EFR - Enhance Full Rate


With the development of the GSM network, subscribers have increasing requirements for high speech quality. Thus, enhanced full rate (EFR) is adopted.

In comparison to FR, EFR optimizes the speech codec algorithm and improves the speech quality, thus improving the user experience.

EFR is implemented on the basis of the Code Excited Linear Prediction (CELP). FR and HR, however, are implemented on the basis of Regular Pulse Excited - Linear Predictive Coder (RPELPC). The differences between CELP and RPE-LPC are as follows: In the CELP model, the excitation signal is a quantified vector. A group of codevectors that are obtained in advance through calculation forms a codebook. For each frame of speech signals, a codevector with the minimum perceptually weighted error is selected from the codebook to serve as the irregular
excitation source. In the RPE-LPC model, a regular excitation source such as the sine wave is adopted, and thus the speech lacks clarity.

The Speech Version parameter specifies whether to enable EFR.


The EFR function can be enabled forcibly on the BSC. That is, when the BSC determines that the circuit pool on the A interface and the MS support the EFR, the BSC can actively selects the EFR as the speech version to improve the speech quality if the speech versions carried in the Assignment Request message do not include the EFR. The parameter Allow Forced EFR in Cell specifies whether the EFR function can be forcibly enabled