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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 compatiblepunctured code,RCPC)进行保护,在正交频分复用(orthogonal frequency division modulation,OFDM)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。
In order to implement real-time reliable voice communication over time-varying high-bit error rate wireless channel, an adaptive joint source channel coding and modulation transmission scheme based on low-rate speech is proposed. The scheme adaptively divides speech parameters into different importance levels according to different degrees of influence on the synthesized speech quality, and protects them with rate compatible punctured code (RCPC) using different efficiency rate matching. In orthogonal frequency Transmission is performed on different subchannels of an orthogonal frequency division modulation (OFDM) system. Each parameter is dynamically adjusted according to the noise level of the current channel, and the instantaneous noise of the sub-channel is estimated according to the change of symbols before and after RCPC decoding. The simulation results show that under Nakagami-m time-varying fading channel, the adaptive joint coding modulation scheme can adapt well to the time-varying fading characteristics of the channel and provide good synthesized speech quality under harsh channel conditions. Compared with the traditional separation and transmission Program, bit error rate reduced by 20% to 30%, voice synthesis quality improved significantly.