Frame Structure Analysis Of Non - Cooperative Demodulation Data

Frame structure analysis of demodulated data in non-cooperative communication is an important part of information processing, as well as an important subject of information access. The purpose of non-cooperative frame structure analysis of demodulated data is to obtain the structure of transmitted frame, such as frame synchronization, the reconstruction of scrambler, channel code identification and the system information analysis and so on. In the past, blind frame synchronization, channel code identification and the reconstruction of scrambler has been analyzed widely, the algorithms proposed are independent and may not be suitable in some conditions. A communication system is composed by Modules, there exists a constraint of input and output between modules, the algorithms may no longer be applicable. Researches about reconstruction of system structure as well as the composited code in a synchronous scrambler placed after a channel encoder are seldom.Frame structure analysis of the non-cooperative communication demodulated data is the main part of this thesis, especially the identification of the composited code. The work done can be summed up as the following aspects.1. This thesis first gives examples of several real communication systems, compares and analyzes the frame structure, finally proposes a frame structure which is applicable for external synchronization with same synchronization information and synchronous scrambler which is placed after channel encoder. This frame structure is the foundation of this thesis.2. This thesis first simulates the algorithm of scramble reconstruction and the estimation of blind frame synchronization, then analyzes the changes in balance and digital characterization of sequence after channel encoder. The results show that the algorithms of scrambler reconstruction are no longer applicable when synchronous scrambler is placed after channel encoder.3. The thesis gets a conclusion that a XOR operation between linear block codes and convolutional codes gets a code which belongs to the same codeword space of the linear block code or the convolutional code. When synchronous scrambler is placed after channel encoder, the method of scrambler cancellation can constructs channel code data stream which has the same parameters as channel code. When the received frames are composed with the same scrambler, channel code parameters are obtained using the algorithm of scrambler cancellation. The thesis simulates the scrambler reconstruction on dual word, it is effective when all dual words in a check matrix have same code weight, and then an improved algorithm based on check matrix instead of dual word when code weights are different is proposed.4. This thesis puts forward a sync-blind identification algorithm of synchronous scrambler and channel code on the condition that the received frames are composited with different scramblers. Then some improvements are made in the blind identification algorithm based on scrambler cancellation and dual words, the blind identification algorithm based on scrambler cancellation and check matrix, and the sync-blind identification algorithm of composited code. Simulations show that better performances are achieved and the calculation decline, but the number of bits required by the new algorithm increased. The simulations show that the algorithm based on scrambler cancellation and check matrix gets the best performance, followed by the algorithm based on scrambler cancellation and dual words, while the sync-blind algorithm gets the worst performance.