Advanced channel coding for space mission telecommand links

We investigate and compare different options for updating the error correcting code currently used in space mission telecommand links. Taking as a reference the solutions recently emerged as the most promising ones, based on Low-Density Parity-Check codes, we explore the behavior of alternative schemes, based on parallel concatenated turbo codes and soft-decision decoded BCH codes. Our analysis shows that these further options can offer similar or even better performance.Comment: 5 pages, 7 figures, presented at IEEE VTC 2013 Fall, Las Vegas, USA, Sep. 2013 Proc. IEEE Vehicular Technology Conference (VTC 2013 Fall), ISBN 978-1-6185-9, Las Vegas, USA, Sep. 201

Guest Editorial: Channel Coding in Wireless Systems

It is our pleasure to introduce this Special Issue on "Channel Coding in Wireless Systems" of the Journal of Communication Software and Systems (JCOMSS). This is one of the initiatives conceived to promote JCOMSS, a relatively new journal born from an idea of the Croatian Communication and Information Society (CCIS) and the University of Split, and endorsed by the IEEE Technical Committee on Communications Software of the IEEE Communications Society. Really, the Croatian group are very active in supporting IEEE activities and proposing original ideas for exchanging experiences and results among researchers coming from universities, industries and research centers. Just to mention an example, it is the main organizer of SoftCOM, the International Conference on Software, Telecommunications and Computer Networks, that is probably the only ICT workshop in the world to be held aboard a ship, cruising along the Croatian and the Italian coasts. This year SoftCOM will celebrate its 14th edition. Then, charmed from so much dynamism, when Prof. Nikola Rozic asked for us to organize a special issue on the theoretical and practical aspects of channel coding for wireless applications, we accepted the invitation with great enthusiasm. Wireless systems are a privileged field to discuss the advantages of channel coding in telecommunications. The wireless channel is a particularly severe test-bed: it is affected by nonlinearities, multipaths, Doppler shifts, fading, shadowing, interference from other users, and many other impairments depicting an involved scenario, difficult to treat but also exciting for proposing new and attractive solutions. The invention of turbo codes in 1993 has been followed by the application of iterative techniques to many other blocks of communication systems, and the rapid implementation of these concepts in practical applications. In the last ten years new schemes have been designed (and old ones reinterpreted) able to approach Shannon capacity limits with reasonable complexity. This way, new applications and services become possible, quite unthinkable in the past

Simple Statistical Analysis of the Impact of Some Nonidealities in Downstream VDSL with Linear Precoding

Abstract This paper considers a VDSL downstream system where crosstalk is compensated by linear precoding. Starting from a recently introduced mathematical model for FEXT channels, simple analytical methods are derived for evaluating the average bit rates achievable, taking into account three of the most important nonidealities. First, absolute and relative estimation errors in the crosstalk coefficients are discussed, and explicit formulas are obtained to express their impact. A simple approach is presented for computing the maximum line length where linear precoding overcomes the noncoordinate system. Then, the effect of out-of-domain crosstalk is analyzed. Finally, quantization errors in precoding coefficients are considered. We show that by the assumption of a midtread quantization law with different thresholds, a relatively small number of quantization bits is sufficient, thus reducing the implementation complexity. The presented formulas allow to quantify the impact of practical impairments and give a useful tool to design engineers and service providers to have a first estimation of the performance achievable in a specified scenario

Lakoff & Johnson lettori di Blumenberg? Le analogie tra metaforologia e teoria della metafora concettuale

This paper aims at showing the analogies between Hans Blumenberg’s Metaphorology and George Lakoff & Mark Johnson’s Conceptual Metaphor Theory. Starting from the analysis of the proportion for which ABSOLUTE METAPHOR: METAPHORICAL EXPRESSIONS = BACKGROUND METAPHOR: CONCEPTUAL METAPHOR, we propose to compare Blumenberg’s Metaphorology with Lakoff & Johnson’s Conceptual Metaphor Theory, outlining similarities and differences in reference to: (a) the fundamental notions on which the two theories are based, (b) the methods and (c) the relationship between language-thought-culture assumed by the two theories. However, the reconstruction of the relation between the two theoretical paradigms is not an end in itself as we will show that the two research paradigms could be integrated to overcome problematic aspects present in both theoretical perspectives

Effect of randomizers on the power spectrum excess of space telemetry signals

none6siThis paper presents a thorough analysis of the spectral characteristics of space telemetry signals when randomizers are used to counter the power excess, that is, the increase of the power spectrum in some measurement bandwidths with respect to the transmission of an ideal random signal. We show that a long randomizer actually improves the spectral characteristics but is not able to solve some critical problems appearing when all-zero frames or almost constant data are transmitted. Suitable solutions are proposed to face these cases, ensuring a small power excess in all possible operation conditions. The impact of high-order modulations and error correcting codes is also investigated.openMassimo Battaglioni, Marco Baldi, Franco Chiaraluce, Roberto Garello, Enrico Vassallo, Gian Paolo CalzolariBattaglioni, Massimo; Baldi, Marco; Chiaraluce, Franco; Garello, Roberto; Vassallo, Enrico; Paolo Calzolari, Gia

Next generation earth‑to‑space telecommand coding and synchronization: ground system design, optimization and software implementation

The Consultative Committee for Space Data Systems, followed by all national and international space agencies, has updated the Telecommand Coding and Synchronization sublayer to introduce new powerful low-density parity-check (LDPC) codes. Their large coding gains significantly improve the system performance and allow new Telecommand services and profiles with higher bit rates and volumes. In this paper, we focus on the Telecommand transmitter implementation in the Ground Station baseband segment. First, we discuss the most important blocks and we focus on the most critical one, i.e., the LDPC encoder. We present and analyze two techniques, one based on a Shift Register Adder Accumulator and the other on Winograd convolution both exploiting the block circulant nature of the LDPC matrix. We show that these techniques provide a significant complexity reduction with respect to the usual encoder mapping, thus allowing to obtain high uplink bit rates. We then discuss the choice of a proper hardware or software platform, and we show that a Central Processing Unit-based software solution is able to achieve the high bit rates requested by the new Telecommand applications. Finally, we present the results of a set of tests on the real-time software implementation of the new system, comparing the performance achievable with the different encoding options

Tailoring the switching efficiency of magnetic tunnel junctions by the fieldlike spin-orbit torque

Current-induced spin-orbit torques provide a versatile tool for switching magnetic devices. In perpendicular magnets, the dampinglike component of the torque is the main driver of magnetization reversal. The degree to which the fieldlike torque assists the switching is a matter of debate. Here we study the switching of magnetic tunnel junctions with a CoFeB free layer and either W or Ta underlayers, which have a ratio of fieldlike to dampinglike torque of 0.3 and 1, respectively. We show that the fieldlike torque can either assist or hinder the switching of CoFeB when the static in-plane magnetic field required to define the polarity of spin-orbit torque switching has a component transverse to the current. In particular, the non-collinear alignment of the field and current can be exploited to increase the switching efficiency and reliability compared to the standard collinear alignment. By probing individual switching events in real-time, we also show that the combination of transverse magnetic field and fieldlike torque can accelerate or decelerate the reversal onset. We validate our observations using micromagnetic simulations and extrapolate the results to materials with different torque ratios. Finally, we propose device geometries that leverage the fieldlike torque for density increase in memory applications and synaptic weight generation