Engineering, Electronics and Electrical

There are various algorithms used for the iterative decoding of two-dimensional systematic convolutional codes in applications such as spread-spectrum communications and CDMA detection. The main objective of these decoding schemes is to approach the Shannon limit in signal-to-noise ratio while keeping the system complexity and processing delay to a minimum. One such scheme proposed recently is termed Turbo (de)coding. Through the use of Log-likelihood algebra, it is shown that a decoder can be developed which accepts soft inputs as a priori information and delivers soft outputs consisting of channel information, a priori information and extrinsic information to subsequent stages of iteration. The output is then used as the a priori input information for the next iteration. Realization of the Turbo decoder is performed on the digital signal processing chip, TMS320C30 by Texas Instruments using a low complexity soft-input soft-output decoding algorithm. Hardware issues such as memory and processing time are addressed and how they are impacted by the chosen decoding scheme. Test results of the BER performance are presented for various block sizes and number of iterations.

The cochlea provides frequency selectivity for acoustic input signal processing in mammals. The excellent performance of human hearing for speech processing leads to examination of the cochlea as a paradigm for signal processing. The components of the hearing process are examined and suitable models are selected for each component's function. The signal processing function is simulated by a computer program and the ensemble is examined for behavior and improvement. The models reveal that the motion of the basilar membrane provides a very selective low pass transmission characteristic. Narrowband frequency resolution is obtained from the motion by computation of spatial differences in the magnitude of the motion as energy propagates along the membrane. Basilar membrane motion is simulated using the integrable model of M. R. Schroeder, but the paradigm is useful for any model that exhibits similar high selectivity. Support is shown for an hypothesis that good frequency discrimination is possible without highly resonant structure. The nonlinear magnitude calculation is performed on signals developed without highly resonant structure, and differences in those magnitudes are signals shown to have good narrowband selectivity. Simultaneously, good transient behavior is preserved due to the avoidance of highly resonant structure. The cochlear paradigm is shown to provide a power spectrum with serendipitous good frequency selectivity and good transient response simultaneously.