
Accurate Navigation Without GPS - mhb
https://spectrum.ieee.org/tech-talk/transportation/sensors/accurate-navigation-without-gps
======
Isamu
What's novel here is that it is a compact, pretty accurate solid-state
inertial navigation unit.

[https://en.wikipedia.org/wiki/Inertial_navigation_system](https://en.wikipedia.org/wiki/Inertial_navigation_system)

[edit] Here's a paper from 2017 to give some context to the problem of
inertial navigation using the solid-state gyros and accelerometers you find in
smartphones:

[https://arxiv.org/pdf/1703.00154.pdf](https://arxiv.org/pdf/1703.00154.pdf)

> Abstract— Building a complete inertial navigation system using the limited
> quality data provided by current smartphones has been regarded challenging,
> if not impossible. We present a probabilistic approach for orientation and
> use-case free inertial odometry, which is based on double-integrating
> rotated accelerations. Our approach uses a probabilistic approach in fusing
> the noisy sensor data and learning the model parameters online. It is able
> to track the phone position, velocity, and pose in real-time and in a
> computationally lightweight fashion. The information fusion is completed
> with altitude correction from barometric pressure readings (if available),
> zero-velocity updates (if the phone remains stationary), and pseudo-updates
> limiting the momentary speed. We demonstrate our approach using a standard
> iPad and iPhone in several indoor deadreckoning applications and in a
> measurement tool setup.

Also: Apple is reportedly working on a full inertial navigation solution,
probably for indoor use.

~~~
nomel
No, it’s that a cheap compact unit can be used accurately by using an
understanding of the foot-planting gait of a human to remove low frequency
drift in that cheap unit.

The whole concept is that, using a foot, which is only moving quickly or
still, you can filter out the the low frequency component of all of the
signals. These sensors are relatively accurate under movement and large
signals, just not so much when stil, since their signal strengths become
relatively low to the offsets and noise in the system.

~~~
mapmap
So it measures the difference from zero in the accelerometer signals when the
foot is planted and then accounts for that when the foot is moving?

~~~
IshKebab
Yes, but that technique isn't new either. Here's a 2014 paper that cites a
2009 paper about it (I didn't follow the trail):

[https://www.omicsonline.org/open-access/understanding-the-
pe...](https://www.omicsonline.org/open-access/understanding-the-performance-
of-zero-velocity-updates-in-memsbased-pedestrian-
navigation-0976-4860-5-53-60.pdf)

~~~
mapmap
But there is still going to be cumulative error and drift, right? Has this
system reduced the cumulative error so that in some pedestrian use cases it is
accurate enough?

~~~
AstralStorm
Both. Long term drift will be extra challenging to correct as the cumulative
error is staircase. (Beta distribution)

What this is is actually a step counter, combined with step length and heading
estimate from an accelerometer w/ gyroscope plus compass. When the counter
makes a mistake, the effects will be catastrophic.

------
DamnInteresting
Strange that they don't use the age-old term for this sort of position-
tracking: dead reckoning.

[https://en.wikipedia.org/wiki/Dead_reckoning](https://en.wikipedia.org/wiki/Dead_reckoning)

~~~
SpikeDad
True but drift is inherent in dead reckoning due to cumulative errors and
evidently the trick this guy used eliminates the drifting or limits it (the
prototype was accurate to 5 meters).

~~~
DamnInteresting
Well, Wikipedia defines dead reckoning as:

> _the process of calculating one 's current position by using a previously
> determined position, or fix, and advancing that position based upon known or
> estimated speeds over elapsed time and course._

It still seems applicable, even if the hardware has advanced sufficiently that
errors are minimized.

~~~
fisherjeff
Dead reckoning is exactly as described in that pull quote, but the problem is
that when you integrate, e.g., accelerometer readings to get velocity, you
also integrate its bias, which varies over time, and in the case of MEMS
sensors will cause very significant errors.

The solution described in this article significantly improves on that by using
the pressure data on foot strike as an observation to estimate the IMU's
biases and correct the IMU-only position and attitude.

EDITED TO ADD: In many inertial navigation systems - presumably including this
one - dead reckoning will still be used as a fallback in the case where
corrections fail (i.e., no GPS or insufficient pressure data)

------
Moru
And then there was this solution before GPS...

[https://www.fastcompany.com/3047828/who-needs-gps-the-
forgot...](https://www.fastcompany.com/3047828/who-needs-gps-the-forgotten-
story-of-etaks-amazing-1985-car-navigation-system)

------
xori
Funny that all it took was to re-compensate for the noise of the accelerometer
on every step. Sometimes, simplest is best.

------
cryptonector
One would think that this could be used with GPS to protect against GPS
jammers trying to fool the device's view of where it is -- useful for
avionics!

~~~
PoachedSausage
It is pity that Loran-C is being shutdown. It could have made use of all those
old Long Wave broadcast transmitters.

[https://en.wikipedia.org/wiki/Loran-C](https://en.wikipedia.org/wiki/Loran-C)

~~~
cryptonector
But all systems using radio frequencies would be susceptible to jamming. There
are alternative GPS systems from Russia, China, and the EU now, no? I suppose
the more such systems, the harder for an adversary to jam them all. Of course,
some of those are run by potential adversaries, so there's that.

You really need inertial guidance and/or terrain recognition (as the Tomahawks
used to do back in 1990) as a fallback.

~~~
PoachedSausage
Not all RF based systems are equal.

GPS received signal strength at the Earths surface is around -130 dBm, barely
above the thermal noise floor even in a good receiver.

Around 1000km (most populated areas) from a Loran-C transmitter putting out
1000kW the signal strength is around -50 dBm. That is 9 orders of magnitude
harder to jam. All bets are off if your opponent can wheel out 1000kW jammers.

------
forapurpose
Last I knew, the US military was working hard on this problem. Against 'near-
peer' adversaries (e.g., China as opposed to ISIL), they need to function when
communication networks are shut down.

------
js2
I wonder how long before this shows up in foot pods for runners. I would
expect companies like Stryd and Garmin to be all over this.

~~~
jcdavis
That was my first thought as well. Accurate navigation from footpod data that
could eliminate or at least drastically reduce gps usage would be a
gamechanger for watch battery life.

~~~
dllthomas
The sampling rate you need from the inertial sensors is such that I'm not sure
it's likely to use much less power than the GPS for similar accuracy.

~~~
js2
Interestingly, both my Stryd foot pod and Garmin 935 watch (with GPS active)
last about 24 hours. The Stryd generally provides more accurate distance/pace
measurements. At least in one person's testing, the Stryd is the most accurate
device currently available for distance/pace:

[http://fellrnr.com/wiki/GPS_Accuracy](http://fellrnr.com/wiki/GPS_Accuracy)

~~~
dllthomas
Distance travelled is quite a bit easier than actual position.

Granted, I haven't touched the tech in almost a decade :-P

------
w_t
[http://ieeexplore.ieee.org/document/6851424/?reload=true](http://ieeexplore.ieee.org/document/6851424/?reload=true)

~~~
tntn
This is not the paper corresponding to the research described in the article.

A paper that describes a similar system by the same researchers from 2015 is
here:
[http://ieeexplore.ieee.org/document/7181113/](http://ieeexplore.ieee.org/document/7181113/)

Its not clear if the system presented at ISSCC differs at all.

------
tananaev
I have a small Android app that uses steps sensor to track location:

[https://github.com/tananaev/steps-
navigation](https://github.com/tananaev/steps-navigation)

It's not very accurate and there are some improvements that can be done, but
it was an interesting experiment.

------
RandallBrown
Pretty neat, but you would still need to give it a starting location since
this only tells relative position.

~~~
SpikeDad
The example they gave about inside building navigation does kinda make sense.
Imagine firefighters with this device in their boots. They all get to the fire
and press a snyc button (or click their heels three times) and their device
gets the current position from the GPS in their fire truck.

Now they can be accurately (well sort of) tracked inside the building without
requiring sky access for GPS.

~~~
jtuente
There will need to be an adjustment made to account for running vs walking,
since the foot does not necessarily rest for the same 100ms period while
running. Granted, if the sensors are simply measuring the "stillness" of the
foot planting, then calculation adjustments should only be limited by the
reset period/accuracy of the sensors.

~~~
londons_explore
The time period of stillness isn't important for this technique.

~~~
mirashii
It is, for a few reasons. For one, you need to be able to detect the period of
stillness, and so how certainly you can detect that time window is a function
of how long it is.

Second, you need to be able to make a number of measurements from your IMU
during the downtime. If you have an IMU that works at 20Hz and your period if
stillness is 100ms, then you know you can get a measurement in. If your period
of stillness is 10ms, then you can't.

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zipwitch
And here I clicked expecting Bowditch's.

[https://en.m.wikipedia.org/wiki/Bowditch%27s_American_Practi...](https://en.m.wikipedia.org/wiki/Bowditch%27s_American_Practical_Navigator)

------
dllthomas
Looks a lot like something I worked on at Michigan, years back -
[https://lojeda.engin.umich.edu/pps/](https://lojeda.engin.umich.edu/pps/)

Cool stuff!

