629 research outputs found
Distortion Exponent in MIMO Fading Channels with Time-Varying Source Side Information
Transmission of a Gaussian source over a time-varying multiple-input
multiple-output (MIMO) channel is studied under strict delay constraints.
Availability of a correlated side information at the receiver is assumed, whose
quality, i.e., correlation with the source signal, also varies over time. A
block-fading model is considered for the states of the time-varying channel and
the time-varying side information; and perfect state information at the
receiver is assumed, while the transmitter knows only the statistics. The high
SNR performance, characterized by the \textit{distortion exponent}, is studied
for this joint source-channel coding problem. An upper bound is derived and
compared with lowers based on list decoding, hybrid digital-analog
transmission, as well as multi-layer schemes which transmit successive
refinements of the source, relying on progressive and superposed transmission
with list decoding. The optimal distortion exponent is characterized for the
single-input multiple-output (SIMO) and multiple-input single-output (MISO)
scenarios by showing that the distortion exponent achieved by multi-layer
superpositon encoding with joint decoding meets the proposed upper bound. In
the MIMO scenario, the optimal distortion exponent is characterized in the low
bandwidth ratio regime, and it is shown that the multi-layer superposition
encoding performs very close to the upper bound in the high bandwidth expansion
regime.Comment: Submitted to IEEE Transactions on Information Theor
On Optimum End-to-End Distortion in MIMO Systems
This paper presents the joint impact of the numbers of antennas,
source-to-channel bandwidth ratio and spatial correlation on the optimum
expected end-to-end distortion in an outage-free MIMO system. In particular,
based on an analytical expression valid for any SNR, a closed-form expression
of the optimum asymptotic expected end-to-end distortion valid for high SNR is
derived. It is comprised of the optimum distortion exponent and the
multiplicative optimum distortion factor. Demonstrated by the simulation
results, the analysis on the joint impact of the optimum distortion exponent
and the optimum distortion factor explains the behavior of the optimum expected
end-to-end distortion varying with the numbers of antennas, source-to-channel
bandwidth ratio and spatial correlation. It is also proved that as the
correlation tends to zero, the optimum asymptotic expected end-to-end
distortion in the setting of correlated channel approaches that in the setting
of uncorrelated channel. The results in this paper could be performance
objectives for analog-source transmission systems. To some extend, they are
instructive for system design.Comment: 35 pages, 10 figures, submitted to EURASIP Journal on Wireless
Communications and Networkin
Joint Source-Channel Coding with Time-Varying Channel and Side-Information
Transmission of a Gaussian source over a time-varying Gaussian channel is
studied in the presence of time-varying correlated side information at the
receiver. A block fading model is considered for both the channel and the side
information, whose states are assumed to be known only at the receiver. The
optimality of separate source and channel coding in terms of average end-to-end
distortion is shown when the channel is static while the side information state
follows a discrete or a continuous and quasiconcave distribution. When both the
channel and side information states are time-varying, separate source and
channel coding is suboptimal in general. A partially informed encoder lower
bound is studied by providing the channel state information to the encoder.
Several achievable transmission schemes are proposed based on uncoded
transmission, separate source and channel coding, joint decoding as well as
hybrid digital-analog transmission. Uncoded transmission is shown to be optimal
for a class of continuous and quasiconcave side information state
distributions, while the channel gain may have an arbitrary distribution. To
the best of our knowledge, this is the first example in which the uncoded
transmission achieves the optimal performance thanks to the time-varying nature
of the states, while it is suboptimal in the static version of the same
problem. Then, the optimal \emph{distortion exponent}, that quantifies the
exponential decay rate of the expected distortion in the high SNR regime, is
characterized for Nakagami distributed channel and side information states, and
it is shown to be achieved by hybrid digital-analog and joint decoding schemes
in certain cases, illustrating the suboptimality of pure digital or analog
transmission in general.Comment: Submitted to IEEE Transactions on Information Theor
Side information aware source and channel coding in wireless networks
Signals in communication networks exhibit significant correlation, which can stem from the physical nature of the underlying sources, or can be created within the system. Current layered network architectures, in which, based on Shannon’s separation theorem, data is compressed and transmitted over independent bit-pipes, are in general not able to exploit such correlation efficiently. Moreover, this strictly layered architecture was developed for wired networks and ignore the broadcast and highly dynamic nature of the wireless medium, creating a bottleneck in the wireless network design. Technologies that exploit correlated information and go beyond the layered network architecture can become a key feature of future wireless networks, as information theory promises significant gains. In this thesis, we study from an information theoretic perspective, three distinct, yet fundamental, problems involving the availability of correlated information in wireless networks and develop novel communication techniques to exploit it efficiently. We first look at two joint source-channel coding problems involving the lossy transmission of Gaussian sources in a multi-terminal and a time-varying setting in which correlated side information is present in the network. In these two problems, the optimality of Shannon’s separation breaks down and separate source and channel coding is shown to perform poorly compared to the proposed joint source-channel coding designs, which are shown to achieve the optimal performance in some setups. Then, we characterize the capacity of a class of orthogonal relay channels in the presence of channel side information at the destination, and show that joint decoding and compression of the received signal at the relay is required to optimally exploit the available side information. Our results in these three different scenarios emphasize the benefits of exploiting correlated side information at the destination when designing a communication system, even though the nature of the side information and the performance measure in the three scenarios are quite different.Open Acces
Expected Distortion with Fading MIMO Channel and Side Information Quality
Projecte final de carrera fet en col.laboració amb CTTCCatalà: Considerem el problema de codificació conjunta de font i canal d'enviar una font Gaussiana sobre un canal fading multi-antena (MIMO) quan el decodificador té informació adicional correlada amb la font, amb una qualitat també variant amb el temps. Assumim un model block fading per ambdues qualitats del canal i la informació adicional, i assumim coneixement perfecte de canal a recepció, mentre que el transmissor només disposa de coneixement estadístic. Estem interessats en la distorsió quadràtica mitja d'aquest sistema. Estudiem separació en la codificació canal font, transmissió no codificada i dues tècniques de codificació conjunta de font i canal basades en decodificació conjunta a recepció: NBJD, que no utilitza binning no explicit i decodificació conjunta a recepció i HDA, que comprimeix la font i transmet l?error. Al decodificador, la paraula comprimida es recupera per decodificació conjunta amb l?error transmès i la informació adicional. Extenem aquestes tècniques a esquemes híbrids analògics-digitals i esquemes multi-capa. Estudiem numèricament el problema i donem resultats per el règim de SNR finita. Proporcionem expresions tancades per el Distortion exponent a regim de alta SNR. ////// Castellà: Consideramos el problema de codificación conjunta de fuente y canal de enviar una fuente Gaussiana sobre un canal fading multi-antena (MIMO) cuando el decodificador tiene información adicional correlada con la fuente, con una cualidad también variante en el tiempo. Asumimos un modelo block fading para ambas calidades del canal y la información adicional. Asumimos conocimiento perfecto de canal en recepción, mientras que el transmisor solo dispone de conocimiento estadístico. Estamos interesados en la distorsión cuadrática media de este sistema. Estudiamos separación en la codificación canal fuente, transmisión no codificada y dos técnicas de codificación conjunta de fuente y canal basadas en decodificación conjunta en recepción: NBJD, que no utiliza binning no explicito y decodificación conjunta, y HDA, que comprime la fuente y transmite el error. Al decodificar, la palabra comprimida es recuperada por decodificación conjunta entre el error transmitido y la información adicional. Extendemos estas técnicas a esquemas híbridos analógico-digitales y esquemas multi-capa. Estudiamos numéricamente el problema y damos resultados para el régimen de SNR finita. Proporcionamos expresiones cerradas para el Distortion exponent en régimen de alta SNR ////// English: We consider the joint source-channel coding problem of sending a Gaussian source over a multiple input-multiple output (MIMO) fading channel when the decoder has additional correlated side information whose quality is also time-varying. We assume a block fading model for both the channel and side information qualities, and assume perfect state information at the receiver, while the transmitter has only a statistical knowledge. We are interested in the expected squared-error distortion for this system. We study separate source-channel coding, uncoded transmission and two joint source-channel transmission schemes based on joint decoding at the receiver: NBJD, that uses no explicit binning and joint decoding of the side information and the channel output at the decoder and HDA, that compresses the source and transmits the error. At the decoder, the quantized codeword is recovered by means of joint decoding of the error and the side information. We extend such techniques to hybrid digital-analog and multi-layer schemes. We study numerically the problem and give results in the finite SNR regime. We provide closed form expressions for the distortion exponent in the high SNR regime
Degrees of Freedom of Time Correlated MISO Broadcast Channel with Delayed CSIT
We consider the time correlated multiple-input single-output (MISO) broadcast
channel where the transmitter has imperfect knowledge on the current channel
state, in addition to delayed channel state information. By representing the
quality of the current channel state information as P^-{\alpha} for the
signal-to-noise ratio P and some constant {\alpha} \geq 0, we characterize the
optimal degree of freedom region for this more general two-user MISO broadcast
correlated channel. The essential ingredients of the proposed scheme lie in the
quantization and multicasting of the overheard interferences, while
broadcasting new private messages. Our proposed scheme smoothly bridges between
the scheme recently proposed by Maddah-Ali and Tse with no current state
information and a simple zero-forcing beamforming with perfect current state
information.Comment: revised and final version, to appear in IEEE transactions on
Information Theor
On the Non-Orthogonal Layered Broadcast Codes in Cooperative Wireless Networks
A multi-fold increase in spectral efficiency and throughput are envisioned in the fifth generation of cellular networks to meet the requirements of International Telecommunication Union (ITU) IMT-2020 on massive connectivity and tremendous data traffic. This is achieved by evolution in three aspects of current networks. The first aspect is shrinking the cell sizes and deploying dense picocells and femtocells to boost the spectral reuse. The second is to allocate more spectrum resources including millimeter-wave bands. The third is deploying highly efficient communications and multiple access techniques. Non-orthogonal multiple access (NOMA) is a promising communication technique that complements the current commercial spectrum access approach to boost the spectral efficiency, where different data streams/users’ data share the same time, frequency and code resource blocks (sub-bands) via superimposition with each other. The receivers decode their own messages by deploying the successive interference cancellation (SIC) decoding rule. It is known that the NOMA coding is superior to conventional orthogonal multiple access (OMA) coding, where the resources are split among the users in either time or frequency domain. The NOMA based coding has been incorporated into other coding techniques including multi-input multi-output (MIMO), orthogonal frequency division multiplexing (OFDM), cognitive radio and cooperative techniques. In cooperative NOMA codes, either dedicated relay stations or stronger users with better channel conditions, act as relay to leverage the spatial diversity and to boost the performance of the other users. The advantage of spatial diversity gain in relay-based NOMA codes, is deployed to extend the coverage area of the network, to mitigate the fading effect of multipath channel and to increase the system throughput, hence improving the system efficiency. In this dissertation we consider the multimedia content delivery and machine type communications over 5G networks, where scalable content and low complexity encoders is of interest. We propose cross-layer design for transmission of successive refinement (SR) source code interplayed with non-orthogonal layered broadcast code for deployment in several cooperative network architectures. Firstly, we consider a multi-relay coding scheme where a source node is assisted by a half-duplex multi-relay non-orthogonal amplify-forward (NAF) network to communicate with a destination node. Assuming the channel state information (CSI) is not available at the source node, the achievable layered diversity multiplexing tradeoff (DMT) curve is derived. Then, by taking distortion exponent (DE) as the figure of merit, several achievable lower bounds are proved, and the optimal expected distortion performance under high signal to noise ratio (SNR) approximation is explicitly obtained. It is shown that the proposed coding can achieve the multi-input single-output (MISO) upper bound under certain regions of bandwidth ratios, by which the optimal performance in these regions can be explicitly characterized. Further the non-orthogonal layered coding scheme is extended to a multi-hop MIMO decode-forward (DF) relay network where a set of DE lower bounds is derived.
Secondly, we propose a layered cooperative multi-user scheme based on non-orthogonal amplify-forward (NAF) relaying and non-orthogonal multiple access (NOMA) codes, aiming to achieve multi-user uplink transmissions with low complexity and low signaling overhead, particularly applicable to the machine type communications (MTC) and internet of things (IoT) systems. By assuming no CSI available at the transmitting nodes, the proposed layered codes make the transmission rate of each user adaptive to the channel realization. We derive the close-form analytical results on outage probability and the DMT curve of the proposed layered NAF codes in the asymptotic regime of high SNR, and optimize the end-to-end performance in terms of the exponential decay rate of expected distortion.
Thirdly, we consider a single relay network and study the non-orthogonal layered scheme in the general SNR regime. A layered relaying scheme based on compress-forward (CF) is introduced, where optimization of end to end performance in terms of expected distortion is conducted to jointly determine network parameters. We further derive the explicit analytical optimal solution with two layers in the absence of channel knowledge.
Finally, we consider the problem of multicast of multi-resolution layered messages over downlink of a cellular system with the assumption of CSI is not available at the base station (BS). Without loss generality, spatially random users are divided into two groups, where the near group users with better channel conditions decode for both layers, while the users in the second group decode for base layer only. Once the BS launches a multicast message, the first group users who successfully decoded the message, deploy a distributed cooperating scheme to assist the transmission to the other users. The cooperative scheme is naive but we will prove it can effectively enhance the network capacity. Closed form outage probability is explicitly derived for the two groups of users. Further it is shown that diversity order equal to the number of users in the near group is achievable, hence the coding gain of the proposed distributed scheme fully compensate the lack of CSI at the BS in terms of diversity order
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