You are right. I guess, one of the transmitters' preamble
overlaps another's data. (Because gnuradio sends preamble in all
carriers). I have attached my receiver and transmitters' FGs. Both
of them uses 256 carrier OFDM. One transmitter use half of the
carriers as occupied and another uses other half. I guess our
receiver structure is wrong.
Hi Ramazan - My primary wondering
about your specific OFDM setup is whether the sync preambles are
abiding by your carrier separation (256 carriers: -120:-1 for
one Tx and 1:120 for the other). It certainly looks from the
images that the payload portion is working as you desire.
Depending on the payload length, when using a spectrum analyzer
you might not even see the blip of the sync preambles ...
Are you using pre-existing GR OFDM
blocks in GRC, or something you created yourself?
Do you have GRC or Python / C++
scripts you'd be willing to share?
Some of the more involved
(typically hierarchical) GR blocks such as OFDM provide settable
variables that sometimes don't work well if not the default or
not set -very- carefully.
Hope this is useful! - MLD
ps> Reminder to "reply all" to
keep the discussion on the GR email list. More eyes reading
means greater chances of someone providing useful help!
On Thu, Jun 20, 2019, at 9:27 AM, Ramazan Çetin
wrote:
Hello all,
I have implemented OFDM system that has one receiver and
two
transmitters. Receiver can receive signals correctly, when
one of the
transmitters is active. However, when both of them are
active, receiver
cannot receive all the packets. They are interfering each
other.
To overcome this situation, i tried to allocate different
carriers to
transmitters. For example; in 256 carriers OFDM system, 1
to 120 is for
transmitter 1 and -120 to -1 is for transmitter 2. In this
situation,
receiver cannot still receive entire packets, when both of
them are active.
At the end, i decided to give some gap between
transmitters. So, 36 to
90 and -36 to -90 are assigned to transmitters. But, result
is same. I
have attached two pictures of spectrum. They represents
state of one and
two transmitters are active. You can check the situation
from there.
So, can you suggest a way to receive from two transmitters
without
interference?
Best regards.
Ramazan
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