Utilisation des antennes multiples dans un lien descendant des systèmes sans fils

par Mari Kobayashi

Thèse de doctorat en Électronique et communications

Sous la direction de Giuseppe Caire.

Soutenue en 2005

à Paris, ENST .

mots clés

• Mimo
• Codage treillis
• Décodage
• Antenne
• évaluation de ^performance
• Mise forme faisceau

Résumé

For point-to-point communication, Multi-Input Multi-Output technology has emerged as an attractive solution to increase the capacity by providing multiplexing gain and/or to improve the link quality by diversity. The first part focuses on the use of multiple antennas to increase the reliability of wireless links via space-time coding (STC). For frequency selective multi-input single-output fading channels, we propose a STC scheme that concatenates trellis-coded modulation with time-reversal orthogonal space-time block coding. Numerical examples show that our scheme offers superior performance at lower complexity than the existing schemes thanks to reduced-state joint equalization and decoding. The second and third parts investigate the use of multiple transmit antennas in a point-to-multipoint downlink system with channel state information at transmitter (CSIT). In the second part, we compare and random "opportunistic" beamforming by restricting ourselves to a rate feedback. We take into account the realistic aspects such as random packet arrivals, correlated block-fading channels, and a feedback delay. The realistic assumption of non-perfect CSIT yields a non-trivial tradeoff between multiuser diversity achieved by opportunistic beamforming and transmit diversity achieved by STC. In the third part, we consider a more qualitative "analog feedback" in which each user sends back its estimated channel without quantizing and coding. We propose a novel method for user selection and linear beamforming that maximizes a weighted sum rate over a beamforming matrix. Over a time-varying channel, our scheme achieves a smaller average delay than the previously considered schemes

Titre traduit

On the use of multiple antennas in a downlink of wireless systems

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