23-06-2012, 03:37 PM
Seminar on Adaptive Multi Rate (AMR)
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Introduction
Adaptive Multi Rate (AMR) is a new speech and channel codec for both half rate and full rate channels. By adapting the codec rate to the radio conditions the speech quality is enhanced. At low C/I, a large amount of channel coding is applied and less speech coding. When the C/I increases the speech coding is increased and the channel coding is decreased.
Both the BTS (uplink ) and the MS (downlink) continuously measures the radio quality (C/I) and based on these measurements the codec rate is changed. AMR requires support in all network nodes, i.e. MSC, BSC, BTS and MS and AMR is only supported in cells where all TRUs are AMR capable.
Capabilities
The feature AMR makes it possible to offer an enhanced speech quality for AMR mobiles in a network. The enhanced speech quality also provides better coverage at the edges of the cell, thus making it possible to increase the coverage area. AMR also tolerates more interference than the old speech codecs. This enables higher traffic loads which leads to higher capacity.
The speech quality enhancement is divided in two parts and can therefore be of different interest to the operator. The first is the robust FR channel that provides high speech quality at low C/I. This makes it possible to tighten the cell planning in a network with only AMR mobiles. The second is an audible better HR codec than the ones on the market today. This will increase the capacity in the networks and reduce transmission costs.
Inband Signalling
To be able to perform the codec mode adaptation the receiving side performs quality measurements on the incoming link. This measurement results in a Quality Indicator. The Quality Indicator produced on the MS side is converted to a Mode Request that is sent to the BTS using inband signalling. There, a codec mode control entity selects the codec mode to be used on the downlink, based on the Mode Request sent by the MS.
The codec mode control entity also selects the codec mode to be used on the uplink, based on the Quality Indicator produced in the BTS. The selected uplink mode is sent inband to the MS. The presently applied codec mode is also sent in band both uplink and downlink. This mode indication is sent every second speech frame and the Mode Request (uplink)/Mode Command (downlink) is sent in the speech frames in between, see 3GPP TS 45.009.
Multirate Configuration
At setup and handover the codec set to be used is sent from the BSC to the MS and the BTS together with the decision threshold and hysteresis values. There are two full rate codec sets and two half rate codec sets pre-defined in the BSC.
[attachment=25285]
Introduction
Adaptive Multi Rate (AMR) is a new speech and channel codec for both half rate and full rate channels. By adapting the codec rate to the radio conditions the speech quality is enhanced. At low C/I, a large amount of channel coding is applied and less speech coding. When the C/I increases the speech coding is increased and the channel coding is decreased.
Both the BTS (uplink ) and the MS (downlink) continuously measures the radio quality (C/I) and based on these measurements the codec rate is changed. AMR requires support in all network nodes, i.e. MSC, BSC, BTS and MS and AMR is only supported in cells where all TRUs are AMR capable.
Capabilities
The feature AMR makes it possible to offer an enhanced speech quality for AMR mobiles in a network. The enhanced speech quality also provides better coverage at the edges of the cell, thus making it possible to increase the coverage area. AMR also tolerates more interference than the old speech codecs. This enables higher traffic loads which leads to higher capacity.
The speech quality enhancement is divided in two parts and can therefore be of different interest to the operator. The first is the robust FR channel that provides high speech quality at low C/I. This makes it possible to tighten the cell planning in a network with only AMR mobiles. The second is an audible better HR codec than the ones on the market today. This will increase the capacity in the networks and reduce transmission costs.
Inband Signalling
To be able to perform the codec mode adaptation the receiving side performs quality measurements on the incoming link. This measurement results in a Quality Indicator. The Quality Indicator produced on the MS side is converted to a Mode Request that is sent to the BTS using inband signalling. There, a codec mode control entity selects the codec mode to be used on the downlink, based on the Mode Request sent by the MS.
The codec mode control entity also selects the codec mode to be used on the uplink, based on the Quality Indicator produced in the BTS. The selected uplink mode is sent inband to the MS. The presently applied codec mode is also sent in band both uplink and downlink. This mode indication is sent every second speech frame and the Mode Request (uplink)/Mode Command (downlink) is sent in the speech frames in between, see 3GPP TS 45.009.
Multirate Configuration
At setup and handover the codec set to be used is sent from the BSC to the MS and the BTS together with the decision threshold and hysteresis values. There are two full rate codec sets and two half rate codec sets pre-defined in the BSC.