Re: [Discuss-gnuradio] BBN 802.11 bbn_80211b_rx.py

[yyzhuang]

But when I use one usrp for tx and another for rx, no need to specify "-d 8".
Could you tell me why is this? Thanks


Mohammad Hamed Firooz wrote:
> 
> 802.11b standard use barker spreading, So if you want to receive data 
> from a standard 802.11b transmitter you have to use barker. For 
> decimation it should be as high as possible because 802.11b receiver 
> needs more more than 22M complex sample per sec to work correctly. But 
> USB cannot handle that much bit-rate so we have to downsample it to 
> 8McSps. This reduces SNR which reduces receiver performance and range 
> of activity.
> 
> regards,
> hamed
> 
> Quoting yyzhuang <address@hidden>:
> 
>>
>> Thanks.
>>
>> When I use "./bbn_80211b_rx.py -f 2.44G -v -b ", no packets get printed
>> out.
>> But the output of "./bbn_80211b_rx.py -f 2.462G -d 8 -b -v " is normal,
>> we
>> got a bunch of packets:
>>
>> Bits Per Encoded Sample = 8
>> adc frequency =  64000000
>> decimation frequency =  8
>> input_rate =  8000000
>> gain =  45.0
>> desired freq =  2462000000.0
>> baseband frequency 2460000000.0
>> dxc frequency -2000000.0
>> Samples per data bit =  8
>>>>> gr_fir_ccf: using SSE
>> PKT: len=77, rssi=-22, src=00:13:46:16:28:AA, time=557560, rate=1 Mbps
>> PKT: len=77, rssi=-29, src=00:13:46:16:28:AA, time=1786312, rate=1 Mbps
>> PKT: len=77, rssi=-26, src=00:13:46:16:28:AA, time=1991192, rate=1 Mbps
>> ...........
>>
>> I checked the code:
>>
>> parser.add_option("-d", "--decim", type="int", default=16,
>>                          help="set fgpa decimation rate to DECIM
>> [default=%default]")
>> parser.add_option("-b", "--barker", action="store_true",
>>                          default=False,
>>                          help="Use Barker Spreading [default=%default]")
>>
>> -d 8 is setting the fpga decimation rate to 8, and -b means Use Barker
>> Spreading. How should we know what decimation rate and spreading to use?
>> Thanks.
>>
>> BTW, if one ursp for tx and one for rx, we dont have to specify these
>> options:
>> on the sending side: ./bbn_80211b_rx.py -f 2.44G -v -b
>> Using TX d'board A: Flex 2400 Tx MIMO B
>>>>> gr_fir_ccf: using SSE
>> spb:       8
>> interp:   32
>> (spb = samples/baud, default 8; interp = fpga interpolation rate, default
>> 32
>> )
>>
>> on the receiving side: ./bbn_80211b_tx.py -f 2.44G
>> Bits Per Encoded Sample = 8
>> adc frequency =  64000000
>> decimation frequency =  16
>> input_rate =  4000000
>> gain =  45.0
>> desired freq =  2440000000.0
>> baseband frequency 2436000000.0
>> dxc frequency -4000000.0
>> Samples per data bit =  8
>>>>> gr_fir_ccf: using SSE
>> PKT: len=1477, rssi=-10, src=20:61:6e:64:20:73, time=16024824, rate=1
>> Mbps
>> PKT: len=1477, rssi=-12, src=20:61:6e:64:20:73, time=16036920, rate=1
>> Mbps
>> PKT: len=1477, rssi=-11, src=20:61:6e:64:20:73, time=16049016, rate=1
>> Mbps
>> PKT: len=1477, rssi=-13, src=20:61:6e:64:20:73, time=16061112, rate=1
>> Mbps
>>
>> Thanks!
>>
>>
>> Brian Padalino wrote:
>>>
>>> On Mon, Jul 28, 2008 at 12:28 PM, yyzhuang <address@hidden> wrote:
>>>>
>>>> What does "combination of the LO in the front end and the digital
>>>> downconverter" mean please?
>>>
>>> For general radio architecture, please see:
>>>
>>>     http://en.wikipedia.org/wiki/Superheterodyne
>>>
>>> Generally, the LO/synthesizer has some discrete step size (12.5kHz,
>>> 250kHz, etc).  To get down to baseband, the resultant signal is then
>>> shifted in frequency down using the digital downconverter:
>>>
>>>     http://en.wikipedia.org/wiki/Digital_Down_Converter
>>>
>>> Brian
>>>
>>>
>>> _______________________________________________
>>> Discuss-gnuradio mailing list
>>> address@hidden
>>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>
>>>
>>
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>>
>>
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> 
> 
> 
> ----- End forwarded message -----
> 
> 
> -- 
> Mohammad Hamed Firooz
> ECE Department, U of Utah
> Salt Lake City
> UT, 48112
> 
> 
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