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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