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Re: [Discuss-gnuradio] tx_ofdm


From: Martin Braun
Subject: Re: [Discuss-gnuradio] tx_ofdm
Date: Fri, 23 May 2014 10:40:55 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

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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