Capacity Of Communication Links Research Articles

Secrecy capacity of hybrid FSO-RF communication links

Secrecy capacity of hybrid FSO-RF communication links

Generation of Photon Orbital Angular Momentum and Its Application in Space Division Multiplexing

In the last three decades, light’s orbital angular momentum (OAM) has been of great interest because it has unique characteristics that make it sought after in many research fields, especially in optical communications. To address the exponentially increasing demands for higher data rates and capacity in optical communication systems, OAM has emerged as an additional degree of freedom for multiplexing and transmitting multiple independent data streams within a single spatial mode using the spatial division multiplexing (SDM) technology. Innumerable research findings have proven to scale up the channel capacity of communication links by a very high order of magnitude, allowing it to circumvent the reaching of optical fiber’s non-linear Shannon limit. This review paper provides a background and overview of OAM beams, covering the fundamental concepts, the various OAM generators, and the recent experimental and commercial applications of the OAM-SDM multiplexing technique in optical communications.

A 32-Channel C-Band Hybrid Wavelength/ Polarization Division (de)multiplexer on Silicon

A 32-channel hybrid (de)multiplexer on silicon is designed and experimentally demonstrated to enable polarization division multiplexing (PDM) and wavelength division multiplexing (WDM) for improving the capacity of optical communication links. The hybrid (de)multiplexer is realized by monolithically integrating a polarization rotator and splitter (PRS) and two 16-channel microring resonators (MRRs) arrays. The through and cross ports of the PRS are connected to the bus waveguide of the MRR arrays, respectively. In order to ensure a larger free spectrum range (FSR) to cover all wavelength channels, the radius of the microring is about 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m and the wavelength-channel spacing is 1.6 nm. For the hybrid (de)multiplexer, the crosstalk between the adjacent channels and the non-adjacent channels are -20 dB and -25 dB, respectively. When TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{0}$</tex-math></inline-formula> mode input, the insertion loss is 1.5 dB - 3.8 dB, the crosstalk between the through and cross port is less than -24 dB. When TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{0}$</tex-math></inline-formula> mode inputs, the insertion loss is 1.9 dB - 4.5 dB and the polarization crosstalk is less than -22 dB. In order to eliminate the influence of the fabrication errors and temperature on resonance wavelength, a TiN thermal tuning electrode is added to calibrate the deviation of the wavelength.

Low-crosstalk mode-group demultiplexers based on Fabry-Perot thin-film filters.

Mode-group multiplexing (MGM) can increase the capacity of short-reach few-mode optical fiber communication links while avoiding complex digital signal processing. In this paper, we present the design and experimental demonstration of a novel mode-group demultiplexer (MG DeMux) using Fabry-Perot (FP) thin-film filters (TFFs). The MG DeMux supports low-crosstalk mode-group demultiplexing, with degeneracies commensurate with those of graded-index (GRIN) multimode fibers. We experimentally demonstrate this functionality by using a commercial six-cavity TFF that was intended for 100 GHz channel spaced wavelength-division multiplexing (WDM) system.

Capacity of the Weakly Absorbent Turbulent Ocean Channel with the Coaxial Double-Position Power Gaussian Vortex

Turbulence and absorption of seawater are two important factors affecting the signal transmission quality of underwater optical communication link. Here, we study the channel capacity and bit error rate of an underwater extinction communication link with a coaxial double-position power Gaussian vortex carrier based on Rytov approximation theory. The study finds that channel capacity and bit error rate are the nonlinear functions of the dimensionless structural parameter and reach maximum and minimum values at |α| = 1, respectively. The seawater absorption has a great influence on the channel capacity but not bit error rate. The communication link with large receiving aperture, small transmitting beam diameter, long wavelength of light source in a seawater window, and more OAM channels has high channel capacity.

Vortex Beam Generation Based on Plasma Reflect- Array Surface at Microwave Frequencies

Orbital angular momentum (OAM) is a promising feature of electromagnetic (EM) wave to increase the communication link capacity. It is possible to use the OAM over the whole spectrum from radio frequency to optic. EM waves would experience a vortex phase boundary while transmitting the data. According to the infinite number of vortex modes, there would be infinite data transmission in theory. Here, a plasma medium with a complex structure is exploited to construct the vortex phase plane at microwave frequencies. Plasma as the ionized gas transmits, reflects, and absorbs EM wave under some conditions. The ratio of plasma physical parameters with the impinging wave frequency presents the condition of wave interaction with the plasma medium. A reflector plane is realized with the help of multilayered low-pressure plasma. By radiation of a plane wave toward the reflector surface, vortex beams of several modes are realized. The controllability of plasma electron frequency makes it a reconfigurable reflect-array antenna for vortex beam generation. The design is based on the scattering theory of the dielectric plasma model for a vast frequency of 8-16 GHz. The proposed advanced EM structure to generate the vortex beams is simulated with a full-wave analysis that verifies the studied design.

Guaranteed Minimization of the Bit Error Ratio for MIMO Systems: A Mathematical Viewpoint

Abstract Multiplying the capacity of communication links by using the multiple-input multiple-output (MIMO) mechanism has become an essential part of various wireless standards. In this paper, we focus on the bit error ratio (BER) in such systems and consider its optimization under parameter uncertainty from a formal point of view (including methods with result verification). The theoretical results are demonstrated using a close-to-life application.

Experimental analysis of adaptive optics correction methods on the beam carrying orbital angular momentum mode through oceanic turbulence

In recent years, as the demand for underwater communication has increased, underwater wireless optical communication (UWOC) has attracted a lot of attentions. Meanwhile, orbital angular momentum (OAM) has been applied in UWOC system to increase communication link capacity. However, the aberrations caused by oceanic turbulence (OT) is unavoidable, which results in serious intermodal crosstalk. Usually, adaptive optics (AO) is used to compensate these distortion aberrations. In this work, we experimentally demonstrate the influence of the distortion caused by OT, and evaluate the performance of AO correction algorithms, including Shack-Hartmann (SH), Stochastic-Parallel-Gradient-Descent (SPGD) and Gerchberg-Saxton (GS) algorithms. During the experiment, OT is simulated by using improved random phase screen model. We discuss the influence of various parameters of OT, including relative strength of temperature and salinity, strength of OT Cn2, and propagation distance, on the compensation effect with and without correction algorithms. The results show that all the three AO algorithms have good compensation effect on the distortion caused by OT, and GS algorithm has a better capability than the other two algorithms. Additionally, when the iteration numbers is less than 100, the compensation effect of GS and SPGD algorithms becomes more obvious as the iteration numbers increases, and GS algorithm is superior to SPGD algorithm. This work is beneficial to aberration correction of OAM-based UWOC system.

Modeling Ground-Air Wireless Connectivity: Continuous Connection Probability Analysis

In this paper, we consider three ground-aircraft communication issues, namely, ground-centric connectivity, aircraft-centric connectivity, and link capacity analysis. Particularly, we propose the continuous connection probability over at least τ seconds, termed as τ-connectivity, for the ground-centric link and aircraft-centric link respectively, which are derived in the expression of several key parameters such as the aircraft/ground station density, the aircraft velocity, and the connectable elevation angle threshold. Theoretical tradeoff between ergodic outage capacity and the number of connected aircraft is analyzed for low and high transmit power regimes. The hypotheses in the ground-centric τ-connectivity model are tested, and we observe a good match between the theoretic probability and the real world data-based probability although some real world aircraft statistic characters do not match the ideal assumption perfectly. Next, the aircraft-centric τ-connectivity is analyzed theoretically. Approximate yet practically accurate closed form aircraft-centric connection probabilities are derived and verified with Monte Carlo simulations. Furthermore, considering atmospheric gas and cloud attenuation, we compare the link budget and capacity between the ground-centric ground-to-aircraft link and the ground-to-satellite link under the τ-connectivity and demonstrate the advantage of ground-aircraft communication.

Ultimate Capacity Analysis of Orbital Angular Momentum Channels

Orbital angular momentum (OAM) multiplexing has recently been proposed as a solution to the ultimate goal of increasing the channel capacity of wireless communication links because of the existence of infinite orthogonal modes. It can be combined with the existing conventional multiplexing techniques to boost up the data rate multiple times for future wireless communication systems. We analyze the fundamental behavior of the channel capacity of OAM channels based on two concepts for the most common Laguerre-Gaussian OAM beams: paraxiality and orthogonality. We also confirm our general theory by applying the proposed method to the evanescing OAM beams, circular transverse electric beams. Our study is based on calculating the paraxial estimator of these OAM beams and relating it as a parameter that limits the degree of freedom in OAM channels. In particular, we investigate the dependency on physical parameters, such as transmitter and receiver sizes, in our calculation to define the capacity of OAM channels.

Capacity of communication link with carrier of vortex localized wave in absorptive turbulent seawater

We explore the influence of absorption, anisotropy and unstable layered turbulence on the channel capacity of horizontal seawater link. By developing the spectrum average coherence length of collimated beam wave in the absorptive seawater turbulence, we propose a model of the channel capacity of links with carrier Bessel-Gaussian vortex localized wave. Our model shows that the capacity of links increases with the increasing of the half-modulated pulse width of the input pulse, the rate of dissipation of kinetic energy per unit mass of fluid and the anisotropic factor of turbulence, but it decreases with the increasing of the Bessel cone angle and the dissipation rate of the mean-squared temperature. We also find that there is a maximum effective beam waist for a given receiving aperture, the channel capacity is more sensitive to salinity fluctuations than to temperature fluctuations in turbulence, and the influences of the inner scale and outer scale of turbulence on channel capacity of links in anisotropic turbulence and isotropic turbulence are different.

Perspective on using multiple orbital-angular-momentum beams for enhanced capacity in free-space optical communication links

Abstract Structured light has gained much interest in increasing communications capacity through the simultaneous transmission of multiple orthogonal beams. This paper gives a perspective on the current state of the art and future challenges, especially with regards to the use of multiple orbital angular momentum modes for system performance enhancement.

Study on Integrated Communication Enhanced Link Based on Signal Detection, Frequency Conversion and Forwarding

Remote mountainous areas have complex terrain, so the information transmission capacity of communication links have been greatly restricted. In addition, the maritime areas have the problem of limited communication base stations and limited communication links as well. Currently, the most commonly used air-based platforms for spectrum forwarding, which only support a small coverage of areas, fail to achieve wide-area or cross-regional signal connectivity, and only support a limited number of concurrent users. Therefore, this paper proposes an integrated communication enhanced link based on frequency detection, conversion and forwarding, which solves the problem that information sharing is not stable. And the simulation results verify that the proposed integrated communication enhanced link addresses the problem of multiple users (up to 150) to communicate concurrently in a cross-region area (radius 50 km) which may have mountains in between. And also, the proposed air-based platform only requires a low power of energy, so that the platform can work longer time in the air.

Eight-channel laser array with 100 GHz channel spacing based on surface-slotted structures fabricated by standard lithography.

An eight-channel laser array with 100GHz channel spacing based on surface-slotted structures is demonstrated. Wavelength selection is realized by using a group of micrometer-order slots fabricated by standard lithography technology. An output power of over 14mW and a side-mode suppression ratio of better than 35dB for each laser within the array are achieved. A laser array without tuning for 100GHz channel spacing by standard lithography was realized for the first time, to the best of our knowledge. The laser array can be used to enhance the capacity of communication links and provides a promising light source for photonic-integrated circuits.

Distributed Adaptive Primal Algorithm for P2P-ETS over Unreliable Communication Links

Algorithms for distributed coordination and control are increasingly being used in smart grid applications including peer-to-peer energy trading and sharing to improve reliability and efficiency of the power system. However, for realistic deployment of these algorithms, their designs should take into account the suboptimal conditions of the communication network, in particular the communication links that connect the energy trading entities in the energy network. This study proposes a distributed adaptive primal (DAP) routing algorithm to facilitate communication and coordination among proactive prosumers in an energy network over imperfect communication links. The proposed technique employs a multi-commodity flow optimization scheme in its formulation with the objective to minimize both the communication delay and loss of energy transactional messages due to suboptimal network conditions. Taking into account realistic constraints relating to network delay and communication link capacity between the peers, the DAP routing algorithm is used to evaluate network performance using various figures of merit such as probability of signal loss, message delay, congestion and different network topologies. Further, we address the link communication delay problem by redirecting traffic from congested links to less utilized ones. The results show that the proposed routing algorithm is robust to packet loss on the communication links with a 20% reduction in delay compared with hop-by-hop adaptive link state routing algorithm.

Effects of anisotropic oceanic turbulence on the propagation of the OAM mode of a partially coherent modified Bessel correlated vortex beam

ABSTRACTWe have studied the impacts of anisotropic turbulence on the orbital angular momentum (OAM) mode of a partially coherent modified Bessel correlated vortex beam propagation in an oceanic channel. In the weak turbulence paraxial channel, a new model of the probability density of OAM modes has been established. Effects of specific parameters of the oceanic turbulence on it have been studied, it is shown that there is an optimizing receiving aperture diameter in the specific interval of the ratio of temperature and salinity , which can reduce the effect of on the normalized energy weight of OAM modes and the reception of fluctuation signal. The effect of oceanic turbulence with higher anisotropy on the OAM signal is weaker than the turbulence possessing lower anisotropy. We can choose the mode carrying lower OAM quantum number to transfer information more efficiently, and we can utilize the OAM mode with large energy level difference between modes and so on to reduce mode interference and enhance the information capacity of optical communication links.

Improving the Capacity of Molecular Communication Using Enzymatic Reaction Cycles.

This paper considers the capacity of a diffusion-based molecular communication link assuming the receiver uses chemical reactions. The key contribution is we show that enzymatic reaction cycles, which is a class of chemical reactions commonly found in cells consisting of a forward and a backward enzymatic reaction, can improve the capacity of the communication link. The technical difficulty in analyzing enzymatic reaction cycles is that their reaction rates are nonlinear. We deal with this by assuming that the amount of certain chemicals in the enzymatic reaction cycle is large. In order to simplify the problem further, we use singular perturbation to study a particular operating regime of the enzymatic reaction cycles. This allows us to derive a closed-form expression of the channel gain. This expression suggests that we can improve the channel gain by increasing the total amount of substrate in the enzymatic reaction cycle. By using numerical calculations, we show that the effect of the enzymatic reaction cycle is to increase the channel gain and to reduce the noise, which results in a better signal-to-noise ratio and in turn a higher communication capacity. Furthermore, we show that we can increase the capacity by increasing the total amount of substrate in the enzymatic reaction cycle.

Capacity upgrade in short-reach optical fibre networks: simultaneous 4-PAM 20 Gbps data and polarization-modulated PPS clock signal using a single VCSEL carrier

In this work, a four-level pulse amplitude modulation (4-PAM) format with a polarization-modulated pulse per second (PPS) clock signal using a single vertical cavity surface emitting laser (VCSEL) carrier is for the first time experimentally demonstrated. We propose uncomplex alternative technique for increasing capacity and flexibility in short-reach optical communication links through multi-signal modulation onto a single VCSEL carrier. A 20 Gbps 4-PAM data signal is directly modulated onto a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm, therefore, doubling the network bit rate. Carrier spectral efficiency is further maximized by exploiting the inherent orthogonal polarization switching of the VCSEL carrier with changing bias in transmission of a PPS clock signal. We, therefore, simultaneously transmit a 20 Gbps 4-PAM data signal and a polarization-based PPS clock signal using a single VCSEL carrier. It is the first time a signal VCSEL carrier is reported to simultaneously transmit a directly modulated 20 Gbps 4-PAM data signal and a polarization-based PPS clock signal. We further demonstrate on the design of a software-defined digital signal processing (DSP)-assisted receiver as an alternative to costly receiver hardware. Experimental results show that a 3.21 km fibre transmission with simultaneous 20 Gbps 4-PAM data signal and polarization-based PPS clock signal introduced a penalty of 3.76 dB. The contribution of polarization-based PPS clock signal to this penalty was found out to be 0.41 dB. Simultaneous distribution of data and timing clock signals over shared network infrastructure significantly increases the aggregated data rate at different optical network units (ONUs), without costly investment.

Channel characterization and empirical model for ergodic capacity of free-space optical communication link

In this paper, we present experimental results on channel characterization of single input single output (SISO) free-space optical (FSO) communication link that is based on channel measurements. The histograms of the FSO channel samples and the log-normal distribution fittings are presented along with the measured scintillation index. Furthermore, we extend our studies to diversity schemes and propose a closed-form expression for determining ergodic channel capacity of multiple input multiple output (MIMO) FSO communication systems over atmospheric turbulence fading channels. The proposed empirical model is based on SISO FSO channel characterization. Also, the scintillation effects on the system performance are analyzed and results for different turbulence conditions are presented. Moreover, we observed that the histograms of the FSO channel samples that we collected from a 1548.51nm link have good fits with log-normal distributions and the proposed model for MIMO FSO channel capacity is in conformity with the simulation results in terms of normalized mean-square error (NMSE).

Average capacity of the ground to train communication link of a curved track in the turbulence of gamma-gamma distribution

A model of the average capacity of optical wireless communication link with pointing errors for the ground-to-train of the curved track is established based on the non-Kolmogorov. By adopting the gamma-gamma distribution model, we derive the average capacity expression for this channel. The numerical analysis reveals that heavier fog reduces the average capacity of link. The strength of atmospheric turbulence, the variance of pointing errors, and the covered track length need to be reduced for the larger average capacity of link. The normalized beamwidth and the average signal-to-noise ratio (SNR) of the turbulence-free link need to be increased. We can increase the transmit aperture to expand the beamwidth and enhance the signal intensity, thereby decreasing the impact of the beam wander accordingly. As the system adopting the automatic tracking of beam at the receiver positioned on the roof of the train, for eliminating the pointing errors caused by beam wander and train vibration, the equivalent average capacity of the channel will achieve a maximum value. The impact of the non-Kolmogorov spectral index's variation on the average capacity of link can be ignored.