無線傳輸及網際網路環境下之

G.729與G.723.1語音傳輸

摘要

G.729語音編碼器為ITU-T於1996所訂定的高品質低延遲8kbit/s語音編碼標準，而G.723.1亦為ITU-T於1996所訂定的6.3kbit/s及5.3kbit/s雙速元語音編碼標準，這兩種語音編碼器均是針對語音與多媒體的音訊訊號之壓縮處理所設計的，主要的應用方向為網際網路環境下之語音傳輸系統的語音編碼標準，並且為H.323網際網路音視訊會議系統下之音訊訊號的編碼標準。

由於G.729的語音編碼方式，並無錯誤更正之機制，然而在無線的傳輸通道中，雜訊或是訊號的干擾是無法避免的，因此我們分析封包中各位元之重要性，並提出與標準相容的BCH（31, 26）碼的重要位元保護模式，使得重建語音在低通道錯誤率下有較佳之語音品質；此外，在網際網路即時性的應用中，經常會有封包遺失的情形發生，因此我們將錯誤隱藏的處理方法應用於G.729及G.723.1中，使得重建語音在不同的封包遺失情形下，皆能有最佳之語音品質。

G.723.1 and G.729 Speech Transmission over Wireless and Internet Environments

Abstract

G.723.1 and G.729 are both ITU-T speech coding standards. These two speech coders are designed for the compression of speech and audio signals in multimedia applications. The target applications are the voice transmission over Internet and the voice coding of H.323 based Internet video conferences.

To enhance the error robustness of G.729, we propose an error protection scheme by applying BCH(31, 26) to protect significant bits in a frame. Furthermore, the BCH(31, 26) scheme is compatible to G.729 standard. In Internet environment, the packets often get lost and the error propagation effect degrades the speech quality substantially. Therefore, we apply the error concealment techniques to both G.729 and G.723.1. In simulations, the objective and subjective evaluation tests all show that the G.729 BCH(31, 26) error protect scheme and the error concealment techniques of G.729 and G.723.1 can improve speech quality significantly.