Session B5: Receiver Design, Signal Processing, and Antennas

Design of Dual-mode DPE Receiver Based on GPS L1/BDS B1C Signals
Qiongqiong Jia and Qiqi Guo, Tianjin Key Laboratory of Intelligent Signal and Image Processing, Civil Aviation University of China
Location: Beacon B

Introduction
With the gradual expansion of the application fields of the Global Navigation Satellite System (GNSS), its operational environment has become increasingly complex, characterized by multipath effects, non-line-of-sight (NLOS) propagation, and signal attenuation caused by urban structures such as tall buildings and trees[1-3]. Consequently, traditional GNSS receivers encounter significant challenges. To address the inadequate performance, or even failure to operate effectively, of conventional GNSS receivers in complex environments, more robust receiver architectures have been developed, including the Direct Position Estimation (DPE) receiver. The fundamental principle of the DPE is to obtain the navigation solution by directly integrating all visible satellite signals in the navigation domain, thereby facilitating deeper mutual assistance among the signals [4].
Literature[5-7] has demonstrated that the DPE receiver exhibits superior performance compared to traditional receivers in environments characterized by weak signals, multipath effects, and spoofing interference. However, its effectiveness in complex urban environment is still compromised by severe signal attenuation, multipath, NLOS propagation, and limited satellite availability[8-9]. To enhance the performance of DPE in complex urban environment. visual sensor [10] and three-dimensional (3D) building model [11] are employed to mitigate the multipath or NLOS induced biased. Nonetheless, these approaches depend on the support of external resources.
To address the challenges in complex urban environments, this paper designed a dual-mode DPE receiver, which utilize the GPS L1 and BDS B1C satellite signals. By combining the signals from the two constellations directly in the navigation domain, the dual-mode receiver enhances the number of visible satellites with good quality, resulting in improved performance.
Methodology
The dual-mode DPE receiver, based on GPS L1 and BDS B1C signals, designed in this paper directly combines and accumulates satellite signals from these two constellations in the navigation domain to derive the navigation solution. Since the dual-mode approach involves satellite signals from two constellations, resulting in a state vector composed of three-dimensional position coordinates, three-dimensional velocity, and the clock offsets and drifts from both constellations, encompassing 10 unknowns in the state vector. Therefore, calculating the joint accumulation in the navigation domain within this 10-dimensional state space entails substantial computational complexity.
The designed dual-mode DPE receiver leverages the implementation scheme of the existing DPE receiver [12] by utilizing prior information of the state vector to preset the possible grid space in the navigation domain. The joint accumulation at all grid points are calculated, then the grid point corresponding to the maximum joint accumulation result is selected as the user state observation.
To further reduce the computational burden in calculating the joint accumulation in the navigation domain, the high-dimensional state space is decomposed into two low-dimensional spaces: the position-clock offset domain and the velocity-clock drift domain [13]. The correlation function and Doppler spectrum of the visible satellite signals in the received data are calculated using the Fast Fourier Transform (FFT). Next, the code delay and Doppler frequency for each preset grid point are determined, and the corresponding correlation and spectrum values are extracted from the pre-calculated correlation function and Doppler spectrum in a "look-up table" manner. Then the extracted values for each grid are accumulated to obtain the joint accumulation of that grid. The joint accumulations for the position-clock offset domain space and the velocity-clock drift domain space are calculated respectively.
Additionally, the designed dual-mode DPE receiver incorporates a Kalman filter as the navigation filter, inputting the state vector observations obtained from the joint accumulation in the navigation domain to derive the final navigation solution.
Results
To evaluate the performance of the designed dual-mode DPE receiver in a real-world environment, GNSS measured data was utilized for testing. The experiment was conducted near the overpass of the Aegean Shopping Center in Hedong District, Tianjin. The data collection system remained stationary for the first 36 seconds in a relatively open environment, during which the number of visible satellite is 8 for GPS L1 and 6 for BDS B1C. After 36 seconds, the data collection system is moved in a straight line at a relatively uniform speed. During this movement, some satellite signals were obstructed by obstacles such as overpasses.
In the experiment, the following receivers were utilized to process the collected data: the single-mode DPE receiver based solely on the GPS L1 signal, the single-mode DPE receiver based exclusively on the BDS B1C signal, the dual-mode conventional receiver combining GPS L1 and BDS B1C, and the designed dual-mode DPE receiver. The experimental results indicate that the three-dimensional positioning errors of all four receivers fluctuated to varying degrees, with the designed dual-mode DPE receiver exhibiting the smallest positioning error and the best overall performance throughout the process. The root mean square error of the dual-mode DPE receiver was reduced by 32.2% and 50.2%, respectively, compared to the single-mode BDS B1C DPE receiver and the single-mode GPS L1 DPE receiver.
Reference
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