How to Improve GNSS Accuracy?
Brief Introduction of QZSS/MADOCA
Dinesh Manandhar, Associate Professor (Project)
Center for Spatial Information Science (CSIS), The University of Tokyo
dinesh@csis.u-tokyo.ac.jp

Slide : 1

What is GNSS?
L5/E5/B2/L3

L2

L6/E6/B3

L1/E1/B1• GNSS or Global Navigation Satellite System is an acronym used to represent
all navigation satellite systems such as

Satellite

Country

Coverage

GPSUSA

GlobalGLONASS

RussiaGlobalGalileoEurope

Global

BeiDou (BDS)

China

GlobalQZSS (Michibiki)

JapanRegional

NavICIndiaRegional✓ GPS and GLONASS have signals for civilian and military usage❖ Military signals are encrypted and not available for civilian use✓ Galileo and BeiDou also have Open and Restricted Signals✓ All civilian signals are freely available✓ Technical information for civilian signals are made public❖ Its called ICD (Interface Control Document) or IS (InterfaceSpecification)❖ Provides necessary information to develop a GNSS receiverhttps://gssc.esa.int/navipedia/images/c/cf/GNSS_All_Signals.png

Slide : 2

How to Improve GPS Accuracy?

Slide : 3

GPS Position Accuracy
How to achieve accuracy from few meters to few centimeters?
metercentimeter

50 cm grid

50 cm grid

5 cm grid

SPP (Single Point Position)

DGPS (Differential GPS)
Code-phase observation

RTK (Real Time Kinematic)
Carrier-phase observation
Slide : 4Error sources
Satellite Orbit Error
V = 4km/s

Satellite Clock Error

Ionospheric Delay
50 – 200Km

Tropospheric Delay
10Km
Multipath

Thermal Noise

Receiver Clock Error
Slide : 5

Errors in GPS Observation (L1C/A Signal)
Error Sources

One-Sigma Error , mSatellite Orbit
Satellite ClockTotal
2.02.0DGPS
0.00.0

Ionosphere Error
Troposphere Error
Multipath

4.00.71.4

0.40.2
1.4

Receiver Circuits

0.50.5

Comments
Common errors are removed

Common errors are reduced

If we can remove common errors, position accuracy can be increased.
Common errors are: Satellite Orbit Errors, Satellite Clock Errors and Atmospheric Errors (within few km)
Values in the Table are just for illustrative purpose, not the exact measured values.
Table Source : http://www.edu-observatory.org/gps/gps_accuracy.html#Multipath
Slide : 6

How to Remove or Minimize Common Errors?
Use Differential Correction (DGPS / RTK)
30

Recommended Base-length < 40Km
Send Observation Data to Roverfor Real-Time Position
Base-Station

RoverFor RTK, both base and rover receivers need toAntenna is installed at aUser in the Field
use data from the same satellites
known-position(Either fixed or moving)Base-station Antenna position
Use RINEX data for post-processing
shall be known in advance
Slide : 7

How to Remove or Minimize Common Errors?
Use QZSS Service MADOCA or CLAS
QZSS

GPSCorrection Data:
MADOCA:
Satellite Orbit Error of GPS and Other Satellites
Satellite Clock Error of GPS and Other Satellites
CLAS:
All of MDOCA plus the following:
Ionospheric Correction Data

Currently, MADOCA provides correction data for GPS, GLONASS andQZSS.
It will be extended for Galileo in future.
➢ Base-Station is not required.
➢ The receiver should be able to receive MADOCA / CLAS signal in L6band.
➢ MADOCA provides 10 – 20cm accuracy (Global)➢ MADOCA correction data is also available online➢ CLAS provides 2 – 5 cm accuracy (Japan Only)

RoverSlide : 8

Low-Cost High-Accuracy Receiver Systems
RTKDROID, MADROID, MAD-WIN, MAD-π

Slide : 9

How to Make a Low-Cost GNSS Receiver System?
MemoryExternal
Memory Device

Hard DiskRaspberryPi

Arduino

GNSS Moduleor Receiver
Micro-Controller
orMicro-Processor

Single Board
ComputerSony, Spresense

Low-Cost SDR Device$30••

External
Interface

WiFi, BT,Ethernet, MQTT,IoT links
ESP32 is a powerful Microcontroller with WiFi/BT

A smart-phone haseverything that weneed• CPU• Memory• ExternalInterface• GNSS Receiver• Sensors

Note: We use these modules for high accuracy positioning system based on RTK and MADOCA PPP or other GNSS/QZSS special applications.
There are many other GNSS modules as well. We have no intention of any purpose to name some of the makers here.

Slide : 10

QZSS MADOCA Solution: MADOCA PPP Receiver System

Use this baud-rate to receiver
GNSS Raw Data

Use this baud-rate to receiver
MADOCA Data

65Antenna
GNSS Receiver
L1/L2/E5B

50

MADOCA Decoder
QZSS L6

COM Port: 1
GNSS DataCOM Port: 2
MADOCA Data

GNSS Antenna

Slide : 11

Low-Cost High-Accuracy GNSS Receiver System
GNSS MADOCA Receiver with Windows PC (MAD-WIN)

Antenna Cable

MADOCACompatible
GNSS Receiver

Micro-USB toUSB Cable➢ Connect Antenna to the GNSS/MADOCA receiver using theprovided antenna cable.
➢ Connect the receiver to an Android device using a “microUSB to USB” cable and an OTG cable.
➢ OTG (On-The-Go) cable may be either Type-C or Micro-USB
Type depending upon android device’s connection port.

6550

GNSS Antenna

UT RECEIVER

Micro-USB toUSB Cable

Slide : 12

Low-Cost High-Accuracy GNSS Receiver System
GNSS MADOCA Receiver with RaspberryPi Device (MAD-PI)

Antenna Cable

MADOCACompatible
GNSS Receiver

RasPi4 withTouch Screen

Micro-USB toUSB Cable➢ Connect Antenna to the GNSS/MADOCA receiver using theprovided antenna cable.
➢ Connect the receiver to a RaspberryPi 4 device using a“micro-USB to USB” cable.
➢ Connect a USB Memory Drive to RasPi device.
➢ Either use a Power Bank or an AC Adapter for power supply.

65

OR50

GNSS Antenna

UT RECEIVER

Micro-USB toUSB Cable

Micro-USB toUSB Cable

PowerAdapter forRaspI4

USB Memory

Slide : 13

Low-Cost High-Accuracy GNSS Receiver System
GNSS MADOCA Receiver with Android Device (MADROID)

Antenna Cable

MADOCACompatible
GNSS Receiver

Micro-USB toUSB Cable➢ Connect Antenna to the GNSS/MADOCA receiver using theprovided antenna cable.
➢ Connect the receiver to an Android device using a “microUSB to USB” cable and an OTG cable.
➢ OTG (On-The-Go) cable may be either Type-C or Micro-USB
Type depending upon android device’s connection port.

OTG Cable
Select OTG Cable based onAndroid Device Connector Type

6550

GNSS Antenna

UT RECEIVER

Micro-USB toUSB CableOTG Cable
Type: COTG Cable
Type: Micro USB

Slide : 14

MADOCA System: Direct from QZSS or Online Correction Data
If you have
GNSS Receiver Only

If you have
GNSS + MADOCA ReceiverQZSS

QZSSQZSS Signal

QZSS Signal

Antenna

Antenna

GNSS +MADOCAReceiver

MADOCA PPP
Processor

GNSSReceiver

Position
OutputOnline MADOCACorrection Data

MADOCA PPPProcessor

Position
OutputIt requires internet access
Slide : 15

QZSS MADOCA Solution: Using GNSS/MADOCA Receiver
GNSS + MADOCA ReceiverQZSS

QZSS Signal➢ GNSS Receiver:➢ Multi-Frequency GNSS Receiver➢ MADOCA Correction Data:➢ QZSS L6E Signal Decoder➢ U-Blox Module:➢ GNSS: F9P Module➢ QZSS L6 Signal Decoder: D9C➢ Septentrio➢ MOSAIC Module➢ GNSS + L6 Signal combinedAntenna

GNSS +MADOCAReceiver

MADOCA PPP
Processor

Position
OutputSlide : 16

QZSS MADOCA Solution: Using GNSS only ReceiverQZSS

QZSS Signal➢ GNSS Receiver:➢ Multi-Frequency GNSS Receiver➢ MADOCA Correction Data:➢ Online Correction Service➢ U-Blox Module:➢ GNSS: F9P Module➢ Septentrio➢ MOSAIC Module➢ GNSS + L6 Signal combined

If you have
GNSS Receiver OnlyAntenna

GNSSReceiver

Online MADOCA
Correction Data

MADOCA PPP
Processor

Position
OutputIt requires internet access
Slide : 17

Screen Shots of RTKDROID and MADROIDConnect GNSS receiver toAndroid device(1) RTKDROID :For RTK or PPK(2) MADROID:for MADOCA-PPP,
MADOCA-PPP/AR (future)

Slide : 18

MAD-WIN / MAD-PI / MADROID
MAD-WIN

MAD-PI

MADROID

MAD-WIN and MAD-PI GUIs are the same
Slide : 19

MAD-WIN / MAD-PI User Interface

Receiver Output FilesSolution

MADOCA PPP Solution

NMEA Format

Rover

Rover RAW Data in receiver’s proprietary format
Can be used for PPK (Post-Processing Kinematic) Solution or Post-Processing PPPUBX, SBF, BINEX or RTCM3Correction

MADOCA PPP Correction Data in receiver’s proprietary format
Can be used for Post-Processing MADOCAUBX or SBFSlide : 20

MADOCA PPP Position Accuracy

Reset every 3 hour interval to analyze convergence time

Slide : 21

Low-Cost MADOCA Receiver for Sea-Level Rise Measurement

Source: Technical Report, GNSS/QZSS MADOCA PPP Data Acquisition for Sea Level Rise Measurement, DR. ROSALIE B. REYES, UP DGE and Project Leader, CLSR-Phil Project

Slide : 22

MADOCA DEMO

Slide : 23