AMR (Adaptive Multi Rate)


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 increase 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.

AMR makes it possible to change codec rate during a call. There are 8 different codec rates available in the AMR transcoder: 12.2kbps, 10.2kbps, 7.95kbps, 7.40kbps, 6.70kbps, 5.90kbps, 5.15kbps, and 4.75kbps

According to the standard, 12.2 kbps and 10.2 kbps can only be used in FR channels and the other six can be used in both FR and HR channels, on the air interface.

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