RTK with Smartphone and Need of Sensor Fusion · RTK with Retransmission •Configuration Parameters Parameter Value Positioning Mode Static Frequency and Constellation L1+L5 and

RTK with Smartphone and Need of Sensor Fusion

Universität der Bundeswehr München

Institute of Space Technology and Space Applications (ISTA)

Germany

M.Sc. Himanshu Sharma

M.Sc. Mohamed Bochkati

THIRD ANNUAL GNSS RAW MEASUREMENTS TASK FORCE WORKSHOP GSA Prague

26.06.2019

225-Jun-19

Conference/Workshop/Event 2GNSS RAW MEASUREMENT TASK

FORCE WORKSHOP- GSA26.06.2019

Multi Satellite Navigation Analysis Tool (MuSNAT)

• Integrated RTKLib for RTK Processing

325-Jun-19



GNSS Raw Data Processing with MuSNAT

425-Jun-19



Android Application Development

• GNSS/INS data logger• Android based GNSS/INS data

logger for Smartphones

• GNSS Raw data (based upon GNSSlogger from google)

• Embedded IMU (Acceelerometer, Gyroscope, Magnetometer) data logging

• GNSS raw Data to Rinex 3.03 Converter

• IMU data compatable with Interital Explorer

• Seperate GNSS and IMU data

• Synchronized GNSS/INS data

525-Jun-19



Analysis Breakdown

Front End

Antenna

Interference

Baseband

Processing

Acquisition

Tracking

Navigation Module

•Kalman Filter Tuning

•Cycle Slip Detection

•GNSS/INS Fusion

625-Jun-19



Antenna Analysis

• Antenna• Standard PIFA antenna with low multipath suppression

• Better estimation of Antenna phase center is must

• Proposed Ideas :

• Retransmission Scenario

• Antenna phase center bias cancellation by rotating smartphone on a platform

• Interference• Smartphone antenna positioning inside the case is not

optimized

• Expected interference due other Tx-Rx (Bluetooth, Wi-Fi)

• Proposed Ideas :

• Using the Standalone chip (Evaluation board)• Results from Trimble shows that Ambiguity fix with evaluation board (dual

freq.) is possible (approx. 6min)

725-Jun-19



Retransmission Setup

• Both L1 and L5 signals were amplified

• Helix antenna was kept near to smartphone so as to minimize the reception of signal directly from satellite.

Splitter

NetR9

Roof Top Antenna

MI8

LNA (30 dB)

Helix Antenna

825-Jun-19



C/No for MI8 with Retransmission

925-Jun-19



RTK with Retransmission

• Configuration Parameters

Parameter Value

Positioning Mode Static

Frequency and Constellation L1+L5 and GPS only

Integer Ambiguity Res. Cont.

Base Station coordinates (roof top antenna :61) 48 04 41.238610, 11 37 47.942650, 606.5840

Ionosphere Correction OFF

Troposphere Correction OFF

Satellite Ephemeris Broadcast

Filter Type Combined

1025-Jun-19



Double Difference - Retransmission

Epochs [sec]

1125-Jun-19



RTK with Retransmission-Ground Track

• RMS value E/N/U = 2.4/3.5/3.1 mm

• Standard deviation = 0.5/0.8/0.12 mm

Roof Top Antenna 61

1225-Jun-19



RTK with Retransmission-Position Accuracy

2.4 mm

3.5 mm

3.1 mm

1325-Jun-19



RTK with Retransmission-Ambiguity Ratio

• Ambiguity threshold set to 3 with 100% fix

• No. of satellites used 7

1425-Jun-19



RTK with Retransmission-Residuals

• Code and Carrier Residuals

Code Residual RMS = 1.802m

Carrier Residual RMS = 4 mm

1525-Jun-19



Standard RTK with ≈15 cm baseline

• Gaps between the data (no epoch missing but satellite is missing) ?

1625-Jun-19



Double Difference – Outdoor

Epochs [sec]

Cycle slips

1725-Jun-19



RTK with ≈15 cm baseline – Ground track

4x4 meter

1825-Jun-19



RTK with ≈15 cm baseline – Position Accuracy

1.015 m

0.423 m

1.895 m

1925-Jun-19



RTK with ≈15 cm baseline –Ambiguity Ratio

No of Satellites

Ambiguity Ratio

Ambiguity Ratio threshold

2025-Jun-19



RTK with ≈15 cm baseline –Residuals

outliers

Satellite not tracked

2125-Jun-19



Duty Cycle and Cycle slip

• Developer Option for Full GNSS measurement can be set to deactivate duty cycling (Android P)

• RTKLib does not have an optimum cycle slip detection mechnism. Many cases, cycles slips are not detected at all (outliers)

• RTKLib has no mechanism to correct cycle slips

• Cycle slip sets the Kalman filter to intializing stage and thus obstructing the convergence to cm level accuracy

• Praposed Mecahnism for Cycle slip Correction • Integrating the IMU data from the embedded sensors

2225-Jun-19



Xiaomi Mi8 Inertial Navigation

Bias Instability≈ 6 deg/h Bias Instability≈ 10 deg/h

ARW≈ 0.2 deg/sqrt(h)

ARW≈ 0.4 deg/sqrt(h)

• Gyro Allan Deviation

1€ Smartphone IMU Commercial 2000 € MEMS IMU

2325-Jun-19



Xiaomi Mi8 Inertial Navigation

• Accelerometer Allan Deviation

1€ Smartphone IMU Commercial 2000 € MEMS IMU

Bias Instabality≈ 20 µg

VRW≈ 85 µg/sqrt(Hz)

Bias Instabality≈ 40 µg

VRW≈ 91 µg/sqrt(Hz)

2425-Jun-19



Fusion: Trimble RTK + Mi8 IMU

GNSS-only (Trimble Net R9)

Gap due to signal blockage

Float Ambiguity

2525-Jun-19




Loose coupling-INS/GNSS (Trimble Net R9 + Xiaomi Mi8 built-in IMU)

IMU interpolation

IMU interpolation

2625-Jun-19




Contribution of Smartphone-IMU

Fîxed Ambiguity

Artificial GNSS gap, duration 20 sec

GNSS-only (Trimble Net R9) – One artificial gap was introduced

2725-Jun-19




GNSS gap interpolated with strapdown solution

Loose-coupling-INS/GNSS (Trimble Net R9 + Xiaomi Mi8 Built-In IMU)– One artificial gap was introduced

2825-Jun-19



Fusion: Mi8 RTK + Mi8 IMU

GNSS-only (Xiaomi Mi8)

2925-Jun-19



Fusion: Mi8 RTK + Mi8 IMU

Loose-coupling-INS/GNSS (Xiaomi Mi8)

3025-Jun-19



Points under consideration

• How efficient is the tracking without retransmission ?

• Missing satellites observation data• May be tracking (but C/No is quite high as compared to minimum

required (26 DB-Hz) for normal receivers)

• May be Duty cycling (but not all the satellites are vanishing during that epoch)

• Optimizing the solution to use best satellite combinations improves the accuracy (but float solution or wrong fix)

• Limited dual frequency satellites (GPS) in view

• Further investigation in the quality of GNSS raw data is needed

• Iono-free Linear combination

• Successfully fused GNSS/INS data• Further investigation about the quality improvement is still to be

evaluated

Thank You !

Universität der Bundeswehr München

Institute of Space Technology and Space Applications (ISTA)

Munich, GermanyHimanshu Sharma, Mohamed Bochkati, Prof. Thomas Pany

Documents

RTK with Smartphone and Need of Sensor Fusion · RTK with Retransmission •Configuration Parameters Parameter Value Positioning Mode Static Frequency and Constellation L1+L5 and