Archive for the “gps” Category

Today we are going to speak about GPS, or rather GNSS. A few days ago a very explanatory document fell into my hands, made by my colleague Jesús Santos, as a result of a new product launched by the company Fastrax which many of you know. I think that it could be quite interesting for a lot of you, especially those of you who are dedicated to the issue of positioning. So I included it in the article.

What is GNSS?

GNSS stands for Global Navigation Satellite System. “GNSS modules” are satellite receivers whatever brand they are or whatever country they come from. What happens is that we use the word GPS receivers for everything related to positioning. It’s suitable but this American system is not the only one that exists, there are many others:

Russian GLONASS system
Chinese Beiuou-2/Compass
Japanese QZSS
Indian Gagan

And we are waiting for the European Galileo system expected in 2014…

Fastrax has a GNSS module. The IT6000 is based on an ST chipset. The great thing about this GPS module is that it works with the American GPS system as well as the Russian GLONASS system simultaneously.

Some would think…would this benefit me?

The answer is that the receiver will work in the most extreme conditions. Imagine a street with tall buildings (what we call the urban canyon). The receiver will not only be able to see the few GPS satellites, but it will also be able use the GLONASS satellites.

Let’s look at an example. Pay attention to the following chart. GPS satellites are light blue. GLONASS satellites are dark blue. There you have the IT600 module working with 22 satellites simultaneously.


To make it clearer, here it is on a map. Here you have a test drive in Dallas. In yellow you have GPS only module traces, the “best” working all the time with 4-6 satellites. In blue you have the same route working with an IT600 module and with 8-12 satellites simultaneously (as many GPS as GLONASS). The result? Amazing, the picture says it all.


Can I make use of the same antenna that I use with my GPS module now with the IT600?

Not really. The GPS and GLONASS frequencies differ slightly. For these GNSS receivers to work well, you need an antenna that is ready to receive the 2 signals. Do these antennas exist? Yes, they do.

That’s very interesting. What other stand out features does this module have?

It has a many but here are a few:

  • The IT600 module can be assisted (AGPS) which is what we know as Autonomous AGPS or predictive AGPS. The first one is the most interesting. We can simply say that it collects the ephemerides, it works out a 5 day prediction of them and stores then in an SQI flash memory (fast bus) which is inside. For the other possibility you need the classic AGPS server in order to collect them periodically using GPRS/HSPA.
  • DR support (Odometro/Gyro or CAN DWP).
  • So what is this?
  • Dead reckoning. Receiver’s capacity to continue giving its position without satellite visibility thanks to external sensors (nearly always Gyro and Odometer). Note that this feature is not implemented yet.
  • CAN. CAN bus.
  • DWP: Differential Wheel Pulse info. (something like the odometer)
  • I2C  for MEMS sensors

Most important of all are the sensors that we can connect to the IT600. An accelerometer gives an idea of the acceleration that the module undergoes. There has to be a change in the speed for it to work. An e-compass or magnetometer measures the earth’s magnetic field, like a compass. That’s what it really is, an electronic compass that helps the accelerometer to find the way at low speeds or if it has stopped. Many mobiles and PDAs incorporate the compass to help positioning. Sensor summary: speed (odometer o even DWP), acceleration (accelerometer), turns (gyroscope) and magnetometer (electronic compass).

These sensors are put close together in the I2C bus carrying the IT600 and it will use and it will get information by itself from the same UART serial port. Furthermore, it can be connected to the vehicle’s CAN bus.


Wow this module has some mind-blowing features…

Well there’s more. It’s a programmable device; you can make your own application and embed it inside. This means that the module is used as a microprocessor as it has an ARM946 processor with programmable GPIOs, 3 UART, SPI, I2C, CAN, 2ADC… a 208MHz micro with 8MB flash memory capacity and 128KB of SRAM.

I hope that it has been interesting talking about GNSS for those who did not know of any other systems. I’ll take this opportunity to wish you all a Merry Christmas and a Happy New Year for 2012 (and of course, good luck with the Christmas lottery tomorrow) what a pipe dream… ;)


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