Voice Communications over Tandem Heterogeneous Networks

语音是实时通信的首选方法。语音对于人类通信是如此重要，以至于我们已经构建了以语音为中心的整个网络，即公共交换电话网(PSTN)和模拟/数字蜂窝网络。随着互联网协议语音(VoIP)和无线局域网语音(Wi-Fi)的出现，未来的语音呼叫可能包括通过VoIP骨干网络与Wi-Fi语音用户通信的数字蜂窝用户，从而通过VoIP网络将数字蜂窝网络连接到Wi-Fi链路。虽然数字蜂窝网络利用了相对复杂的错误检测和纠正、不等错误保护和错误隐藏，但VoIP和Wi-Fi语音的错误控制、分组丢失机制和分组丢失隐藏方法相对原始。此外，由于这些网络中的每一个具有不同的信道行为，并且可能使用不同的语音编解码器和不同的网络协议，因此在这样的连接上可能无法实现可接受的、带宽高效的语音服务。这项研究涉及汇接异质网络上的语音通信和Wi-Fi链路上的语音。我们研究(1)通过开发语音模式自适应后置滤波器和感知失真测量，通过移除后置滤波器并在合成分析循环中插入额外的滤波，以及通过在合成分析循环中整形激励，来改善语音编解码器串联性能；以及(2)通过联合设计用于无线局域网的分组丢失隐藏方法和协议，以及通过开发分组丢失平滑算法以使用“延迟”分组来改进后续重建，来改进分组丢失隐藏和减少延迟。语音通信的端到端网络性能评估使用NS2网络模拟器和语音质量指标。

Voice is the method of choice for real time communications. Voice is so important to human communications that we have constructed entire networks centered around voice, namely, the public switched telephone network (PSTN) and the analog/digital cellular networks. With the emergence of voice over the Internet Protocol (VoIP) and voice over wireless local area networks (Wi-Fi), a future voice call might consist of a digital cellular user communicating through a VoIP backbone network with a voice over Wi-Fi user, resulting in the connection of a digital cellular network through a VoIP network into a Wi-Fi link. Although the digital cellular networks utilize relatively sophisticated error detection and correction, unequal error protection, and error concealment, the error control, packet loss mechanisms, and packet loss concealment methods for VoIP and voice over Wi-Fi are relatively primitive. Furthermore, since each of these networks has different channel behaviors and may use different voice codecs and different network protocols, acceptable, bandwidth efficient voice service may not be achievable over such a connection. This research involves voice communications over tandem heterogeneous networks and voice over Wi-Fi links. We examine (1) improved voice codec tandem performance, by developing speech-mode-adaptive postfilters and perceptual distortion measures, by removing the postfilter and inserting additional filtering within the analysis-by-synthesis loop, and by shaping the excitation within the analysis-by-synthesis loop; and (2) improved packet loss concealment and reduced latency, by jointly designing packet loss concealment methods and protocols for wireless LANs and by developing packet loss smoothing algorithms to use "late" packets to improve later reconstruction. The evaluation of the end-to-end network performance for voice communications uses the NS2 network simulator and voice quality metrics.