PS call drop rate increase after activating CELL_PCH in Huawei RAN 13

[FrankPintor]

In "my" network, Huawei RAN 13, V900R013ENGC00SPC586, we recently activated CELL_PCH. The PS inactivity timers for background and interactive timers are 900s (15 mins) to take advantage of the CELL_PCH state and reduce the RRC and RAB signaling load.

Huawei advise of an increase in dropped calls while the UE is in CELL_PCH (and also in the transitions D2P and F2P), and recommend a new formula to discount these drops as they don't affect the user experience.

So far so good...

However, we are seeing a considerable increase in dropped PS calls in dedicated mode, including HSDPA and HSUPA. The main causes are UL sync failure and TRB reset. This was unexpected as we didn't change anything related to the dedicated states.

Anyone have any ideas? Any similar experience?

[captain_jejemon]

RNC call drop rate will be degraded after CELL-PCH feature launched.PS Call Drop Ratio = PS RAB abnormal release times/(PS RAB abnormal release times+ PSRAB normal release times)After CELL_PCH or EFD feature enable, The PS inactive timer will extend then wholenetwork “PS RAB Normal Release Times” will reduce, further “PS Call Drop Ratio” willincrease.More PS user will keep in CELL_FACH, the CELL_FACH call drop will increase a littlehigher than CELL_DCH. the “PS RAB Abnormal Release Times” will increase a little bitprobably.The reason of “PS Call Drop Ratio” increase is the “PS RAB normal release times” decline, Sothat the user perception is still normal.

[ranflinho]

Hi FrankPintor,

Can you share the formula that Huawei gave you to compensate the drops?

Thanks,

[FrankPintor]

You can find some modified PS DCR formulas at the back of this document: http://www.scribd.com/doc/89114097/CELL-PCH-Feature-Implementation-Guild-in-3G-Network

There is also a section about the expected impact of implementing CELL_PCH.

However, it doesn't address my problem, which is specifically that the UL sync and TRB failures have increased, these are failures that happen with an active radio link, and where we didn't make any changes to the timers.

If anyone has seen this problem I'd be very grateful if they'd share their experience.

[Iluxus]

I had the similar experience when upgrading from R10 to R12. PS Drop calls, specially in HSDPA, and were related o SRB and TRB. The suggested solution, and actually it worked, was to add a new SCCPCH channel, in order to separate PCH and FACH channels in differtne SCCPCH in each cell in the network. From that time, every time we add a new cell in every RNC, it's added with this configuration.

[FrankPintor]

Worked it out in the end, without CELL_PCH enabled (i.e. only CELL_DCH, CELL_FACH, and idle mode), Huawei have a simple solution to drops in CELL_FACH... don't count them :o

So when you enable CELL_PCH with sensible PS inactivity timers (e.g. 15-30 mins to keep the active UEs in CELL_PCH and not have them go to idle mode), the drops in CELL_FACH that were always there but ignored are now counted. Nice one Huawei!