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[Discuss-gnuradio] problem with 2Mbps of BBN code(802.11b)


From: Mohammad Hamed Firooz
Subject: [Discuss-gnuradio] problem with 2Mbps of BBN code(802.11b)
Date: Sun, 11 Nov 2007 23:48:17 -0700
User-agent: Internet Messaging Program (IMP) H3 (4.1.4)


   Hi
I hope at least one of the members of BBN group read this email.
I used BBN implementation of IEEE802.11b to receive packets from
commercial products. So I always use Barker code as the spreading key.
As it had been reported before, Their code works with 1Mbps and
doesn't work with 2Mbps. I cannot understand why. Since bandwidth of
DBPSK and DQPSK are the same, the problem is not because of low
sampling rate. I went precisely through thier code step by step and
everything seems to be correct. In fact, there is a little difference
between 1Mbps and 2Mbps modes.
To explain the problem clearly I copy and paste results of receiving
preamble and header of the short PLCP. You may know that for short
PLCP, preamble is sent by 1Mbps while Header is transmitted using
DQPSK (2Mbps) and both of them uses Barker code.

Recieved (short) header!
   signal: 0xBA
   service: 0xE7
   length: 0x640D
   crc: 0x388A
Calculated crc: 0x5112
Recieved (short) header!
   signal: 0xFF
   service: 0xCB
   length: 0x1A50
   crc: 0x2C29
Calculated crc: 0x761C
Recieved (short) header!
   signal: 0xF9
   service: 0x11
   length: 0x8340
   crc: 0x8B78
Calculated crc: 0x5D2A
Recieved (short) header!
   signal: 0x31
   service: 0x1F
   length: 0xC729
   crc: 0xA902
Calculated crc: 0x255D
Recieved (short) header!
   signal: 0x04
   service: 0x09
   length: 0x9170
   crc: 0xBD57
Calculated crc: 0x67E8

Almost never header is received correctly. I am looking for the reason
of the bug. As I mentioned before it is not because of low sampling
rate (the sampling rate is 8MSPs)

regards,
hamed






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