Impact of AMR on Call Drop Rate

AMR improves the robustness of the AMR speech frame but not the robustness of the SACCH frame (robustness indicates the anti-interference capability of the AMR). Theoretically therefore, AMR does not affect the TCH call drop rate. In practice, however, when AMR is enabled, the TCH call drop rate increases because of the following causes:

As for EFR/FR/HR, the difference between the robustness of the SACCH frame and that of the speech frame is not great. A user in a weak coverage area may hang up the phone because of the poor speech quality. Such a situation is not counted as a call drop.

  When AMR is enabled, the robustness of the AMR FR speech frame is higher than that of the SACCH frame. Thus, the speech frame in a weak coverage area can be appropriately decoded, and the user will not hang up the phone. The SACCH frame, however, cannot be appropriately decoded. Thus, RLT expires, and a call drop occurs. In this way, the TCH call drop rate increases.

AMR introduces parameters such as AFRDSBLCNT, AHRDSBLCNT, AFRSAMULFRM, and AHRSAMULFRM.

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