Re: [Discuss-gnuradio] tx

Hi Martin:

Thank you for your reply.

But,

1.I see the virual Source(Stream ID:Payload Bits)->Chunks to Symbols(Symbol Table(-0.707...))(modulate:qpsk)?When I input 800 bits to the Packet Header Generator,then chunks to symbols.How many symbols generate in this way?When I input 800 bits to the Repack Bits,then chunks to symbols.How many symbols generate in this way?Thank you very much.

2.I also see another ofdm in the old version of gnuradio.And the module structure is attached.And the connect code in python:

self.connect((self,0), self.chan_filt) # filter the input channel

self.connect((self,0), self.ofdm_sync) # into the synchronization alg.

self.connect((self.ofdm_sync,0), self.nco, (self.sigmix,1)) # use sync freq. offset output to derotate input signal

self.connect((self,0), (self.sigmix,0)) # signal to be derotated

self.connect(self.sigmix, (self.sampler,0)) # sample off timing signal detected in sync alg

self.connect((self.ofdm_sync,1), (self.sampler,1)) # timing signal to sample at

self.connect((self.sampler,0), self.fft_demod) # send derotated sampled signal to FFT

self.connect((self.sampler,1), (self.ofdm_null,0)) # send timing signal to decoder

self.connect(self.fft_demod, (self.ofdm_null,1)) # send freq-domain samples to decoder

self.connect(self.fft_demod, (self.ofdm_frame_acq,0)) # find frame start and equalize signal

self.connect((self.sampler,1), (self.ofdm_frame_acq,1)) # send timing signal to signal frame start

self.connect((self.ofdm_frame_acq,0), (self,0)) # finished with fine/coarse freq correction,

self.connect((self.ofdm_frame_acq,1), (self,1)) # frame and symbol timing, and equalization

And someone tell me the new version of gnuradio is just expand to the old version.Can you tell me how much parts adjust?And the main code of gnuradio is in gnuradio/gr-digital/examples/ofdm?And whether other code needed?Where are they?

3.And i use two usrps to run the tx_ofdm.grc and rx_ofdm.grc.The adjust code I also attached. But in the transmit,so many U U U display.Why?And in the receive part,I also encouter problem.Can you help me explain it?

Thank you very much.I see the ofdm part many days.And the 3 questions I encounter.Thank you.Sorry for my poor English if you can't understand.Thank you in advance.Thank you for your patience.

Best regards


At 2014-05-23 16:40:55,"Martin Braun" <address@hidden> wrote:
>On 05/23/2014 02:29 AM, xianda wrote:
>> Hi:
>>      Thank you so much.
>>      1.But from "chunks to symbols"  I see you use the bpsk and qpsk both.Right?What is the relationship between 800 bits and 17 symbols?Namely,how to calculate the 17 symbols?
>> 17*64=1088.Can you explain?
>
>1 OFDM symbol @ BPSK == 48 bits in this configuration.
>ceil(800/48) == 17.
>
>>      2.I have looked at your ppt about the ofdm.You say now have two version ofdm.Can you give me some links to them?Or some advices?Thank you.
>
>They're both in the tree. If you start working off of rx_ofdm an tx_ofdm
>you're already using the new stuff; no need to worry about this.
>
>M
>
>
>> Best regards
>> At 2014-05-23 04:33:44,"Martin Braun" <address@hidden> wrote:
>>> On 05/22/2014 10:12 PM, eontool wrote:
>>>> IIRC,  the tx and rx files are just a very general implementation of the OFDM
>>>> model.
>>>>
>>>> Here's my understanding:
>>>>
>>>> - Packet length refers to the data necessary to produce n symbols (48 data
>>>> carriers, 2 symbols = 96).
>>>
>>> Er, no. This is the number of bytes per packet. It's 96 because we add 4
>>> bytes for CRC, and then the packet number is a round value.
>>>
>>> At 100 bytes per packet, the payload is 800 bits. With BPSK, that would
>>> be 17 OFDM symbols (plus 1 OFDM symbol for header, and 2 for preamble).
>>>
>>> You can set whatever here, but remember that the stock equalizers don't
>>> do a good job on long packets. Also, the length can vary per packet.
>>>
>>>> - The number of total carriers in the systems equals the FFT length.
>>>> In this case, 48 data carriers and 4 pilots, 52 total and the rest are set
>>>> to 0.
>>>
>>> This is correct (compare 802.11a standard).
>>>
>>> M
>>>
>>>
>>> _______________________________________________
>>> Discuss-gnuradio mailing list
>>> address@hidden
>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
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From:	xianda
Subject:	Re: [Discuss-gnuradio] tx_ofdm
Date:	Fri, 23 May 2014 17:33:33 +0800 (CST)

Re: [Discuss-gnuradio] tx_ofdm