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.muel...@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!
 >