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" <mmuel...@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.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!
>> >
