Denis Rouffet

Robust VLC sequence decoding exploiting additional video stream properties with reduced complexity

Joint source-channel decoding of variable length codes (VLC) for image and video streaming transmission over unreliable links, such as wireless networks, is a subject of increasing interest. Much more residual source redundancy can be exploited when both types of correlation: (i) the correlation between bits inside a VLC codeword as well as; (ii) the correlation between VLC codewords of a VLC sequence unit (e.g. corresponding to one image block), are taken into account. The paper (Hang Nguyen et al, IEEE Int. Conf. on Acoustics, Speech, and Sigpro., 2004) proposes an optimum maximum likelihood (ML) decoder of VLC sequences which can exploit these two kinds of correlation and outperforms the existing VLC decoders. This paper proposes a reduced complexity version of this optimal VLC decoder. Simulation results show that the complexity is reduced by 5 in terms of number of possible candidates, while the performance is only slightly sub-optimal compared with the optimal version of the Hang Nguyen paper.

Optimal VLC sequence decoding exploiting additional video stream properties

Joint source-channel decoding of variable length codes (VLC) for image and video streaming transmission over unreliable links, such as wireless networks, is a subject of increasing interest. This paper proposes an optimum maximum likelihood (ML) decoder of VLC sequences which exploits additional inherent redundancy in the source information, namely: (i) the correlation between bits, inside a VLC codeword; as well as (ii) the correlation between VLC codewords of a VLC sequence unit (e.g. corresponding to one image block). Performance results for improving video decoding over AWGN channels are then presented and compared to the prefix-based decoder as well as the recently proposed VLC decoders.

Progressive set-up of LEO inclined constellations

Low Earth Orbiting satellites constellations are proposed for mobile satellite services. The constellation optimization can be driven by several factors in order to provide a high capacity worlwide telephony system and a minimized total cost. This paper proposes a set-up procedure of the constellation in order to take into account the time-dependent penetration of the system. At the begining of the service a first part of the constellation is launched in order to offer the service to the first users. During the second phase of service, a second part of the constellation is launched in order to offer the required capacity for a growing demand. The last phase corresponds to the maximum penetration of the market where the constellation is completed. This set-up procedure allows to spread the total invesment cost, and to offer a capacity matching the customers demand. The orbit altitude, the inclination angle and the orbital phasings are chosen in order to minimize the total number of satellites in accordance with the ability to offer a progressive set-up of the constellation.