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

[Antonio Albanese]

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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