Re: [Discuss-gnuradio] Multiple-Transmitter OFDM

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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