LT Encoding Based On Pseudo-random Matrix And Its Application In Satellite Navigation

The satellite navigation system has a large number of users which in a variety of user environment,which brought great inconvenience to the design of navigation and positioning signals.Fountain code is designed to meet the needs of heterogeneous users.The design of fountain code is simple,and it does not need feedback information in the process of transmission and reception.The most important thing is that it has lower complexity and higher decoding success rate.Therefore,fountain code is suitable for the design of navigation and positioning signals.In terms of theory,the applications of fountain codes to satellite navigation system can greatly improve the performance of the navigation and positioning to heterogeneous users.The coding structure has a great influence on the performance of fountain codes,and the degree distribution function determines the coding structure.According to the characteristic that navigation message is short.A LT encoding scheme based on pseudo random matrix is proposed.Compared with the traditional LT coding,it can reduce the redundant information bits in the encoded packets,which can greatly save the cost of encoding and decoding.And compared with the traditional LT coding scheme based on the robust soliton distribution in the filed of decoding complexity,decoding rate and decoding success rate.Finally,combined with unequal error protection thought,further research and design of the unequal error protection of pseudo random matrix.And analyzing its unequal error protection ability in the navigation system.Compared with the traditional LT coding scheme which use the equal probability selection strategy,the decoding rate of the important packets is improved under the same decoding cost in the condition of lower packet loss rate.The traditional navigation message is encoded by LDPC,and its performance is easily affected by the user's environment.When the user environment is poor,the decoding success rate is very low.In this paper,the LT coding scheme based on pseudo-random matrix is introduced.When the user is in good condition,receive a few packets can be successful decoding.When the user's environment is poor,you just need to continue to receive packets to complete the decoding process.In this paper,a simulation platform is build by the Simulink library in the matlab.Using the navigation signal SNR as external disturbance which is measured in different user's environment,comparing the LT coding scheme based on pseudo random matrix with traditional navigation message coding scheme in terms of the decoding success rate.When receiving three complete data frames,Using traditional navigation message coding scheme,the probability of collect almanac can reach more than 95% only when the user channel condition is good.While using the LT coding scheme based on pseudorandom matrix,the probability of collect almanac can reach 100% when the user channel condition is poor.