Tech Briefs Magazine - June 2021 - ST-20

Applications
+X (Ux)
+Y (Uy)
Roll
GNSS
Pitch
Yaw
+Z (Uz)
Figure 2. The six degrees of freedom. (Courtesy
of ACEINNA, Inc.)
We also have six degrees of freedom:
the three accelerometers and three
gyros measure the XYZ axes. The gyros
measure rotational speed, which when
integrated, gives change in angular position.
The accelerometer measures acceleration,
which when integrated gives
velocity and when integrated again, gives
position. By processing gyro data and
accelerometer data, and using filters
and algorithms optimized for a given
application, we get really accurate angular
data for roll, pitch, and yaw (See
Figure 2). The most critical data for an
automotive application is yaw, which
indicates the degree the car is drifting.
Pitch indicates whether you are going
up or down a hill. Hopefully, you will
never see a roll in your car.
Tech Briefs: What kind of accuracy
could you sustain over what time period?
Ustun: That's very difficult to say
because it depends on so many different
scenarios. Currently we have to achieve
lane level accuracy. A lane is about three
meters wide, and a passenger car is
about two meters wide. Since you want
to make sure that you're not going
beyond the lane, you have about plus or
minus half a meter before you're drifting
too far. At typical automobile speeds,
a correction of half a meter could be
achieved in less than a second. Since,
under dead reckoning, you can keep the
required accuracy for 60 to 90 seconds,
our IMU can easily keep a car within its
lane.
Tech Briefs: So, an IMU gives you relative
accuracy. What about absolute
accuracy?
Ustun: Absolute location data is generally
derived from a GNSS signal.
Historically, the positional accuracy of
GNSS receivers has been a meter or
20
Cov
Base
4G
Modem
Internet
Rover with Integrated IMU,
4G Modem and Dual Antenna
Installed in vehicle
Figure 3. Real-Time Kinematics (RTK) is a technique to improve the positional accuracy of a GNSS
receiver. (Courtesy of ACEINNA, Inc.)
Aceinna CloudRTK
OpenIM033
Triple redundant
6-DOF IMU @
1.5°/hr Bi
Rover Units
RTK
Dual-frequency
GNSS received
4G/LTE
openarc.aceinna.com
RTK Precise
positioning engine
& sensor fusion
op
4G/LTE
aggregated
corrections
RTK
Smart Antenna
Base Station
OPEN SOURCE IDE
Sensor fused, open sourced positioning systems
with cm-acurracy
Figure 4. Complete positioning system. (Courtesy of ACEINNA, Inc.)
more. So, GNSS by itself is not good
enough for the required automobile
lane-level accuracy of down to 2 cm.
Real-Time Kinematics (RTK) is a technique
to improve the positional accuracy
of a GNSS receiver. It uses a network
of base stations that can send corrections
to our vehicle-mounted RTK positioning
engine, which uses them to
recalculate its position more accurately.
RTK is a service that you can buy or
subscribe to from many sources. What
we're seeing more and more is communication
infrastructure - even telecom
service providers like Verizon, Softbank,
or China Mobile - have started offering
RTK services. From our product perspective
we are agnostic to the service
provider - we intend to support any
and every one of those RTK service
providers to help our customers achieve
the accuracy limits they're looking for.
www.techbriefs.com
ToC
We're providing a solution that's both
hardware and software.
Although we do not provide the service,
we enable our customers to choose
the one that's most suitable to them.
However, we do qualify those services
first. We make sure that they are compatible
with our hardware and software.
And then we put it up on our website to
give customers the flexibility to choose
from a list of service providers. Most
commonly, RTK comes as a service over
a 4G LTE network. If there is no 4G LTE
reception, there are alternative ways to
receive the correction signals, such as
satellite-based communication.
For RTK, you put base stations across
a network: there's a rule of thumb that
usually you put base stations on a 50mile
radius. These base stations are positioned
so that their locations are known
very accurately. Corrections are generatSensor
Technology, June 2021
RTCM
RTCM
RTCM

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Tech Briefs Magazine - June 2021

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