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In hybrid analog-digital schemes, proposed to reduce the number of RF chains especially at millimeter waves, the precoding at the transmitter and the combining at the receiver are split into digital and analog parts. We analyze the sensitivity of hybrid schemes to phase noise and channel estimation errors and we compare them to a full-digital approach. The scheme adopted for the analog part employs fixed phase shifters, then the digital part is optimized by a singular-value decomposition. We derive analytical expressions for the interference and the SNR degradation arising from the imperfect decomposition due to phase noise and the channel estimation error, for typical millimter-wave massive MIMO channels. In particular we show that when the channel estimation is made in the beam-space, this hybrid scheme is more robust to the phase noise and to the channel estimation errors than a full-digital approach.

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 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.

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

The performance of an overlay Bluetooth and IEEE 802.11b (WiFi) network is considered in terms of quality of service parameters such as the packet latency, the packet error rate, and the throughput, in the presence of a vertical handover procedure, taking into account the mutual Bluetooth-WiFi interference and showing the influence of the main system parameters. The objective is to maximize the user QoS allowing the mobile to switch from a network to the other, with the so-called vertical handover. The basic idea is to activate the vertical handover, not on the basis of the received power level, but by the crossing of thresholds defined by the user profile, which comprises objective values for parameters such as the packet error rate and the packet delay. The results show that the use of the vertical handover procedure can lead to an improvement in the QoS parameters

OFDM is recognized to be one of the best transmission techniques for wideband wireless communication systems. However, it exhibits two main drawbacks: its large amplitude fluctuation and its sensitivity to phase noise. Here we consider the phase noise impairments, taking care of the phase noise spectrum, which diverges form the classical Wiener model as the carrier frequency increases. Moreover, we show that the phase noise distortion can be decomposed in two terms, one dependent on the symbol under detection and the other dependent on the symbols of adjacent subcarriers, so that the performance degradation depends on both the constellation used in each subcarrier and the phase noise spectrum. As a consequence of this new results, the penalty due to phase noise expressed in terms of the average signal/noise plus interference ratio is not applicable in the case of modulations with non-constant amplitude constellations, such as 16- or 64-QAM. The method proposed here achieves a good accuracy, while keeping a low computational complexity, and it is confirmed by simulations.

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.

This work focuses on the fairness in the distribution of the achievable rate per user in a cellular environment where clusters of base stations coordinate their transmissions in the downlink. Block Diagonalization is employed within the cluster to remove interference among users while the interference coming from other clusters remains. The probability distribution of the achievable rate per user shows a perfect match with a Gamma distribution so that a characterization in terms of mean and variance can provide a useful tool for the design of the clusters and the implementation of fairness strategies in a coordinated base station network with Block Diagonalization. This work is partly funded by the projects “GRE3N”: TEC2011-29006- C03-03, and “COMONSENS”: CSD2008-00010. Publicado

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 quantum discrimination, the value of the minimum error probability and the set of measurement operators which achieve this minimum are often difficult to derive. Here we present a comparison of the performance obtained by the optimal solution and by the available bounds, namely the square root measurement (SRM) and the Chernoff bound. Applied to some Gaussian states, namely to coherent states with thermal noise, it is shown that the SRM provides a much tighter bound with respect to the Chernoff bound, with a comparable numerical complexity.

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. >

We present the main design issues and the tests in the setup of a long distance free-space quantum link under development within the project "QuantumFuture" of the University of Padova. In particular, new achievements in the actual engineering of the link are presented, both for polarization quantum states encoding and for coherent quantum 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

In a Coordinated Base Station Transmission scenario for the downlink, we propose a precoding scheme based on a MMSE criterion to manage the inter-user interference. In order to allocate the transmitted power to each user's signal, we set up an iterative procedure based on a modified waterfilling distribution, which approaches the optimal performance with a viable complexity with respect to the numerical optimization. A further simplification may be introduced, giving a simple iterative waterfilling scheme, at the expense of some performance loss. The performance is illustrated obtaining the achievable rates for different antenna configurations and different kinds of power constraints. A comparison with a Block-Diagonalization approach shows the advantage of MMSE, in particular at low SNR.

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.

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. >

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.

The effect of phase noise in multiple-input–multiple-output systems employing orthogonal frequency division multiplexing is analyzed in a realistic scenario where channel estimation is not perfect, and the phase noise effects are only partially compensated. In particular, the degradation in terms of SNR is derived and the effects of the receiver and channel parameters are considered, showing that the penalty is different for different receiver schemes. Moreover it depends on the channel characteristics and on the channel estimation error. An analytical expression is used to evaluate the residual inter-channel interference variance and therefore the degradation. The effects of multipath and antenna diversity are shown to be different for the two types of linear receivers considered, the zero-forcing scheme and the minimum mean squared error receiver. This work has been partly funded by projects “MACAWI” TEC2005-07477-C02-02 and “MULTI-ADAPTIVE” TEC2008-06327-C03-02. Publicado

Handover in a Bluetooth scatternet is studied. The inquiry procedure defined by the Bluetooth standard to create and manage an ad-hoc network could also be used to perform handover, but is too slow to keep communication active. An on-demand procedure, based on accurate paging, is proposed. The parameters needed to perform the handover are exchanged when necessary, thus information is not required to be stored on the devices. The handover performance is studied by giving a statistical description of the time needed to terminate it. We show that handover in a reasonable time is feasible, and is suitable for many of the asynchronous communications applications envisaged for Bluetooth.

The performance of mobile communications is critically dependent on the multiple access protocol used to access the network from the mobiles. In recent years many proposals have been compared on the basis of spectrum efficiency measured as the number of voice channels which can be accommodated in a given bandwidth per unit area and TDMA versus CDMA has captured the major attention in the past. Hereafter we propose a new packet-voice random access protocol by taking into account the effect of ACKs, random channel attenuation due to fading, shadowing and interference. The system efficiency is reasonable for a slotted Aloha random access protocol and suggests further studies in this direction. >

The authors report the analysis and the performance evaluation of a coherent optical receiver with binary frequency shift keying (FSK) modulation. The receiver makes use of envelope detection with two branches for the two transmitted frequencies. The analysis is performed also in the presence of a low-pass post-detection filter. The analysis accounts for the effect of phase noise, modeled as a Brownian motion, which strongly affects the system performance. The numerical evaluation is carried out by the use of Gaussian quadrature rules and is based on previous results on the moment characterization of the phase noise. >

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.

Multimedia services require a large amount of bandwidth for the delivery of the video and audio signal with adequate quality of service. Hence, the bandwith allocation has to efficiently managed. CDMA is a flexible multiple access technique since it allows a dynamic configuration of the resources allotted to the users of the system. The paper describes a CDMA-based satellite multimedia system, detailing the DSP implementation of the satellite modem.

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. >