Workshop on GNSS for Policy and Decision Makers
21st January 2022

Receiver Selection Guidelines

Dinesh Manandhar, Associate Professor (Project)
Center for Spatial Information Science (CSIS), The University of Tokyo
dinesh@csis.u-tokyo.ac.jp
We have no intention to prefer any brand names mentioned in these slides. They are used only for reference.
There are many other products in this category from different manufacturers, please search in internet

2022/02/02 8:24 PM

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 1

Target Usage of the Receiver• What is the purpose of the receiver?

• What is the purpose of the receiver?

• Use as a CORS (Continuous Operating Reference
Station)• Setup as a local Base-Station for RTK services• Field Survey• Geodetic Survey, Control Point Survey, Mapping• Agriculture• Timing Services• Space Weather• Scientific Applications• GIS, Facilities Management• Drone / UAV• Transport Monitoring• Tracking of vehicles, public transport for safety andsecurity• Tracking of bicycles (Share-riding)• Trains• Marine

We will focus our discussions on High-End GNSS Receivers
Because it costs tens of thousands of dollars and should
last for more than 10 years of continuous operation• Vessels•

100tons or more than 300 tons require AIS for VMS• Passenger Boats• Smaller Fishing Boats, Pleasure boats
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 2

High-End Survey Grade GNSS Receivers

We have no intention to prefer any brand names mentioned in these slides. They are used only for reference.
There are many other products in this category from different manufacturers, please search in internet
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 3

Antenna for CORS or High-Accuracy Measurement

 Antenna with Choke Ring and Dome is used for CORS
 Choke ring helps to minimize multipath effects
 Dome protects from snow cover and other dusts as well as birds, animals or insects
 A normal base-station may use antenna without choke-ring and dome

We have no intention to prefer any brand names mentioned in these slides. They are used only for reference.
There are many other products in this category from different manufacturers, please search in internet
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 4

Different Types of GNSS Antenna

Patch Antenna

Helical Antenna

Chip Antenna

Antenna for Aviation

Paper Like Adhesive Antenna

We have no intention to prefer any brand names mentioned in these slides. They are used only for reference.
There are many other products in this category from different manufacturers, please search in internet
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 5

Antenna for CORS or High-Accuracy Measurement
Select antenna with calibration data

10cm

Antenna Gain Pattern

Antenna Phase Center

Also Refer:
https://www.ngs.noaa.gov/ANTCAL/FAQ.xhtml
https://igs.org/

Antenna Phase Variation

 Select an antenna for CORS with technical documents such as Antenna Gain Pattern, Antenna Phase Center
Offset (PCO) and Antenna Phase Center Variation (PCV) Data.
 PCO and PCV data for CORS antenna are also available at IGS website.

We have no intention to prefer any brand names mentioned in these slides. They are used only for reference.
There are many other products in this category from different manufacturers, please search in internet
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 6

Specification Parameters to be CheckedNoSpecification Category

Details

Comments

1

GNSS Systems

GPS, GLONASS, GALILEO, BEIDOU, QZSS, NAVIC,
SBAS

Select the satellite systems that you would like to use. Normally GPS and GLONASS are
already implemented. Other systems may be available with additional cost. QZSS andNavIC are regional systems and hence may not be visible in your region.

2

GNSS Signal Capabilities

GPS: L1C/A, L1C, L2, L5
GLONASS: L1, L2, L3
QZSS: L1C/A, L1C, L2, L5, L6
Galileo: E1, E5a, E5b, E5AltBOC
Beidou: B1, B2, B3NavIC: L5, S

Depending upon GNSS Systems, select the required signals.
Many makers charge separately for each additional signal. RTK and PPP requires dualfrequency signals such as L1C/A, L1P(Y), L2P(Y). It is recommended to include L1, L2 andL5 navigation signals.
QZSS L6 provides CLAS and MADOCA correction signals for high-accuracy. CLAS can beused only in Japan. Since QZSS is regional system, it may not be visible in your area.

3

Signal Processing
Capability for HighAccuracy

RTK, PPP
L-Band Correction, CLAS, MADOCA

All receivers designed for CORS provide RTK, PPP and many other signal processing
technologies required for high-accuracy positioning.
L-Band correction, CLAS and MADOCA are satellite and service provider specific.

4

Performance and Accuracy

SPS, DGPS, RTK, PPP Accuracy

Check the accuracy values the receiver can provide for each type of signal processing
method. Also notice the conditions and affecting factors if given in the document withfootnotes.
Accuracy for RTK or differential observation are mentioned as XX cm + YY ppm.
XX cm error is fixed error and YY error varies depending upon base-length (distance
between base-station and field receiver (rover unit)). If YY = 1ppm, then every 10Km ofbase-length will have 1cm of error. If XX is 2cm, the total error is 2 + 1 = 3 cm for abase-length of 10Km.

5

Physical DataSize, Weight, Shock, Vibration

If the receiver has to be used in machines such as tractors, excavators, heavy machines,
construction machines etc. make sure that the receiver performance well under severe
shock and vibration conditions.

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 7

Specification Parameters to be CheckedNoSpecification Category

Details

Comments

6

Electrical Data

Power consumption, Internal Battery, ExternalPower Supply System

CORS are sometime installed in remote locations where continuous electrical power
may not be available or where power outages are very common. In such locations, itsbetter to have a receiver with internal battery. An external power source from Solarpanel or battery system is required. Make sure that the receiver also has input port forbattery power supply (12volt DC or similar).

7

Environment

Operating Temperature, Humidity, Dust, IP Rating,Operating temperature is very important since CORS receivers are installed in various
locations, sometimes outdoors (with simple enclosure) where temperature can’t becontrolled. Depending upon location, day and night temperature may vary more than
20 degrees. Temperature variation may be as large as 50 degrees Celsius between
summer and winter in some locations. Thus, the receiver must perform well even in thislarge variation of temperature. Though, outside air temperature varies a lot, thereceiver temperature may not vary at the same level due to electrical circuits in thereceiver.
At least a receiver that performs from -20 to +60 deg. Celcius is required and should
provide the performance accuracies mentioned in the technical specifications.
However, internal battery performance degrades when the temperature goes down to-10C or lower.
If your region has severe variation in temperature in winter and summer, -40 to >+60
deg. C is recommended.
An IP rating of 67 is recommended to protect from dust and water.

8

Connectivity

Serial, USB, Ethernet, WiFi, BT, NTRIP, Radio Link

Different types of interface (I/O ports) are available. An USB port will be quite easy tosetup the receiver. An Ethernet port is required to connect the receiver to internet for
remote access and logging etc. WiFi and BT (BlueTooth) are optional.
NTRIP Caster and Server is strongly recommended for CORS receiver for remote data
access via NTRIP.

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 8

Specification Parameters to be CheckedNoSpecification Category

Details

Comments

9

Data Storage

Internal Memory, External Storage Memory

An internal memory is strongly recommended. Select memory size that canaccommodate for one month of raw observation data.
Better to have also a connection port to an external memory device (USB Drive or Hard
Disk).

10

Data Output Format

NMEA, RTCM., RINEX, BINEX, NAV Data,
Proprietary

Normally high-end receivers provide all these output data formats.
Need to confirm version for each data output format.

11

Clock Output

1PPS, 10MHz Clock Input / Output

1PPS output is required to feed timing signal to other devices for clock synchronization.
Some, receivers also provide 10Mhz clock I/O.

12

Other Special Features

Multipath Rejection, Interference protection, AntiJamming, Spectrum, Ionosphere Mitigation, RAIM,
A-RAIM

Some makers provide various types of proprietary technologies for multipath
mitigation, interference mitigation, anti-jamming, IF data spectrum viewing, RAIM, ARAIM etc.

13

Maintenance

Remote Logging, FW Upgrade,

Make sure that remote maintenance such as FW Update etc. can be done. This saves
lots of time, efforts and money when receivers are installed in remote areas.
But, all the receivers may not have this feature. Or it may require additional external
systems.

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 9

Receiver and Antenna Test Setup If possible, setup a test area with four pillars as shown below.
 Measure the pillar reference points by Total-Station with mm-level accuracy
 Log GNSS data by setting antenna on top of the pillar
 Compute position of the pillar reference points using GNSS observation data Compute position difference between GNSS and True value for each point
 Also, compute all distance d1, d2, d3, d4, d5 and d6 as well as height of pillar h1, h2, h3 and h4
 By using these pillar control points, various types of receivers and antenna performance can be analysed Make sure that the pillars are set in an open area
1

d1

2

d1

d4

d2

d3

d2

d4

4
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jpd3

3
Slide : 10

Exercise Download Technical Specification Documents from GNSS Makers for High-End Survey Grade Receivers
 Such as Trimble, Septentrio, Novatel, Topcon etc.
 Download Technical Specification Document from GNSS Makers for Low-Cost Receivers
 Such as u-blox, Septentrio MOSAIC etc.
 Compare the technical specifications using Excel file [TechSpec_SampleSheet_R1.xls]

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 11

Reference Slides

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 12

GNSS Errors

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 13

Background Information: Accuracy vs. Precision• Accuracy• Capable of providing a correct measurement• Measurement is compared with true value• Affected by systematic error• Precision• Capable of providing repeatable and reliable measurement• Statistical analysis of measurement provides the precision• Measure of random error• Systematic error has no effect

Neither Precise nor Accurate Precise but Not Accurate

Accurate but Not Precise

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Precise and Accurate
14 Slide : 14

GNSS Measurement Errors
MeasureAbbreviation

Definition

Root Mean SquareRMS

The square root of the average of the squared errors

Twice Distance RMS

2D RMS

Twice the RMS of the horizontal errors

Circular Error Probable

CEP

A circle's radius, centered at the true antenna position,
containing 50% of the points in the horizontal scatter plot

Horizontal 95%
Accuracy

R95

A circle's radius, centered at the true antenna position,
containing 95% of the points in the horizontal scatter plot

SEP

A sphere’s radius centered at the true antenna position,
containing 50% of the points in the three dimensional scatter
plot

Spherical Error Probable

Source: GPS Accuracy: Lies, Damn Lies, and Statistics, GPS World, JAN 1998
https://www.gpsworld.com/gps-accuracy-lies-damn-lies-and-statistics/
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 15

Commonly Used GNSS Performance Measurements• TTFF• True Time to First Fix• Parameter: Cold Start, Warm Start, Hot Start• Standard Accuracy• Accuracy attainable without any correction techniques• DGPS Accuracy• Accuracy attainable by differential correction data
• Code-phase correction• RTK Accuracy• Accuracy attainable by differential correction data
• Use both Code-Phase and Carrier Phase correction
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 16

TTFF and Typical Example Values• TTFF• Cold Start : < 36 seconds• Time required to output first position data since the receiver power is on• No reference data like time or almanac are available• Warm Start : < 6 seconds• Time required to output first position data since the receiver power is on with the latest
satellite almanac data in the receiver’s memory• Time and almanac related reference data are already known• Hot Start : < 1 second• Receiver has already output position data
• Time to reacquire an already tracked satellite due to temporary blockage by buildings ortrees

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 17

Performance Measurement of RTK Accuracy• A fix error and a variable error with respect to base-length is given• Such as : x cm + y ppm• Example: 2cm + 1ppm

• There is a fix error of 2cm plus 1ppm error due to base-length between the Base and Rover• 1ppm  1 parts per million•  1cm of error in 1 million centimeter distance between the Base and the Rover•  1cm of error in 1000000 centimeter distance between the Base and the Rover•  1cm of error in 10000 meter distance between the Base and the Rover•  1cm of error in 10 kilometer distance between the Base and the Rover•  1cm of error for every 10Km of distance between the Base and the Rover•  4cm of error for 40Km of distance between the Base and the Rover• Thus the total error is : 2cm + 4cm due to 40Km of base length• The longer the base-length, the larger the error• Do not assume that this error is linear• And it may not be valid for longer base-lines• Normally the recommended base-length for RTK for a Geodetic Receiver is 40Km
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@csis.u-tokyo.ac.jp

Slide : 18