Edwins wiki

Beidou (北斗) is presently aimed at China as a navigation system. You can receive 北斗 satellites fine outside China. But the network of ground stations only provides corrections as far as they are relevant for China. Furthermore satellite coverage is much better over China than over the rest of the world.

北斗 comprises number of geostationary satellites at a static location over China, a number of satellites flying figure eight loops (in inclined geostationary orbits) and a relatively limited number of satellites in lower orbits which lead them all over Earth. Outside China you will therefore see less satellites than in China and the error corrections will not be as good.

Nevertheless you can perfectly well use 北斗 now, especially in combination with the GPS system. When used in combination you get better locations than using GPS only. Simply because more satellites tend to be better when it comes to satellite navigation.

I have tracked 北斗 satellites for a few months using my home-built Navspark receiver (see The Navspark satellite navigation receiver). I logged my location and some extra data like DOP values. I also logged which satelliets where used in the solution, their location relative to myself and the received signal power.

On the maps you can see some of the first results. These images shows a maps with the location record. For red points 2 or less 北斗 satellites were used for the location, meaning a location cannot be computed with 北斗 alone. Blue points indicate 3 北斗 satellites were used, which is just enough for a 2D location. For green points 4 or more satellites were used in the location. In these locations one can compute a location from the 北斗 system alone.

The second figure shows the number of 北斗 satellites in view at a logged location. Note that there is a limited number of locations with zero satellites in view. Since one 北斗 geostationary satellite is in view from the Netherlands this cannot be right. It merely reflects the fact that sometimes the receiver computes a location from GPS alone, before a 北 斗 satellite was found by the receiver. It is a start-up effect. From this histogram you can see that there are a fair number of locations where 4 or 5, or even 6 北斗 satellites were in view. Not bad at all.

The third figure shows the number of 北斗 satellites actually used in a location computation. Satellite counts are lower here. This is simply caused by the fact that even when a satellite is over the horizon (in view according to the receiver) it's signal path may be obstructed by buildings. You can see that the 北斗 system presently is not really a very useful system yet. There are simply not enough satellites available for users here in Europe.

The fourth figure shows the histograms for the PRN numbers of the different satellites. There is one geostationary satellite in view (the yellow bar), a fair number of inclined geostationary satellites (the blue bars) and only three MEO satellites (the green bars). This is somewhat surprising since there should be more satellites in MEO available. This is probably due to limitations in the Navspark receiver which actually has a built-in upper limit for 北斗 PRNs.

The last figure shows the actual receiver. The small boards at the top are the actual Navspark receiver and an adapter board with SD card and a battery charger. The screen is a simple Nokia screen. Quite simple really. If i can solder this thing together, so can you.

According to the 北斗 agency the system will be global by 2020. Given how fast it has been built it might be a global system even sooner than that.