Title: PS Data service move to 2G even at good 3G signal level frequently due to Wrong setting of parameters

Keywords: Swap, 3G to 2G PS HO, EDGE

Product Information: Inter-rat PS HO problem

Fault Type: Inter-rat PS HO Problem

Problem Description:

After the swap of UMTS Network form Vendor A to Huawei System in country M, there were complaints received from customer regarding Data service Hand over to Edge (2G) frequently and not returning back to UMTS even after the UMTS signal levels become good.

Handling Process:

To identify the issues Drive Test is arranged in few complaint areas to identify the solution with below setup.

Phone 1: Phone Setup is idle phone/ dual mode /mobile data service off

Even When the 3G signal level is good( Signal level better than INTERRATCSTHD2DRSCP)it is HO to 2G and phone returned back to 3G once the signal level reach very good levels only.

Phone 2: Phone setup is Dual mode with data browsing

When the signal level is low it is ho to 2G and it did not return to 3G even after the signal level became very good. This happens during Data browsing in Phone.

From the above observation, we tried to identify the signal at which 3G is handing over to 2G From the signaling messages.

Msg 810,811 in the below signaling trace, RNC indicate NodeB to start compress mode, then in Msg 815,816,817, RNC indicate UE to start measure interRAT(GSM cells) with measure id=7.

In below signaling trace, In Msg 858,859, UE report 3A event with measure ID7.

RNC receive event 3A, then RNC start the handover to 2G.

When UE in CELL_DCH state, the 3G-to-2G handover in the PS domain is triggered after the UTRAN sends a CELL CHANGE ORDER FROM UTRAN message

Even though 2D and 2F Values are -110 & -107, 3A event triggered at signal level -92 and inter-rat Ho happen.

RSCP Value at Event 3A

According to CFGMML event 3A is based on CPICH RSCP and trigger value is -110dBm (for PS service)

CFGMML Inter-rat HO Thresh-hold values

But it is noticed from CFGMML the Inter-frequency Ho thresh-hold is around -95dBm.

INTERFREQCSTHD2DRSCP=-95, INTERFREQCSTHD2FRSCP=-92

But when cfgmml is checked in detail, it is identified, even for the inter-rat HO interfrequency Ho thresh holds are set due to below configuration Line.

SET UHOCOMM: COEXISTMEASTHDCHOICE=COEXIST_MEAS_THD_CHOICE_INTERFREQ

Meaning: event 2D/2F measurement threshold of which measurement type (inter-frequency or inter-RAT measurements) will be used, when inter-frequency and inter-RAT measurements coexist.When COEXIST_MEAS_THD_CHOICE_INTERFREQ is selected, event 2D/2F measurement thresholds oriented towards inter-frequency configuration are selected. When COEXIST_MEAS_THD_CHOICE_INTERRAT is selected, event 2D/2F measurement thresholds oriented towards inter-RAT configuration are selected.

CauseSince The COEXISTMEASTHDCHOICE is set to COEXIST_MEAS_THD_CHOICE_INTERFREQ,Thresh-hold of Inter-freq is only taken for Inter-rat Handovers also.Since inter-frequency Handover setting is high RSCP values, even at good RSCP levels 3G Handover to 2G.

Solution:As a solution to this COEXIST_MEAS_THD_CHOICE_INTERRAT is selected.ADD UCELLHOCOMM: CellId=xxx, InterFreqRATSwitch=SIMINTERFREQRAT, CoexistMeasThdChoice=COEXIST_MEAS_THD_CHOICE_INTERRAT; As a result inter-rat Ho to 2G came down drastically as shown in the below diagram.

Suggestion:It is worthwhile check two other things if the Data services are struck in Edge frequently.

1. In the UE tracing from “System Information Type2quarter” Qsearch P Value can be checked. For example if the value is 14, that won’t allow the phone to reselect to 3G Data easily once the phone moves to 2G. It will search for 3G if the signal level of 2G is better than -54 only. Then the chances of moving back to 3G are low.

2. Threshold of below parameters can be adjusted to reduce the movement to 2G. Parameters Default l values

InterRATR99PsThd2DEcN0 -15InterRATHThd2DEcN0 -15

InterRATR99PsThd2FEcN0 -13InterRATHThd2FEcN0 -13TargetRatR99PsThd 16

TargetRatHThd 16UsedFreqHThdEcN0 -13

UsedFreqR99PSThdEcN0 -13