Implementation And Optimization Of ILBC Codec Algorithm On 24Bit Fixed-Piont DSP

With the increasing development of voice technology, Internet voice communications applications become increasingly popular.the communicative quality of network telephones becomes an important factor that restricts its own development. To reduce the effect of packet loss to voice in the packet switching network, the iLBC Algorithm, which utilizes the technologies of Long Term Prediction and Packet Loss Concealment, was brought up internationally, thus well solving the problem.The full name of iLBC is Internet Low Bit Rate Codec, which is a new codec algorithm used in IP voice technology brought up by Global IP Sound Company. In nature, iLBC is a frame-based LPC (linear predictive coding) method and a kind of development to CELP (Code Excited Linear Predictive Coding). In relation to previous Codec Algorithm such as G.729A and G.723.1, the unique dynamic codebook update technology, enhancement algorithm and Packet Loss Concealment technology of iLBC give it better performance in application of packet switching network.This thesis is to investigate the iLBC codec algorithm and expects to implement and optimization iLBC codec on a 24-bit, fixed-point digital signal processor。At present, most of the fixed-point DSP is 16-bit data bus width, which will possibly cause the limitation of data precision, thus increase the complexity of algorithm design. It is meaningful to realize the speech codec in AR1688 because of the inexpensive price and high precision. The implementation was in two steps, first make the floating point to fixed-point conversion in C with optimization. Then translate the C to DSP assembly codes. After the speech codec pass the testing sequence, the next work is the optimization of the speech codec using the hardware features and instruction characteristic of AR1688 chip, in order to reduce the complexity of algorithm, improve the speed of codec, adapt the requirements of processor, and reduce the power of equipment. Eventually, we successfully achieved the requirements of real-time speech codec on equipment which the core element is AR1688 chip.