Beidou, the chinese satnav system

Since early 2013 the Chinese 北斗 (Beidou) satellite navigation system is operational. The coverage of the satellites still limits use to China itself. Even though a number of 北斗 satellites have orbits going over the whole Earth the system is of little use outside China since China's ground stations are mostly inside China itself. So corrections which are broadcast in modern satellite navigation systems are simply not available in the rest of the world.

北斗 consists of a number of geostationary satellites, inclined geostationary satellites and medium-Earth orbit satellites. The medium-Earth orbits satellites are in comparable orbits to GPS and Glonass satellites. So these are visible all over Earth. But since there are only 4 operational now (2015) the chance that one is in view is limited. You need about 30 medium-Earth satellites to cover the Earth. The other satellites cover China itself. The four geostationary satellites are all visible from all of China. The inclined geosationary satellites make long figure-eight loops over the area. So China itself is pretty well covered. They have succeeded in building an operational system with a limited number of satellites.

Even though GPS is still widely used even in China 北斗 is being used more and more. Many of its users will probaly not even notice they are using 北斗 since it is simply a feature of the navigation chip in their mobile phone (more about that later). You can receive 北斗 satellites fine, even from northern Europe. There is one geostationary satellite just high enough over the horizon, the inclined geostationary ones come into view when they're in the northern curve of their figure-eight loop and every now and then one of the global 北斗 satellites come into view. The second image in this article shows how the satellites moved over the sky over the course of an evening. As you can see all 北斗 satellites (in red) are sparse compared to the GPS constellation (in blue) and they are pretty low in the sky. Nevertheless, there are enough in view.

To get a receiver you will need to order some equipment from China. I ordered a few small GPS/北斗 receivers from Navspark. Their receivers are not just attractive because they are small and use little power, they are actually Arduino programmable! So you can just run your own software on it and connect pressure sensors, a compass, inertial sensors, LEDs, buttons, whatever you like. The receiver comes with a good viewer application. You can just connect the receiver board to your USB port, start the viewer and see whether there are 北斗birds overhead (see first image). The Navspark does a pretty good job computing a combined solution. Which is not straightforward since the pseudoranges of 北斗 can be off (no corrections over Europe…) I was impressed what the little Navspark could do. You can see it has computed a location using two GPS and two 北斗 satellites. Cool! The next step (still a work in progress) is putting the little Navspark into a receiver i can take out and about. The third image shows the Navspark on a prototype board with a Nokia LCD. The Nokia uses little power as well so it fits nicely with the Navspark. Next step is putting it al a bit more neatly in a receiver box, add some buttons, add the Navspark SD card adapter for logging and i've got my own homebuilt 北斗receiver.

Then i found out my cheap android phone already uses 北斗 for navigation! I got this phone, a Wolfgang, from the Aldi supermarket chain. Turns out it has this modern navigation chip in it. Since the navigation chip is obviously intended for the chinese market it supports 北斗, together with GPS and Glonass. In last image shows the sky view of all used navigation satellites. Those with PRN numbers of 200 and higher are 北斗. So if you are not into soldering your own Navspark receiver, just get the phone from the Aldi.

  • en/ruimte/beidou.txt
  • Last modified: 2019/02/26 21:38
  • by Edwin Wisse