AMR stands for Adaptive Multi Rate.
Full Rate AMR supports 8 voice coding modes : 12.2kb/s, 10.2kb/s, 7.95kb/s, 7.40kb/s, 6.70kb/s, 5.90kb/s, 5.15kb/s, 4.75kb/s
Half Rate AMR supports 6 voice coding modes : 7.95kb/s, 7.40kb/s, 6.70kb/s, 5.90kb/s, 5.15kb/s, 4.75kb/s
Impact of AMR on voice quality :
Accorning to the simulation result, when C/I is greater than 6, the voice quality performance in descending order is AMRFR, EFR, AMRHR,TCHFR and TCHHR.
The voice quality performance of AMRHR is similar to FR. However, radio bandwidth occupied by AMRHR in radio interface is only Half of that occupied by FR. Therfore, AMRHR can not only ensure the good voice quality but also can increase system capacity effectively.