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This paper presents the design and testing of LaserCube, a miniature optical communication terminal conceived for nano and microsatellites. The system architecture has been defined for both the downlink and intersatellite link version of the system. Then, a complete engineering model of LaserCube in its intersatellite link configuration has been developed and tested. It features (1) a dual stage pointing and tracking system based on a coarse pointing mechanism patented by Stellar Project, (2) an optical head with a full–duplex telecom channel with transmission and reception on the same wavelength for two–way links, (3) a transceiver section with telecom laser source and optical receiver and (4) the terminal control unit with onboard computer, actuator drivers and data interface. Experimental validation of the system is achieved through a laboratory simulation of an intersatellite link scenario with realistic dynamic disturbance coming from the host satellite attitude jitter.

This paper investigates scheduling and precoding techniques via hybrid analog-digital transmitters in mm-wave frequency bands. As in spectrum sharing sub-6GHz scenarios, the presence of non-intended receivers limits the overall achievable rates. In order to circumvent this problem, we propose a scheduling and precoding algorithm able to maximize the sumrate while keeping the interference to the external users under a certain threshold. The method consists of a first scheduling algorithm followed by the optimization of the analog and digital beamforming parts. Numerical simulations validate the conceived technique and they show that data rates are increased compared to current designs., Grant numbers : This work has received funding from the Spanish Ministry of Economy and Competitiveness (Ministerio de Economia y Competitividad) under project TEC2014-59255-C3-1-R and TEC2014- 59255-C3-3-R (ELISA); and from the Catalan Government (2014SGR1567 and 2014SGR1551).

The effect of phase noise is considered in a downlink massive multiple-input–multiple-output (MIMO) scenario with linear precoding schemes, namely, zero-forcing (ZF) and maximum ratio transmission (MRT). The degradation in terms of signal-to-interference-plus-noise ratio (SINR) and the achievable rate are analytically obtained and compared with simulations. The effect of phase noise is different for the two linear precoding schemes, with MRT showing greater robustness but a lower achievable rate per user. Interestingly, the SINR degradation due to phase noise tends to be independent of the number of base-station antennas when this number is big enough. Moreover, the effects of imperfect channel knowledge at the transmitter are studied, and the comparison between the two precoders confirms greater robustness with MRT.

Quantum Gaussian states can be considered as the majority of the practical quantum states used in quantum communications and more generally in quantum information. Here we consider their properties in relation with the geometrically uniform symmetry, a property of quantum states that greatly simplifies the derivation of the optimal decision by means of the square root measurements. In a general framework of the $N$-mode Gaussian states we show the general properties of this symmetry and the application of the optimal quantum measurements. An application example is presented, to quantum communication systems employing pulse position modulation. We prove that the geometrically uniform symmetry can be applied to the general class of multimode Gaussian states.

In this study, we propose several power allocation schemes in a coordinated base station downlink transmission with per antenna and per base station power constraints. Block Diagonalization is employed to remove interference among users. For each set of power constraints, two schemes based on the waterfilling distribution are proposed and compared to the optimal solution, which can only be obtained numerically by using convex optimization. We show that the proposed schemes achieve a performance, in terms of weighted sum rate, very close to the optimal, without the heavy computational complexity required by the latter. The sum rates are compared first in a simplified two-user two-cell case where we also compare our approach to the previous solutions available in the literature. Then, we examine the performance in a multi-cell scenario where we also evaluate the degradation of the performance caused by imperfect channel state information This study has been partly funded by projects TEC2008-06327-C03-02, CCG10-UC3M/TIC-4620, and CSD2008-00010. Publicado

Quantum detection in an N-dimensional Hilbert space H involves quantum states and corresponding measurement operators which span an r-dimensional subspace U of H, with r

In this paper we consider the detection of noisy binary quantum optical coherent states transmitted over a turbulent medium, such as terrestrial links or satellite optical connections across the atmosphere. The propagation effect is accounted for by a random attenuation factor, which is characterized in terms of its statistical distribution. Depending on the knowledge of the propagation coefficient, error performance can vary significantly and different receiver structures show different behaviors and robustness to the channel mismatch. The performance of the quantum optimal receiver and the square root measurement (SRM) are compared, and their sensitivity to the variability of the propagation coefficient is considered. It results that the phase variability of the propagation coefficient plays a fundamental role. The optimal receiver, in the absence of instantaneous channel knowledge, performs worse than the SRM, denoting a greater sensitivity to channel estimation accuracy.

In this work we consider the optimization of the power assigned to the user streams, in a coordinated base station downlink environment, when zero-forcing is employed to remove interference among users. Two schemes based on the waterfilling technique are proposed and compared to the optimal solution, which can be obtained numerically, by using convex optimization. We show that the proposed schemes achieve a performance, in terms of weighted sum rate, very close to the optimal, without the heavy computational complexity required by the numerical solution. The sum rates are compared in a realistic multi-cell scenario and some examples of achievable rates are presented also in a simplified two-user two-cell case.

In this work the effect of phase noise in multiple-input-multiple-output systems employing orthogonal frequency division multiplexing is considered in a realistic scenario where channel estimation is not perfect, so that the channel matrix used at the receiver to perform demodulation is affected by an estimation error. In particular, it is shown that the actual degradation depends on the scheme employed in the receiver. The zero-forcing scheme, although giving a slightly worse performance for the perfectly known channel, proves to be more robust to the effects of channel estimation errors in the presence of phase noise.

Phase noise could be the major source of performance degradation in low cost low bit-rate digital systems operating in the millimeter wavelength band. A general model considers the phase noise as the sum of several components, namely a white phase noise, a white frequency noise and a flicker frequency noise. All these components are taken into account in the evaluation of error probability in a DPSK receiver and are compared in terms of performance degradation.

The performance evaluation of M-QAM-OFDM transmission systems in the presence of phase noise and non-linear distortions due to High-Power-Amplifiers (HPA) is presented. A theoretical analysis enables us to derive the Bit Error Rate and to relate it to the HPA-distorted signal spectrum. The phase noise distortion effects are also taken into account by modeling the phase noise as a Wiener Levy process. It is shown that with a simple way to compensate the phase distortion within an OFDM symbol, the system can still work also in the presence of relevant phase noise. An example of application is reported.

Phase diversity coherent systems are gaining increasing interest with the increase of the bit rate in optical transmissions. In this work, an accurate approach for the evaluation of the error probability in ASK phase-diversity lightwave systems is presented. The approach is based on a Gaussian quadrature rule integration, which takes into account the exact characterization of the filtered phase noise through its moments. The effects of the laser linewidth on the error probability for hybrid circuits with different number of ports are derived and discussed. Also, the effects of the frequency offset are considered. >

The narrow channel spacing allowed by coherent systems suggests the use of a frequency division multiplexing (FDM) technique together with coherent detection to get very high speed optical networks. In the paper the effects of interchannel interference on the performance of coherent systems are investigated: indeed, the crosstalk between adjacent channels determines the channel spacing which is one of the most important parameters in FDM systems. The accurate analysis of ASK and FSK heterodyne systems is performed through a moment characterization of the contributions of phase noise and of crosstalk interference. >

In this work we evaluate the performance of an indoor radio system with /spl pi///sub 4/-DQPSK modulation in frequency selective fading channels. For a theoretical analysis of the system, a simplified two-ray channel model has been adopted; each ray has a log-normal distribution. Moreover, in order to enhance system performance, impaired by fading and intersymbol interference, diversity reception in combination with a novel non-linear equalizer has been proposed. For typical in-building environments it is seen that space diversity may improve performance up to 5 dB at BER 10/sup -3/. However, for strong multipath components non-linear intersymbol interference is the predominant disturbance and performance can only be enhanced by the non-linear equalizer. These considerations can be easily extended to more complex channel models, although system performance can only be evaluated by computer simulations.

This article presents an application of a recently published probablistic model for traveling wave optical amplification. Both optical signal and amplified spontaneous emission (ASE) noise are modeled as bunches of photons traveling along the amplifying region with size varying according to simple random rules. The results of the theory enable one to obtain a complete and accurate characterization of the signal and noise counting at the amplifier output. On the basis of the above statistics, we find a realistic evaluation of the limits imposed by both quantum and ASE noise on the performances of a receiver including an optical amplifier at a preamplifier stage.

In this work we evaluate the impairments due to laser phase noise in multichannel coherent optical systems using a heterodyne ASK modulation scheme. The effects of crosstalk due to a finite value of the channel spacing are considered in a system employing a frequency division multiplexing technique. The phase noise and the frequency spacing between adjacent channels are the fundamental parameters which determine the design criteria (e.g. the bandwidth of the intermediate frequency filters) and the performance of the receiver. The accurate statistical characterization of the filtered phase noise and of the crosstalk is the key to get accurate results: to this aim the exact moments of the random processes related to the phase noise and to the crosstalk interference are used together with a Gaussian Quadrature Rule for the evaluation of the error probability.