基于低速率语音的自适应联合编码调制方案

Joint source-channel coding and modulation scheme for low-bit-rate speech

为了在时变衰落的高误码率无线信道上进行实时可靠语音通信，提出一种基于低速率语音的自适应联合信源信道编码与调制传输方案。该方案根据对合成语音质量影响程度不同自适应地将语音参数划分为不同重要性级别，配合采用不同效率的速率匹配的删余卷积码（rate compatible punctured code，RCPC）进行保护，在正交频分复用（orthogonal frequency division modulation，0FDM）系统的不同子信道上进行传输。各参数均根据当前信道的噪声水平跟踪动态调整，子信道的瞬时噪声根据RCPC译码前后序列符号改变情况进行估计。仿真结果表明：在Nakagami—m时变衰落信道下，该自适应联合编码调制方案可以很好地适应信道地时变衰落特性，在恶劣的信道条件下提供良好的合成语音质量，相对传统分离传输方案，误码率降低20％～30％，语音合成质量明显提高。

A novel error resilience joint source-channel coding and modulation scheme based on very low bit rate speech coding was proposed to eliminate the transmission performance degradation caused by time-variant fading interference in wireless channels. Based on the different error sensitivity of speech parameters, the output parameters are divided into different level of importance which later will be protected by relevant RCPC （rate compatible punctured code） with diverse efficiency and transmitted through every subchannel of OFDM （orthogonal frequency division modulation） system. The parameters are dynamically selected according to instantaneous channel BER estimated from the bit sequences before and after the RCPC decoding. Simulation results show that, over Nakagami-m fading channels, the proposed scheme is well adapted to time-variant wireless channels, achieving better reconstructed speech quality and BER is decreased at 20%-30%, compared with classic tandem transmission scheme.