On November 19, 2019, Professor Geng Jianghui and Dr. Li Guangcai published a paper "On the feasibility of resolving Android GNSS carrier-phase ambiguities" in Journal of geodesy, answering the question whether Android devices can provide GNSS ambiguity-fixed solution.
Their research shows that integer ambiguity fixing for centimeter-level GNSS positioning is prevented by the unaligned chipset initial phase biases (IPBs) found within Android carrier-phase data from some smart devices including Nexus 9, Samsung Galaxy S8 and Huawei Honor 8. They investigated the characteristics of those chipset IPBs and tried to resolve ambiguities by presumably correct for them in a post-processing manner with the goal of inspecting the potential of Android GNSS ambiguity resolution if hopefully the IPBs can be gone. By calibrating IPBs, they implemented ambiguity resolution on the Nexus 9 tablet connected with an external survey-grade antenna. For a ~ 480 m static short-baseline, the time-to-first-fix is about 20 min with about 86.0% of all epochs resolved successfully; moreover, the RMS of the positioning differences from benchmark solutions after ambiguity fixing are 0.8, 0.7 and 1.8 cm for the east, north and up components, respectively. For a vehicle-borne Nexus 9 tablet with respect to a survey-grade receiver located 100–2000 m away, they achieve the first ambiguity-fixed solution within 321 s and finally 51.6% of all epochs are resolved; the ambiguity-fixed epochs can achieve a positioning accuracy of 1.4, 2.2 and 3.6 cm for the east, north and up components, respectively.
Finally, they discussed that the chipset phase biases beyond IPBs for dual-frequency GNSS smartphone, and further discussed the portable patch antennas for smart devices. They found that a Xiaomi 8 smartphone can be coupled effectively with a miniaturized portable patch antenna, and then achieve commensurate carrier-phase tracking and ambiguity-fixing performance to those of a commercial μ-blox receiver with its dedicated patch antenna. Specifically, when Xiaomi 8 smartphone connected to an ANN-MS patch antenna in this study, its time-to-first-fix is 670 s with about 90.2% of all epochs resolved successfully; the RMS of the positioning errors after ambiguity fixing are 1.10 cm, 1.11 cm and 3.36 cm for the east, north and up components, respectively. This is encouraging since a compact and inexpensive patch antenna paired with smart devices can promote the democratization of high-precision GNSS.
For more details, please refer to the paper "On the feasibility of resolving Android GNSS carrier phase ambiguities". Link: https://doi.org/10.1007/s00190-019-01323-0
Fig.1 Ten minutes of fractional parts of the double-difference carrier-phase bias estimates color coded for 18 satellites referring to G28, G32 or G14 over seven zero baselines. An external survey-grade antenna TRM57971.00 was used for all smart devices. The four vertical lines indicate when the duty cycle is on. Note that the three panels from left to right correspond to three reference satellites (G28, G32 and G14), because the three zero-baseline experiments were carried out on different days. The Android data logger software used in these three zero-baseline experiments were Geo++ RINEX Logger (Ver. 1.2.1), Geo++ RINEX Logger (Ver. 1.2.4) and GnssLogger (Ver. 2.0.1), as shown in Table 1.
Fig.2 Short-baseline positioning accuracy (cm) for the east, north and up components over a period of two hours for a Xiaomi 8 smartphone and a m-blox receiver (C94-M8P-1) connected to different antennas with respect to station WUHN on November 21, 2018. ANN-MS is a patch antenna manufactured by m-blox. The RMS statistics are calculated using the positions spanning from 8:15 to 10:00 UTC. The vertical dashed lines indicate the time to first fix, and the horizontal red lines mark the threshold of 3.0 for the ratio test. Note that the ratio values of larger than 20 are plotted as 20. The bottom panels show the number of visible satellites (sky blue) and the PDOP values (orange).
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