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#1 2018-Apr-04 09:09:04

Jelena
Member
Registered: 2018-Apr-04
Posts: 4

Siso Ofdm

Hello,
I want to use the SISO OFDM example/ WARPLab Reference Design to sent/receive a picture. Is it enough to replace

'tx_data=randi(MOD_ORDER,1,N_DATA_SYMS)-1;

with picture (array that will represent the picture) and modify the demolulation part?

Thank you for your answer!

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#2 2018-Apr-04 09:49:59

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 4964

Re: Siso Ofdm

That line of code generates a vector of random integers. Each integer represents the bits encoded in one modulated symbol. To send a real payload you can replace these random integers with integers generated from your payload, then update the demodulation process to reconstruct your payload.

I strongly encourage you to build this in simulation first. The WARPLab OFDM examples support simulation-only when USE_WARPLAB_TXRX=0.

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#3 2018-Apr-16 11:49:22

Jelena
Member
Registered: 2018-Apr-04
Posts: 4

Re: Siso Ofdm

Okaay. I am using a imread/reshape matlab functions to get a one-dimensional vector. But problem is now:
''reshape the number of elements must not change''
in line : tx_syms_mat = reshape(tx_syms, length(SC_IND_DATA), N_OFDM_SYMS);
because length(tx_syms is not =  length(SC_IND_DATA)* N_OFDM_SYMS



What should i do?
thank you!

Last edited by Jelena (2018-Apr-16 14:17:08)

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#4 2018-Apr-17 10:20:26

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 4964

Re: Siso Ofdm

I cannot tell you how to build your custom code - you need to figure this out on your own. You have already identified the problem above (your new tx_syms vector is the wrong length).

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#5 2018-Apr-28 08:58:11

Jelena
Member
Registered: 2018-Apr-04
Posts: 4

Re: Siso Ofdm

Thank you for fast answers. I figure it out how to send a picture which dimensions i know. (example: 240x100 bmp ). I now want to send any picture, but i don't know can i modify the numbers of carriers? I can modify number of symbols but occasionally number of symbols is not int (and then i have problem with reshape functions). What should i do?

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#6 2018-Apr-30 09:23:18

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 4964

Re: Siso Ofdm

The OFDM example scripts support payload of arbitrary length, set by the N_OFDM_SYMS variable by default. You should not modify the number of subcarriers to adjust the payload length.

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#7 2018-Sep-03 04:04:32

Nivetha
Member
Registered: 2018-Aug-08
Posts: 2

Re: Siso Ofdm

I am working in warp kit for OFDM FDD. I am using the SISO OFDM example for warpproject website. I used the same coding for two links as A to B (2.4GHz, channel 1) and D to C (2.4GHz, channel 11) in single warpkit. The buffer size as 16K Samples each for two links. And I am facing a problem that " No LTS peak was found" for some time. After running the program for 2 to 3 times I am getting that " Index exceeds matrix dimension" in that case payload index will show 8186

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#8 2018-Sep-03 09:52:56

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 4964

Re: Siso Ofdm

First - please post new threads for new questions; appending a new question to an old thread clutters the forums.

The "No LTS peak was found" message is printed when the Rx code is unable to identify a preamble in the received waveform. This can occur for many reasons - Rx gains are too high (clipping) or too low (noisy); Rx waveform power is at too high (saturation) or too low (noisy); interference in Rx waveform degrades the preamble; Rx waveform contains no preamble (code error, etc.). You need to investigate the Rx waveform you are providing to the Rx OFDM code and determine why the preamble correlator does not detect a preamble.

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#9 2018-Sep-06 10:53:52

Nivetha
Member
Registered: 2018-Aug-08
Posts: 2

Re: Siso Ofdm

murphpo wrote:

First - please post new threads for new questions; appending a new question to an old thread clutters the forums.

The "No LTS peak was found" message is printed when the Rx code is unable to identify a preamble in the received waveform. This can occur for many reasons - Rx gains are too high (clipping) or too low (noisy); Rx waveform power is at too high (saturation) or too low (noisy); interference in Rx waveform degrades the preamble; Rx waveform contains no preamble (code error, etc.). You need to investigate the Rx waveform you are providing to the Rx OFDM code and determine why the preamble correlator does not detect a preamble.

thank you sir. I got the result for OFDM FDD. I made a mistake in enabling TX/RX and TX/RX buffer.Also in assigning frequency for two links.

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