Narrowband Process Quamtization

In this paper we introduce a technique of tracking and quantizing the complex envelope of a narrowband process, which is a continuous time Gauss-Markov process of arbitrary order. The narrowband process is modeled in a state space framework and several quantization schemes using the inphase and the quadrature components of the narrowband process are considered. These inphase and quadrature components are baseband processes, and thus are much more slowly varying than the original narrowband process. The advantage of such a scheme lies in the fact that the sampling in such a system is less sensitive to timing errors. We compare the performance of these schemes with several previously analyzed schemes [2, 31 both with respect to a time averaged smoothed error, and their robustness with respect to the changes in the input spectrum. We compare the performance of the envelope quantization schemes with differential state quantization [3] for a second order narrowband process. The envelope quantization schemes perform better than state vector quantization but worse than differential state quantization. Differential state quantization considers the quantization of a state consisting of the proces and its derivatives and was shown to be a superior quantization scheme for Gauss-Markov processes [3]. Finally, we ‘define a measure of robustness for different source coding systems when the input spectrum changes and compare the performance of this envelope quantization scheme with several other previously analyzed schemes.