Page 6 - 卫星导航2021年第1-2合期

Research Summary
Volume 2, Issue 1-2, July 2021
Smartphone GNSS: Conditioning and PPP processing
The internal positioning solution offered by smartphones, generally, has an accuracy of several tens
to hundreds of meters in realistic environments due to the use of a low-cost antenna and single-
frequency GPS L1 code measurements. To improve the accuracy of the positioning solution, it is
now possible to use Precise Point Positioning (PPP) with multi-constellation, dual-frequency GNSS
measurements. On analysing the raw GNSS measurements from a Xiaomi MI 8 dual-frequency
smartphone in different realistic environments, it was observed that the measurements have low and
irregular carrier-to-noise density ratio, high multipath and data gaps due to frequent phase loss-of-
lock. This research addresses the above challenges by implementing a prediction technique for data
gaps and a carrier-to-noise-density ratio (C/N 0 )-based stochastic model for assigning realistic a priori
weights to the observables in the PPP processing engine. The use of these conditioning techniques
significantly improved the accuracy of the PPP solution and also provided 100% availability despite
the data gaps.
Related article: Conditioning and PPP processing of smartphone GNSS measurements in
realistic environments (doi: 10.1186/ s43020-021-00042-2)
Smartphone BDS positioning in the UK
The last satellite of the third generation BeiDou Navigation Satellite System (BDS-3) constellation
was successfully launched on June 23rd, 2020, and the entire system began to provide Positioning,
Navigation, and Timing (PNT) services worldwide. We evaluated the performance of location
services using BDS with a smartphone that can track the Global Navigation Satellite System (GNSS)
satellites in Nottingham, UK. The static and kinematic experiments were conducted in an open
meadow and a lakeside route covered by trees, respectively. Experimental results show that BDS has
good visibility, and its overall signal carrier-to-noise density ratio (C/N 0 ) is comparable to that of
Global Positioning System (GPS). The average C/N 0 of BDS-3 satellites with elevation angles above
45° in B1 band is up to 40.0 dB • Hz. The noise level of the BDS pseudorange measurements is within
0.5 m, and it has a good consistency among satellites. In the static experiment, the standard deviations
of BDS positioning in the east, north and up directions are 1.09, 1.16, and 3.02 m, respectively, and
the R95 value of the horizontal position is 2.88 m. In harsh environments, the number of BDS satellites
tracked by the smartphone is susceptible to environmental factors. The bias Root Mean Squares
(RMS) in the three directions of the whole kinematic positioning are 6.83, 6.68, 11.67 m, in which the
positioning bias RMS values in a semi-open environment are only 2.81, 1.11, 3.29 m. Furthermore,
the inclusion of BDS in multiple GNSS systems can significantly improve the positioning precision.
This study intends to provide a reference for the further improvements of BDS global PNT services,
particularly for Location-Based Services (LBS).
Related article: First results of BDS positioning for LBS applications in the UK (doi: 10.1186/
s43020-021-00035-1)