A baseband residual vector quantization algorithm for voiceband data signals

A new approach is presented to the digitization and compression of a class of voiceband modem signals. The approach, baseband residual vector quantization (BRVQ), relies heavily on the simple structure present in a modem signal. After the signal is converted to baseband, the magnitude sequence and the sequence of residuals obtained when the phase within each baud of the baseband signals is modeled by a straight line are separately vector quantized. Carrier frequency estimation and baud-rate classification schemes that were designed to carry out these operations are described. Experimental results show that the performance of the BRVQ system at and below 16 kb/s is better than that of a previously developed vector quantization scheme that has itself been shown to outperform traditional speech-compression techniques such as adaptive predictive coding, adaptive transform coding, and subband coding when these techniques are used to compress modem signals