The Communication Technology Of Fm Parasitic Based On Cognitive Radio

Nowadays,with the rapid development of communication technology,transmission speed and communication reliability are not only the main standards when measuring communication system,but also the security of communication has become a major concern in various fields of communication technology.This makes the theory of communication security get the rapid development,the cryptography,information hiding and so on become the important research branch in the field of communication security.The traditional theory is that the secret files are encrypted by password,so that the illegal receiver can't obtain the secret information because of no password.But the fatal weakness of this approach is that it can easily attract the attention of the illegal attacker,thus increasing the possibility of information being cracked.The attacker may break the information using exhaustive method,so that the legitimate recipient does not receive information.Especially now the rapid development of hardware technology and the use of the Internet for distributed computing to carry out violent crack,the traditional encryption algorithms are faced with a huge challenge.In this paper,we mainly study the information hiding technology,which is a combination of communication technology and cognitive radio.The main research contents and results are as follows:1.Parasitic communication system based on spread spectrum or MFSKBy sensing the external changes of the spectrum in public channel,we choose the suitable carrier frequency point and insert the parasitic information in the public channel through a modulation.The paper studies the parasitic communication system based on spread spectrum and the parasitic communication system based on MFSK,and analysis the advantages and disadvantages of the spread spectrum and MFSK as the modulation mode of parasitic signal,and the corresponding parameters of the system communication,such as the spread spectrum,the multiple of frequency shift keying,and so on,are given by the system simulation of two kinds of parasitic communication systems.2.The joint demodulation of MFSK modulation:As it is difficult to accurately synchronize with the low signal to noise ratio of the parasitic system based on MFSK,we give the optimal demodulation mode of the receiver under the condition of non-ideal channel.After the two demodulator at the receiving end,received the same signal,we calculated point sampling probability density of the received signal,and merge the probability density of the soft information,and then decoding soft decision information,to obtain the better demodulation performance.In this paper,the related research is the basic research work for the realization of the parasitic communication system.