Rodolfo Mann Pelz

On the optimisation of a noncoherent CDMA system based on M‐ary orthogonal modulation

This paper concerns the optimisation of a DS-CDMA based mobile communication system with respect to the transmission quality in the case of data and video services respectively. For combatting transmission errors, forward error protection based on convolutional codes and interleaving in connection with soft decision maximum-likelihood (ML) decoding through the Viterbi algorithm is applied. In this context, a technique to generate post-decision reliability information in the case of a noncoherent DS-CDMA receiver for a given ML metric is presented. The proposed error control strategy involves the application of equal error protection for raw data transmission with the average post-decoding BER as an optimisation criterion. In the case of a video transmission, a-priori knowledge regarding the error sensitivity of individual parameter sets suggests an unequal error protection strategy based on punctured convolutional codes, where the segmental SNR at the source codec output represents the optimisation criterion. Due to the high complexity of the system under investigation, corresponding results are obtained through simulation of the point-to-point transmission link. A significant gain regarding the achievable transmission quality with respect to conventional approaches can be achieved in connection with a compound design of source coding, channel coding and spectral spreading.

Error concealment for robust arithmetic decoding in mobile radio environments

Abstract Arithmetic coding is a technique for achieving maximum compression in video codecs by exploiting any residual correlation exhibited by parameter sets delivered by the source coding algorithm. This inherent characteristic implies poor error resilience, specially in the interesting case of low bit-rate video transmission over mobile networks. In this paper, a modified arithmetic decoding algorithm based on the adaptation of the underlying model probabilities according to reliability information delivered by a soft output channel decoder is presented. Furthermore, additional techniques for enhancement of the concatenated channel-source decoding scheme based on spatial linear prediction in conjunction with reliability estimates of the received video frame are presented. The performance of the addressed error concealment techniques is evaluated and analyzed through simulations in the case of an error protected video transmission over a Gaussian and mobile Rayleigh fading channel.