What to do when GPS isn’t accurate enough? Turn on your TV!

Well you have the idea that GPS tracking can do a lot for
your business. So, you start evaluating the markets and seeing what’s available.
Suddenly you come across some snags. It
looks like you can’t use GPS for your application because of one or more of the
known GPS accuracy problems:

1. Basic Accuracy: The standard signal is good, at best, to 15 meters.
2. Urban Canyon: If your vehicles are constantly on city streets, in the shadow of tall
   buildings, they won’t attain 15 meter accuracy at all times.
3. People or Vehicles Indoors: If a GPS receiver is under a roof, accuracy is significantly degraded

As I wrote not long ago on my interest in GPS for the blind, as marvelous as
the GPS is, like any system it has its limits.

The first ’stone wall’ limit one runs up against is the basic accuracy of the
civil signal. Pus or minus 45 is not good enough for some
applications. As an example, let’s say you’re managing thousands of
railroad locomotives in operation. Obviously, you need to know which of
possibly many side-by-side tracks they are on. Rail tracks are as close
together as 16 feet, center to center. Hmmm.

Second is the so-called ‘urban canyon’ effect. When the vehicle is on
congested city streets in the shadow of tall buildings, the tracking results
are going to be severely degraded. The receiver can’t reliably ’see’ the
minimum of 4 satellites it need to see, and the signals it does ’see’ are
affected by reflecting off adjacent buildings … a phenomenon known as
“multipathing’.

The last big ‘insurmountable’ problem is indoors or under a roof. GPS inside
buildings just doesn’t work very well. There are some commercial schemes
using cell phone technology to help with this, and these schemes have some benefit
…but cell phones sometimes have penetration problems too.

Enter a great idea … using the commercial television signal to help. Television
is available across a large percentage of the country, often a much larger
percentage, reliably, than are cell phone signals. Also, the power levels
of commercial TV are higher. And television is very accurately timed …
timing is the key to the GPS navigation solution, and the
enhancements/corrections supplied via TV can make a dramatic improvement.
Here’s a really interesting article on a proposed commercial venture and
also some deep technical background from GPS World magazine (by the way,
if you are at all interested in this technology, you ought to get GPS World …
it’s free and it’s an outstanding resource.)

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