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List:       gnuradio-discuss
Subject:    =?UTF-8?B?UmU6IOWbnuWkje+8miDlm57lpI3vvJogUHJvYmxlbXMgaW1wbGVtZW50?= =?UTF-8?Q?ing_USRP_b210_dual_ch
From:       Marcus_Müller <mueller () kit ! edu>
Date:       2022-12-08 10:23:31
Message-ID: 028d4a71-5d7f-a726-9e68-3af6b5dc9bec () kit ! edu
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On 12/7/22 13:49, 能书能言 wrote:
>     The number of data packets in ① is not correct, but the number of 
> data packets in ② is correct. Therefore, to avoid more problems, I 
> choose ②.
You were probably operating on a different frequency than you've thought!
> By viewing the pictures in the attachment and your explanation, f_ RF 
> is LO frequency? Then the two channels share one LO, so setting f_ 
> Offset adjusts the frequency to f_ target?
Exactly!
>      I tried the following:
>         freq1=   2.4G
>         freq2=   2.39G
>         lo_off1=   5M
>         lo_off2=  -5M
>         samp_rate=300K
>     But the problem still exists, and the bit error rate is very high : (
well, there might be many reasons for that; one might be that the 
sampling rate of 300 kHz is very low for the USRP, so filtering might be 
suboptimal.
> Another thing I forgot to say is that I did a dual channel 
> transmission experiment before (I call it experiment A. ), and the 
> parameter settings are the same as when I first set them（freq1 = 2.4G, 
> freq2=2.39G, lo_off1=2M, lo_off2=-2M,samp_rate=300k）,which performs 
> very well.

But you cannot have been operating on the frequencies you thought you 
were using, so that success is a bit meaningless?

Best regards,

Marcus

> The only difference between experiment A and this experiment now is 
> that the modulation of the signals on the RFA and RFB of experiment A 
> are different. I copied the USRP sink and USRP source components 
> directly from the GRC of experiment A, and the parameter settings are 
> the same, experiment A performed very well, but in this experiment a 
> high BER occurred, so now I am confused where the problem lies
> Best regards！
>
>
> ------------------ 原始邮件 ------------------
> *发件人:* "Marcus Müller" <mmueller@gnuradio.org>;
> *发送时间:* 2022年12月7日(星期三) 下午5:37
> *收件人:* "discuss-gnuradio"<discuss-gnuradio@gnu.org>;
> *主题:* Re: 回复： Problems implementing USRP b210 dual channel 
> transceiver
>
> Sorry, typo, hit ctrl-enter to send accidentally when trying to fix 
> it. Let me say it
> correctly:
>
> Re: ① But you receive packets! So that's a good thing, I guess?
>
> Re: ② So, maybe the attached figure helps. The offset is the 
> difference between the
> physical LO frequency f_{RF}, and the center frequency of what becomes 
> your baseband.
>
> So, I incorrectly said "the offsets need to add up to 10 MHz"; correct 
> would be to say that
> freq1-offset1 = freq2-offset2.
> Now, since freq2 = freq1 - 10 MHz follows
> freq1-offset1 = freq1 - 10 MHz - offset2
> 10 MHz = offset1 - offset2
>
> Note that offsets can be negative.
>
> Best regards,
> Marcus
>
> On 07.12.22 10:30, Marcus Müller wrote:
> > Your LO offset still don't add up to the difference between freq1 
> and freq2. What
> > frequency is the physical LO supposed to have? It cannot have 
> frequency 2.4 GHz - 5 MHz
> > and 2.39 + 2 MHz at the same time. These are different numbers!
> >
> > Best regards,
> > Marcus
> >
> > On 07.12.22 09:09, 能书能言 wrote:
> >> Hi,
> >>      Thank you for your reply, based on your suggestion I have 
> tried the following:
> >>      ①No LO offset set (no uhd.tune_request)
> >>         Ch0:Center Freq : freq1
> >>         Ch1:Center Freq : freq2
> >>         （freq1 = 2.4G, freq2=2.39G,samp_rate=300k）
> >>       ②Set LO Offset
> >>         Ch0:Center Freq : uhd.tune_request(freq1,lo_off1)
> >>         Ch1:Center Freq : uhd.tune_request(freq2,lo_off2)
> >>         （freq1 = 2.4G, freq2=2.39G, lo_off1=5M, 
> lo_off2=5M,samp_rate=300k）
> >>       or （freq1 = 2.4G, freq2=2.396G, lo_off1=2M, 
> lo_off2=2M,samp_rate=300k）
> >>       or （freq1 = 2.4G, freq2=2.396G, lo_off1=2M, 
> lo_off2=-2M,samp_rate=300k）
> >>
> >>      for ①：
> >>      In this case, the number of packets received is incorrect and 
> the problem becomes
> >> more serious.
> >>      for ②：
> >>      In this case the BER is still very high (I don't think it's my 
> system because the
> >> transmit power is set to 1 (Normalized) and the BER is quite low 
> when using one RF
> >> channel, but I still think I'm using the USRPB210's dual channel 
> transmission mode
> >> incorrectly)
> >> Best Regards！
> >>
> >> ------------------ 原始邮件 ------------------
> >> *发件人:* "Marcus Müller" <marcus.mueller@ettus.com>;
> >> *发送时间:* 2022年12月6日(星期二) 晚上8:49
> >> *收件人:* "discuss-gnuradio"<discuss-gnuradio@gnu.org>;
> >> *主题:* Re: Problems implementing USRP b210 dual channel transceiver
> >>
> >> There's only one physical TX LO; so either you just don't specify 
> offsets, OR they must
> >> add up to the difference between the two target frequencies.
> >>
> >> In your case, the difference is 10 MHz, but your offsets don't add 
> up to 10 MHz, and
> >> you're requesting something impossible.
> >>
> >> Best regards,
> >> Marcus
> >> On 06.12.22 12:45, 能书能言 wrote:
> >>  > Hi,
> >>  >      I am using OFDM + USRPB210 for data transmission. I am 
> using two USRPB210s, one
> >> being
> >>  > used as a transmitter and the other as a receiver. When I use 
> only one of the channels
> >>  > (RFA or RFB) the data can be transmitted properly. I needed to 
> transmit two different
> >> data
> >>  > at the same time, so I used both the USRP RFA and RFB. the 
> baseband processing part
> >> of the
> >>  > link was the same for both channels (including channel coding, 
> modulation, FFT,
> >> etc.), but
> >>  > at this point I found that I was transmitting data with a very 
> high BER (for both
> >> links).
> >>  > again, mentioning that there was no problem when sending on one 
> channel alone, I The
> >> USRP
> >>  > Sink and Source settings are shown in the attached picture.
> >>  >      where
> >>  >      freq1=2.4G
> >>  >      freq2=2.39G
> >>  >      lo_off1=2M
> >>  >      lo_off2=-2M
> >>  >      samp_rate=300K
> >>  >     The two signals are separated using different frequencies, I 
> don't think there
> >> should
> >>  > be any interference between them, and I have troubleshot errors 
> other than USRP
> >> source and
> >>  > sink, so I think there is something wrong with my parameter 
> settings, or I am using the
> >>  > two RF channels in an incorrect way. How should I modify 
> this?Looking forward to your
> >>  > response！
> >>  >
> >>  > Best Regards!
> >>  >

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