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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