we design frame synchronization, channel mapping, channel decoding modules on physical layer; design link management, message restructuring modules on data link layer; design cell configuration, radio resource management modules on network layer. In this paper, functions on each layer can be divided into several modules, for each module are described in its implementation process. This software system coordinated with FPGA could successfully provide signaling monitoring to multiple users among multiple cells, receive both uplink and downlink signal, track call procedure including handover. Afterwards, the software is added with application layer functions. For example, we found that the measurement report signaling could provide the signal strength information of nearby base stations and we have studied fingerprint matching localization algorithm so that the location technology based on measurement report signaling is put forward.In order to verify the correctness of this software, we did some experiments, and results show the software can successfully monitor various signaling on network layer, and track the establishment, handover disconnection procedure of the call, which also proves the correct design of physical layer and data link layer modules. We also did experiments on location function and get good results which show the location technology based on measurement report is suitable for indoor environment.