1,721,150 research outputs found
Le parole dei bambini al termine della Scuola Primaria.
No full textNel contributo si indaga sulle parole, sulla loro qualità e quantità, alla fine della scuola primaria
Rapid search algorithms for code acquisition in UWB impulse radio communications
No full textUltrawideband (UWB) impulse radio is an emerging technology suitable for high-rate tactical wireless communications. One of the crucial challenges for a connecting station remains the initial code acquisition, in a hostile propagation environment (e.g., urban combat). In this paper, we address the coarse acquisition of pseudonoise (PN) codes and propose algorithms for speeding up the acquisition process and/or reducing the complexity of the acquisition algorithm itself. Also, in the case of energy detection, we show that the front-end sampling rate may be reduced. An in-depth analysis, supported by simulations in the presence of multipath is presented, and the results discussed
Pseudo-chaotic communication method exploiting symbolic dynamics
No full textA pseudo-chaotic coding/modulation method. The coding method exploits symbolic dynamics of a chaotic map at the transmitter to encode data. The encoding synthesizes the chaotic map based upon the data to be transmitted. In a preferred embodiment, pseudo-chaotic iterates are generated from a digital implementation of a Bernoulli shift map. The output of the shift map is translated by a mapping, preferably implemented by a digital signal processor, to allow transitions between states in a transmitted signal to differ, and the translated map is used to drive a modulator (for example PPM, FSK, PSK, QAM, etc.). In the specific case of pulse-position modulation (PPM) the translated map is used to modulate pulse train positions within a periodic synchronization frame.; The preferred embodiment uses a shift register to implement an approximation of the Bernoulli shift map acting as a form of convolutional code with a number of states equal to the symbolic states defined on the chaotic map. A receiver may use fewer states and still decode the data signal, allowing receiver scalability
Orthogonal Convolutional Modulation for UWB-Impulse Radio Systems: Performance Analysis and Adaptive Schemes
No full textIn the context of UWB (ultra-wide band) Impulse Radio (IR) heterogeneous low data-rate networks, the need for coding/modulation schemes amenable of both coherent and noncoherent detection has emerged. The rationale is the potential coexistence of different classes of nodes, characterized by different complexity and performances. In such scenario, one of the main technical challenges is the design of efficient coding/modulation schemes incorporating forward error correction (FEC) and spreading capabilities, thus providing the necessary processing and coding gain, to guarantee robust communications. In this work, we introduce novel coding schemes exploiting the trellis structure of Orthogonal Convolutional Codes for generating time hopping sequences suitable for UWB-IR, while simultaneously mapping the information bits onto the transmitted waveforms.
Namely, we present a new class of Orthogonal Convolutional
Modulation (OCM) schemes, highlighting the trade-offs in terms of coherent vs. non-coherent detection performance. Then we develop an adaptive OCM scheme (AOCM) for application to broadcast transmission in heterogeneous UWB-IR networks, illustrating advantages in terms of energy savings and potential drawbacks
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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