653 research outputs found
Améliorations des transmissions VLC (Visible Light Communication) sous contrainte d'éclairage : études théoriques et expérimentations
Abstract : Indoor visible light communication (VLC) networks based on light-emitting diodes (LEDs)
currently enjoy growing interest thanks in part to their robustness against interference,
wide license-free available bandwidth, low cost, good energy efficiency and compatibility
with existing lighting infrastructure. In this thesis, we investigate spectral-efficient modulation
techniques for the physical layer of VLC to increase throughput while considering
the quality of illumination as well as implementation costs. Numerical and experimental
studies are performed employing pulse amplitude modulation (PAM) and carrierless amplitude
and phase (CAP) modulation under illumination constraints and for high modulation
orders. Furthermore, the impact of LED nonlinearity is investigated and a postdistortion
technique is evaluated to compensate these nonlinear effects. Within this framework,
transmission rates in the order of a few hundred Mb/s are achieved using a test bench made
of low-cost components. In addition, an imaging multiple input multiple-output (MIMO)
system is developed and the impact on performance of imaging lens misalignment is theoretically
and numerically assessed. Finally, a polynomial matrix decomposition technique
based on the classical LU factorization method is studied and applied for the first time to
MIMO VLC systems in large space indoor environments.Les rĂ©seaux de communication en lumiĂšre visible (VLC) sâappuyant sur lâutilisation de diodes Ă©lectroluminescentes (LED) bĂ©nĂ©ficient actuellement dâun intĂ©rĂȘt grandissant, en partie grĂące Ă leur robustesse face aux interfĂ©rences Ă©lectromagnĂ©tiques, leur large bande disponible non-rĂ©gulĂ©e, leur faible coĂ»t, leur bonne efficacitĂ© Ă©nergĂ©tique, ainsi que leur compatibilitĂ© avec les infrastructures dâĂ©clairage dĂ©jĂ existantes. Dans cette thĂšse, nous Ă©tudions des techniques de modulation Ă haute efficacitĂ© spectrale pour la couche physique des VLC pour augmenter les dĂ©bits tout en considĂ©rant la qualitĂ© de lâĂ©clairage ainsi que les coĂ»ts dâimplĂ©mentation. Des Ă©tudes numĂ©riques et expĂ©rimentales sont rĂ©alisĂ©es sur la modulation dâimpulsion dâamplitude (PAM) et sur la modulation dâamplitude et de phase sans porteuse (CAP) sous des contraintes dâĂ©clairage et pour des grands ordres de modulation. De plus, lâimpact des non-linĂ©aritĂ©s de la LED est Ă©tudiĂ© et une technique de post-distorsion est Ă©valuĂ©e pour corriger ces effets non-linĂ©aires. Dans ce cadre, des dĂ©bits de plusieurs centaines de Mb/s sont atteints en utilisant un banc de test rĂ©alisĂ© Ă partir de composants Ă bas coĂ»ts. Par ailleurs, un systĂšme multi-entrĂ©es multi-sorties (MIMO) imageant est Ă©galement dĂ©veloppĂ© et lâimpact du dĂ©saxage de lâimageur sur les performances est Ă©tudiĂ©. Finalement, une technique de dĂ©composition polynomiale basĂ©e sur la mĂ©thode de factorisation classique LU est Ă©tudiĂ©e et appliquĂ©e aux systĂšmes MIMO VLC dans des grands espaces intĂ©rieurs
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MOCZ for Blind Short-Packet Communication: Practical Aspects
We investigate practical aspects of a recently introduced blind (noncoherent) communication scheme, called modulation on conjugate-reciprocal zeros (MOCZ). MOCZ is suitable for a reliable transmission of sporadic and short-packets at ultra-low latency and high spectral efficiency via unknown multipath channels, which are assumed to be static over the receive duration of one packet. The information is modulated on the zeros of the transmitted discrete-time baseband signalâs zâ transform. Because of ubiquitous impairments between the transmitter and receiver clocks, a carrier frequency offset occurs after down-conversion to the baseband. This results in a common rotation of the zeros. To identify fractional rotations of the base angle in the zero-pattern, we propose an oversampled direct zero-testing decoder to identify the most likely one. Integer rotations correspond to cyclic shifts of the binary message, which we determine by cyclically permutable codes (CPC). Additionally, the embedding of CPCs into cyclic codes, enables additive error-correction which reduces the bit-error-rate tremendously. Furthermore, we exploit the trident structure in the signalâs autocorrelation for an energy based detector to estimate timing offsets and the effective channel delay spread. We finally demonstrate how this joint data and channel estimation can be largely improved by receive antenna diversity at low SNR
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