Design of high quality speech coders and echo-cancelation schemes for wireless networks is a challenging task since good quality should be maintained with low power consumption under time-varying channel conditions and limited bandwidth. The design should account for a number of parameters such as bit rate, delay, power consumption, complexity, and quality of coded speech. Available bandwidth will depend on network protocols. Depending on the application, a set of parameters is optimized.
In the past, speech codec design has mostly been driven by bandwidth-efficiency considerations; the target application being telephonic where the channel does not vary considerably with time and the Signal-to-Noise (SNR) is relatively high. For example, Code Excited Linear Prediction (CELP) based coders, are popular because of their low bit rates. The performance of these coders, however, deteriorates significantly in the presence of background noise, and the coders' complexity is rather high. In addition, the performance of CELP coders is poor for female speech and for non-speech signals, such as music. As a result, new standards for personal communication services are likely to use high-quality, medium bit-rate speech codecs such as the codec we have developed.
Work supported by ARPA CSTO and by NSF IRI 9309418.
Wireless Communication, Perceptual Coding, Echo Cancelation.
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Philbert Bangayan (bangayan@icsl.ucla.edu)