Deep Information Networks

We describe a novel classifier with a tree structure, designed using information theory concepts. This Information Network is made of information nodes, that compress the input data, and multiplexers, that connect two or more input nodes to an output node. Each information node is trained, independently of the others, to minimize a local cost function that minimizes the mutual information between its input and output with the constraint of keeping a given mutual information between its output and the target (information bottleneck). We show that the system is able to provide good results in terms of accuracy, while it shows many advantages in terms of modularity and reduced complexity

Dynamic link budget simulation

A new simulator named DLBS (Dynamic Link Budget Simulator) was written to simulate the time-varying communication link between a vehicle that re-enters the atmosphere from the outer space, and a ground station. During the vehicle descent trajectory, communications blackouts typically occur due to the effects of plasma that forms around the vehicle. A companion simulator, AIPT (Antenna In Plasma Tool), evaluates the electric field at the input of the ground station antenna, taking into consideration the vehicle structure, its antenna, the characteristics of plasma at some specified points along the vehicle trajectory, and the obtained values are stored in a file. DLBS processes the data read from the AIPT output file and evaluates the corresponding channel transfer functions. DLBS then allows to simulate the typical telemetry and telecommand links, using both CCSDS standardised and some non standard channel encoding schemes and modulations. For each generated frame, DLBS uses a channel transfer function obtained by adequately interpolating the two nearest transfer functions evaluated in the initial phase. DLBS includes realistic frame, frequency, phase and bit synchronisation, so that synchronisation errors are also included as source of performance degradation, and measures both the average bit and frame error rates, and the bit error rate at frame level, so that it is possible to appreciate the dynamic system behaviour. The paper will show the results obtained for a case study

Performance of GMSK for telemetry and PN ranging under realistic conditions

In the frame of CCSDS activities, a system capable of simultaneously transmitting high rate telemetry and ranging has been studied in the last years. In this system the telemetry is transmitted through a GMSK modulator with the PN (Pseudo Noise) ranging sequence included as an additional phase shift. The receiver first estimates the transmitted telemetry bits, regenerates and removes the estimated GMSK signal from the received signal, and then estimates the ranging chips and, through a bank of correlators, the round trip delay of the received ranging signal. Ranging is an interfering signal which degrades the performance of the telemetry subsystem, while errors in the estimation of telemetry bits compromise the correct detection of the ranging chips. The first simulation results obtained by ESOC were presented at TTC 2010 in the paper “Analysis of GMSK for Simultaneous Transmission of Ranging and Telemetry” and were limited to ideal synchronization and to the case of a telemetry bit rate equal to the ranging chip rate. In this new paper we describe additional results obtained from the simulation of the complete system, including realistic synchronization, and for telemetry rates which are different from the chip rate. The paper will: 1) consider the effects of the receiver telemetry clock jitter on the regenerated GMSK signal and on the subsequent ranging receiver: it will be shown that regeneration through the Laurent OQPSK approximation or through a look-up table, which directly stores the GMSK phase for each combination of input bits, achieve good performance with low complexity; 2) discuss the effects of perfect synchronization between the transmitted telemetry and ranging signals: in this case, depending on the relative delay between the two signals, the recovered ranging clock may suffer from a bias, which corresponds to an error in the range estimation (lack of accuracy); 3) estimate the system losses when the telemetry bit rate is different from the ranging chip rate; 4) estimate the loss due to phase noise. The analysis will be limited to the case of GMSK with BTb=0.5 and ranging code T2B, which is the suggested scheme for deep space missions with demanding acquisition time requirements

Adaptive equalization in coherent receivers using a Stokes space update algorithm

A coherent optical receiver including an optical transducer, an adaptive filter, and a processor updates the adaptive filter according to a metric derived in Stokes space. The optical transducer receives an optical signal corresponding to a modulated signal of symbols. The optical transducer also determines a first signal corresponding to a first polarization of the optical signal and a second signal corresponding to a second polarization of the optical signal. The adaptive filter recovers a first equalized signal and a second equalized signal from the first signal and the second signal. The first equalized signal and the second equalized signal form an equalized modulated signal of symbols. The processor calculates a set of Stokes parameters from the equalized modulated signal and updates the adaptive filter based on a metric derived from the set of Stokes parameters

Reentry vehicles: evaluation of plasma effects on RF propagation

In the frame of communication technology relevant to the re-entry vehicles, the communication black-out occurring in the presence of plasma is one of the main challenging issues. The re-entry plasma is a complex physical system, where the ionization derives from a shock-wave and non-equilibrium phenomena. As discussed elsewhere, the time scales of plasma dynamics (including its evolution along mission trajectory) and radio wave propagation are well separated so that radio wave propagation is solved at an appropriate number of time "snapshots" in which plasma dynamics is held unchanged and considered as known. In this activity, a consistent effort has been devoted to model the electromagnetic problem. For the involved range of oprative frequencies and expected densities, the plasma can be considered as an inhomogeneous dielectric. The associated electromagnetic problem is solved in two steps, via use of the field equivalence principle. The vehicle-plasma system is substituted by equivalent (Love's) currents on its boundary, radiating in free space; the fields at the boundary are obtained by solving the propagation problem from the antenna, installed on the spacecraft, up to the plasma boundary, through the Eikonal approximation. Radiation is then obtained without further approximations. Unlike other well-known numerical methods (e.g. FEM), this technique is not intrinsecally limited by the electrical dimension of the vehicle-plasma system. This enables to analyze high frequency problems. Since the formation of the re-entry plasma critically depends on the re-entry vehicle shape and kinematics, the related model has been directly derived from the output data of the Computational Fluid Dynamics simulations. All the results of the above mentioned activities have been collected in a new software, the AIPT (Antenna In Plasma Tool, integrated into ADF-EMS Antenna Design Framework Electromagnetic Satellite) able to predict the electromagnetic propagation in the presence of plasm

DTTL-like symbol synchronizers for GMSK signals

Final report of ESA/ESOC contract 17136/03/D/CS(SC

Di Echidna, e di altre femmine anguiformi

Di Echidna, e di altre femmine anguiformi (pp. 205-221) Un bref parcours à travers les textes dans lesquels apparaît la figure inquiétante de la femme serpent montre combien il est difficile de ramener des manifestations en apparence similaires d'un même motif animal à une unité symbolique de significations et d'interprétations. Image de terreur dans la Théogonie d'Hésiode, la queue serpentine de la μείξοπάρθενος devient dans l'Enquête d'Hérodote et chez Diodore de Sicile un emblème de l'autochthonie. Dans le Vème Discours de Dion Chrysostome, les femmes serpents sont des transfigurations allégoriques des passions qui dressent des embûches à l'homme quand il a perdu les références éthiques de la civilisation.Visintin Monica. Di Echidna, e di altre femmine anguiformi. In: Mètis. Anthropologie des mondes grecs anciens, vol. 12, 1997. pp. 205-221