Narratives

This section describes the optional feature LOFD-111207 VoLTE Rate Control.

4.2.4.1 Introduction

VoLTE Rate Control adjusts the AMR-NB/AMR-WB rate for uplink voice services depending on the uplink channel quality and voice quality.

l When the uplink channel quality and voice quality are favorable, a high voice coding rate is used to further improve voice quality.

l When the uplink channel quality and voice quality are poor, a low voice coding rate is used to reduce the uplink packet loss rate and improve uplink voice coverage. In scenarios where downlink coverage is limited prior to uplink coverage (for example, in the coverage area of a micro or LampSite base station), UEs' uplink channel quality and voice quality may not meet the conditions for using low voice coding rates. In such scenarios, it is difficult to trigger the decrease of voice coding rates.

4.2.4.2 Principles

Voice Rate Adjustment

The eNodeB determines whether to adjust the voice rate depending on the uplink channel quality and voice quality. If yes, the eNodeB or SBC adjusts the voice rate of the UE. Voice rate adjustment is controlled by the CellAlgoSwitch.UlAmrcMode parameter as follows:

l If this parameter is set to

ULAMRC_ENB_CONTROL(ULAMRC_ENB_CONTROL), the eNodeB adjusts the voice rate of the UE, as shown in Figure 4-7.

l If this parameter is set to

ULAMRC_SBC_CONTROL(ULAMRC_SBC_CONTROL), the eNodeB requests the SBC, through RTCP, to adjust the voice rate of the UE. If IMS signaling is encrypted, the eNodeB cannot obtain the rate set supported by the UE. In this situation, SBC can be used to perform voice rate control, as shown in Figure 4-8.

Figure 4-7 Voice rate adjusted by the eNodeB

Figure 4-8 Voice rate adjusted by the SBC

As shown in Figure 4-9, the VoLTE Rate Control feature supports the following rates for AMR-NB services: 12.2 kbit/s, 7.4 kbit/s, and 4.75 kbit/s; the VoLTE Rate Control feature supports the following rates for AMR-WB services: 23.85 kbit/s, 12.65 kbit/s, and 6.6 kbit/s.

Both rates in each AMR group can be allocated to a UE.

AMR groups are controlled by the following parameters:

l VoiceAmrControl.VoiceAmrCtrlParaGroupId l VoiceAmrControl. HighAmrCodingMode l VoiceAmrControl. LowAmrCodingMode

NOTE

The VoLTE Rate Control feature supports rate adjustment within AMR-NB services or within AMR-WB services, not between AMR-NB and AMR-WB services.

Figure 4-9 is only an example. In actual configuration, you can configure 12.2 kbit/s and 4.75 kbit/s as AMR Group 0 and 23.85 kbit/s and 6.6 kbit/s as AMR Group 1 so that UE rates can be adjusted between the highest and lowest rates.

Figure 4-9 Example of AMR voice rate adjustment

After the VoLTE Rate Control feature is enabled:

l The AMR coding rate increases if the following conditions are both met:

– The TBS of the UE is greater than TbsUpTh.

– The uplink packet loss rate for services with a QCI of 1 is less than VoiceAmrControl.PlrThdForIncreasingAmr for two consecutive times.

If the UlAmrcExceedingInitialSw(UlAmrcExceedingInitialSw) option of the CellAlgoSwitch.AmrcAlgoSwitch parameter is selected, the increased coding rate can exceed the initial coding rate of this call. Otherwise, the increased coding rate cannot exceed the initial coding rate of this call.

l The AMR coding rate will be decreased if the following conditions are both met:

– The TBS of the UE is less than TbsDownTh.

– The uplink packet loss rate for services with a QCI of 1 is greater than VoiceAmrControl.PlrThdForDecreasingAmr for two consecutive times.

NOTE

TbsUpTh and TbsDownTh are automatically calculated based on

VoiceAmrControl.PlrThdForIncreasingAmr and VoiceAmrControl.PlrThdForDecreasingAmr respectively.

Inapplicable Scenarios

The VoLTE Rate Control feature does not take effect in the following scenarios:

l The voice coding format is not AMR-NB or AMR-WB.

l RTP packets are encrypted.

The number of rates in the intersection of the rate set supported by UEs and the rate range configured is less than or equal to 1.

If the eNodeB is used for rate adjustment and IMS signaling is encrypted:

l When UlAmrCheckSw(UlAmrCheckSw) is selected in the

CellAlgoSwitch.AmrcAlgoSwitch parameter, the VoLTE Rate Control feature does not take effect.

l When UlAmrCheckSw(UlAmrCheckSw) is deselected in the CellAlgoSwitch.AmrcAlgoSwitch parameter:

– If the UE supports the rate indicated by the eNodeB, the eNodeB performs rate adjustment for the UE.

– If the UE does not support the rate indicated by the eNodeB, the eNodeB does not perform rate adjustment for the UE.

The reason is that the eNodeB cannot obtain the rate set supported by the UE due to the encryption of IMS signaling.

UE Whitelist and Blacklist

The VoLTE Rate Control feature can be enabled or disabled for specified UE types, that is, a whitelist and a blacklist can be configured. Table 4-2 describes the whitelist and blacklist configurations.

Table 4-2 Whitelist and blacklist configurations Is the

UL_AMRC_SWITCH_O FF Option of the

UeCompatOpt.BlkLstCtr lSwitch Parameter Selected

Is the

UL_AMRC_SWITCH_O N Option of the

UeCompatOpt.WhiteLst CtrlSwitch Parameter Selected

Description

No Yes The VoLTE Rate Control

feature takes effect for UEs of this type.

Yes No The VoLTE Rate Control

feature does not take effect for UEs of this type.