[srslte-users] srsUE sufferd scheduling request failed.

[Ismael Gomez]

On Wed, 25 May 2016 at 02:14 David Yu ( III ) <wcyu at iii.org.tw> wrote:

> Hi Ismael,
> We found that PUSCH was good with QPSK modulation when srsUE just ping to
> external server. No "scheduling request failed" arose.
> But in every time, PUSCH was bed with QPSK modulation when srsUE play
> youtube. And after 2~4 mins, "scheduling request failed" arose.
>
>
In that case that could be a CPU issue. In our tests we usually can watch
youtube perfectly in a dual-core system @ 10 MHz and have decent rates.
However, you have to make sure that the CPU is clocked to the maximum and
the power-saving clock governor is disabled (so that frequency is fixed to
a max always). Maybe another problem could be lack of GPU drivers and the
OS using the CPU for playing video?

Can you use other forms of testing, like iperf UDP flow from the ENB to the
UE for instance?

Do you have access to an Amarisoft ENB to verify that you see the same
behaviour?

1. What "scheduling request failed" stands for? Is it MAC layer issue?
>

That means that the ENB did not respond to a Scheduling Request (SR) signal
transmitted on PUCCH after some number of attempts (configured by the enb).


> 2. Have you ever suffered "scheduling request failed" on your srsUE?
>

This can happen eventually, as I said when you push the limits of the CPU
the system may loss synchronization and the SR signals is transmitted at
incorrect time slots. The UE follows the standardised procedure in this
case. When SR fails starts a PRACH with MAC CE if that fails starts
Reestablishment procedure.

One way to verify that it is not a CPU issue is to activate the "trace
mode" (type "t" in the terminal). You will see some RF messages printed in
the console if there is some problem with the sample flow.


> 3. What is the possible cause for "scheduling request failed"? except for
> UL/DL signal quality.
>

As I said before, CPU can lead to out of sync which then leads to SR
failure.


> Many Thanks.
>
> Regards,
> David
>
> -----Original Message-----
> From: Ismael Gomez [mailto:ismael.gomez at softwareradiosystems.com]
> Sent: Thursday, May 19, 2016 4:15 PM
> To: David Yu ( III ); srslte-users at lists.softwareradiosystems.com
> Subject: Re: [srslte-users] srsUE sufferd scheduling request failed.
>
> Hi David,
>
> Looking at your logs I see a problem with the Uplink. The Downlink is OK,
> the SNR is very good and most of the packets are received OK. In the UL
> however there are many NACKs on the PHICH, more or less ~50%, which means
> that the signal is very poor at the ENB. Every once a while, the ENB does
> not receive the SR signal from the UE (there are up to 4 attempts) and does
> not allocate the corresponding UL grant therefore the UE assumes the
> connection is lost and restarts RA procedure.
>
> You can try to increase the maximum number of SR attempts at the ENB, but
> I'd rather suggest that you improve the signal received at the ENB. How
> does the constellation look like? You could try increasing the tx power at
> the ue (param tx_power in ue.conf).
>
> Cheers
> Ismael
>
> On Thu, 19 May 2016 at 10:11 David Yu ( III ) <wcyu at iii.org.tw <mailto:
> wcyu at iii.org.tw> > wrote:
>
>
>         Hi SRS,
>         We successfully connected to OAI network and to internet.
>         But for a while, tt disconnected and show "scheduling request
> failed" almost every time.
>         Could you help me analyze this issue?
>         Thanks.
>         Regards,
>         David
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>
>
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