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 > <mailto: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 <mailto: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 list >>> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > >
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
