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

[Xavier Arteaga]

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
>>> _______________________________________________
>>> srslte-users mailing list
>>> srslte-users at lists.softwareradiosystems.com
>>> http://www.softwareradiosystems.com/mailman/listinfo/srslte-users
>>>
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