Dependence between accuracy and the number of GPS receivers.

[Horsa]

Q: Is it possible to increase the accuracy of GlobalTop GPS receivers by increasing their number?

Since all receivers are receiving almost the same satellite signal with the same kind of errors that are naturally introduced by the ionosphere, the average of those measurements could increase their precision (or, conversely, decrease their variance or their standard deviation) but not their accuracy (difference between the actual position and the nominal position).

There are several ways to increase the accuracy of GPS receivers:

• DGPS (WAAS, EGNOS), RTCM: By comparing the GPS signal received with a precisely known location, it is possible to increase the accuracy to around 2.5 m. It is not sub-meter quality, but it is the best GlobalTop can offer for now.
• RTK: Using phase carrier to correct the error of the signals through real time kinetics. This can offer centimetre grade accuracy, but need a lot of processing power and proprietary algorithm, this is a very expansive solution targeted towards professional market, and MediaTek has no plan to develop this solution.
• Multi-frequency system: By using multiple frequencies, such as L1 + L2, can help correct for the errors, but again, L2 is an encrypted military channel and MediaTek only support L1 for now.
• Multi-GNSS system: e.g., GPS + Galileo. The latest we've heard is that Galileo is still in testing stages (2 satellites) with a 21 planned for 2014. But it is very possible we see another delay.

So, overall, the best GlobalTop can currently do is through the use of DGPS and RTCM, but this will not have the sub-meter accuracy some customers seek. The best cost/performance ratio right now though is GlobalTop's, anything that goes sub-meter will cost significantly more.

However, the Pednavi mode firmware is currently available for GlobalTop GPS modules and they are designed for slow travelling applications. It reduces the amount of drifting through MediaTek proprietary algorithm. You are welcome to try this mode!