Tuesday, August 21, 2012

The GPS tracker to beat (smallest, lightest, and most durable)

Figure 0: Please read below.
From the very early days of GPS snapshot technology has been proposed as a way of reducing power consumption and footprint of a radio positioning device. Some papers about NASA microGPS date back to late ‘90ies:

Later on many Companies tried to patent this technology and bring it to the market. Most of them have been acquired or have merged - see the latest acquisition of CSR “mobile business” (whatever that means!) from Samsung.
To our knowledge until today all development efforts led to products with disputable market readiness, if otherwise mostly devoted to picture geo-tagging.
Instead, the assumption that a snapshot approach could beat (from the cost and power consumption point of view) a hardware baseband has always been contradicted by Moore’s law and market demand. Lead manufacturers now release complete GPS engines on a chip smaller than what was before the RF Front-End part only. Compare e.g. the CSR GSD4e (3.5 x 3.2 x 0.6mm 42-ball WLCSP) and the Skyworks SE4150L (4 x 4 x 0.9 mm 24-pin QFN). That is probably why the complexity associated to a snapshot positioning approach has never won over a slightly more expensive and power consuming standard GPS receiver.
Probably the real value of a snapshot approach has not been identified yet and in our opinion is to be searched in other domains such as geoencryption and GNSS authentication:

So we longed for a Company that would own the technological skills to provide a new standard in terms of snapshot positioning. 
Cellguide has been in the business several years now but only recently released a real hardware module – simple to use and available for sale – that works with a snapshot positioning approach and has specifications that could dramatically change the tracking business: the Robin.

We bought an evaluation kit (expensive, but breaks the ice) and we are testing it together with other 
enthusiastic engineers. 

A Robin device on its cradle (used for charging, programming, and downloading the snapshots on the PC) looks like this:

Figure 1: Robin device on its cradle
 A couple of Robin devices next to each other:

Figure 2: Two robin devices next to each other

The Robin brochure says already a lot, but I wanted to show the results of a real test (on the beach – it is summer after all).
The reference path was roughly this one:

Figure 3: Approximate reference path
The little wire antenna in the pictures above was used (which is terrible compared to a patch antenna of course). 
Please note that each snapshot is - by design - completely independent from the others.

64ms snapshots (at 1Hz) lead to the following positioning results:

Figure 4a: 64ms snapshots, raw
Figure 4b: 64ms snapshots at 1Hz, Kalman filtered
Figure 4c: 64ms snapshots at 0.2Hz, Kalman filtered
The same was test was also reproduced by taking 512ms snapshots (higher sensitivity) at 1Hz.

Figure 5a: 512ms snapshots at 1Hz, raw
Figure 5b: 512ms snapshots at 1Hz, Kalman filtered
Figure 5c: 512ms snapshots at 0.2Hz, Kalman filtered
 Results can be summarised in the following:

Figure 6a: 64ms snapshots, raw (red) and filtered (green)
Figure 6b: 512ms snapshots, raw (red) and filtered (green)
Figure 6c: filtered output for 64ms (diamonds) and 512 (circles)

Robin was born at Cellguide for wildlife tracking but as we came across it we could not help thinking it shall be employed in lots of other cases as well. The Aclys chip (earth of Robin) has a low data rate, low pin count SPI bus compatible even with simple 16bit micro-controllers. It can therefore be embedded in very small and cost effective devices to enable tracking capability where it was not possible before.
We see potential in this technique and we hope you enjoyed reading as as much as we did running the tests!


P.S.: For further information please contact directly the Cell-guide guys at info@cell-guide.com