| The ground-based radio navigation system generally consists of a ground reference station and four more ground slave stations as a new type of pseudo-satellite system.Different from the traditional pseudo-satellite system,the system can not only transmit GNSSlike signals to help GNSS to improve positioning capability and accuracy under complex circumstances such as indoor or shading environments.Besides,it is able to autonomously form a network and transmit new scheme signals to achieve high precision positioning if GNSS denies.These advantages have made the ground-based navigation system an important issues in the sphere of navigation in recent years.However,due to the immature technology system and the lack of in-depth research at home,especially the design and the generation of particular signal system,the ground base system has not been widely used.In response to this situation,this thesis has carried out research on key technologies of ground-based radio navigation signal processing,and mainly has completed the design and verification test of the baseband signal processing at the transmitter of station.The main contents are as follows:1.Investigating the development path and the latest research progress of groundbased radio navigation systems in the domestic and foreign,and summarizing the operation and positioning methods of the representative systems.Conducting in-depth study of TH/DS-CDMA signal system and its modulation method and error analysis for critical problems such as near-far effect and multi-path effect.Executing theoretical research on two-way ranging time synchronization method based on carrier phase smoothing pseudorange,which is verified by simulation that the time synchronization accuracy can reach nanosecond level by smoothing pseudo-range on the basis of carrier phase difference measurement accuracy up to half a cycle.2.On the basis of theoretical research,carrying out research on key technologies of signal processing at the transmitter of ground-based navigation base stations,mainly including the design of time-hopping schemes based on specially constructed congruent codes and the method and design of special text processing for ground-based navigation.The former can generate a time-hopping signal at any duty,which is better than the Locata in time-hopping sequence detection performance at the same duty,and is more suitable for small systems at a high duty.The latter gives the design of navigation message structure and processing methods of tropospheric error model,coordinate conversion,and acquisition of time base.3.According to the technical requirements and application scenarios of the groundbased radio navigation system,the indicators and architecture of the base station transmitter are proposed.Bottom on the FPGA+ARM architecture,the baseband signal processing module and embedded control program design of the transmitter have been designed,which can achieve TH-DSSS modulation in used of the proposed time-hopping sequence code and navigation message.The function of the signal processing module of the transmitter is verified on the hardware platform,the performance of the transmitted signal is calibrated,and the availability of the navigation signal is verified through the baseband transceiver test.The signal processing scheme of the transmitter at the base station of the groundbased radio navigation system designed in this thesis realizes the generation of TH/DSCDMA navigation signals based on BPSK(10),whose transmitting power is higher than 3d Bm and adjustable frequency range is 2.4-2.45 GHz.The overall scheme has the advantages of high precision,good versatility,and strong scalability,which provides a research basis and technical approach for the realization of ground-based navigation system base station engineering. |
PDF Full Text Request