Research On The Effect Of Pointing Error On Performance Of Space Chaos Laser Communication System

Compared with traditional microwave communication,free space laser communication has the advantages of broadband,large information transmission capacity,and low power consumption,and has attracted widespread attention.Light may travel thousands of kilometers in free space channel,thus increasing the possibility of eavesdropping.The security of the common key encryption method of traditional space laser communication will be threatened under the rapid development of quantum communication technology.Therefore,the space laser communication system needs a new encryption method.Chaotic encryption,as a hardware-based encryption method,has good compatibility with existing free space laser communication system.The possibility of applying chaotic synchronization to free space channel has also been verified.Therefore,space chaos laser communication technology has now become an important development direction.When light is transmitted in free space channel,the system will be affected by pointing error.Pointing error will introduce radial displacement between the beam center.Beam wander will further deteriorate the receiving power based on pointing error,so the research on the effect of pointing error plays an important role in space laser communication technology.At present,the effect of pointing error on the performance of space chaos laser communication system has not been widely studied.Therefore,it is very necessary to carry out relevant researches.In this thesis,the effect of pointing error on space chaos laser communication system is firstly explored.The synchronization of chaos carrier at transmitter and receiver is very important for the optoelectronic delay feedback chaotic security system.Pointing error is composed of boresight and jitter which will both introduce external mismatch and internal mismatch.Then chaos carrier at the transmitter and receiver cannot be cancelled completely and the system performance will be affected.The system bit error rate(BER)formulae effected by pointing error is derived and analyzed.Results show that the increase of jitter and boresight will increase external mismatch and internal mismatch then deteriorate the system performance.Jitter will affect the system performance more than boresight,and internal mismatch will affect the system performance more than external mismatch.Beam wander will further deteriorate the receiving power and affect system performance based on pointing error,so the effect of pointing error and bean wander is analyzed.The system BER formulae effected by pointing error and beam wander is derived and analyzed.Results show that beam wander will further increase the external mismatch and internal mismatch based on pointing error,then deteriorate the system performance.When pointing error is relatively small,optimization beam wander will improve the system performance more.When pointing error is relatively large,optimization internal mismatch will improve the system performance more.Under the influence of beam wander,the effect of optimizing system performance by reducing pointing error is not obvious.Next,an indoor space chaos laser communication system is built,and a preliminary experiment of the space chaos laser communication system affected by pointing error is carried out.The average radius offset under different boresight and jitter is calculated then average power attenuation is calculated.The effect of pointing error on space chaos laser communication is simulated by power attenuation.Experimental results show that the increase of pointing error will deteriorate the signal,however,BER of the signal will not be affected.When the chaos encryption is turned on,whether the increase of boresight or jitter will deteriorate the performance of space chaos laser communication system.In this thesis,we study the effect of pointing error,pointing error and beam wander on the performance of space chaos laser communication system.The research results above have a great reference for the design of space chaos laser communication system in practice,and have positive significance for improving the performance of space chaos laser communication system.