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Etude et optimisation des systèmes multi-antennes associés à des modulations multiporteuses

Abstract : Since several years, multi-antenna systems are foreseen as a potential solution for increasing
the throughput of future wireless communication systems. The aim of this thesis is to study
and to improve the transmitter and receiver's techniques of these MIMO (Multiple Input
Multiple Output) systems in the context of a multi-carrier transmission.
On the one hand, the OFDM (Orthogonal Frequency Division Multiplex) modulation,
which transform a frequency selective channel into multiple non frequency selective channels,
is particularly well adapted to the conception of MIMO receivers with low complexity.
On the other hand, two techniques allowing to improve the exploitation of frequential
and/or temporal diversities are associated with OFDM, namely linear precoding (LP-OFDM)
and CDMA in a MC-CDMA (Multicarrier Code division Multiplex Access) scheme.
We have associated LP-OFDM and MC-CDMA with two MIMO techniques which require
no channel state information at the transmitter, that is STBC (Space-Time Block Coding)
and spatial multiplexing.
It is shown that for these two systems MIMO MC-CDMA and MIMO LP-OFDM, spatial,
temporal and frequential diversities are efficiently exploited.
The advantage of the association with orthogonal STBC is that low complexity receivers
can be implemented. In fact, for a STBC LP-OFDM system, a simple linear MMSE equalizer
leads to performance close to those obtained with a Maximum Likelihood (ML) receiver allowing
the use of large linear precoding matrices. For STBC MC-CDMA, like SISO MC-CDMA,
single-user detectors leads to the best tradeoff performance/complexity.
When LP-OFDM or MC-CDMA are associated with spatial multiplexing, the surplus
of complexity for the receivers is inherent to the multi-antenna interference. We have also
demonstrated that the implementation of a simple MMSE receiver requiring the inversion of
the MIMO channel matrix leads to very good performance. A similar process can be applied
for non orthogonal STBC.
Combined with an iterative process when channel coding is inserted at the transmitter,
all these systems can reach the matched filter bound performance close to the gaussian curve
performance using simple operations.
The gain in spectral efficiency and performance is to the advantage of spatial multiplexing
techniques because they benefit from the linear augmentation of the capacity with the minimum
number of transmit and receive antennas. The trade-off between throughput and
complexity will indicate the choice of the MIMO system to associate with LP-OFDM and
MC-CDMA. Theoretical channels as well as realistic channels are simulated with or without
correlation between antennas.
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-00009531
Contributor : Vincent Le Nir <>
Submitted on : Friday, June 17, 2005 - 8:22:44 PM
Last modification on : Wednesday, November 6, 2019 - 1:26:15 AM
Long-term archiving on: : Friday, April 2, 2010 - 9:59:39 PM

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  • HAL Id : tel-00009531, version 1

Citation

Vincent Le Nir. Etude et optimisation des systèmes multi-antennes associés à des modulations multiporteuses. Traitement du signal et de l'image [eess.SP]. INSA de Rennes, 2004. Français. ⟨tel-00009531⟩

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