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Re: [Discuss-gnuradio] FSK modulation

From: Vijay Pillai
Subject: Re: [Discuss-gnuradio] FSK modulation
Date: Fri, 29 Apr 2011 18:43:13 -0700 (PDT)

HI Pascal,

If you google for GRC tutorials, you should easily find some good ones on the web. FSK is definitely possible to the best of my knowledge.

Data packets with header,.. CRC can be transmitted but I think you need to store the bit sequence in a file and the received and demodulated data also gets stored in a file. I think it might be possible to dynamically generate CRC, data and all, but this needs some special custom block at least within GRC (anyone please feel free to correct me).  If you do figure out how to do this, please do write up a tutorial on this :-)

You can easily get I/Q data at least with python and GRC. Alexandru Csete, a poster on this forum has written some good examples that cover all of the above (you can easily google his website and download all the GRC examples that he has written; thank you Alex!!).

Best regards,

--- On Fri, 4/29/11, Pascal Matthieu <address@hidden> wrote:

From: Pascal Matthieu <address@hidden>
Subject: [Discuss-gnuradio] FSK modulation
To: "address@hidden" <address@hidden>
Date: Friday, April 29, 2011, 2:05 PM


    I would like to ask a few questions regarding USRP, UHD and GNU Radio. I have 2 USRP devices and one module I bought that's able transmitt and receive on 433.92 MHz. I installed UHD on 2 computers (both with Win XP OS), connected to each one a USRP1 that has a WBX daughterboard and a Log Periodic type antenna by Kent Electronics that's on Ettus order page. Both USRP's are recognized. 

1. I would like to send some data packets that will have FSK and GFSK modulation. With one USRP I will receive data coming from the module and data coming from the second USRP. Each packet will have some data in it to be identified, so that I could log it. As I am a newbie I would like to ask if there are any test examples for GRC or simply Python to modify it to meet my requirements. Honestly I don't know where to start. There are blocks for AM, FM, DPSK, GMSK, QAM and others, each one heaving a MOD and DEMOD block but no blocks for FSK.

2. My packets will have the following layout a Preamble, a Header for identification, a number of bytes of data, and CRC data at the end. At transmitter I send data packets (many 1/0 values that are put on a carrier signal - in FSK signal we have a frequency for the 1 and a different frequency for 0). If there were a block to demodulate FSK modulated sugnals it would pass me some 1 0 1 0 1 1 0 1 1 1 1 1 0 0 1 .... from which I would have to recognize my header, if I recognize it, then the next byte of data should be the representation of the length of data, to know how many bytes I will have to receive until I reach to the end where I will have to know the length of my CRC data. After I receive the CRC the packet is finished, I can process data that I will put previously into a buffer and start to interprete bytes of data (who sent the packet, etc.). If CRC is not the same as received then it means it has errors and data is not usable. Is it correct how I'm thinking the problem or I should tink in a different way. 

3. My first steps will be to try some source code in Python but after that I plan to make my own interface to control these devices (the second USRP and the module). I don't really know how to get the I/Q data from USRP, how to set different parameters like center frequency and others. There's any partial or full documentation related to this. If I could use the Visual Studio I would be able to make some GUI. If there's no souce code written for FSK maybe based on other codes written for other modulation types, I will make one, but ther's little chance for that to work, anyway I will have to know how to get I/Q data from USRP, how to write .rbf file to FPGA, and others.

Thank you very much.


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