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[Discuss-gnuradio] changing carrier map in ofdm

From: Sahoo, Anirudha
Subject: [Discuss-gnuradio] changing carrier map in ofdm
Date: Tue, 12 Mar 2013 12:03:07 -0400


  I have modified “benchmark_ofdm_rx.py” (and tx) so that the transmitter and receiver

can change the subcarrier map (based on some event, e.g., sensing outcome) and

send packet with the new carrier map.  I have a simple handshake protocol through

which the sender and receiver synchronize their carrier map setting.

I am seeing the following problem:

  Even though the two sides are with the same carrier map, sometimes the receiver

does not receive packets (although sender is sending the packets). This happens

at a very high rate. At other times packets are received correctly.  The sender and

the receiver (USRP N210) are connected through a channel emulator, which emulates a perfect

channel (so it could not be because of channel error).


    As per my understanding, resetting carrier map (done in “digital_ofdm_mapper_bcv.cc”) is

asynchronous. So, the python layer resets the carrier map and then at a later time the ofdm_mapper

actually sets the carrier map in the usrp device (through its “work()” function). So, I thought, perhaps

the receiver is not ready to receive next set of packets using the new carrier map. So, I put a

sleep(0.5sec) on the sender side after sender resets its carrier map to give enough time to the

receiver. But that did not fix the problem.

   Will appreciate if someone can let me know what could be the problem and how to fix it.


thanks and regards


--Anirudh Sahoo

Advanced Network Technology Div.

National Institute of Standards and Technology (NIST)

100 Bureau Drive,

Gaithersburg, MD - 20878

Room – B230, bldg.- 222

Phone- 301-975-4439


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