1,720,959 research outputs found
Advanced Joint Detection and Synchronization Techniques
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RNN BCJR: a fully trainable version of the additive BCJR algorithm
No full textWe present a new version of the additive BCJR algorithm based on a recurrent neural network whose structure reflects an underlying trellis diagram. Starting from a matrix version of the equations of the additive BCJR algorithm, we derive the equivalent trainable recurrent neural network model, named Recurrent Neural Network (RNN) BCJR. The RNN BCJR consists of a linear layer to form the edge metrics from the state and input metrics, followed by a SOFTMAX/max* layer to marginalize the edge metrics back to the state and output spaces. We derive the recursions for delta propagation to train the two-layer mixing matrices from the output cost function. Unlike the previous approaches, the proposed RNN BCJR can completely replace the BCJR and is trainable from the cost functions of the outputs. The trained RNN BCJR achieves the same optimal performance as the BCJR when the model is known but at the same time can adapt itself to model mismatch, thus outperforming BCJR
On the use of PN Ranging with High-rate Spectrally-efficient Modulations in Satellite Payload Telemetry Links
Full text linkPseudo Noise (PN) ranging is a ranging technique that has been recently introduced in near-Earth space research (SR) missions. For these, at the state-of-the-art, the PN ranging signal is combined with a high-rate telemetry stream binary modulated in phase. The coupling of the two, together with the 10 MHz bandwidth constraint imposed for this class of missions, translates into a data rate bound of approximately 10 Mbps. The purpose of this article is to prove the feasibility of overcoming the current data rate limitation by defining a communication architecture that foresees the coupling of the PN ranging signal with a high-order modulated telemetry stream. To achieve the goal, we study the feasibility of pairing the PN ranging with filtered high-order modulations in satellite payload telemetry links and investigate the simultaneous demodulation of the telemetry stream while tracking the ranging sequence. Accordingly, we design a receiver scheme that is able to perform a closed-loop parallel cancellation of the ranging and the telemetry signal, reciprocally. From our analysis, we find that the non-constant envelope property, characterizing the considered modulation set, causes an additional jitter on the PN ranging timing estimation that, on the other hand, can be controlled and reduced by properly sizing the receiver loop bandwidth, without limiting the timing synchronization dynamic. Our study proves that the use of filtered high-order modulations combined with PN ranging outperforms the state-of-the-art in terms of spectral efficiency and achievable data rate while having comparable ranging performance
A multi-sample discrete-phase BCJR algorithm for phase noise channels
Full text linkIn this paper, we consider channels affected by Wiener phase noise and derive a detection algorithm that exploits oversampling at the receiver for tracking better the phase noise variations. The resulting algorithm is a multi-sample discrete-phase BCJR that outperforms receivers using a single sample per symbol and maximizes the achievable information rate over phase noise channels. Finally, we assess the suitability of the multi-sample discrete-phase BCJR for performing iterative detection and decoding with standard codes
Digital PLLs for phase noise channels: a concept based on the Tikhonov distribution
Full text linkWe explore the concept of a digital phase-locked loop (PLL) of the first type, derived as an alternative solution to Kalman's estimation problem by employing the Tikhonov distribution rather than the traditional Gaussian model.
The resulting Tikhonov PLL is a complex-valued nonlinear filter that is simple to implement and demonstrates interesting features in channels affected by strong phase noise. We present a comparative analysis including the classical PLL and Kalman filter to highlight the strengths of the Tikhonov PLL in such contexts
C) for Space Missions
Full text linkThis paper presents a tutorial on the Tracking, Telemetry, and Command (TT&C) for spacecraft and satellite missions. In particular, it provides a thorough summary of the design of the TT&C, starting from elementary system aspects and going down to the details of the on-board TT&C subsystem design, its units, and the physical layer. The paper is then complemented with a description of emerging TT&C techniques and technologies, the standardization framework, and practical examples of actual spacecraft design of European space missions. The here-presented tutorial is thought for professionals (also in other telecommunication engineering fields) willing to face the challenges and state-of-the-art of the TT&C, and know more about this fundamental function that allows us to control and monitor our spacecraft on a daily basis
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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