# Analysis of BDS/GPS Signals' Characteristics and Navigation Accuracy for a Geostationary Satellite
###### Abstract  
The utilization of Global Navigation Satellite System (GNSS) is becoming an attractive navigation approach for geostationary orbit (GEO) satellites. A high-sensitivity receiver compatible with Global Position System (GPS) developed by the United States and BeilDou Navigation Satellite System (BDS) developed by China has been used in a GEO satellite named TJS-5 to demonstrate feasibility of real-time navigation. According to inflight data, the GNSS signal characteristics including availability, position dilution of precision (PDOP), carrier-to-noise ratio (C/N\({}_{0}\)), observations quantity and accuracy are analyzed. The mean number of GPS and GPS + BDS satellites tracked are 7.4 and 11.7 and the mean PDOP of GPS and GPS + BDS are 10.24 and 3.91, respectively. The use of BDS significantly increases the number of available navigation satellites and improves the PDOP. The number of observations with respect to C/N\({}_{0}\) is illustrated in detail. The standard deviation of the pseudorange noises are less than 4 m, and the corresponding carrier phase noises are mostly less than 8 mm. We present the navigation performance using only GPS observations and GPS + BDS observations combination at different weights through comparisons with the precision reference orbits. When GPS combined with BDS observations, the root mean square (RMS) of the single-epoch least square position accuracy can improve from 32.1 m to 16.5 m and the corresponding velocity accuracy can improve from 0.238 m/s to 0.165 m/s. The RMS of real-time orbit determination position accuracy is 5.55 m and the corresponding velocity accuracy is 0.697 mm/s when using GPS and BDS combinations. Especially, the position accuracy in x-axis direction reduced from 7.24 m to 4.09 m when combined GPS with BDS observations. GEO; GPS; BDS; orbit determination; navigation Article  
Analysis of BDS/GPS Signals' Characteristics and Navigation Accuracy for a Geostationary Satellite  
[PERSON], H.  
of the main-lobe and the side-lobe signals for three typical SSV missions is conducted based on antenna patterns from the actual mission design data [5; 6]. However, the use of GNSS signals for SSV users has special challenges. Several researches have carried out studies in signal link budgets and performance for SSV applications. In GEO missions, the altitude of GNSS receiver is higher than that of the navigation satellite constellation and the geometric distribution of the navigation satellite is poor. Most of the signals from the main lobe of the GNSS transmitting antenna are blocked by the earth [7; 8; 9]. It is necessary to receive the side lobe signals to increase the number of available navigation satellites and improve the geometric distribution [9]. Because the power of side-lobe signals are generally about 20 dB lower than that of the main-lobe ones, we need to improve sensitivity of the receiver to process these signals [10; 11; 12]. In spite of these difficulties, several feasibility studies for orbit determination with GNSS in GEO missions have been presented. A software simulation was made to assess the performance of autonomous orbit determination using GPS and Galileo signals. The accuracy of GEO orbit determination in this simulation was less than 100 m [13]. An iterative Kalman filter based on nonlinear dynamic model was used with GPS measurements for GEO spacecraft navigation. The tests of this filter were conducted with a GPS signal simulator and a dual-star single-frequency receiver [14]. Comprehensive simulation results and analysis show that using GPS and Galileo navigation for GEO orbits has operational benefits, even current space borne state-of-the-art receivers are considered [15]. A system-level performance and qualification test for GEO missions has been conducted using a space borne GPS receiver, named General Dynamics' Viceroy-4. It has demonstrated the ability to provide 100% position, velocity, and time data by acquiring and tracking a significant number of side lobe signals [11].