ABSTRACT
　　　ASN.1 (Abstract Syntax Notation 1) has been widely applied in various fields. It is a markup language used to describe structured information, mostly used to define protocol standards for different computer systems, application program, and the information transmited and exchanged among network. ASN.1 provides rich data types, flexible extension mechanism and efficient encoding and decoding rules, and it is suitable for complex protocols. At present, message formats of many network protocol are all described by ASN.1 syntax. The studying object of this paper--RRC message data structures of LTE protocol stack layer three are also described by ASN.1 syntax.
　　　This article mainly researches the designing and partial implementation of ASN.1 encoding and decoding module in LTE system. Firstly of all, it introduces the basic concepts of ASN.1, grammar principles and BER, PER encoding and decoding rules; and then, analyzes the application processes of ASN.1 and the requirements of LTE protocol stack, and for LTE protocol stack designs the ASN.1 encoding and decoding module; and finally, take BCCH_BCH_Message as an example, partly implements the ASN.1 encoding and decoding modules. The realization first changes the ASN.1 of RRC messages in LTE protocol into C language data structures according to certain rules; then based on the converted C language data structure for each data structure achieveing encoding and decoding functions in accordance with the encoding rules.
　　　
【Key words】LTE system  RRC message  ASN.1  encoding and decoding module

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