1,720,978 research outputs found
On a fast digital method of estimating the autocorrelation of a gaussian stationary process
No full textMethods for Estimating the Autocorrelation Function of Complex Gaussian Stationary Processes
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Performance of nonlinear adaptive SbS-MAP detector using soft-statistics for digital transmissions over HF channels
No full textThe effectiveness of the recently proposed adaptive Maximum A Posteriori (MAP) receiver in Cusani and Mattila is verified for digital HF links between mobile and/or fixed units. Following Cusani and Mattila, a suitable MAP algorithm is employed to compute Symbol-by-Symbol (SBS) the A Posteriori Probabilities (APP's) of the channel state; from these, the detected data stream is obtained. The same APP's are employed by an adaptive nonlinear Kalman-like filter to estimate recursively the time-varying channel with fast convergence and good tracking properties, overcoming the delay problem suffered by conventional adaptive MLSE-VA detectors. Computer simulations allow to compare the adaptive SBS-MAP with other receivers (DFE, MLSE) and verify its effectiveness in the HF environment
Use of second-order statistics in texture synthesis-by-analysis
No full textSynthesis-by-analysis is a well established paradigm for reproduction of textures having random appearance. In this contribution, in order to simplify the overall procedure in the case of colored textures, we exploit the second-order correlation existing between the texture chrominance and luminance components. Specifically, we perform the synthesis exclusively on the luminance component, while the chrominance components are reproduced by applying properly designed Wiener filters, whose coefficients have been previously calculated in the analysis stage. This approach yields excellent results especially on natural textures, which intrinsically present a high degree of correlation between the luminance and chrominance components. Moreover, to enhance the synthesis resolution, the same paradigm is then applied to reproduce high-order components of a texture multi-resolution representation based on the Circular Harmonic Functions expansion
Optimal Territorial Resources Placement for Multipurpose Wireless Services Using Genetic Algorithms
No full textThis paper presents a study for finding a solution to the placement of territorial resources for multipurpose wireless services considering also the restrictions imposed by the orography of the territory itself. To solve this problem genetic algorithms are used to identify sites where to place the resources for the optimal coverage of a given area. The used algorithm has demonstrated to be able to find optimal solutions in a variety of considered situations
Estimation of Number of Sources Impinging on a Uniformly Spaced Linear Array of Sensors
No full textA novel estimation method of number of sources emitting waves on an uniformly spaced linear array of sensors is described. Similarly to well-known existing techniques, it is inspired by certain properties hold by the eigenvalues of the correlation matrix of the received signal. Numerical results show the feasibility of the here presented novel estimator in comparison with popular, Information Theoretic Criteria based estimators
On the Effect of Channel Knowledge in Underwater Acoustic Communications: Estimation, Prediction and Protocol
Full text linkUnderwater acoustic communications are limited by the following channel impairments: time variability, narrow bandwidth, multipath, frequency selective fading and the Doppler effect. Orthogonal Frequency Division Modulation (OFDM) is recognized as an effective solution to such impairments, especially when optimally designed according to the propagation conditions. On the other hand, OFDM implementation requires accurate channel knowledge atboth transmitter and receiver sides. Long propagation delay may lead to outdated channel information. In this work, we present an adaptive OFDM scheme where channel state information is predicted through a Kalman-like filter so as to optimize communication parameters, including the cyclic prefix length. This mechanism aims to mitigate the variability of channel delay spread. This is cast in a protocol where channel estimation/prediction are jointly considered, so as to allow efficiency. The performance obtained through extensive simulations using real channels and interference show the effectiveness of the proposed scheme, both in terms of rate and reliability, at the expense of an increasing complexity. However, this solution is significantly preferable to the conventional mechanism, where channel estimation is performed only at the receiver, with channel coefficients sent back to the transmit node by means of frequent overhead signaling
Modulation precoding for MISO visible light communications
No full textIndoor Visible Light Communication is recognized as a viable and smart solution to provide both illumination and wireless connectivity by conveniently modulating optical signals generated by Light Emitting Diodes. When dealing with multiple independent sources, the communication reliability is tied to the capability of separating signals. Such task is typically accomplished by realizing Multiple-Input Multiple-Output architectures, with efficient spatial equalization affordable thanks to the presence of several photodetectors equipping the receiver. On the other hand, dealing with reliability issue, it becomes very challenging in Multiple-Input Single-Output scenarios where channels spatial correlation may severely impact on the communication performance. In this context, we propose a modulation precoding scheme aiming to maximize the minimum distance between received signal power levels at the receiver thus lowering the symbol error probability. To do so, channel state information is required at the transmit side. At the same time, the solution offered by the presented scheme guarantees the lighting constraints, explicitly requested in terms of received optical power, to be met as well
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