The Research Of Precise Method For Time Delay Measurement In Telephone Channel

With the development of technology, diversified applications based on telephone timeservice emerge in national various professions. Time service based on Public SwitchedTelephone Network (PSTN) has already been widely used in telecommunications, electricity,transportation and financial sectors. The heart of the matter in telephone time service is howto measure the delay of transmission time exactly, since the measurement error of time delayin current telephone time service is a bit large. This thesis aims to improve the measurementaccuracy of telephone channel delay in order to meet the needs of telephone time service.Firstly, this paper gives us a brief introduction about the general structure of publictelephone network; this part focuses more on the characteristics of the time delay in switchingequipments. Then the paper compares different methods of time delay measurement, and afterresearching and analyzing those methods, the author put forward a new way to measure timedelay based on those existing telephone channel delay measurements, which is measuring thetime delay by using correlation properties(through inspect related function peak) ofpseudo-random (PN) code.Next, the paper design out the overall program about time delay measurement systembased on PN code on the basis of the analysis of PSTN principle, including designations aboutsignal system, signal management alternative and how to achieve the project. Then，accordingto those features in the measurement signal of time delay system, the author design out thecapture scheme based on DMF, the carrier tracking loop based on the Costas loop and PNCode tracking loop based on DLL.Finally, the digitalized telephone channel time delay measurement experimental boardbased on FPGA and DSP is developed, and also finished the text of its function in the wholedelay measurement system, for example, in PSTN. From the test result, we can conclude that in this area, the fluctuation is less than6.67microseconds with the new method in telephonechannel, much more accurate than traditional method, which just meet the expected goal.