# Regarding demodulation in ofdm

**URL:** <https://www.ruby-forum.com/t/regarding-demodulation-in-ofdm/234447>\
**Category:** GNU Radio\
**Created:** [March 5, 2015, 7:04am UTC](https://www.ruby-forum.com/t/regarding-demodulation-in-ofdm/234447 "2015-03-05T07:04:42Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [March 5, 2015, 7:04am UTC](https://www.ruby-forum.com/t/regarding-demodulation-in-ofdm/234447/1 "2015-03-05T07:04:42Z")

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sir,  
i am new to gnc and i am doing a project on ofdm implementation  
using gnu radio.i am fine with modulation part but got stuck with  
demodulation.i am requesting you to plz help me in doing demodulation.i  
am  
attaching block diagram of demodulation circuit.

thank you.

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**Author:** ![roja\_yadav](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ea666f/32.png) [@roja\_yadav](https://www.ruby-forum.com/u/roja_yadav)\
**Post date:** [March 5, 2015, 11:47am UTC](https://www.ruby-forum.com/t/regarding-demodulation-in-ofdm/234447/2 "2015-03-05T11:47:01Z")

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Hi Roja,

you forgot to actually explain what does not work. I’ll refer you to [1]

there’s a few things odd with your flow graph, nevertheless:

1. Double throttle: you’ll only ever need one throttle block. I’d  
explain, but I think it’s easy enough to understand once one realizes  
what throttle does.
2. You want to send binary data, but you convert that to float before  
passing it to OFDM mod. I’m pretty sure that’s not what you really want  
to do – just set the input type in the OFDM mod block to byte, short or  
int, and generate random numbers between 0 and 2^8, 2^16 or 2^32,  
respectively, using the corresponding output type of your random source.
3. This is really just nitpicking, but I assume you’re a student and  
this won’t be the last time you ask someone else for help: Please rotate  
all your blocks so that one can read them, and they don’t overlap, try  
to align them and place them logically sound etc., when sharing.  
It doesn’t take much effort with the current versions of GNU Radio  
Companion, and it gives the people you ask the feeling that you already  
went through “tidying up” and don’t force them to do that mentally.  
Actually, there’s another feature in GRC that makes taking nice  
screenshots easier: Under “File” you’ll find “Screen Capture”, which  
will give you a correctly-sized image of only your flow graph, not the  
whole desktop.

If you’re asking about the warning you see in the console window: it’s  
exactly that, a warning, not an error. It means GNU Radio had to  
allocate a bit more of buffer, but it doesn’t impact the functionality  
of your flow graph.

Greetings, and happy hacking 🙂  
Marcus

[1][http://gnuradio.org/redmine/projects/gnuradio/wiki/ReportingErrors](http://gnuradio.org/redmine/projects/gnuradio/wiki/ReportingErrors)

On 03/05/2015 07:03 AM, roja yadav wrote:

> sir,  
> PS: there are ladies in here, too. If I’m new to a mailing list, I  
> usually start greeting by “Hello,”, or something like “Dear XY  
> community,”, until I get a feeling how people respond.

> ```
> i am new to gnc
> 
> ```

I think you mean GRC, \_G\_NU \_R\_adio \_C\_ompanion.

> and i am doing a project on ofdm implementation using gnu radio.i am  
> fine with modulation part but got stuck with demodulation.i am  
> requesting you to plz help me in doing demodulation.i am attaching  
> block diagram of demodulation circuit.  
> That’s a flow graph, not a circuit. Circuit is only used for electronic  
> circuits (with capacitors, resistors, stuff like that); in GNU Radio,  
> you actually can’t have cycles in your flow graph, making this even less  
> a circuit (just in case you need to write a report later on 😉 ).

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**Author:** ![roja\_yadav](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/ea666f/32.png) [@roja\_yadav](https://www.ruby-forum.com/u/roja_yadav)\
**Post date:** [March 5, 2015, 4:17pm UTC](https://www.ruby-forum.com/t/regarding-demodulation-in-ofdm/234447/3 "2015-03-05T16:17:34Z")

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Also, you’re using the old-style OFDM blocks. I suggest looking at  
ofdm\_loopback.grc for an example on how to use the new ones.

M