Hi,
please remember to always reply to the list.
If you mix your baseband signal in a way that no part of your spectrum
includes negative frequencies BEFORE doing the complex-to-real
conversion, this should work. At least from a signal processing
perspective. I never used my soundcard as a transmitter, so I can't
really help you with that.
--Felix
On 03.06.2015 15:02, [email protected] wrote:
hi felix,
>>I implemented a transmitter for the DRM(30) standard in GNU Radio
and published it on github (https://github.com/kit-cel/gr-drm).
i have already installed your transmitter and tested it with DREAM. it
works perfect. excellent job!
if i have an expert right here i can be more specific for my project:
the aim for this work is not to implement a DRM transmitter/receiver,
it's to implement an OFDM transmitter/receiver. previous
implementations from my colleagues are done in Matlab. now i have to
implement this work with an open source software (GRC) because there
were problems with licensing and changed or removed functions in
higher versions of Matlab. they used two computers with their sound
cards, one for tx and one for rx. that's the reason why a center
frequency of 12khz is used. the signal, slightly specified by the DRM
standard (RM A, SO 3 --> bandwidth 10khz, occupied carriers 228 (-114
to +114)) has the highest frequency at 17khz. this signal you can
handle with your sound card.
to your comments:
1) i know there are only specific sample rates allowed for DRM but as
written previously i will not implement the full standard. at the
moment i use a random source block to get in some random data.
2) i don't have an USRP. i want to use a sound card to get my signal
out to the world (at 12khz). is this possible by using a
complex-to-float block and an audio sink?
thank you very much for your help and your answers!
alphonso
*Gesendet:* Mittwoch, 03. Juni 2015 um 04:57 Uhr
*Von:* "Wunsch, Felix (CEL)" <[email protected]>
*An:* "[email protected]" <[email protected]>, "[email protected]"
<[email protected]>
*Betreff:* Re: [Discuss-gnuradio] problem with ofdm bandwidth and
sampling rate
Hi Alphonso,
I implemented a transmitter for the DRM(30) standard in GNU Radio and
published it on github (https://github.com/kit-cel/gr-drm).
To (partly) answer your questions:
1) DRM only accepts specific audio sample rates, make sure to read the
standard documents carefully.
2) Mixing is usually done by the USRP. You as the user only deal with
the complex baseband centered around DC. 12 kHz would also be a VERY
low carrier frequency, short-wave radio usually uses frequencies
between 3 and 30 MHz.
--Felix
On 03.06.2015 12:57, [email protected] wrote:
hello,
i'm trying to implement an ofdm transmitter (and afterwards a
receiver) for demonstration. the parameters should match the drm
standard. so my first try was to implement the transmitter with
the following main parameters:
ofdm transmitter block
fft length = 256 (--> fft length >= occupied carriers)
cyclic prefix = 64 (--> 256/4)
occupied carriers = 228 (--> (-114, -113, ..., 113, 114))
for this try no pilot carriers and symbols and no sync words.
everything works fine but there is a problem with the spectrum of
this ofdm signal. from older posts i have the following equation
to set the bandwidth (bw) of my ofdm output signal:
bw = sampling_rate * occupied_carriers / fft_length
with the parameters above and the wish of a bandwidth of 10khz (to
match the drm standard) i will get the following sampling rate:
sampling_rate = bw * fft_length / occupied_carriers = 10khz * 256
/ 228 = 11.228khz
now i have two questions:
1) if there is an input source with a sampling rate higher than
11.228khz (maybe from my sound card (44.1khz) or a wav file (48
khz)) should i use a resampler block because there is a problem
with nyquist? how can i handle this problem?
2) the same problem goes with the output. if i mix up the ofdm
signal to a carrier frequency (for example 12khz) how can i handle
this? there is also a problem with nyquist.
thanks in advance!
alphonso
--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)
Felix Wunsch, M. Sc.
Research Associate
Kaiserstraße 12
Building 05.01
76131 Karlsruhe
Phone: +49 721 608-46276
Fax: +49 721 608-46071
E-Mail:[email protected]
www.cel.kit.edu
KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association
--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)
Felix Wunsch, M. Sc.
Research Associate
Kaiserstraße 12
Building 05.01
76131 Karlsruhe
Phone: +49 721 608-46276
Fax: +49 721 608-46071
E-Mail: [email protected]
www.cel.kit.edu
KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association
_______________________________________________
Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
