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Precise Positioning with Dual Frequency 

Smartphones

René Warnant, Mathilde Debelle University of Liege‐Geodesy and GNSS

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Smartphones and GNSS

GNSS = Global Navigation Satellite Systems 

GPS (USA), GLONASS (Russia), Galileo (Europe), Beidou (China)

For many years, smartphones are equipped with a GNSS (at least GPS) chip

GNSS market is dominated by smartphones (more than 80% of total market)

Major progress ongoing in smartphone‐based positioning  2

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Positioning with GNSS: Raw measurements

In GNSS, the base observable is the satellite‐to‐receiver range.

The simultaneous measurement of ranges to (at least) 4 different  satellites allows to compute the user position.

Two possible ways to measure the satellite‐to‐receiver range:

Ranging code.

Phase difference.

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Ranging Code

Simplest observable available on ALL GNSS devices.

Provides users with 5‐10 m positioning accuracy (GPS).

Used by smartphones to compute positions. 

Phase difference

Most precise observable.

Provides cm‐level positioning accuracy.

Until recently, was only available on high end devices (geodetic receivers).

Code and Phase measurements can be performed on several frequencies

Further improves accuracy and reliability.

Until recently, was only available on high end device. 4

Positioning with GNSS: Raw measurements

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Positioning under IOS or Android up to v6

The smartphone only provides the user with computed position and some  ancillary information about satellites (azimuth, elevation, health, …).

Users do not have access to raw GNSS measurements. 

The positioning accuracy depends on the environment (rural, urban, …): 5‐10 m

in optimal conditions using GPS only.

The position is computed based on a “manufacturer receipt” which is not  documented (Black Box !)

Depending on the model, the position can be obtained from sensor fusion, for example from  GNSS, WIFI, inertial sensors, …

No information about integrity (does the computed position fit my requirements ?)

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Positioning under Android 7 or later

During it “I/O 2016” (June 2016), Google announced that the raw GNSS 

measurements collected by devices running Android 7 would be made available  to users on compatible smartphones. 

This announcement opens new opportunities !

Indeed, the development of advanced processing strategies might lead to  decimeter‐level positioning capabilities allowing the emergence of new 

applications. 

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Android v>=7 : which raw data ?

Raw GNSS data are not necessarily available on all Android v>=7  smartphones

Most “sophisticated” compatible devices : 

Xiaomi Mi 8 (June 2018).

Huawei Mate 20 (November 2018).

Xiaomi Mi 9 (March 2019). 

Available observables:

Code(expected).

Phase(unexpected).

Two frequencies for GPS and Galileo (VERY unexpected)

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In addition, these smartphones are multi‐constellation

GPS (USA)

GLONASS (Russia)

Beidou (China)

Galileo (Europe)

QZSS (Japanese regional navigation system) 8

Android v>=7 : which raw data ?

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Short Baseline experiment

Experiment on the roof of our building (open sky)

Carrier phase‐based static relative positioning  using GPS and Galileo (L1/E1+L5/E5a)

Short Baseline between 2 Xiaomi Mi 8.

dNorth=0,000 m

dEast=‐0,075 m

dUp=0,000m

2 Sessions of 1 hour on DOY 246 (03 Sept. 2018). North

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Positioning results – Session 1

10

Session 1: DOY246, 10h00‐11h00.

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RTK results – Session 2

Session 2: DOY246, 12h00‐13h00.

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Applications

Everyday life applications :

Any application which requires cheap and quick precise positioning 

Location‐based services

Virtual (augmented) reality

Autonomous car

Earth Sciences/Earth Observation

Precise positioning

Atmosphere Monitoring (Ionosphere and Water vapour)

? Reflectometry ? (soil moisture, …)

Millions of smartphones might send atmospheric information through the internet to a  central computing facility allowing to feed models (collaborative networks) 12

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Conclusions and outlook

The availability of dual frequency multi‐constellation GNSS code and phase data  on smartphones running android v=>7 allows real‐time positioning at sub‐ decimetre level in “ideal” conditions.

Further experiments have to be conducted in more difficult environments.

Main weakness: smartphone antenna

Low‐quality linearly polarized antenna optimized for voice communication but not for  navigation signals which are circularly polarized (right‐handed).

Very susceptible to multipath (in particular in urban environment).

No information about antenna phase centre (mandatory for precise positioning).

Patch antennas for smartphones are being developed.

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