Meaning of some functions

Toate mesajele

• 28 iunie 2011 16:24

   

   
  

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  1) CopyGI(info->cSymbol, info->cSymbol + 128) in Ofdmsymbol.h

  - When I compare with NSDI09 paper (Sora: High Performance Software Radio Using General Purpose Multi-core Processors), this is equivalent to GI addition. However, I don't understand how this function works as GI addition.  Moreover, what is value of sizeof(vcs)?

  CopyGI: just copy the last few samples to the front of an OFDM symbol (:) you know why.).

  sizeof(vcs) is 128 bytes, and a vcs contains 4 complex16 samples.

  2) Window(Info->cSymbol, pcLast) in Ofdmsymbol.h

  - I have no idea on the meaning of this function

  windowing (Hamming window, Hanning window, bla bla bla....). Ref the window function in the 802.11a standard.

  3) UpsampleAndCopyNT(info, pcOutput, info->cSymbol, COMPLEX_PER_OFDM_SYMBOL) in Ofdmsymbol.h

  - I have no idea on the meaning of this function.

  This is an optional function.

  Upsample: If the sampling rate of your SORA is 44MHz, then you should use this function to upsample the baseband samples from 40MHz to 44MHz, so that SORA can communicate to a commercial card. If you are working on SORA to SORA communication, you can omit this function.

  CopyNT: convert the raw samples from complex16 to complex8 (8-bit raw IQ samples) and make sure all samples are written to transmission buffer.

  4) DigitalAGC<128 / vcs::size>(__pcTemp, pRxContextA->digitalAGC) in Arx_fd.c

  - I have no idea on the meaning of this function.

  Digital AGC: make samples fill the dynamic range of complex16, I think.

  5) When I compare receiving part in NSDI09 paper (Figure1), I don't find Decimation function and Remove GI function in SORA code. How these two functions realized in SORA code?

  Decimation: you can see this function: FetchDMADataTouchDownSampled. It performs the decimation.

  Remove GI: you can find the code like this in arx_fd.c:
  

          // ignore first 8 complexes

          // we use no. 8 - 72 to do fft, 

          // this has the same alignment for 24 - 84 complex in

          // long preamble

          __pcTemp += SYM_CP_SKIP; 

  Note “__pcTemp += SYM_CP_SKIP; ”  this is equivalent to removing GI.

   

  Hope my answers will help you!

  ---

  Danial.F

  • Marcat ca răspuns de Kun TanOwner 2 iulie 2011 03:00
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  • Mesaj
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• 2 iulie 2011 03:00

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  Hi Danial,

   

  Thank you for the answers! That is great!

   

  - Kun

  • Mesaj
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