A Research About Reliability Of Cognitive Links Based On Lt Codes

The cognitive radio (Cognitive Radio, CR) technology is an advanced radio technology. CR technology is based on the spectrum sensing, spectrum sharing spectrum switching technology, to break the limitations of conventional fixed subscriber access communications network spectrum, to achieve a dynamic access of the spectrum, and greatly improve the efficiency of spectrum utilization. LT codes is an advanced channel coding technology, which uses a random encoding, the encoded data stream of arbitrary length can be generated, and thus better able to adapt to changes in the channel condition. In this thesis, a separate study on the CR technology and LT fountain code, after the combination of CR and LT codes, based on the reliability of the cognitive transmission link of dynamic LT coding mechanism, by contrast, does not use dynamic LT coding proved cognitive transmission link can guarantee the reliability of the LT encoding based on dynamic mode and uses the performance curves of the dynamic LT code way, and comparing the performance curves of the retransmission mode and dynamic LT codes.First of all, discusses the main content, basic knowledge of CR technology of CR and the development situation, main research model in CR, what problems still exist and the key techniques for the research and the current CR system, introduces how to focus on the development of reliability research on CR cognitive transmission link.Then the basic concept of fountain codes LT codes is discussed in detail, and the analysis method of encoding and decoding. Study of LT code BP gives the belief propagation algorithm design scheme based on LT coding, BP decoding algorithm achieves high in the iteration number can have a good decoding performance.Finally, combined with the technology of LT, studies the CR system based on LT coding and did not use CR system LT code after the authorized user access system how to ensure the transmission performance of the link of cognitive users, the system dynamics based on LT code and did not use dynamic LT two system code security, the simulation results show that, dynamically adjust the code rate LT code can guarantee the reliability of the cognitive transmission link. Research on CR system based on LT coding and uses a retransmission scheme to ensure the system transmission performance of cognitive link, the simulation results show that, dynamically adjust the code rate LT code can save time cognitive cost transmission link reliability.