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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.

In continuous-variables quantum key distribution with coherent states, the advantage of performing the detection by using standard telecoms components is counterbalanced by the lack of a stable phase reference in homodyne detection due to the complexity of optical phase-locking circuits and to the unavoidable phase noise of lasers, which introduces a degradation on the achievable secure key rate. Pilot-assisted phase-noise estimation and postdetection compensation techniques are used to implement a protocol with coherent states where a local laser is employed and it is not locked to the received signal, but a postdetection phase correction is applied. Here the reduction of the secure key rate determined by the laser phase noise, for both individual and collective attacks, is analytically evaluated and a scheme of pilot-assisted phase estimation proposed, outlining the tradeoff in the system design between phase noise and spectral efficiency. The optimal modulation variance as a function of the phase-noise amount is derived.

The design of massive MIMO, especially at millimeter waves, requires a trade-off between cost and power consumption, balancing the complexity and the performance in terms of achievable rate. A recent trend in the design is to split the pre-coding at the transmitter and the combining at the receiver into a digital and analog part, with hybrid analog-digital schemes. In this paper the effect of phase noise is considered in the design of different hybrid analog-digital alternatives to implement massive MIMO, in particular at very high frequencies.Its effect depending on the number of RF chains, oscillators, and groups of antennas is analyzed providing some insights for the system design. In order to limit the penalty introduced by the phase noise to values below 6 dB, with a number of antennas around 64, the value of phase noise increment variance should be limited below 0.005. This limit is slightly lower in a simplified architecture with more blocks driven by independent oscillators., Grant numbers : This work has received funding from the Spanish Ministry of Economy and Competitiveness (Ministerio de Economia y Competitividad) under projects TEC2014-59255-C3-1-R and TEC2014-59255-C3-3-R (ELISA).

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 phase noise effect in multiple-input-multipleoutput systems employing orthogonal frequency division multiplexing is considered in a realistic scenario where the estimated channel matrix is affected by an error. The analytical SINR degradation due to phase noise and channel estimation is obtained for linear receivers (ZF and MMSE) This work is partly funded by the projects "COMONSENS" CSD2008- 00010 and "MULTI-ADAPTIVE" TEC2008-06327-C03-02 Publicado

Orthogonal frequency-division multiplexing (OFDM) systems, such as the new wireless standards or the schemes proposed for third-generation (3G) evolution, exhibit great sensitivity to the effects of phase noise and the time-varying propagation channel, which can introduce interchannel interference (ICI) due to the loss of orthogonality among subcarriers. In this paper, joint channel estimation and ICI reduction schemes are investigated, which compensate the effects of phase noise and multipath channel in a realistic scenario, where the channel is not assumed perfectly known, whereas its estimation is obtained by combining a decision-feedback scheme and a pilot-aided estimator. We propose a technique for ICI compensation that has reduced complexity by only considering the most significant terms of ICI Publicado

Phase noise can be a major source of performance degradation in low-cost, low-bit-rate digital systems operating in the millimeter wavelength band. The use of code-division multiple access (CDMA) for several new applications is envisaged, and the study of the effects of phase noise shows that even CDMA systems exhibit a performance degradation comparable to that of standard modulation formats. The use of CDMA with a differential modulation at the chip level improves the system performance with a simpler demodulator at the expense of the enhancement of multiuser interference. In this paper we propose a new approach to CDMA modulation, and a possible solution is suggested to obtain a tradeoff between the performance degradation due to the phase noise and to the multiuser interference.

We focus on the mean achievable rate per user of the coordinated base station downlink transmission in a clustered cellular environment, with transmit power constraints at the base stations. Block Diagonalization is employed within the cluster to remove interference among users while the interference from other clusters remains. The average achievable rate per user is evaluated considering the effects of the propagation channel and the interference and a theoretical framework is presented to provide its analytical expression, validated by simulation results with different power allocation schemes. As an application, the number of cells of the cluster that maximizes the mean achievable rate per user is investigated. It can be seen that in most of the cases a reduced cluster size, close to seven cells, guarantees a rate very close to the maximum achievable This work is partly funded by projects "GRE3N": TEC2011-29006-C03-03 and "COMONSENS": CSD2008-00010 En-prensa

In this work, the impairment due to crosstalk interference in a FSK coherent optical system is investigated. The crosstalk can arise from both co-channel interference due to the dual-filter receiver structure, and inter-channel interference due to the frequency division multiplexing technique in multichannel systems. Here, we perform the analysis of a multichannel system, taking into account simultaneously the two contributions to interference. An approximation of the crosstalk contributions seems necessary in order to carry out the analysis. The joint moment characterization of the filtered phase noise and of the interference is suitable to get accurate results. >

An accurate performance evaluation approach which uses a closed-form exact analytical expression of the phase noise moments is presented. This enables one to derive a high-order Gaussian quadrature rule for the integrations needed to take into account the phase noise in the computation of error probability. A systematic comparison with results obtained through a Monte Carlo simulation shows that the approach is more accurate than previous methods. The analysis is performed on ASK and FSK heterodyne receivers with integrate-and-dump filtering, envelope detection, and optimized postdetection low-pass filtering. The feasibility of ASK and FSK heterodyne systems at bit rates comparable to the spectral line bandwidth of the laser sources is confirmed. The theory applied seems to be adequate to attack other problems, such as the evaluation of the effects of crosstalk between the FSK filters or among frequency division multiplexed channels. >

OFDM systems such as the schemes proposed for 3G evolution exhibit a great sensitivity to the effects of phase noise and channel estimation, which can introduce inter-channel interference due to the loss of orthogonality among sub-carriers. In this work channel estimation and tracking schemes are investigated, proposing to compensate jointly the effects of phase noise and of the channel. A decision feedback scheme is proposed together with an estimator based on the pilots, to improve the performance also in the presence of fast fading multipath.

Phase noise can be the major source of performance degradation in low cost low bit-rate digital systems operating in the millimeter wavelength band. The use of CDMA with a differential modulation at the chip level will permit an improvement in system performance and a simpler demodulation. However, the enhancement of CDMA multi-user interference arising from the differential receiver has to be considered. In this study different approaches are considered and a possible solution is suggested to obtain a compromise between the effects of the phase noise and of the multi-user interference.

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.

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.