I use the Shmdil and Cox gnuradio block and it does time recovery based on what I have
read. I also can retrieve the transmitted data.
But what I am confused about the presence of constellation rotation when I used
the USRP.
On Thursday, May 18, 2023 at 12:32:22 PM CDT, Marcus Müller
<mmueller@gnuradio.org> wrote:
Your OFDM receiver already does Schmidl&Cox, I thought? So, if you correctly
designed the
length of your OFDM symbols and the subcarrier spacing, that should be
sufficient. What
you described, a "constellation rotation for OFDM subcarriers" is
unproblematic; you're
doing subcarrier-wise multiplication with the inverse of your channel estimate,
anyways,
and that cancels that.
Best regards,
Marcus
On 18.05.23 19:08, Hamed Al-Zubi wrote:
> Okay. I need to figure out how can I do that.
>
> Thanks!
> HZ
>
> On Thursday, May 18, 2023 at 11:54:42 AM CDT, Marcus Müller <marcus.mueller@ettus.com
<mailto:marcus.mueller@ettus.com>> wrote:
>
>
> No, that's the opposite of what I said. (also, why would you need a GPSDO
when these USRPs
> are colocated?)
>
> You *always* have time offset at a receiver – due to the finiteness of the
speed of light.
>
> So, *any* working receiver you have has to have timing recovery, there's no
way around it.
> So, getting better hardware-level synchronization *does not help you at
all*. Not if you
> do it badly, not if you do it really really well.
>
> Best,
>
> Marcus
>
> On 18.05.23 18:21, Hamed Al-Zubi wrote:
>
> So, I have to get GPS modules and use GPSDO synchronization.
>
>
>
> On Thursday, May 18, 2023 at 11:20:02 AM CDT, Marcus Müller <marcus.mueller@ettus.com
<mailto:marcus.mueller@ettus.com>>
> <mailto:marcus.mueller@ettus.com> wrote:
>
>
>
> On 18.05.23 18:10, Hamed Al-Zubi wrote:
>> Actually, I don't know. I thought that by using PC clock in UHD sink and
source block in
>> gnuradio allows synchronization.
> Not in a way meaningful for synchronizing transceivers, no.
>> Also, I thought that Schmidl and Cox algorithm used for timing recovery in
OFDM receivers.
> Exactly, that's why your PC clock synchronization would contribute nothing,
even if it was
> more accurate. You just don't benefit from synchronization.
>>
>> On Thursday, May 18, 2023 at 10:46:38 AM CDT, Marcus Müller <mmueller@gnuradio.org
<mailto:mmueller@gnuradio.org>>
>> <mailto:mmueller@gnuradio.org> wrote:
>>
>>
>> Any OFDM receiver needs a timing recovery method anyways, so that has
nothing to do with
>> how well your PC is suitable for synchronizing two devices.
>>
>>
>> On 18.05.23 17:43, Hamed Al-Zubi wrote:
>> > Thanks for your response, Marcus!
>> > I have observed a constellation rotation for OFDM subcarriers when I use the PC
clock for
>> > synchronization. However, by using the channel model, I am able to see
the QPSK
>> > constellation.
>> >
>> > Thanks!
>> > HZ
>> >
>> > On Thursday, May 18, 2023 at 10:35:01 AM CDT, Marcus Müller
<marcus.mueller@ettus.com <mailto:marcus.mueller@ettus.com>
>> <mailto:marcus.mueller@ettus.com>> wrote:
>> >
>> >
>> > No, it's several orders of magnitude worse and generally insufficient for
anything where
>> > you need synchronization.
>> >
>> > Best,
>> > Marcus
>> >
>> > On 18.05.23 17:12, Hamed Al-Zubi wrote:
>> > Hello Dears,
>> >
>> > I would like to inquire about the synchronization of two USRPs X300, one
acting as a
>> > transmitter (Tx) and the other as a receiver (Rx). If both USRPs are
connected to the
>> same
>> > laptop, I'm wondering if the accuracy provided by PC clock synchronization is
similar (or
>> > close) to that achieved through GPSDO synchronization?
>> >
>> > Regards,
>> > HZ
>>