Design Of GNSS-R Real-time Software Defined Receiver And Its Applications

In recent years,GNSS-R has achieved fruitful research results in the field of marine and land remote sensing.Different from the traditional GNSS PNT application,its core observation is no longer the distance between stations and satellites,but the information such as direct/reflected signal path difference and Delay-Doppler-Map.In order to meet the needs of personalized applications,GNSS-R receiver have to design different baseband signal processing algorithms.However,there are many factors affecting the characteristics of the reflected signal,and the receiver baseband processing algorithm is not yet mature.In order to extract effective remote sensing information,it is necessary to repeatedly test various algorithms.Therefore,SDR(software defined receiver)which is easy to debug and upgrade algorithm has been widely used in GNSS-R.Since GNSS-R SDR needs to process the digital intermediate frequency signal at a very high A/D sampling rate,the amount of data is large and CPU cannot support real-time operation.In order to improve the efficiency,GNSS-R real-time SDR based on CPU+GPU is developed for the application of sea surface altimetry and soil moisture monitoring.The main work are as follows:(1)Develop GNSS-R real-time SDR based on CPU+GPU.In order to ensure the accuracy,the test data use signals with high bandwidth,and the sampling rate is as high as 62MHz,which greatly increases the amount of data.In addition,the sea surface height altimetry needs to output a large amount of data in a short time,while the soil moisture monitoring needs hundreds of milliseconds incoherent integration for signal acquisition.These further improves the requirements of the computing power of the receiver.Combined with the characteristics that CPU is good at logic control and GPU is suitable for large-scale parallel computing,this paper designs the receiver architecture to make it have the ability of real-time operation under a very high amount of data.(2)According to the application requirements,the relevant parameters and algorithms are designed and optimized.When testing the accuracy and efficiency of the receiver,for the application of sea surface altimetry,the different strategies mainly lie in changing two variables:the coherent integration time to increase the gain required by the weak signal and the number of path delay values used in the adjustment;For the application of soil moisture measurement,different models are used in inversion,and the better one is selected through comparative analysis.(3)The ground-based experiment is carried out to test the performance of application modules of the SDR.The results show that:The sea surface altimetry application module can realize real-time data processing.At the same time,it can obtain the height accuracy of decimeter level or even centimeter level;The application module of soil moisture estimate can also realize real-time operation while ensuring high accuracy.To sum up,this paper designs a GNSS-R SDR based on CPU+GPU,and carried out experiments to collect data.And then,these data are used to test the performance of the receiver.The results show that this SDR can operate in real time with a large amount of data,and can obtain high-precision results at the same time.