[srslte-users] Dual Monitor Mode for Radio

Mon Feb 4 14:32:53 UTC 2019

My response wasn't posted to the list until today, so since the time I 
sent the message to the list I've made a bit of progress. I was able to 
capture the RAR messages and get the timing advance that the eNodeB sent 
to the DUT UE. Oddly, though, it didn't always catch the RAR messages. 
I'm not sure if it was due to interference, as we have some testing of 
amplifiers going now and again here in the lab, with some being near the 
downlink frequency. At this stage of the process, though, it doesn't 
matter. I can just change the frequency band being used.

Now I just have to figure out how to get another receiver process 
running within the srsue code base that uses that timing advance to know 
when it can "listen".

Regards,

-Saverio

On 2/1/2019 8:43 AM, Saverio Mercurio wrote:
> Thanks for the response.
>
> Initially we were looking at by starting with the srsenb code, but 
> that started to get gnarly. We had also been using the pdsch_ue 
> example. While that only looks at the downlink, it did allow us to get 
> some of the information we were trying to get. Hence, we reevaluated 
> the problem and considered using srsue as the start point. However, 
> before getting too far into it we wanted to ask to see if it's even 
> practical to do this. I did know that we initially had to get the 
> monitor UE to think it had sent the PRACH and get it to catch the RAR 
> as if it had sent it. I will try your suggestions.
>
> Initially we were also looking at using some tool like Airscope. The 
> blog entry for that has links, but the product itself doesn't seem to 
> actually exist.
>
> Regards,
>
> -Saverio
>
> On 1/31/2019 2:21 PM, Justin Tallon wrote:
>> Hey Saverio,
>>
>> Have you started to do this or is this just a plan at the moment?
>> If you have not started, this is how I would start.
>>
>> The first thing you want is the monitor UE to receive the RAR that 
>> has been sent to the DUT UE so you can pull out the time advance. 
>> However, you don't want the monitor UE to make any transmission.
>>
>>  it will need to behave as normal up until the point that it sends 
>> the prach, you want to let the monitor UE think its sent the PRACH 
>> but to not actually send it so just set the UE to send zeros in 
>> phch_common.worker_end() .
>> Secondly, you will need to have the monitor UE to look for a RAR of 
>> all possible prach preambles since you don't know which preamble id 
>> has been used by the DUT UE. A good way to start would be to set the 
>> number of preamble ids to the minimum in the sib.conf by 
>> setting num_ra_preambles to 4. Change proc_ra.c in the monitor UE to 
>> allow all preamble RAs by getting rid of 
>> the (rar_pdu_msg.get()->get_rapid() == sel_preamble) conditional. 
>> Then you should process the TA command intended for the other UE.
>>
>> See how this goes as a first step, or sorry if you have already done 
>> this!
>>
>>
>> Regards,
>> Justin
>> ____
>> Justin Tallon Ph.D.
>>
>> Software Radio Systems (SRS)
>> http://www.softwareradiosystems.com 
>> <http://www.softwareradiosystems.com/>
>>
>> +353-86-067-0753 | justin.tallon at softwareradiosystems.com 
>> <mailto:justin.tallon at softwareradiosystems.com>
>>
>>
>> On Thu, Jan 31, 2019 at 8:21 PM Saverio Mercurio 
>> <smercurio at prescientwireless.com 
>> <mailto:smercurio at prescientwireless.com>> wrote:
>>
>>     Hi,
>>
>>     We're trying to set up a system to test a UE. I'm somewhat
>>     restricted in
>>     what information I can give, but I will try to convey as much as
>>     I can.
>>     The DUT (Device Under Test) UE is implemented using srsue, with
>>     another
>>     radio running srsenb. The radios we are using are the Ettus B200.
>>     For
>>     part of the testing we would like to monitor part of the
>>     communication
>>     between the eNodeB and the UE by using a third radio. We're not sure
>>     about the best way to go about this. In a way, it's sort of half of
>>     srsenb and half of srsue. We thought of having this third radio
>>     running
>>     srsue with the same configuration as the DUT UE. That would set
>>     up the
>>     monitor radio to receive the same downlink signal that the DUT UE
>>     receives. By having it sit right next to the DUT the timing advance
>>     information the DUT UE receives from the eNodeB during connection
>>     would
>>     also apply to the monitor UE. Once this information is acquired
>>     we can
>>     force the monitor UE to think it's connected and attached. With the
>>     timing information acquired, would this allow us to synchronize the
>>     timing with the DUT UE's uplink message timing? This monitoring DUT
>>     would not be transmitting, so we wanted to reconfigure that
>>     antenna to
>>     receive the DUT UE's uplink. We're not sure about how to go about
>>     setting up a second receiver with the srsue code. Do you have any
>>     suggestions?
>>
>>     Thanks
>>
>>     -Saverio
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>
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