BeiDou B2b and QZSS L6 Message Decoding Accuracy in a Low-power Low-cost Platform

With the advent of the recently available Quasi-Zenith Satellite System (QZSS) L6D and L6E correction signals, its use in the Asia-Pacific region has become a reality [1,2]. In the same way, the BeiDou III satellites are broadcasting the B2b signal, carrying orbit, clock, differential code biases (DCBs), and ionosphere refraction corrections valid also for the Asia-Pacific region [3]. In this paper, a new frontier is being explored by Allystar with the multi-band, low cost and ultra-low power HD9310 GNSS chip and the proprietary Cynosure III technology. This chip, consuming less than 170 mW of power under nominal conditions, is capable of tracking all GNSS constellations and the majority of signals broadcast by GNSS satellites within 40 simultaneous channels. Allystar’s mass-manufacturing capabilities, make this solution immediately available and suitable for the most efficiency-demanding applications. Even with the low power characteristics of this chip, both QZSS L6 and BeiDou B2b signals can be successfully tracked and decoded with sufficient latency to be applied in real-time positioning by the HD9310 chip. In this context, this paper explores the messaging decoding accuracy and latency of both L6 and B2b signals under different conditions using the Allystar HD9310 chip. Once signals are received by the receiver, the transmitting satellite azimuth, elevation and signal strengths are recorded and correlated with the parity-check success rate of the LD/E and B2b received messages over time. Considering the QZSS L6D signal, as an example, each frame of the stream contains 2000 bits that must be correctly registered by the receiver. The Reed-Solomon encoding, applied in error correction and parity checking, is traditionally used in low, medium, and geostationary orbit communication, as well as deep-space communications. Albeit an already traditional and proven encoding algorithm, its application in very low power platforms is still a challenge. The BeiDou B2b signal, on the other hand, has a frame size of 1000 symbols, and the parity check is based on a low-density parity check (LDPC) algorithm. Presenting the same challenges as the L6D messages, the B2b frames transmit orbits, clocks, DCBs, and ionosphere refraction corrections that can also be used by the HD9310 chip in real-time. In order to assess and showcase the capabilities of the HD9310 chip to decode and utilize such signals, several datasets are taken in consideration ranging from static open-sky data to challenging kinematic datasets. Since the message streams considered hereafter have more bandwidth that regular RTCM orbits and clocks, proper error code handling and parity checks are paramount, and must be especially crafted for computationally constrained modules with low power consumption. This paper shows the potential of the Allystar HD9310 chip to be applied in mass-market applications for a low-cost, without compromising accuracy, reliability and power. REFERENCES 1. Harima, K., Choy, S., Wakabayashi, Y., Kogure, S., Rizos, C., "Transmission of Augmentation Messages for Precise Point Positioning Utilizing Japanese QZSS LEX Signal," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 2467-2477. 2. Motooka, N., Hirokawa, R., Nakakuki, K., Fujita, S., Miya, M., Sato, Y., "CLASLIB: An Open-source Toolkit for Low-cost high-precision PPP-RTK Positioning," Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), Miami, Florida, September 2019, pp. 3695-3707. 3. Yang Y, Gao W, Guo S,Mao Y, Yang Y. Introduction to BeiDou?3navigation satellite system. NAVIGATION.2019; 1–12. https://doi.org/10.1002/navi.291