Re: [Discuss-gnuradio] how to get wireless carrier signal in GNU Radio

[Shirve]

Hi Zenghao,

Thank you for your reply. I have few more queries regarding the carrier
sense module in probe_avg_mag_sqrd_c.cc file. It looks like to find the
presence of carrier in air, there is a variable d_unmuted, which is being
checked. This variable is set whenever pre_output_iir variable is more than
d_threshold value. I have two doubts about it.

First, How can d_threshold be compared with d_iir.prev_output variable? It
seems that d_ threshold is the ratio of Signal to Noise. Does it mean,
d_iir.prev_output is also ratio os signal ro noise?

Second, is there any way to define the threshold signal strength? Or does
the packet initiation detection not depended on carrier's strength and
rather dependent on S/N ratio? 

Hoping for the kind reply again.

- Sachin



Zenny Zhang wrote:
> 
> Sachin,
> 
> Sure, here is the related code I use:
> 
>     # get a probe
>     alpha = 0.001
>     thresh = 30
> 
>     self.probe = gr.probe_avg_mag_sqrd_c(thresh,alpha)
> 
> 
>     # connect usrp to the probe
>     self._fg.connect(self.u, self.probe)
> 
> 
>     # wait until the medium is free
>     while objDemod1.probe.level() > threshold:
>         time.sleep(0.0001)
> 
> 
> Zhenghao
> 
> 
> On Thu, Oct 23, 2008 at 4:59 PM, Shirve <address@hidden> wrote:
>>
>> Hi Zhenghao,
>> Thank you for your valuable reply. I appreciate it. As per your supplied
>> information, I will start looking for CSMA code in tunnel.py, though if
>> you
>> can send me your code, it will be quite helpful too. I hope that using
>> tunnel.py code and help from you I will be able to get the carrier sense
>> capability for my application.
>>
>> Thanks
>> -Sachin
>>
>>
>> Zenny Zhang wrote:
>>>
>>> Sachin,
>>>
>>> I don't know if this is helpful, just sharing my experience.
>>>
>>> 1. You may want to check tunnel.py, in which there is a CSMA scheme --
>>> Eric told me this a couple of weeks ago.
>>> 2. It is possible to do some carrier sensing by ourself. You can just
>>> read the signal from the USRP and compare the signal strength level
>>> with a threshold. Of course a filter is needed. I tried this last week
>>> and it is working, although the threshold may need some tuning. If you
>>> need I can send you the code written in python.
>>>
>>> Zhenghao
>>>
>>> On Wed, Oct 22, 2008 at 6:19 PM, Shirve <address@hidden> wrote:
>>>>
>>>> Hi,
>>>> As per the current status of GNU Radio, I got to know that there is no
>>>> MAC
>>>> (CSMA) implementation. Therefore I am not sure if I can get the signal
>>>> from
>>>> signal processing blocks of GNU Radio about the carrier sensed by USRP
>>>> receiver.
>>>>
>>>> Please help me in this regard.
>>>>
>>>> Till now I am able to locate the message queue mechanism to get the
>>>> received
>>>> packets from the other USRP transmitter, which is in gr_msg_que.cc in
>>>> runtime library of GNUradio-core. But this mechanism just indicates the
>>>> received packets (correct or corrupted), while the signal sensing
>>>> (packet
>>>> start) starts much earlier than the complete packet reception.
>>>>
>>>> Is it possible to get the information about the wireless carrier signal
>>>> in
>>>> the vicinity of USRP receiver from the current GNU Radio framework? I
>>>> am
>>>> using GNU Radio 3.1.1 version.
>>>>
>>>> Your help will greatly help me in my goal. Thanks in advance and
>>>> expecting
>>>> your kind reply.
>>>>
>>>> - Sachin
>>>> --
>>>> View this message in context:
>>>> http://www.nabble.com/how-to-get-wireless-carrier-signal-in-GNU-Radio-tp20120856p20120856.html
>>>> Sent from the GnuRadio mailing list archive at Nabble.com.
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Discuss-gnuradio mailing list
>>>> address@hidden
>>>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>>
>>>
>>>
>>> _______________________________________________
>>> Discuss-gnuradio mailing list
>>> address@hidden
>>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>
>>>
>>
>> --
>> View this message in context:
>> http://www.nabble.com/how-to-get-wireless-carrier-signal-in-GNU-Radio-tp20120856p20139200.html
>> Sent from the GnuRadio mailing list archive at Nabble.com.
>>
>>
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
>> address@hidden
>> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>
> 
> 
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> 
> 

-- 
View this message in context: 
http://www.nabble.com/how-to-get-wireless-carrier-signal-in-GNU-Radio-tp20120856p20169595.html
Sent from the GnuRadio mailing list archive at Nabble.com.