The Research Of The Transmission Protocol Of DGPS Message

With the increasing popularity of GPS technology, standard GPS positioning service can not meet the demand of the high-precision positioning for people. A shortcut of improving the positioning precision is provided for People with the introduction of DGPS. At present, DGPS technology has already been mature. And it is widely used in every field.Any information including DGPS information can not be transmitted without certain formation (protocol). Many organizations in the world have defined the DGPS information transmission protocol for the purpose of extending DGPS technology. At present, RTCM SC-104 protocol and RTCA DO-229 protocol are used mostly among all the protocols. Both the two protocols were researched in detail in this paper. The users of DGPS could reference this paper when selecting the proper DGPS protocol. In addition, more or less benefit will get for the developing of DGPS receiver from the research.Firstly, the main causes of GPS positioning error and principles of how to get rid of the positioning error using three DGPS methods (position differential, pseudorange differential and phase differential) were introducted.Secondly, the research of both RTCM-SC-104 protocol and RTCA DO-229 protocols has been done. A detail of the main message types of the two protocols including the structure of the block, the parameters in messages and the meaning of the parameters was described also.After the description of RTCM protocol and RTCA protocol, the research of the decoding method for both two protocols was done. Software for decoding the two protocols was also developed using the VC 6.0 develop kit. The decoding software can read, save and extract the valid data of the two protocols. Moreover, this software can also accomplish the functions of displaying the decoding data, selecting the visible content and so on.At last, on the base of the analyze and the research above, this paper compared the two different protocols and appointed the differential and common ground including the constitution of the transport system, the main rectification arithmetic, appropriate range and so on.At last, on the base of the analyze and the research above, a contrast between RTCM protocol and RTCA protocol including the constitution of the transmission system, the main correction algorithm, appropriate range and so on was done. Similarities and differences between the two protocols have obtained through the contrast.The research subject comes from the Jilin Communications Ministry's project "Watercraft Dynamic Monitoring information system" which is undertaken by GNSS Institute in Dalian Maritime University. The result of this research has been applied in the technology of improving the positioning precision for watercraft.