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[Discuss-gnuradio] FSK modulation

From: Pascal Matthieu
Subject: [Discuss-gnuradio] FSK modulation
Date: Fri, 29 Apr 2011 11:05:51 -0700 (PDT)


    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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