Research And Implementation Of Embedded Real-time Compass Receiver Software

With the growing demand for user needs, satellite navigation systems have been widely applied to various fields. In order to break the monopoly of the United States and Russia in the field of global satellite navigation, China has independently developed the Beidou satellite navigation system – “Compass II”, which can operate independently. Beidou navigation system is similar to GPS navigation system in terms of navigation and positioning principles, but also has its own unique advantages. Currently, the "Compass II" is being developed and improved constantly. As the user terminal, Compass receiver is an important part of the satellite navigation system. It needs to be improved, developed and optimized. So, at the present stage, the research and the implementation of real-time receiver based on Beidou navigation is of great significance.Given Compass receiver needs to signal real-time processing, we chose the DSP and FPGA as the hardware platform for the receiver in our design. In this paper we mainly research, design and implement the part of the software and signal processing algorithm for the receiver, and eventually complete the positioning and other tasks. This paper introduces the current situation and development trend of domestic and international satellite navigation system and satellite navigation receiver. This paper also introduces the basic principle of the Compass receiver. Then we design the system framework for Compass receiver and program module framework for FPGA and DSP. Based on DSP and FPGA, Compass receiver uses DSP as the core controller and process the baseband signal by FPGA; we capture, track and synchronize signal by DSP, exchange data with FPGA and adjust FPGA to process the base band signal in real time; finally, we extract and save the navigation message by DSP and use the pseudo-range positioning algorithm to calculate the location results. Each module of the FPGA is studied, designed and implemented. We emphatically discuss the main design idea of the bit synchronization and frame synchronization and the method for extraction, error correction and calibration of navigation message. The baseband signal processing module consists of a clock module, the carrier NCO module, digital down conversion module, the code NCO module, a ranging code generator, a code correlation calculator and the frame synchronization module. These modules are connected to each other, thus the baseband signal processing is realized. This paper also describes the acquisition algorithm, tracking algorithm and pseudo-range positioning theory and algorithms. And the appropriate algorithm is implemented on DSP according to the actual situation: the serial capture method is used for baseband signal capture; second-order PLL is used for the code loop signal tracking; second-order FLL assisted third-order PLL is used for carrier loop; Newton method and least squares method are used for positioning algorithm.The result of the positioning test of the receiver is given in the conclusion part of the paper, which is also compared with the standard GPS positioning result. Each module and algorithm used in this paper are summarized. Finally, we discuss that the receiver needs to be improved in next work.