sorry ,forget to reply the list
thank you --Ekko 2015-11-05 23:15 GMT+08:00 Marcus Müller <marcus.muel...@ettus.com>: > Hi Ekko, > > please reply to the list, not to individual people :) > > 1.i can use source block generate digita signal, > > Every block in GNU Radio is a digital block (your computer is a digital > device)! > > 2.i am not sure whether "chunks to symbol"block make the job of > digital-to-analog > > no. Digital to analog conversion only happens in your SDR peripheral, in > your case, the USRP. > > 3.mixing it up to carrier ferq is done by uhd_sink right? > > No, not by the usrp_sink (which is but a piece of software), but by the > hardware in the USRP. > > Best regards, > Marcus > > > On 11/05/2015 04:11 PM, chai E wrote: > > hello marcus > as A newer ,i have made some Stupid questions， > so very thank you , for your Patiently answers， > > i connect the usrp“tx and rx pin whit a wire to imitate that no error,so i > think the ber should be zero. > > i got that this opion is wrong from your last email > > also > my question: > 1.i can use source block generate digita signal, > 2.i am not sure whether "chunks to symbol"block make the job of > digital-to-analog > 3.mixing it up to carrier ferq is done by uhd_sink right? > > thank you > > ---Ekko > > > > 2015-11-05 22:33 GMT+08:00 Marcus Müller <marcus.muel...@ettus.com>: > >> Hi Ekko, >> >> i connect the usrp“tx and rx pin whit a wire to imitate that no error,so >> i think the ber should be zero. >> >> If you still think that, you have understood neither mine nor Marcus >> Leech's email; I'm afraid I can only ask you to read them again. >> >> my problem is that if i want to use uhd_sink and source to test this >> grc,is there some other work i need to do compare with the connect of >> virtual sink +source. >> >> Again: Virtual sink/source are not doing *anything* to the signal, >> whereas the USRP does. >> I feel like I shouldn't be simplifying as much, but consider this: >> digital complex baseband is *in theory **equivalent* to a real RF >> bandpass signal, but it's not the same. >> If you directly connect digital things (which is what virtual sink/source >> does) then it would be like taking a cake recipe, and giving it to your >> neighbor, to read it. Your neighbor will have no problems reading it. >> >> Transmitting something with a real piece of SDR hardware and receiving it >> is more like: >> >> 1. writing down that recipe (generating the digital signal) >> 2. baking that cake, (digital-to-analog conversion, yielding a >> physical baseband signal) >> 3. putting that in a box, (mixing it up to the carrier frequency) >> 4. bringing that box to a post office, (transporting it through a >> coax/microwave connection to your channel) >> 5. sending that box to your neighbor, (sending the RF signal through >> that channel, i.e. your direct cable) >> 6. your neighbor getting that box, (your receiver getting that signal) >> 7. taking the cake out of the box, (receiver mixes down to I/Q >> baseband), >> 8. and decomposing the cake to finally (analog-to-digital conversion) >> 9. get an estimate for the original recipe (SDR algorithm) >> >> You will *never* get a zero BER (which means of *infinitely *many >> recipes you transmit with the bake-cake-box-post-box-cake-decompose method, >> *every >> single one *is perfectly estimated), but you can get one that is >> *sufficiently >> small *for a given application if you can get your SNR to be good >> enough. >> >> Best regards, >> Marcus >> >> >> >> On 11/05/2015 02:37 PM, chai E wrote: >> >> hello marcus >> i connect the usrp“tx and rx pin whit a wire to imitate that no error,so >> i think the ber should be zero. >> my problem is that if i want to use uhd_sink and source to test this >> grc,is there some other work i need to do compare with the connect of >> virtual sink +source. >> this is my question : with the connect of virtual sink+source the ber is >> zero ,i think with the connect of uhd_sink+source the ber should be 0.01 or >> other number clear to zero,but when i use uhd_sink +source the ber is clear >> to 1. >> thank for you reply >> >> --Ekko >> >> 2015-11-03 22:49 GMT+08:00 Marcus Müller <marcus.muel...@ettus.com>: >> >>> 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 >>> >>> >>> 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 >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing >>> listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> Discuss-gnuradio@gnu.org >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> > >
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