Research And Optimization On Speech Coding In Digital Trunking Communication System

Trunking communication system is a command and dispatching system which has exchange and control functions. Along with the development of the digital communication technique, the digital trunking communication system becomes a hot research aspect gradually. Speech communication is one of the most used modes in the digital trunking communication system. Excellent algorithm of speech coding can save the bandwidth resource, improve the utilization of frequency, so it has important value for investigation.Three optimization methods are presented by researching the Algebraic Codebook Excitation Linear Prediction (ACELP) algorithm, and optimized the feel weighted filter, the search algorithm of the Linear Spectrum Pair(LSP), and the search method of the algebraic codebook respectively.The quantized LP coefficients are replaced by the unquantized LP coefficients in the frequency domain expression of the feel weighted filter. The error signal has more similar envelope shape, and the hearing effect is better than before because the unquantized LP coefficients have more accuracy than quantized LP coefficients.The optimization of the LSP parameters is realized by choosing two different distortion estimate criterions. One is combined with the maximum average error criterion and the mean square error criterion, and the other is combined with the absolute value average error criterion and the mean square error criterion. Theory analysis shows that the two new search methods have less computational complexity than that of the non-optimal method.Focused search method is replaced by the pulse replacement procedure to optimize the search method of the algebraic codebook. The search load of the pulse replacement procedure is only about 24% of non-optimized method.Emulation results show that the modified feel weighted filter can reduce the effect of the noise interference by taking good use of the masking effect. Both of the optimized methods for LSP parameters and algebraic codebooks can provide the similar performance as the standard method with less search load.