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Theses

Analyse de performances de systèmes de communication sans-fils exploitant micro- et macro-diversité

Abstract : Wireless systems are now popular worldwide to help people and machines to communicate with each other independently
of their location. Hence, the demand for capacity in cellular and wireless local area networks has grown
in a literally explosive manner during the last decade. But, data transmission over wireless communication suffers
from several channel impairements such as fading and cochannel interference. An efficient technique to mitigate
the fading and increase the communication link robustness is the spatial diversity.
This thesis deals with the perfomance analysis of wireless communication systems exploiting spatial micro- and
macro-diversity. The first part is concerned with the investigation of Multiple-Input Multiple-Output (MIMO)
systems using Orthogonal Frequency division Multiplexing (OFDM), in the micro-diversity context. It is shown
that taking into account the real channel delay profile can have an impact on the MIMO/OFDM system ergodic and
outage capacities, when a parametrized cannel model is considered. Then, two space-time block coding schemes
are proposed for a MIMO/OFDM system using two transmit antennas. These schemes, based on the Alamouti
code, partially simulate the spatial diversity by the frequency one by taking advantages of the OFDM modulation,
and present a rate of a half. We find that the diversity order of the proposed schemes converges to a half-rate
scheme using 4 antennas instead of 2.
The second part deals with the performance of wireless systems exploiting spatial macro-diversity. First, a realistic
channel model based on a refinement of the Radio-Frequency Fornt-End (RFFE) is proposed. The impact of
this realistic channel model on the MIMO system capacity is investigated, in both the micro- and macro-diversity
contexts. It is shown that this refined channel model can describe the capacity behavior as observed in real implementations.
Then, an optimal power allocation algorithm is proposed for the two-relay regenerative parallel
transmission system. This optimization, subject to a cartain power budget to be allocated between the two relays,
is done in order to minimize the BER at the destination. It is found that the relayed transmission can give better
results than the direct transmission, and that the optimal power allocation is more useful when the relayed links
are unbalanced.
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https://tel.archives-ouvertes.fr/tel-00011058
Contributor : Ilham Ouachani <>
Submitted on : Saturday, November 19, 2005 - 10:28:36 PM
Last modification on : Wednesday, September 16, 2020 - 4:43:24 PM
Long-term archiving on: : Friday, April 2, 2010 - 11:03:10 PM

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Ilham Ouachani. Analyse de performances de systèmes de communication sans-fils exploitant micro- et macro-diversité. Réseaux et télécommunications [cs.NI]. Université Paris Sud - Paris XI, 2005. Français. ⟨tel-00011058⟩

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