Re: 回复： Problems implementing USRP b210 dual channel transceiver

[Marcus Müller]

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!
> >  >

bw_vis.png
Description: PNG image