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[Discuss-gnuradio] OFMD TX and RX

From: Chris_Spain
Subject: [Discuss-gnuradio] OFMD TX and RX
Date: Sun, 13 Jun 2010 05:38:46 -0700 (PDT)

Hello everybody,

I' am trying to test and understand the OFDM Modulation implemented in GNU
Radio. I'm using the deafult values, fft_lenth=512, occupied_tones =200,
cp_length= 128 and bpsk modulation, besides, I'm using a RFX900
Daughterboards on USPR and I'm connecting the TX and RX with a coaxial

I try to send a package of 1024 bytes but I'm not receiving all packets,
always lost the first packet and then is a little bit random, sometimes I
receive and I demodulated the 2º,3º,4º package and lost 5º, or lost 3º and
recive ok 2 ºand 4º...
I don't know what are happening, because I don't know how the OFDM
implementation map the 1024 bytes onto 200 carriers of data.

If I'm understanding the OFDM theory, with a bpsk modulation each carrier
are modulated for two bits and my OFDM symbol length are 512+128
(fft_length+cp_length).So, ¿with 2 bits per data carrier (200), each symbol
transport 400 bits, 50 bytes? 

That can´t be true because I receive some packages with no errors. Somebody
can explain me, How works OFDM Modulation implemented in GNU Radio?

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