Re: [Discuss-gnuradio] tx_ofdm

[Martin Braun]

On 05/23/2014 11:33 AM, xianda wrote:
> 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.

I'm pretty sure I've answered all of these questions already.

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

Just ignore that. The new stuff is a complete rewrite.

>               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?

Your computer is too slow.

M

>               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
>>>>
>>>>
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