I have been trying to send and receive data using a 2G cell phone network. I wish to communicate the bare minimum needed for telemetry and send waypoints to the uav. I hope that when i graduate to 3G, i can use a 3G video call for sending video and use the audio channel for telemetry,

These are my first attempts at this problem.

Got the following

1)2 sim900 modules for gsm communication

2)XR2206 for FSK

I realized that if i send a signal with frequency outside the 2-3.5KHz range, it gets severely attenuated. So i decided to use frequency shift keying to encapsulate the digital data into 2Khz for logic 1 and 3KHz for logic 1.

FSK seems to work well as seen on the oscilloscope. However when i send this signal from 1 GSM module to another, there is too much noise in the channel and i can't demodulate the signal using a PLL chip. There are even occasional random spikes that occur at around 10KHz.

Any thoughts?

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Replies

  • Developer

    There's a group for Telemetry over 3G and cellular modem on DIYDrones. There's code for the APM to initialize the SIM900 and send telemetry over it. It has been tested to 57,600 on the SIM900. Basically, this has already been done and is working. 

    I'm currently working on the 3G version with a HUAWEI 3G modem. 

  • It sounds like you're getting really close to an AX.25 implementation, which is a real protocol used by Ham Radio ops for APRS and Packet modes.  There are libraries available for it for a number of microcontrollers (most linux distros have native support for it, too).  Given that you're attempting a PLL demod, I assume that you've thought of this already, but a good bandpass filter can go a long way toward clearing up noise, especially 10kHz spurs in a 2-3kHz signal.  I can't claim any experience with this project, but thought I might pass it along for reference: it's an AX.25 encode/decode sheild for an Arduino.

    Looking forward to hearing more about this effort - it's a very creative way to get around the challenge of communicating with a drone via audio!  Out of curiosity, what kind of latency do you experience through your link?

    Cheers!

  • Why don't you use the cell tower to route the signal for you?  If both phones have a data plan then it shouldn't be a problem.  Or is the whole point to operate without the tower?

     I'm surprised more people are not using GSM in their drones.   It's a long range radio modem perfect for drones and has wide coverage across the world.  

    I plan on using GSM in my drone.  LTE specifically.

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