[srslte-users] Measuring propagation time between srsLTE and a commercial UE

[Antonio Albanese]

Hey Xavier, all,

As far as I have understood, the LTE standard prescribes to measure the
time advance but srsLTE uses a fixed value. This would mean that there is
no way to measure the propagation time by directly calling the function we
mentioned before. Am I right?

Thank you again!

Antonio

Il giorno mar 4 dic 2018 alle ore 11:06 Xavier Arteaga <
xavier at softwareradiosystems.com> ha scritto:

> Hi Antonio,
> You can get some theory here
> <http://howltestuffworks.blogspot.com/2014/07/timing-advance-and-time-alignment-timer.html>
> .
>
> There is a fixed Tx/Rx time offset, you need to calibrate setting
> time_adv_nsamples in the ue.conf file.
>
> Regards,
> Xavier
>
>
> On Mon, 3 Dec 2018 at 19:20, Antonio Albanese <antonioalbanese15 at gmail.com>
> wrote:
>
>> Hi Justin, all,
>>
>> Thank you for you prompt feedback.
>>
>> I played a bit with the *rach_detected()* function but I always get zero
>> offset. Then I had a look at *run_tti() *in srsenb/phy/prach_worker.cc
>> which calls the function *srslte_prach_detect_offset(). *With the latter
>> I always get offset equal to 1.7us, that is not compatible with my
>> propagation environment (a small lab room) . Do you know if 1.7us is the
>> minimum granularity ensured by the 3GPP standard? Are you aware of any
>> other reason why I always get the same value?
>>
>> Thanks and Regards,
>> Antonio
>>
>> Il giorno lun 3 dic 2018 alle ore 10:06 Justin Tallon <
>> justin.tallon at softwareradiosystems.com> ha scritto:
>>
>>> Hey Antonio!
>>>
>>> This feature is a part of the standard of LTE as it is needed to
>>> synchronize the Downlink and the Uplink, it is called Time Advance and it
>>> appears in the rach_detected() function in srsenb/src/mac/mac.cc .
>>>  You could print it to a file during the attach procedure directly from
>>> this function.
>>>
>>> Hope this helps!
>>>
>>> Regards,
>>> Justin
>>> ____
>>> Justin Tallon Ph.D.
>>>
>>> Software Radio Systems (SRS)
>>> http://www.softwareradiosystems.com
>>>
>>> +353-86-067-0753 | justin.tallon at softwareradiosystems.com
>>>
>>>
>>> On Mon, Dec 3, 2018 at 9:16 AM Antonio Albanese <
>>> antonioalbanese15 at gmail.com> wrote:
>>>
>>>> Hello everyone,
>>>>
>>>> I need to measure the propagation time between a srsLTE eNB and a
>>>> commercial UE.
>>>> My initial idea was to measure the Round Trip Time of a couple of
>>>> exchanged messages by looking at the eNB pcap file. Apparently, the CPU
>>>> time is dominant (leading to a RTT of around 1 ms in my lab environment)
>>>> and I could not figure out how to discard it. Indeed, I doubt it would be
>>>> even possible to do it using a commercial UE.
>>>>
>>>> My current idea is to use the built-in synchronization module of srsLTE
>>>> to get a measure of the time offset between eNB and UE. I am having a
>>>> closer look at the physical layer functions but it takes me a lot of time
>>>> to understand the reasoning behind most of them.
>>>>
>>>> Has anyone tried to measure the time offset this way before? Do you
>>>> have any other suggestion on how to do do it?
>>>>
>>>> Thanks a lot!
>>>> Antonio
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>>>>
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>
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