Hi all,
I am working on the OFDM in GnuRadio. After reading the code files and going
through the presentation on the OFDM implementation I did understand most
part of OFDM. But I still have few questions to ask:
1) how symbols_per_packet is calculated ? I know the following formula
symbols_per_packet = math.ceil(((4+options.size+4) * 8) /
options.occupied_tones)
but why 4+4 ? why these 8 bytes are added to calculate the symbol per
packet?
If these 8 bytes are for packet header and CRC32 ??
2) Why 2 is added to following formula while calculating samples_per_packet
?
samples_per_packet = (symbols_per_packet+2) *
(options.fft_length+options. cp_length). If this 2 is for preamble
symbols?
3) How many preamble symbols are inserted for one packet ? I think there is
one preamble symbol for one packet ? right ?
4) What is the format of OFDM packet transmitted. I got the following idea
after reading the code
------------------------------------------------------------------------------------------------------------------
packet Head(4bytes) | payload(option.size bytes) | CRC32(4bytes) |
something extra(1byte)
--------------------------------------------------------------------------------------------------------------------
my question is what is the purpose of packet head ? And what is
this* last
byte* for ? I know this byte comes from the following code
pkt_dt = ''.join((payload_with_crc, '\x55'))
what is its purpose ??
5) I know from the source code that whitening is done in order to ensure
transition in data. am I right? But what is effect of variable
"*whitener_offset"
?*it is set to 0.
6) Which thing really invokes the call to rx_callback() ?
Thank you very much for precious time. waiting for your response
Best Regards
Usman
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