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[Discuss-gnuradio] [USRP2] - BBN 802.11b project - transmitter and recei

From: Juan Ramon Gutierrez Agullo
Subject: [Discuss-gnuradio] [USRP2] - BBN 802.11b project - transmitter and receiver issue
Date: Thu, 17 Dec 2009 16:37:11 +0100

Hello everyone,

I was running the examples proposed ( bbn_80211b_tx.py & bbn_80211b_rx.py ) and I noticed that something was wrong. First of all, I've installed succesfully GNU Radio toolkit and BBN project.
The issue is:
I run bbn_80211b_tx.py (transmitter) with an USRP2 in a computer with random arguments (f=2.4GHz, ...) and at the same time I run bbn_80211b_rx.py (receiver) with another USRP2 in another computer with random arguments too. And the result is....


$ ./bbn_80211b_tx.py
>>> gr_fir_ccf: using SSE

Network interface:  eth0
USRP2 address:  xx:xx:xx:xx:xx:xx (MAC hidden)
Using TX d'board id 0x0060
Tx baseband frequency:  2.4G
Tx DUC frequency:  0
Tx residual frequency:  0
Tx interpolation rate:  4
Samples per data bit:  25


Hello world

Four score ...
[11 textlines]
... shall not perish from the earth.

Sending pkt  0
Sending pkt  1
Sending pkt  2
Sending pkt  3
Sending pkt  4
Sending pkt  5
Sending pkt  6
Sending pkt  7
Sending pkt  8
Sending pkt  9

>>> gr_fir_ccf: using SSE
Recieved (short) header!
  signal: 0x50
  service: 0xCD
  length: 0x3ADD
  crc: 0x7B3B
Calculated crc: 0xADB7
*** BAD CRC ***

Recieved header!
  signal: 0x1B
  service: 0x26
  length: 0xCB69
  crc: 0xD9EA
Calculated crc: 0xE01A
*** BAD CRC ***

Recieved (short) header!
  signal: 0x00
  service: 0xA5
  length: 0x111D
  crc: 0xCA9E
Calculated crc: 0xEE55
*** BAD CRC ***

(... and more) still receiving frames when the transmitter isn't running.

I've been reading the code of the tx and don't see where I could test the value of the fields (signal, service, length, crc) have each packet.
Am I running propertly the examples? I don't have too much experience with this code.
Why rx calculates always a bad CRC?

Thank you very much for your help,

Juan Ramon Gutierrez Agullo <address@hidden>

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