Hi, I'm working on a small parallel FFT core (either 8 or 16 point FFT). The idea is that this core will be surrounded by a lot of memory blocks in an FPGA and data will be routed into and out of it by some other logic. This will be a building block for a 8K FFT or whatever. Anyway, is COFDM transmition systems there is an I and a Q stream of symbols. I know that the I and Q are refered to real and imaginary, but do I need a complex FFT or two real FFT's? Thanks, Brian -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.opencores.org/forums.cgi/cores/attachments/20040121/a00463e2/attachment.htm

Hello


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Complex FFT of course, if s(t) = q(t)+i(t) then S(w) != Q(w) + I(w); I think so. Jerzy Gbur -- "Everything is simple until it'll be comprehensible" - furia ---------------------------------------------------- Załóż konto pocztowe i odbierz nagrodę! http://klik.wp.pl/?adr=http%3A%2F%2Fabc.wp.pl%2Fopenoffice&sid=101

On Thu, 22 Jan 2004 10:13:35 +0100 Jerzy G furia1024 at wp.pl> wrote: I have understood, that in radio technology it is quite common to send data on "I" and "Q" portions of the carrier. The carrier can be only real or have also the imaginary part and imaginary differs pi/2 from real as a vector... as sin/cos won't correlate with same frequency signal with 90 degrees phase difference, it is possible to use such carriers to convey totally different information. So allthough the names come from complex mathematics, these signals might not have nothing to do with each other (could be even different tv-channels). I do not remember how is the case in DVB and such, but "O" in COFDM comes from "orthogonal", might hint that they are dependent... Check the standard; if investigating DVB, as it would seem, go to "http://portal.etsi.org", thereon broadcast and dvb... hopefully you find out what you need... Teemu Erkko

Thank you, This is sort of the interpretation I have. The O does stand for orthogonal but has nothing to do with the I and Q. It has to do with the fact that all the carriers (something like 1705 in 2K mode) are orthogonal after the iFFT conversion. I guess I will work on a real FFT first because it is much easier than the complex. Then if I have to, I will make a complex. -Brian " I have understood, that in radio technology it is quite common to send data on "I" and "Q" portions of the carrier. The carrier can be only real or have also the imaginary part and imaginary differs pi/2 from real as a vector... as sin/cos won't correlate with same frequency signal with 90 degrees phase difference, it is possible to use such carriers to convey totally different information. So allthough the names come from complex mathematics, these signals might not have nothing to do with each other (could be even different tv-channels). I do not remember how is the case in DVB and such, but "O" in COFDM comes from "orthogonal", might hint that they are dependent... Check the standard; if investigating DVB, as it would seem, go to "http://portal.etsi.org", thereon broadcast and dvb... hopefully you find out what you need... Teemu Erkko " _______________________________________________ http://www.opencores.org/mailman/listinfo/cores -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/ms-tnef Size: 3144 bytes Desc: not available Url : http://www.opencores.org/forums.cgi/cores/attachments/20040123/4633c2a1/attachment.bin