On 04/13/2021 10:17 AM, 王璀 WANG Cui wrote:
I am testing with software generated GPS L1 C/A signal and the
sampling rate is 1.023M sps, same as the C/A code rate 1.023M chips/s.
The result baseband signal file can be tracked and positioned by
gnss-sdr receiver.
So I am wondering: I am not using 2B sampling rate (say 2.046 sps),
but seems the signal is still well recognized and decoded?
GPS L1 C/A is a BPSK system operating at a notional 1.023Mbits/second,
which as a BPSK system occupies a bandwidth of 2X the
notional bit rate, or 2.046MHz, requiring actually a minimum sample
rate of 4.096Msps. That's according to my cursory
understanding of the GPS L1 C/A signal, but there are others here
with more experience with GPS than me.
*From:*Marcus D. Leech <patchvonbr...@gmail.com>
*Sent:* Tuesday, April 13, 2021 10:03 PM
*To:* 王璀WANG Cui <iucg...@msn.com>
*Cc:* USRP-users@lists.ettus.com
*Subject:* Re: [USRP-users] How to tx s16 file with tx_samples_from_file
On 04/13/2021 12:21 AM, 王璀 WANG Cui wrote:
I am not expert in this, do you mean if sample in real format, we
must double the sample rate, to contain both I phase and Q phase
information?
In my application, I just sample at baseband digital code rate
(Nyquist Freq), and seems it works well when transmit. And when I
convert it into I/Q, it just doubled the size, but seems doesn’t
bring more benefit?
Is there good article can help me to clarify this concept? :)
Well, this is drifting into much-more-generic territory about signals
and signal processing.
Indeed, the Nyquist sampling theorem states that a signal with
bandwidth B must be sampled at 2B in order to properly contain
all the information in a signal.
That can either be achieved by real-mode sampling at 2B, or
complex-baseband sampling at B. You can see that for the
same sample-size, the amount of space occupied by such samples is
identical.
I think we need to understand exactly what you have sampled, and how,
and at what rate. I think *you* need to understand
that in more depth as well, before we can provide much meaningful help.
*From:*Marcus D Leech <patchvonbr...@gmail.com>
<mailto:patchvonbr...@gmail.com>
*Sent:* Tuesday, April 13, 2021 12:08 PM
*To:* 王璀WANG Cui <iucg...@msn.com> <mailto:iucg...@msn.com>
*Cc:* USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] How to tx s16 file with
tx_samples_from_file
No. A real-sampled signal would
Need to be sampled at twice the notional bandwidth. So the data
rate is the same.
Sent from my iPhone
On Apr 12, 2021, at 11:59 PM, 王璀 WANG Cui <iucg...@msn.com
<mailto:iucg...@msn.com>> wrote:
That make sense, I guess I would modify it to accept more format.
However, for the hardware side, it accept only Complex OTW
format, which means it need double bandwidth from host (I am
using B210, USB3). When transmit high sample rate signal, it
is very easy to underflow. If we can upgrade firmware to
handle format conversion on hardware level, it will ease a lot
on host computing resource and USB/NIC bandwidth and performance.
Thanks!
*From:*Marcus D Leech <patchvonbr...@gmail.com
<mailto:patchvonbr...@gmail.com>>
*Sent:* Tuesday, April 13, 2021 11:45 AM
*To:* 王璀WANG Cui <iucg...@msn.com <mailto:iucg...@msn.com>>
*Cc:* USRP-users@lists.ettus.com
<mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] How to tx s16 file with
tx_samples_from_file
The tx_samples_from_file application is just an example
application. You are free to modify it to meet your needs,
including converting real-samples data to complex baseband data
The hardware, however, supports complex baseband data, In
either sc16 or sc8 format “over the wire”. The host software
(whether that’s the tx_samples_from_file example code or your
own) is free to accept and convert files into the baseband
format accepted by the radio hardware.
Sent from my iPhone
On Apr 12, 2021, at 10:08 PM, 王璀 WANG Cui
<iucg...@msn.com <mailto:iucg...@msn.com>> wrote:
Thanks for reply.
However for RF signal, IQ Complex signal double the file
size, which is quite inconvenient, it will be best that
USRP can natively support such format. (Even sometimes RF
signal is in 4-bit, 1 bit format, and convert to I/Q will
be more than 10 times larger...)
*From:*Marcus D Leech <patchvonbr...@gmail.com
<mailto:patchvonbr...@gmail.com>>
*Sent:* Tuesday, April 13, 2021 09:44 AM
*To:* ?? WANG Cui <iucg...@msn.com <mailto:iucg...@msn.com>>
*Cc:* USRP-users@lists.ettus.com
<mailto:USRP-users@lists.ettus.com>
*Subject:* Re: [USRP-users] How to tx s16 file with
tx_samples_from_file
Complex baseband is the natural format for this stuff. If
you have real-sampled data you’ll have to convert it into
complex baseband first.
Sent from my iPhone
On Apr 12, 2021, at 9:32 PM, ?? WANG Cui
<iucg...@msn.com <mailto:iucg...@msn.com>> wrote:
Hi,
When I try tx_samples_from_file example, looks like it
only take Complex data format.
However I have signal file in RF direct sample format
(each data element represent a sample value), say it
is “s8” or “s16” format as defined in UHD term.
I wonder how can I transmit such file? Or must I
convert it into Interleaved I/Q (Complex) format?
Thanks in advance,
iucganw
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