| In the Internet of Things(Io T)scenario,with the large growth of the number of users on the ground,the data is transmitted from the satellites to the data center on the ground.People have higher and higher requirements for the downlink rate of satellite signals.At present,the communication capacity of most existing navigation satellite systems is insufficient and the signal rate is low.The combination of navigation and communication can improve the communication rate and carry out rapid positioning.A novel Navigation and Communication Integrated(NCI)signal is introduced in this paper.And the cross-correlation optimization design of the signal is carried out.A code phase optimization algorithm and fuzzy judging algorithm are proposed,which can raise the communication rate of the signal and enhance the reliability and compatibility of the system.The main research contents of this paper are as follows:Firstly,the NCI signal is introduced in this paper,in which the GNSS signal is used as the navigation signal and CCSK signal is used as the communication signal.The navigation signal can provide synchronization capability for the communication signal,and the communication signal can improve the transmission rate.The two signals can enhance each other,and deep fusion at the signal level is realized.Secondly,a code phase optimization algorithm is proposed to avoid the cross-correlation interference for the characteristics of the NCI signal.The algorithm aims to align the larger value of cross-correlation function with the self-correlation peak by designing the Optimal Cyclic Shift Set(OCSS)of communication signal.The simulation results show that the code phase optimization algorithm can improve the detection performance and symbol error performance when receiving signals.In order to realize the compatibility between the NCI signal and satellite navigation system,a design strategy of OCSS based on double-threshold is proposed basing on the code phase optimization algorithm.This strategy makes the number of elements of the OCSS an integral power of 2,and error correction coding and interleaving technique can be applied to the NCI signal to improve the reliability of the system.And then,a fuzzy judging algorithm is proposed for receiving the NCI signal which is performed cross-correlation optimization design.Based on the statistical distribution of the correlation peak offset of the signal,the algorithm receives the signal by segmenting the correlation domain to solve the phase jitter and synchronization deviation.Compared with the traditional algorithm,the fuzzy judging algorithm can improve the fault tolerance of signal reception.When the Signal-to-Noise Ratio(SNR)is-21 d B,the fault tolerance can be improved by about 87%.Finally,combined with the actual engineering needs,the NCI signal and BDS are combined at the practical level.The communication signal is selected basing on the code phase optimization algorithm.In addition,the frame format of the communication channel is redesigned because of the increase of signal transmission rate.The navigation message parameters are rearranged and inserted into the communication frame to achieve the purpose of fast positioning.The signal rate is 140 times higher than that of the original,and the Time to First Fix(TTFF)is correspondingly reduced. |
