Thèse soutenue

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Auteur / Autrice : Sheng Yang
Direction : Jean-Claude Belfiore
Type : Thèse de doctorat
Discipline(s) : Télécommunications
Date : Soutenance en 2007
Etablissement(s) : Paris 6

Résumé

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Amplify-and-forward cooperation is an attractive scheme probably because of its low relaying complexity and its nature of linearity. In this thesis, we show that it is indeed efficient and optimal in various scenarios as far as the diversity is concerned. Using the diversity-multiplexing tradeoff (DMT) as our evaluation tool, two scenarios are considered : the large network scenario and the small network scenario. In large networks, requiring the relay terminals to decode the source message imposes a harsh constraint and limits the achievable multiplexing gain in general, especially when the source and the destination have multiple antennas. A naive amplify-and-forward scheme is space-only processing that achieves the maximum multiplexing gain but suffers from diversity loss. By introducing a simple temporal processing, a flip-and-forward scheme achieves both the maximum diversity and maximum multiplexing gain provided by the channel. It is the best known cooperative scheme in this scenario, in terms of the DMT. In small networks, the non-orthogonal amplify-and-forward (NAF) scheme is first studied. It is generalized to the MIMO case, where upper and lower bounds on the DMT the NAF scheme are derived. We then propose a non-orthogonal flip-and-forward scheme that achieves the maximum diversity of the channel. All the known half-duplex cooperation schemes, including both the class of decode-and-forward and amplify-and-forward schemes, are inefficient in the high multiplexing gain regime. With multiple relays, we show that the diversity gain can be improved by letting as much the source signal as possible be forwarded by the relays. A simple sequential slotted amplify-and-forward scheme is proposed. It is shown that this scheme tends to the cut-set bound in some particular cases when the number of slots goes to infinity. The proposed cooperation schemes in this thesis have equivalent MIMO or parallel MIMO channels. Both construction criterion and implementation of approximately universal codes are developed. The construction is then applied to studied cooperative channels.