ISDB-T Modulator in GNU Radio Companion

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• published: 01 Apr 2015
• views: 725

I have done this video for a presentation of my Master degree defense, that I concluded in Feb. 2015. The audio is in portuguese and the video was recorded at the Digital TV Research Center of Mackenzie Presbyterian University (São Paulo, Brazil), where I studied and currently work. My professor (tutor) was Dr. Cristiano Akamine, a well known researcher/scientist of many different areas, such as Digital Television, ISDB-T, COFDM, DVB and SDR. In my master thesis I have developed a ISDB-T modulator using SDR tools, that are GNU Radio Companion and USRP. So far I have not found any work about this theme (ISDB-T modulation and SDR), many studies care about the reception portion, so we have decided to develop the transmission part. Iniatially we have decided to do a different aproach and to develop a modulator that would transmit only one-segment (1-seg) of the ISDB-T bandwidth. That is portion of the ISDB-T spectrum directed to the mobile reception. There are only a few commercial equipments that do this. But later we also decided to do a "normal" modulator. Both work very well so far. There are some functions of ISDB-T that are common to other communications systems, such as Reed-Solomon encoder and Convolutional Encoder. This are functions available in many libraries around the web and also are ready to use inside GNU Radio library as well. But again we decided, due to perfomance criteria, to develop the modulator "from the scratch". In other words we have developed most of the codes (C++) that do some kind of processing, except the Convolutional enconder, FFT, Cyclic Prefix and other data managments (such as conversion from vectors to stream and vice-versa) available in the GNU Radio Companion library. The modulator is based in the Brazilian Digital TV standard ABNT NBR 15601 (which discusses about the transmission system). What I show in this video is that the modulators (partial modulation and complete modulation) work. It is possible to see that commercial receivers (cell phone and one IRD+LCD display) available in the Brazilian market work without any errors. Also it is possible to see in a professional Signal Analyzer some characteristics of the transmission signals (Spectrum bandwidth, constellation and MER). Note that the bandwidth of the partial modulation is smaller than that for the complete spectrum.