Re: [Discuss-gnuradio] signal cancellation example using GRC and USRP B210

[CEL]

Dear Inkyu,

there's no guarantee that the phases of both TX are exactly identical.
In fact, you should expect an unknown offset.

Also, you'll notice that your two antennas are at two different
positions in the room. You're accidentally building a beamforming
system! So, these nulls will not be everywhere in the room, but only in
a specific direction in the far field of the TX antenna. And with a
carrier frequency of nearly 6 GHz, a wavelength in air is

c/f ≈ (3·10⁸ m/s) / (6·10⁹ 1/s) = 0.05 m = 50 cm

and half that distance from a (single) transmit antenna would be the
distance at which two received signals would be exactly of opposite
phase.

So, I'm not sure what you want to demonstrate, but unless it's
beamforming, you're probably not doing it right :) Which is no shame,
but it would be interesting to hear what it is that you want to
achieve.

Best regards,

Marcus

On Fri, 2018-04-27 at 20:44 +0800, Inkyu Bang wrote:
> Hi, all !!
> 
> I am trying to make a simple example of signal cancellation using GRC.
> However, I did not get any good results.
> 
> Here is my setting
> 
> Plan: sending two sine wave with different phases and receiving canceled 
> signal (only noise)
> Center frequency: 5.89GHz (I am using the antenna supporting this center 
> frequency)
> Sampling rate: 5MHz
> Frequency of sine wave: 1kHz
> 
> USRP: B210
> Tx GRC flow graph: signal source block + USRP sink (two channels)
> Rx GRC flow graph: USRP sink + QT GUI time sink
> 
> When I send two sine signals, I used two RF chains in the same USRP.
> I received those signals at the other USRP.
> 
> I expected to see canceled signals (i.e., only noise level power in time 
> domain) 
> but still, I see sine wave signal.
> 
> I thought frequency offset in the receiving USRP is applied to both sine 
> waves.
> 
> Do I need to consider frequency offset first?
> Could anyone help me to solve this problem?
> 
> Thank you.
> Regards,
> 
> Inkyu
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