Study On The Independent Time Service And Date Communication Over Loran-C

Improving and ameliorating the ability of Loran-C for time service are the main objective of our study in this paper. Although GPS has been widely used , Loran-C is still highly desirable to be as an alternative PRS(primary timing reference source) for an important part of a nation's infrastructure in Europe ,Asia, and others areas, even in United States. The current standard Loran-C signals lack of enough information to mark the precision reference pulses, Loran-C couldn't be considered as an independent system in precision timing applications. The paper will show that, if appropriate time information are added into the signals over the Loran-C data channel(studied in the first part of the paper) or in which the current multi-chains signals can be skillfully dealt with(studied in the second part of the paper), the independence of Loran-C for precision timing can be perfected, as well as the precision of timing signals and the automatization level of UTC synchronization can be improved , thereby the Loran-C can be acceptant and employed widely.Two approaches are advanced in the first time and studied in detail in this paper. The first approach , which is the emphases and main body of this dissertation, is additional PPM(Pulse Position Modulation) through which new time message will be modulated onto the Loran-C pulses signal. Using the Multi-chains Loran-C signals to implement the independent UTC synchronization is the second approach, which is relied on the Coincidence Rule among TOCs of different Loran-C chains.In this paper, the basic concept of PPM and experiment results are introduced. On the basis of these achievement, we put forward a general method of PPM. The performance of PPM in influencing normal Loran-C operation, raw data rate ,as well as possibility of error are analyzed, too. Results are also given to the Loran-C systems in China according to their charateristic parameters. Our test results show that the PPM is feasible.The principle of independent TOC(Time of Coincidence) synchronization over Loran-C data channel is studied . The essential requirement of TOC synchronization is analyzed according to the characteristic of TOC. The concept of TOC Message is defined. In this paper, we put forward and define a new message type-TOC message type, which is coincident with the latest ITU-R recommendation M589.3. The corresponding communication protocol is presented. The relationships between GRI pulse sequences and reference pulses, as well as between modulation code groups and Loran-C pulse groups are analyzed. Finally, as examples, the method of independent TOC synchronization are studied for the mode of burst transmission and continuous transmission.The formats of data coding and frame structures are studied. The structure of all possible data information is discussed, as well as the calculation methods and equations for some important parameters and data are given. The selection of data for broadcasting depends on the expected time service function of Loran-C, and the data layout is related to the adopted technique. The details of the message bit assignment and time code format and frame structures are given. The TOC message will obtain UTC time code, the corrections of the time of emission UTC(Transmitting Clock)-UTC(k), leap seconds, as well as the TOC(Time of Coincidence) distance data which is used to locate the TOC automatically.The algorithms and approach for TOC message broadcasting control are studied in this paper. The function of TOC message we suggest here is so distinctly different with the current DGNSS message be broadcasting in NELS that a precision transmission control of the UTC message is needed, in order that the information and data in the message could be consistent with the reference pulse and denote the pulse. The TOC message can be broadcasted, solely or alternating with DGNSS message, over one Loran-C data channel. The availability of the messages in alternating broadcast mode is analyzed. The recurrence formulae of the sequence number of the header of the TOC...