摘要
The enhanced variable rate codec (EVRC) is a standard for the 'Speech ServiceOption 3 for Wideband Spread Spectrum Digital System,' which has been employed in both IS-95cellular systems and ANSI J-STC-008 PCS (personal communications systems). This paper concentrateson channel decoders that exploit the residual redundancy inherent in the enhanced variable ratecodec bitstream. This residual redundancy is quantified by modeling the parameters as first orderMarkov chains and computing the entropy rate based on the relative frequencies of transitions.Moreover, this residual redundancy can be exploited by an appropriately 'tuned' channel decoder toprovide substantial coding gain when compared with the decoders that do not exploit it. Channelcoding schemes include convolutional codes, and iteratively decoded parallel concatenatedconvolutional 'turbo' codes.
宽带扩频系统的语音服务采用增强型的可变比率编码器 ,该标准已在IS 95和JSTC0 0 8个人移动通信系统得到应用 .本文致力于利用增强可变比率编码器中内在残留冗余信息的信道解码器 .由于残留冗余信息可以用一阶马尔夫模型表示 ,同时相关频率的变化可以用熵率来表示 ,从而 ,信道解码器可利用这种残留冗余量 .仿真结果表明 ,和没有利用这种信息量的解码器相比 ,由于编码增益 ,系统性能有明显改善 ,其中 ,信道编码采用了卷积码。
基金
TheprojectsupportedbytheNationalNaturalScienceFoundationofChina(6972 5 0 0 1)
