A real-time, high-accuracy, hardware-based integrated parameter estimator for deep space navigation and planetary radio science experiments

Abstract

Real-time, high-accuracy frequency-phase estimation is the critical mission of Doppler tracking, which is a primary technique for deep space spacecraft navigation and planetary radio science experiments. Usually, the analog intermediate frequency signal is digitalized and converted to baseband by signal processing hardware platforms called digital back-ends (DBEs) and parameter estimation is performed by extra high performance computers. In this paper, a novel real-time, high-accuracy parameter estimator called a hardware-based integrated parameter estimator (HIPE) is proposed and implemented inside DBEs. An adaptive frequency tracker is proposed to make the initial signal detection, frequency tracking, and data reduction. Then a parameter estimation is sequentially obtained by a modified dechirp technique and a high-resolution spectral analysis technique called spec-zooming. Further, a folding architecture is designed to save hardware resources when realizing spec-zooming in a field programmable gate array (FPGA). An example design is deployed on a DBE with Xilinx Virtex-6 FPGA and an ARM processor. The performance is verified by X-band observations of Mars Express (MEX) and New Horizons (NH). Under an integration time of 1 s, HIPE only takes 2.2 ms to process single-channel baseband data and provides frequency accuracies of 7 mHz and 30 mHz for the tested MEX and NH data. HIPE is implemented inside DBE, so the extra computer is no longer required and the pressure of data transmission or storage is greatly relieved. It could easily be extended to parallel multi-channel, real-time processing and would be a powerful method for Doppler measurement in deep space exploration missions, such as the Chinese mission to Mars to be undertaken by 2020.

Retrieving Doppler Frequency via Local Correlation Method of Segmented Modeling

“…Ref. [19] The study in [4] shows that the Doppler accuracy of MEX obtained by ESA and NASA was around 3.2 mHz in 1 s integration, and 1.2 mHz in 60 s integration [4]. These measurement results were obtained by the digital baseband receivers of ESA and NASA in closed-loop mode.…”

“…The study in [17] shows that 1.7 mHz precision (30 µm/s at a 10 s integration time) for radial three-way Doppler estimates for MEX was obtained by the PRIDE technique [17]. The study in [26] shows that the average 4.14 mHz precision of MEX in 5 s integration was obtained by CVN [28]; 7.0 mHz precision of MEX in 1 s integration was obtained by CVN [19]. The results are shown in Table 2.…”

“…The results are shown in Table 2. Since the raw signals in references [4,10,17,19,28] and in this paper were sampled and recorded by different ground station assemblies that do not have the same set of raw signals for processing, the comparison results are for reference. From the above results of the MEX Doppler accuracy and the results of Table 2, we can see that the accuracy of the open-loop Doppler by CDSS in this paper is approximately consistent with ESA and NASA, is a little better than EVN and VLBA, and is about two times better than CVN.…”

“…Furthermore, the Doppler measurement results of MEX obtained by the proposed method in this paper are compared with that of MEX obtained by ESA, NASA, Very Large Baseline Array (VLBA), European VLBI Network (EVN), and the Chinese VLBI network (CVN), respectively [4,10,17,19,28]. For quantitative comparison, the Doppler frequency results of MEX by the proposed method are obtained within 1 s, 5 s, 10 s, and 60 s integration respectively, as shown in Table 2.…”

“…Although PRIDE has been successfully and effectively utilized in several radio science experiments, the algorithm requires massive scale computing, due to PRIDE being designed to process the large wideband VLBI signal received by VLBI telescope. Currently, among the existing open-loop algorithms, some have the disadvantages of complicated algorithms and a huge amount of calculation [6,8], some require special hardware platforms for signal processing [19,20], and others utilize the PLL technique such as real-time PLL in closed-loop mode [10,12], in which the risk of loss-of-lock exists. The post-processing techniques of the open-loop Doppler may differ because different radio science or engineer teams develop their own software for signal processing and application.…”