Performance enhanced multi-rate iLBC

The internet Low Bit-rate Codec (iLBC) inherently possesses high robustness to packet loss which is one of the essential properties of Voice over Internet Protocol (IP) applications. Another important feature is the rate flexibility, which allows the speech codec to adapt its bit rate to constantly changing network condition. Previously, the multi-rate operation of the iLBC was enabled by utilizing the Discrete Cosine Transform (DCT) and entropy coding. In this paper, various approaches to improve performance are presented. The simulation results show that when all the improvement schemes are combined, the performance is improved at all the bit rates compared to the previous results despite the fact that the Huffman table structure is significantly simplified.