693 research outputs found

    Distortion Exponent in MIMO Fading Channels with Time-Varying Source Side Information

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    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

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    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

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    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

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    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

    Towards a Realistic Assessment of Multiple Antenna HCNs: Residual Additive Transceiver Hardware Impairments and Channel Aging

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    Given the critical dependence of broadcast channels by the accuracy of channel state information at the transmitter (CSIT), we develop a general downlink model with zero-forcing (ZF) precoding, applied in realistic heterogeneous cellular systems with multiple antenna base stations (BSs). Specifically, we take into consideration imperfect CSIT due to pilot contamination, channel aging due to users relative movement, and unavoidable residual additive transceiver hardware impairments (RATHIs). Assuming that the BSs are Poisson distributed, the main contributions focus on the derivations of the upper bound of the coverage probability and the achievable user rate for this general model. We show that both the coverage probability and the user rate are dependent on the imperfect CSIT and RATHIs. More concretely, we quantify the resultant performance loss of the network due to these effects. We depict that the uplink RATHIs have equal impact, but the downlink transmit BS distortion has a greater impact than the receive hardware impairment of the user. Thus, the transmit BS hardware should be of better quality than user's receive hardware. Furthermore, we characterise both the coverage probability and user rate in terms of the time variation of the channel. It is shown that both of them decrease with increasing user mobility, but after a specific value of the normalised Doppler shift, they increase again. Actually, the time variation, following the Jakes autocorrelation function, mirrors this effect on coverage probability and user rate. Finally, we consider space division multiple access (SDMA), single user beamforming (SU-BF), and baseline single-input single-output (SISO) transmission. A comparison among these schemes reveals that the coverage by means of SU-BF outperforms SDMA in terms of coverage.Comment: accepted in IEEE TV

    Degrees of Freedom of Time Correlated MISO Broadcast Channel with Delayed CSIT

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    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

    Expected Distortion with Fading MIMO Channel and Side Information Quality

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    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
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