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A simple interworking algorithm between fast power control and link adaptation for AMR

IP.com Disclosure Number: IPCOM000021084D
Published in the IP.com Journal: Volume 4 Issue 1 (2004-01-25)
Included in the Prior Art Database: 2004-Jan-25
Document File: 7 page(s) / 120K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

With the introduction of AMR (Adaptive Multirate) in TSM dynamic switching between the AMR speech codecs will be possible. The goal is to improve the speech quality, as the user perceives it and, at the same time, keep the interference among users low. The codecs are selected according to the link quality. The worse the link, the more the codec should focus on the most important speech information and thus leave more room for channel protection. Fast power control strives to achieve a similar goal. The power is adjusted so that the signal-to-interference ratio (SIR) is maintained at a level where the speech quality is good and interference is as low as possible. Fast power control has been introduced with the beginnings of 3rd generation cellular systems. AMR will follow as a next step. In this document we describe an interworking algorithm between AMR and fast power control that harmonizes the two mechanisms. In order to judge the link quality we need a codec independent quality concept. In this document we assume that the GSM quality concept based on mean opinion scores has been transferred to TSM either by the method described in [1] or through own hearing experiments. Thus, for each codec, there is a curve describing the relation between signal-power-to-interference ratio (CI/ or equivalently SIR) and the mean opinion score MOS.

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© SIEMENS AG 2004 file: 2003J19042.doc page: 1

A simple interworking algorithm between fast power control and link adaptation for AMR

Idea: Koester Gerta, DE-Muenchen; Rocchetti Alfredo, DE-Muenchen

With the introduction of AMR (Adaptive Multirate) in TSM dynamic switching between the AMR speech codecs will be possible. The goal is to improve the speech quality, as the user perceives it and, at the same time, keep the interference among users low. The codecs are selected according to the link quality. The worse the link, the more the codec should focus on the most important speech information and thus leave more room for channel protection.

Fast power control strives to achieve a similar goal. The power is adjusted so that the signal-to- interference ratio (SIR) is maintained at a level where the speech quality is good and interference is as low as possible. Fast power control has been introduced with the beginnings of 3rd generation cellular systems. AMR will follow as a next step. In this document we describe an interworking algorithm between AMR and fast power control that harmonizes the two mechanisms.

In order to judge the link quality we need a codec independent quality concept. In this document we assume that the GSM quality concept based on mean opinion scores has been transferred to TSM either by the method described in [1] or through own hearing experiments. Thus, for each codec, there is a curve describing the relation between signal-power-to-interference ratio (CI/ or equivalently SIR) and the mean opinion score MOS.

We describe an algorithm to switch between codecs based on the quality information given through the MOS. The goal is to keep the algorithm simple and robust and thus to simplify implementation and test phase and - most importantly - to lower operational risks. The method proposed here, leaves the fine-tuning and fast adaptations to fast power control. We choose this approach because, under normal conditions, fast power control performs well and works efficiently. Its reliability has been thoroughly tested. Also, quality measurements and exchange of signaling information are likely to take up to several hundreds of speech frames, whereas fast power control usually reacts on a frame-by- frame basis. Furthermore, the MOS based quality evaluation for AMR is a rather crude instrument making fine-tuning through the choice of codecs almost impossible. Finally, the power is adjusted in small steps making power control the finer and more precise tool.

The mechanism in this document provides a basis for further development, not a comprehensive design. Some of the most important open design issues are listed in the last paragraph. They will be treated in a separate "white paper".

1 Prerequisites

1.1 Goals of AMR

With the introduction of AMR a choice of speech codecs is available that can be selected according to link quality. There are three cases when a change of codec is desirable:

1. We can achieve the same qua...