15 research outputs found
Возможности преобразования Вейля-Гейзенберга в стандарте сжатия JPEG
Статья посвящена разработке и исследованию новой технологии сжатия на основе базисов Вейля-Гейзенберга (WH-технологии) для модификации стандарта сжатия JPEG и улучшения его характеристик. С этой целью в работе анализируются основные этапы алгоритма сжатия JPEG, отмечаются его ключевые особенности и узкие места, ограничивающие дальнейшее повышение его эффективност
Сжатие изображений с использованием дискретного преобразования Вейля-Гейзенберга
Предлагается новый подход к сжатию растровых изображений, основанный на использовании двухстороннего вещественного дискретного преобразования Вейля-Гейзенберг
Synthesis of Real Weyl-Heisenberg Signal Frames with Desired Frequency-Time Localization
An algebraic approach to the synthesis of optimal real Weyl-Heisenberg frames with the best frequency-time localization oriented to the processing of discrete signals is developed. The chosen optimality criterion ensures the construction of a tight signal frame with the lowest standard deviation of frame functions from the desired standard. In addition, a special algebraic structure of the synthesis algorithm in the form of a product of sparse matrices allows for efficient computational implementation and flexible adjustment of the frequency-time resolution of the signal functions of the frame. The results of the experiment confirming the effective computational implementation of the algorithm and a desired time-frequency localization of frame functions are presented
Joint bit allocation and precoding for filterbank transceivers in NOFDM systems
Recently, the non orthogonal frequency division multiplexing (NOFDM) systems have
attracted increased interest. They have several advantages over traditional OFDM
systems: higher bandwidth efficiency; reduced sensitivity to carrier frequency offsets,
oscillator phase noise and narrowband interference; and reduced intersymbol/intercarrier
interference (ISI/ICI). In particular, low ISI/ICI will be important for future systems
where Doppler frequencies will be larger (equivalently, channel variations will be
faster) due to higher carrier frequencies and higher mobile velocities.
In the first part of this thesis the duality of multicarrier systems and Gabor frames
is discussed and applied to the design of a generalized multicarrier system based on
a filterbank structure. The efficient polyphase implementation is also discussed.
In this thesis the channel capacity of a GMC systems is evaluated through the
diagonalization of an equivalent matrix model where intersymbol and intercarrier
interferences have been included. Exploiting the majorization theory, the mutual information
can be represented as a Schur-concave function and it is maximized through
a joint transceiver design adding a linear precoder at the transmitter and a LMMSE
equalizer at the receiver. The capacity is derived by the eigenvalue decomposition
of the global system matrix including the noise colored by the receiver filtering and
employing a power allocation of the transmitted power according to the well-known
water-filling solution.
This thesis investigates also the behaviour of the NOFDM systems when a power
and bit allocation algorithm (like the Campello one) is employed in order to satisfy
a certain QoS constrain. A comparison of the performances with OFDM systems is
included.
Finally a simple application of the cognitive radio paradigm employing filterbankbased
multicarrier systems is developed and some interesting results are showed
Noncoherent Capacity of Underspread Fading Channels
We derive bounds on the noncoherent capacity of wide-sense stationary
uncorrelated scattering (WSSUS) channels that are selective both in time and
frequency, and are underspread, i.e., the product of the channel's delay spread
and Doppler spread is small. For input signals that are peak constrained in
time and frequency, we obtain upper and lower bounds on capacity that are
explicit in the channel's scattering function, are accurate for a large range
of bandwidth and allow to coarsely identify the capacity-optimal bandwidth as a
function of the peak power and the channel's scattering function. We also
obtain a closed-form expression for the first-order Taylor series expansion of
capacity in the limit of large bandwidth, and show that our bounds are tight in
the wideband regime. For input signals that are peak constrained in time only
(and, hence, allowed to be peaky in frequency), we provide upper and lower
bounds on the infinite-bandwidth capacity and find cases when the bounds
coincide and the infinite-bandwidth capacity is characterized exactly. Our
lower bound is closely related to a result by Viterbi (1967).
The analysis in this paper is based on a discrete-time discrete-frequency
approximation of WSSUS time- and frequency-selective channels. This
discretization explicitly takes into account the underspread property, which is
satisfied by virtually all wireless communication channels.Comment: Submitted to the IEEE Transactions on Information Theor
Etude et évaluation d un multiplexage fréquentiel basé sur l OFDM/OQAM
Cette thèse est consacrée à l étude de la modulation OFDM/OQAM en tant qu alternative à la modulation OFDM. Nous traitons plus particulièrement le contexte multiusagers. De ce point de vue, les aspects de synchronisation sont déterminants. Les différentes options plus le choix de la forme d onde sont donc examinés de ce point de vue. Un autre objectif est de montrer de manière précise comment la modulation OFDM/OQAM peut s adapter à une transmission de type cellulaire, en prenant comme référence le système 3GPP/LTE. Les principales contributions que nous avons apportées sont : 1) Une analyse des phénomènes de désynchronisation : nous analysons l effet de la désynchronisation, suivant les axes temporel et fréquentiel, sur les performances de l OFDM/OQAM au récepteur. 2) Méthode de synchronisation : nous analysons une méthode de synchronisation temporelle définie dans un contexte de transmission OFDM/OQAM mono-usager et nous l adaptons à un scénario de type multi-usagers. 3) Proposition d un schéma d accès multiple : nous proposons un schéma d accès multiple basé sur la modulation OFDM/OQAM, alternatif aux techniques connues OFDMA et SC-FDMA, pour la transmission en liaison montante dans un contexte de type 3GPP/LTE.This thesis is dedicated to the study of the OFDM/OQAM modulation as an alternative to the OFDM modulation. We treat more especially the multi-user environment. In this respect, synchronization aspects are crucial. The different options plus the choice of the waveform are examined in this point of view. Another objective is to precisely show how the OFDM/OQAM can be adapted to a cellular transmission type, taking as reference the 3GPP/LTE system. The main contributions we have made are : 1) Analysis of the desynchronization phenomena : we analyze the effect of desynchronization, according to the time and frequency axes, on the performance of OFDM/OQAM at the receiver side. 2) Synchronization method : we analyze a method of temporal synchronization defined in a single user OFDM/OQAM transmission and we adapt it to a multi-user scenario type. 3) Proposing for a multiple access scheme : we propose a multiple access scheme based on theOFDM/OQAM modulation, alternative to the known techniques OFDMA and SC-FDMA, for the UL transmission in a 3GPP/LTE context.PARIS-CNAM (751032301) / SudocSudocFranceF
Information Theory of underspread WSSUS channels
The chapter focuses on the ultimate limit on the rate of reliable communication through Rayleigh-fading channels that satisfy the wide-sense stationary (WSS) and uncorrelated scattering (US) assumptions and are underspread. Therefore, the natural setting is an information-theoretic one, and the performance metric is channel capacity. The family of Rayleigh-fading underspread WSSUS channels constitutes a good model for real-world wireless channels: their stochastic properties, like amplitude and phase distributions match channel measurement results. The Rayleigh-fading and the WSSUS assumptions imply that the stochastic properties of the channel are fully described by a two-dimensional power spectral density (PSD) function, often referred to as scattering function. The underspread assumption implies that the scattering function is highly concentrated in the delay-Doppler plane. Two important aspects need to be accounted for by a model that aims at being realistic: neither the transmitter nor the receiver knows the realization of the channel; and the peak power of the transmit signal is limited. Based on these two aspects the chapter provides an information-theoretic analysis of Rayleigh-fading underspread WSSUS channels in the noncoherent setting, under the additional assumption that the transmit signal is peak-constrained
On the Sensitivity of Continuous-Time Noncoherent Fading Channel Capacity
The noncoherent capacity of stationary discrete-time fading channels is known
to be very sensitive to the fine details of the channel model. More
specifically, the measure of the support of the fading-process power spectral
density (PSD) determines if noncoherent capacity grows logarithmically in SNR
or slower than logarithmically. Such a result is unsatisfactory from an
engineering point of view, as the support of the PSD cannot be determined
through measurements. The aim of this paper is to assess whether, for general
continuous-time Rayleigh-fading channels, this sensitivity has a noticeable
impact on capacity at SNR values of practical interest.
To this end, we consider the general class of band-limited continuous-time
Rayleigh-fading channels that satisfy the wide-sense stationary
uncorrelated-scattering (WSSUS) assumption and are, in addition, underspread.
We show that, for all SNR values of practical interest, the noncoherent
capacity of every channel in this class is close to the capacity of an AWGN
channel with the same SNR and bandwidth, independently of the measure of the
support of the scattering function (the two-dimensional channel PSD). Our
result is based on a lower bound on noncoherent capacity, which is built on a
discretization of the channel input-output relation induced by projecting onto
Weyl-Heisenberg (WH) sets. This approach is interesting in its own right as it
yields a mathematically tractable way of dealing with the mutual information
between certain continuous-time random signals.Comment: final versio