AMR Water Noise

Publication Date:  2014-05-27 Views:  1340 Downloads:  47
Issue Description
Water Noise symptom have been appeared during two simple voice call tests, and  the two cases were as below: 

1. A CS RAB was established after a PS RAB establishment.
2. The combined service DRD was triggered due to DR_RAB_COMB_DRD_SWITCH is on.
Alarm Information
NO Alarms,
Handling Process
1.Disable DRD switch for combine RAB and no negative impact
SET UCORRMALGOSWITCH: DR_RAB_COMB_DRD_SWITCH-0;
2.Some UEs consider DRD as RB SETUP based on chapter 8.6.4.3 and HFN does not add 1, some UEs consider DRD as HHO based on chapter 8.6.6.28 and HFN should add 1. So it may cause HFN inconsistency between UEs and RAN, and the different HFN of UEs and RAN will cause the water noise.
Root Cause
1.A CS RAB was established after a PS RAB establishment.
2.The combined service DRD was triggered due to DR_RAB_COMB_DRD_SWITCH is on.
3.In RRC_RB_SETUP_CMP message, we can see new active time for cipher setting from UE side(HFN=64, CFN=248)
4.After RNC received the RB SETUP CMP, RNC will configure the cipher setting according to HFN and CFN from UE. Refer to the Chapter 8.6.6.28 in 3GPP TS25.331, the HFN will add 1 so RNC configured HFN=65to MACD(Start-value is HFN and count-C-Activation Time is CFN).
5.As above, the CFN is the same, but HFN is different, it because of chapter 8.6.6.28 of protocol 25.331 says when UE made a HHO the value of HFN would add 1.
6.In this situation, some UE may not add 1 in HFN configuration, so the cipher between RNC and UE are different and it causes voice quality problem.

Suggestions
1.According to 3GPP TS 25.331, CS DRD may cause water noise. The reason is that chapter 8.6.6.28 says when UE made a HHO the value of HFN would add 1,and the chapter 8.6.4.3 does not require HFN+1 when UE made a DRD.
2.Some UEs consider DRD as RB SETUP based on chapter 8.6.4.3 and HFN does not add 1, some UEs consider DRD as HHO based on chapter 8.6.6.28 and HFN should add 1. So it may cause HFN inconsistency between UEs and RAN, and the different HFN of UEs and RAN will cause the water noise.

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