Outdoor mm-wave 5G/6G transmission with adaptive analog beamforming and IFoF fronthaul.

Adaptive analog beamforming is a key technology to enable spatial control of millimeter-wave wireless signals radiated from phased array antennas (PAAs) which is essential to maximize the capacity of future mobile networks and to ensure efficient usage of scarce spectrum. Intermediate frequency-over-fiber (IFoF), on the other hand, is a promising technology for the millimeter-wave (mm-wave) mobile fronthaul due to its low complexity, high optical spectral efficiency, and low latency. The combination of IFoF and PAA is key to implement mm-wave mobile communications in a scalable, centralized, efficient, and reliable manner.

Beyond 5G Fronthaul Based on FSO Using Spread Spectrum Codes and Graphene Modulators.

High data rate coverage, security, and energy efficiency will play a key role in the continued performance scaling of next-generation mobile systems. Dense, small mobile cells based on a novel network architecture are part of the answer. Motivated by the recent mounting interest in free-space optical (FSO) technologies, this paper addresses a novel mobile fronthaul network architecture based on FSO, spread spectrum codes, and graphene modulators for the creation of dense small cells.

Performance Analysis of a Vertical FSO Link with Energy Harvesting Strategy.

In this paper we investigate the application of free space optical (FSO) communications, energy harvesting, and unmanned aerial vehicles (UAVs) as key technology enablers of a cost-efficient backhaul/fronthaul framework for 5G and beyond (5G+) networks. This novel approach is motivated by several facts. First, the UAVs, acting as relay nodes, represent an easy-to-deploy and adaptive network that can provide line-of-sight between the base stations and the gateways connected to the core network.

Cooperative Terrestrial-Underwater Wireless Optical Links by Using an Amplify-and-Forward Strategy.

In this paper, we analyze a combined terrestrial-underwater optical communication link for providing high-speed optical connectivity between onshore and submerge systems. For this purpose, different transmission signaling schemes were employed to obtain performance results in terms of average bit error rate (ABER). In this sense, from the starting point of a known conditional bit-error-rate (CBER) in the absence of turbulence, the behavior of the entire system is obtained by applying an amplify-and-forward (AF) based dual-hop system: The first link is a terrestrial free-space optical (FSO) system assuming a Málaga distributed turbulence and, the second one, is an underwater FSO system with a Weibull channel model.

Performance analysis of FSO communications under LOS blockage.

We analyze the performance of a free-space optical (FSO) link affected by atmospheric turbulence and line-of-sight (LOS) blockage. For this purpose, the atmospheric turbulence induced fading is modeled by the ℳ distribution, which includes the Gamma-Gamma distribution as special case. We exploit the fact that the physical interpretation of the ℳ distribution allows to split the optical energy through the propagation link into three different components: two coherent components and one incoherent scatter component.

Hybrid optical CDMA-FSO communications network under spatially correlated gamma-gamma scintillation.

In this paper, we propose a new hybrid network solution based on asynchronous optical code-division multiple-access (OCDMA) and free-space optical (FSO) technologies for last-mile access networks, where fiber deployment is impractical. The architecture of the proposed hybrid OCDMA-FSO network is thoroughly described. The users access the network in a fully asynchronous manner by means of assigned fast frequency hopping (FFH)-based codes.

850-nm hybrid fiber/free-space optical communications using orbital angular momentum modes.

Light beams can carry orbital angular momentum (OAM) associated to the helicity of their phasefronts. These OAM modes can be employed to encode information onto a laser beam for transmitting not only in a fiber link but also in a free-space optical (FSO) one. Regarding this latter scenario, FSO communications are considered as an alternative and promising mean complementing the traditional optical communications in many applications where the use of fiber cable is not justified.

General closed-form bit-error rate expressions for coded M-distributed atmospheric optical communications.

In this Letter, general closed-form expressions for the average bit error rate in atmospheric optical links employing rate-adaptive channel coding are derived. To characterize the irradiance fluctuations caused by atmospheric turbulence, the Málaga or M distribution is employed. The proposed expressions allow us to evaluate the performance of atmospheric optical links employing channel coding schemes such as OOK-GSc, OOK-GScc, HHH(1,13), or vw-MPPM with different coding rates and under all regimes of turbulence strength.

Novel formulation of the ℳ model through the Generalized-K distribution for atmospheric optical channels.

In this paper, a novel and deeper physical interpretation on the recently published Málaga or ℳ statistical distribution is provided. This distribution, which is having a wide acceptance by the scientific community, models the optical irradiance scintillation induced by the atmospheric turbulence. Here, the analytical expressions previously published are modified in order to express them by a mixture of the known Generalized-K and discrete Binomial and Negative Binomial distributions.

Spatially correlated gamma-gamma scintillation in atmospheric optical channels.

In this paper, novel analytical closed-form expressions are derived for the probability density function of the sum of identically distributed correlated gamma-gamma random variables that models an optical atmospheric channel communication with receiver spatial diversity. The mathematical expressions here proposed provide a general procedure to obtain information about the scintillation effects induced by turbulence over a diversity reception scheme implementing equal-gain combining method. Both, validity and accuracy of the obtained statistical distribution are corroborated by comparing the analytical results to numerical results obtained by Monte-Carlo simulations.

On the capacity of M-distributed atmospheric optical channels.

In this Letter, closed-form expressions of ergodic capacity, outage probability, and outage rate are derived for an atmospheric optical communication link using intensity modulation and direct detection with unbounded optical wavefront propagating through a homogeneous and isotropic turbulent medium. The optical scintillation of the received signal is modeled with the recently proposed Málaga or M turbulence distribution. By taking advantage of this unifying statistical model, the expressions here presented are valid for all possible irradiance fluctuation conditions, leading to direct relationships between turbulence parameters and link capacity performance.

Impact of pointing errors on the performance of generalized atmospheric optical channels.

Recently, a new and generalized statistical model, called M or Málaga distribution, was proposed to model the irradiance fluctuations of an unbounded optical wavefront (plane and spherical waves) propagating through a turbulent medium under all irradiance fluctuation conditions in homogeneous, isotropic turbulence. Málaga distribution was demonstrated to have the advantage of unifying most of the proposed statistical models derived until now in the bibliography in a closed-form expression providing, in addition, an excellent agreement with published plane wave and spherical wave simulation data over a wide range of turbulence conditions (weak to strong). Now, such a model is completed by including the adverse effect of pointing error losses due to misalignment.

Closed-form BER analysis of variable weight MPPM coding under gamma-gamma scintillation for atmospheric optical communications.

In this paper, the performance of the variable weight multiple pulse-position modulation (MPPM) coding technique in an atmospheric optical communication environment under gamma-gamma optical scintillation is analyzed, proposing a closed-form expression for the average bit error rate (BER). This study is based on a hyperexponential fitting of the conditional BER in absence of turbulence fluctuations, leading to closed-form expressions that characterize the behavior of this nonlinear coding scheme. Finally, conditional and average BER expressions proposed here are corroborated with Monte Carlo simulations results.

General analytical expressions for the bit error rate of atmospheric optical communication systems.

General analytical expressions are derived for the average bit error rate of an intensity modulation and direct detection link using unbounded optical wavefront with on-off keying signalling technique propagating under all possible irradiance fluctuation conditions. These expressions include in a single equation the link performance of most of the proposed statistical models derived until now.

An efficient rate-adaptive transmission technique using shortened pulses for atmospheric optical communications.

In free space optical (FSO) communication, atmospheric turbulence causes fluctuation in both intensity and phase of the received light signal what may seriously impair the link performance. Additionally, turbulent inhomogeneities may produce optical pulse spreading. In this paper, a simple rate adaptive transmission technique based on the use of variable silence periods and on-off keying (OOK) formats with memory is presented.

Numerical model for the temporal broadening of optical pulses propagating through weak atmospheric turbulence.

In atmospheric optical communications, propagating pulses may be influenced by pulse spreading owing to turbulence, above all in scenarios characterized by sand and/or dust atmosphere. The long-term temporal broadening of a space-time Gaussian pulse propagating along a horizontal path through weak optical turbulence is modeled by the behavior of a Gaussian filter, where its cutoff frequency is related to the physical parameters of the link. Thus, it could be incorporated in a direct way to a numerical simulation model.