International Conference on Space,
2014
REAL TIME KINEMATICS
…. OR NOT!
Dr. Faisal A. Khan
Did you precisely know …..
where were we going!?
What’s on the plate today?

Global Navigation Satellite Systems

Precision Requirements



Techniques
Comparative Analysis
Analyzing Situation for Pakistan

Concluding Remarks
Global Navigation Satellite Systems

Global Positioning System (GPS) has been around for long


Offered positioning accuracies


Global Navigation Satellite System (GNSS) era is evolving
As the applications evolve……
Meter to sub-meter level
Classical applications:
Meter-level
accuracies are
 Positioning and timing
not just good enough!
High Precision Requirements

Precision requirements are increasing exponentially with newer
application domains
Mining
Surveying
&
Construction
Aviation
High
Precision
Mapping
Cadastre
Prevision
Agriculture
So what’s possible?
Positioning Techniques
Meter-level Accuracies
Standard
• Low cost
• No strings attached
Possibilities
Centimeter-level Accuracies
• Moderate to high cost
• With a lot of asterisks RTK
***
PPP
Standard Positioning
Highlights
Application
Domains
• Meter-level accuracies
• Most used technique
• Personal
• Professional
• Not good enough for precision applications
Shortcomings
• where the actual potential of GNSS resides
Standard Positioning
Sat 1
Sat 2
Sat 3
Measurement
Carrier Phase or Pseudorange
User
Sat 4
Errors are there…..!

Pseudorange
Paj = raj - cdT j + cdTa + t iono + t tropo + e


Carrier phase measurement
Error Sources
Bounds
Plus…..
A lot more Error
errors
j
j
j
j c
j aIonospheric
=
r
c
d
T
+
c
d
T
t
+
t
N
+e
SolidaEarth Tide
displacements,
Ocean
Loading…….
a
iono
tropo ±4m
a
Effects
f
Error Sources
Tropospheric Effects
±0.7m
ErrorsEphemeris
 Degrading
Positioning Accuracy
& Precision
Errors
±2.1m
dT j
SatelliteClock
ClockError
Errors
Satellite
dTa
±2.1mClock Error
Receiver
Must be removed to achieve Highly Precise Positioning
t iono
t tropo
Ionospheric Error
Tropospheric Error
Aiming high….. Improving Precision
Real-Time Kinematics (RTK)
Differential
Corrections
Base Station
Real-Time Kinematics (RTK)


Applies Differential Positioning Technique
Common Errors Removed
Satellite Clock
Errors

Ionospheric Errors
Tropospheric
Errors
Strings attached
Local Base
Station
RTK/CORS
Network
Communications
Link
Cost Implications
Precise Point Positioning

Sat 1
Sat 3
cm-level accuracies….


Sat 2
Close to RTK… just below the make
Errors removed
Satellite Clock
Errors

Sat 4
Satellite Ephemeris
Errors
Strings attached
Erroneous Position
Communications
Link
User
Error
Estimates
Precise Position
Let’s Compare….
PPP is good….
Aspects
RTK
PPP
Reference Station requirement
• Local infrastructure reqd
• Cost
• maintenance
None
Corrections’ cost
• To corrections provider
None
Mode of operation
• Real-time
• Post-processed
• Real-time
• Post-processed
Communication link
requirement
• Internet connectivity
• Internet connectivity
Reference frames
Isolated (in Pakistan)
Globally uniform
PPP is good…. Not just good enough!
Aspects
RTK
PPP
Single vs. Multi frequency
requirement
Sub-decimeter level with
single frequency
Sub-decimeter level requires
multi frequency
Convergence time
Instant
• In 10s of minutes
• Support from RTK can help
Multi-GNSS support
All supported
Only GPS
Ready-to-use Receiver
availability
High
Negligibly low
Situation for Pakistan

Precision positioning applications requirement is steadily
increasing in Pakistan

This calls for availability of a correction service
Possible Solutions
Situation
Remarks
Single base-station
Typical approach
Non-uniform
High installation time
High cost
Network RTK/CORS
Pak-Rehber
Karachi Coverage
Nationwide availability reqd
PPP
Country-wide availabile
Performance not as good as RTK
Hardware availability issues
Correction Service Requirement
Nationwide
availability
At reasonable
cost to user
Support both
PPP and RTK
Centrally
managed
Uniform
reference
frame
Internet
availability
Support both
real-time and
post-processed
Shorten
convergence
times
Multi-GNSS
support
Concluding Remarks

PPP is good….. Not just good enough





PPP shortcomings need further research
Will improve further as multi-GNSS support becomes available
PPP hardware availability needs attention
Can grow in to a potential complementary technology to RTK
Nationwide Pak-rehber extension will take time


PPP is there until Pak-Rehber arrives….
CORS network planning should consider corrections provisioning to
PPP users