On 11/03/2015 09:49 AM, Marcus Müller wrote:
Hi Ekko,
>difference between uhd_sink+uhd_source with virtual_sink+virtual_source
uhd_sink / _source talk to radio *hardware*, virtual sink and source
are just "invisible" GRC connections, and simply talk to the block
that is attached to them.
> in this grc when i use virtual_sink+virtual_source,the ber is zero
obviously, because it's simply a direct connection, no noise, hence,
no errors.
> but when i use uhd_sink+uhd_source, and i connect the B200's tx and
rx port with a RF wire. but the ber is not zero.
Real world radios have noise (and other imperfections), and hence
there's bit errors. That's the core problem of digital communications,
and has been for the last couple of decades.
> how can i use uhd_sink+uh_source just like virtual_sink+virtual_source
You can't. One reproduces perfectly, the other is the real RF world.
Getting information across the wireless channel without error is what
science has been working on, and since Shannon we know that you can
not achieve a transmission with arbitrarily low BER over a channel
with limited SNR at arbitrary speed. Every real channel has limited SNR.
What you do is apply your signal processing and communication theory
skills to counteract the effects of the channel, check correctness and
correct errors (if possible), possibly make the sender retransmit etc;
but you will never break Shannon's limits.
Best regards,
Marcus
Also, if you loop-back directly, without intervening attenuators, your
"channel" will be very distorted, and you run the risk of damaging
the receiver portion of the hardware.
On 11/03/2015 01:58 PM, chai E wrote:
hello all
i have a question about the difference between uhd_sink+uhd_source
with virtual_sink+virtual_source
the accessory is the grc file i am running.
in this grc when i use virtual_sink+virtual_source,the ber is zero
,in other words,the sorce file is same with the dest file
but when i use uhd_sink+uhd_source, and i connect the B200's tx and
rx port with a RF wire. but the ber is not zero.
i want to konw what is the difference ,and how can i use
uhd_sink+uh_source just like virtual_sink+virtual_source
--Ekko
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