Performance Of Communication Link Research Articles

Performance of a free space optical link employing DCO-OFDM modulated Gaussian-beam

Abstract The paper studies the performance of a free space optical communication link, which consists of a Gaussian Laser beam employing direct-current-biased optical frequency division multiplexing (DCO-OFDM) modulation, to carry information. While optical multi-carrier modulation is capable of alleviating multi-path fading, higher transmit power by virtue of dc-bias, helps the optical beam in partially off-setting signal intensity loss due to beam divergence in free space channel. In order to reduce the overall transmitted power apart from avoiding nonlinearities due to high peak-to-average-power-ratio (PAPR), we utilize a PAPR-dependent dc-bias, to generate a DCO OFDM light beam from a pre-clipped electrical baseband OFDM signal. The radiated optical beam encounters turbulence-induced impairments like beam-spreading, beam-wander, etc., which affect the signal-to-noise ratio (SNR) of the received data symbols. Further signal pre-clipping and optical source linearity generate clipping noise components resulting in compromised receiver performance or reduction of span length, to achieve target bit rate error (BER). In this paper, we derive an analytical model for evaluating the performance of the free-space optical (FSO) link, by modeling various impairments as noise variances and characterizing atmospheric turbulence by refractive index structure parameter under weak- and strong-turbulent conditions. Numerical results are obtained by varying system design parameters in the model, which graphically provide useful insight on the power penalties and various trade-offs involved in operating the link on a longer span, at a higher data rate, and with reduced transmitted power through pre-clipping while ensuring desired signal BER.

Enhancing Performance of Coherent Optical OFDM FSO Communication Link Using Cascaded EDFA

Coherent communication aims to support high-speed dynamic networks by making their installation easier along with their monitoring and maintenance. In addition, Orthogonal Frequency Division Multiplexing (OFDM) which has shown gradual emergence in radio frequency (RF) domain during the past years, has now encroached into the optical domain. Combination of these two provides vigorous dispersion transmission as well as enhanced spectral efficiency. Free Space Optical (FSO) communication link performance deteriorates with scintillations, atmospheric turbulences and weather induced attenuations. The optical amplifiers, their arrangement used in the FSO link design has a drastic influence on the performance of the link. This work involves evaluating the proposed Coherent Optical OFDM FSO communication link at 30 Gbps data rate using Cascaded Erbium Doped Fiber Amplifier. The system has been evaluated in clear weather, rainfall and fog (Moderate to Dense) in terms of Q-Factor, BER, SNR and constellation diagram. The system has been designed considering moderate turbulent environment and geometric losses. The FSO communication link shows optimal performance up to 26 km for clear weather, 3.73 km under rainfall, 1.44 km under moderate foggy and 0.66 km under dense foggy environment.

Reduction of the beam pointing error for improved free-space optical communication link performance

Free-space optical communication is emerging as a low-power, low-cost, and high data rate alternative to radio-frequency communication in short- to medium-range applications. However, it requires a close-to-line-of-sight link between the transmitter and the receiver. This paper proposes a robust H∞ control law for free-space optical (FSO) beam pointing error systems under controlled weak turbulence conditions. The objective is to maintain the transmitter–receiver line, which means the center of the optical beam as close as possible to the center of the receiving aperture within a prescribed disturbance attenuation level. First, we derive an augmented nonlinear discrete-time model for pointing error loss due to misalignment caused by weak atmospheric turbulence. We then investigate the H∞-norm optimization problem that guarantees the closed-loop pointing error is stable and ensures the prescribed weak disturbance attenuation. Furthermore, we evaluate the closed-loop outage probability error and bit error rate (BER) that quantify the free-space optical communication performance in fading channels. Finally, the paper concludes with a numerical simulation of the proposed approach to the FSO link’s error performance.

Modelling on Impact of Building Obstruction for V2I Communication Link in Micro Cellular Environment

In vehicular communication, signal transmission in vehicle-to-infrastructure (V2I) mode typically takes place on highways, urban, suburban and rural environments. The presence of buildings in these environments poses a challenge to model path loss (PL) due to multiple propagation mechanisms such as diffractions and reflections. However, very little attention has been made to address building effects on the performance of V2I communication links in microcell environment. This paper investigates signal propagation characteristics caused by the impact of building under micro-cellular environment whereby the base station or road-side-unit (RSU) is usually located under the rooftop of building to allow communication between RSU and mobile station or on-board-unit (OBU) on the road. The goal of this paper is to validate and discuss available path loss models based on effect of building obstruction towards RSU-OBU links specifically in residential housing area. The channel measurements are conducted based on static line-of-sight (LOS) settings of a real-world environment at 2.4 GHz frequency band using IEEE 802.15.4 XBee S2C compliant device to measure its receive power. The results are demonstrated based on received signal strength indicator (RSSI) and root mean square error (RMSE). The attenuation profile is validated and compared with suitable path loss models to evaluate best fit and most compatible model based on our measurements data and environment. The analysis shows that several V2I path loss models and V2V channel models are applicable to be used as a reference to model in LOS microcell environment with building obstruction. The finding shows that PL Urban yields the best fit V2I path loss model in terms of RMSE when compared to our measurement campaign at 2.4 GHz.

Next Generation X-in-the-Loop Validation Methodology for Automated Vehicle Systems

Testing self-driving vehicles is still a new and immature process; the globally harmonised procedure expected much later. The resource-demanding nature of real-world tests makes it indispensable to develop and improve the efficiency of virtual environment based testing methods. Accordingly, a novel X-in-the-Loop framework is proposed to fully exploit the recent advances in info-communication technologies, vehicle automation, and testing and validation requirements. This methodology real-time connects physical and virtual testing with high correlation while completely blurs the sharp boundaries between them. Measurement results confirm the superior performance of the 5G communication link in providing a stable, real-time connection between the real world and its virtual representation. The live demonstration proved the presented concept at the newly constructed Hungarian proving ground for automated driving. The performed investigation also includes comprehensive benchmarking, focusing on the most up-to-date automotive testing frameworks. The analysis considers the methodologies and techniques applied by the most relevant actors in the automotive testing sector worldwide. Accordingly, the newly developed testing framework is evaluated and validated in light of the state-of-the-art methods used by the automotive industry.

Simulation analysis of adaptive FSO/RF hybrid link under diverse weather conditions of Lahore, Pakistan

Free Space Optical (FSO) communication has higher bandwidth, data rate, quality factor, and secure transmission, making it ideal for future high capacity data links. However, fog, rain and dusty conditions are key hindrances in effective utilization of maximum performance of FSO link. This research work presents a simulation analysis of a typical FSO link of length 1 km (1550 nm) with Tx/Rx aperture diameters 10 cm and 15 cm, respectively, under weather conditions of the capital province Punjab, Lahore. Signal to noise ratio (SNR), Bit error rate (BER) and received power of link under consideration are calculated numerically in MATLAB ®. By proposing a switching technique, an year-round performance analysis was carried out using MATLAB ®. FSO is the primary link as the received power of the FSO link falls below a certain threshold; the communication link adapts the RF link as primary communication channel. Results show that an adaptive technique can successfully operate and enhance the performance of a FSO communication link.

Performance of Two-Hop Links With an Energy Buffer-Aided IoT Source and a Data Buffer-Aided Relay

In this article, we analyze the performance of a two-hop communication link between an energy-buffer-equipped IoT-type self-sustaining source and a destination, aided by a data-buffer-equipped relay. The source harvests radio-frequency energy from the ambience and stores it in an energy buffer. Using a discrete-time continuous-state Markov chain to model the energy buffer and a discrete-state Markov chain to model the data buffer, we analyze outage and throughput performance of the link. In typical applications, feedback of channel state information and buffer state information is not feasible, so simple link selection schemes are evolved. In the first only buffer-status (OBS) scheme, link selection is based on the energy-buffer status alone. A modified OBS scheme is then suggested, and its performance is analyzed. The third scheme uses both energy-buffer status and first-hop channel knowledge for link selection. Expressions are derived for throughput and limiting distributions of stored energy with all the three schemes. We show how the continuous-state energy buffer and the discrete-state data buffer can both be balanced while maximizing the throughput by suitable choice of the source transmit power, relay transmit power, and target information rates at the source and the relay. We also analyze statistical properties of the energy-buffer size with these schemes. The derived analytical expressions are validated by the Monte Carlo simulations.

Enhanced tolerance against optical background noise in VLC link by using line coded signal with receiver filter

The performance of visible light communication (VLC) link is significantly affected by optical background noises generated by fluorescent light or AC driven light emitting diode (LED) and eventually degrades the data rate due to the in-band interference between signal and noise. Here, bandwidth efficient 8b10b dc-balanced line coding and post-detection electrical filter based VLC link is demonstrated to improve the system tolerance against the optical background noises. The 8b10b coded signal with low frequency components near DC ensure that the crosstalk noise is effectively minimized by spectral separation of signal and noise contributions. Moreover, the use of post detection filter for 8b10b coded signal gives an additional attenuation of noise frequency to further improve the system tolerance against optical background noise. The proposed VLC link is investigated thoroughly in several noise power levels as well as different noise frequencies, where the results indicate improved system tolerance against noise power by about 6.5 dB in compare to conventional data signal. The demonstration also shows that the proposed scheme maintains a low BER for the noise frequency up to 500 kHz for 10 Mb/s data modulation having a good eye opening.

Physical Layer Security of Large Reflecting Surface Aided Communications With Phase Errors

The physical layer security (PLS) performance of a wireless communication link through a large reflecting surface (LRS) with phase errors is analyzed. Leveraging recent results that express the LRS-based composite channel as an equivalent scalar fading channel, we show that the eavesdropper's link is Rayleigh distributed and independent of the legitimate link. The different scaling laws of the legitimate and eavesdroppers signal-to-noise ratios with the number of reflecting elements, and the reasonably good performance even in the case of coarse phase quantization, show the great potential of LRS-aided communications to enhance PLS in practical wireless set-ups.

Analysis of Outage Probability in Wavelength Diversity Based FSO Link Under Gamma–Gamma Fading with Varying Atmospheric Attenuation

Free space optical (FSO) communication links offers an emerging alternative to RF communication links because of high speed, secure and cost-effective options to provide the last mile connectivity to end-users. They may be deployed for quick network access temporarily during link failure and natural disaster. This paper focusses on the performance of FSO communication link impaired with strong turbulence and atmospheric attenuation added through varying climatic conditions. A closed-form expression for outage probability is derived to evaluate the performance under different levels of atmospheric attenuation and turbulence strengths. The mathematical analysis clearly shows inimical effects added by atmospheric attenuation over the performance of the communication link. The impact of wavelength diversity on the outage probability of such a link is analyzed with three carrier wavelengths 1550 nm, 1310 nm and 850 nm. The simulation results with wavelength diversity for different atmospheric attenuation levels and turbulence are plotted and analyzed.

G2A Communication Channel Modeling and Characterization Using Confocal Prolates

Characterization of radio environment is an important field of research that helps to analyze the limiting features of the propagation environment and leads to develop a realistic channel model. This paper proposes an appropriate multipath channel model for various ground-to-air (G2A) communication scenarios. An intensive review of the existing literature on A2G/G2A channel models is presented along with a critical analysis with appropriate comments wherever needed. It is observed that most of the research literature supposedly model G2A channels interchangeably in the same manner as that of land mobile communication links. G2A communications systems are generally equipped with directional antennas for dedicated coverage to flying aircrafts that benefits in increasing range and signal strength while restraining interfering signals coming through scattering objects around ground station (G). This research analyzes G2A multipath channel and thus proposes a geometrically-based physical G2A multipath channel model. The proposed channel model clearly justifies the existence of multipath environment in G2A communication due to the existence of aircrafts in the vicinity of the intended aircraft. This model is based on a three-dimensional confocal prolate spheroids and uses the principle of single-bounce multipath geometry. Moreover, the model gives an insight to analyze multipath multiuser G2A communication in wide-beam and narrow-beam communication link scenarios. This model is equally applicable to the networks of passenger aircrafts, flocks of jet fighters and mesh of UAV drones. This model can be used to analyze the performance of high data-rate communication links with high mobile speeds over sparsely distributed multipath channels.

Spectrum Sharing for UAV Communications: Spatial Spectrum Sensing and Open Issues

Unmanned aerial vehicles (UAVs) are attracting increasing attention for applications such as video streaming, surveillance, and delivery using reliable line-of-sight (LOS) links. Nevertheless, due to the large radio-frequency (RF) transmission footprint from a UAV transmitted to ground nodes, UAV communications may significantly deteriorate the performance of cochannel ground communication links. With the lack of a dedicated spectrum, researchers need to design efficient spectrum-sharing policies for UAV communications to enhance spectral efficiency (SE) and control interference-to-ground communications. One technique for spectrum sharing is spatial spectrum sensing (SSS), which enables devices to sense spatial spectrum opportunities and reuse them aggressively and efficiently by controlling the SSS radius. The goal of this article is to introduce the fundamentals, challenges, and applications of SSS for UAV spectrum access and discuss open research problems for realizing UAV spectrum sharing, including dynamic spectrum access for swarm UAV networks, artificial intelligence (AI)-enabled UAV spectrum access, blockchain-based UAV spectrum access, multichannel access for UAVs, and the integration of UAVs into cellular networks.

Improving system performance by using adaptive optics and aperture averaging for laser communications in oceanic turbulence.

We theoretically investigate the effectiveness of adaptive optics correction for Gaussian beams affected by oceanic turbulence. Action of an idealized adaptive optics system is modeled as a perfect removal of a certain number of Zernike modes from the aberrated wavefront. We focused on direct detection systems and we used the aperture-averaged scintillation as the main metric to evaluate optical system performances. We found that, similar to laser beam propagation in atmospheric turbulence, adaptive optics is very effective in improving the performance of laser communication links if an optimum aperture size is used. For the specific cases we analyzed in this study, scintillation was reduced by a factor of ∼7 when 15 modes were removed and when the aperture size of the transceiver was large enough to capture 4-5 speckles of the oceanic turbulence-affected beam.

On the performance of optical wireless communication links impaired by time jitter, M-turbulence and pointing errors

The interest for the optical wireless communication systems increases significantly the last years due to the very high advantages of this technology. More specifically, the FSO links can achieve very high data rate and secure communications with low installation and operational cost. However, the main disadvantage of the FSO links is that their performance is dominated by the weather conditions and the turbulence of the atmosphere, where the optical beam propagates. The atmospheric turbulence mitigates significantly the performance of the FSO links and causes the scintillation effect, which results in rapid irradiance fluctuations at the receivers. Furthermore, another factor which increases the influence of the atmospheric turbulence and causes further fast changes at the receivers’ irradianceis the pointing errors. Additionally, the performance of most of the high data rate communication systems, is reduced by the time jitter effect, which causes the detection of each digital pulse before or later than the ideal time spot. Thus, in this work, the performance of a terrestrial FSO link is investigated, for first time under the simultaneous action of the M(alaga) atmospheric turbulence, the pointing errors and the time jitter effects for various, commonly used in FSO links, modulation schemes. Taking into account their joint influence, new accurate closed form mathematical expressions are derived for the average BER estimation. Finally, the corresponding numerical results and conclusions are shown and derived.

Impact of Pointing Error on the BER Performance of an OFDM Optical Wireless Communication Link over Turbulent Condition

Abstract An analytical approach is developed in this paper to evaluate the bit error rate (BER) performance of an optical wireless (OW) communication system with multiplexing of the RF orthogonal frequency division (OFDM) over turbulent condition taking into account the effect of pointing error. The received signal is detected through direct detection receiver followed by RF synchronous demodulation including the effect of OW channel and different form of noises such as receiver thermal noise, background channel noise and photo detector shot noise. Analysis is developed for an OFDM system over the OW channel, taking into account the effect of pointing error between the transmitter and the receiver in turbulent condition and the analysis reveals that the OFDM OW system is less affected by pointing error with deference to the major power penalty at BER performance. For instance, power penalty at BER 10−9 is found to be 3 dB for 256 OFDM subcarriers with 9 millidegree displacement angle at a data rate of 10 Gbps under turbulent condition. It is found that the system is more influenced by the atmospheric turbulence at a higher data rate.

Time Jitter, Turbulence and Chromatic Dispersion in Underwater Optical Wireless Links

The performance of an underwater optical wireless communication link is investigated by taking into account—for the first time and to the best of our knowledge—the simultaneous influence of the chromatic dispersion, the time jitter and the turbulence effects, by assuming chirped longitudinal Gaussian pulse propagation as information carriers. The estimation procedure is presented and a novel probability density function is extracted in order to describe the irradiance fluctuations at the receiver side. Furthermore, the availability of the link is investigated by means of its probability of fade and various numerical results are presented using typical parameters for the underwater optical wireless communication systems.

An Improved Low-Power Coding for Serial Network-On-Chip Links

In the fast nanosilicon revolution era, network-on-chip (NoC) architecture offers a significant research solution to on-chip multiprocessor-based real-time applications. As the number of cores increases, power consumption of the resources of NoC also increases. Links are the major power dissipator in NoC architecture owing to switching activity of data bits communicated through them. The performance of data communication links in NoC is strongly dependent on the factor of power dissipation. An efficient coding method is needed to reduce both coupling and self-switching activity of data bits of NoC links. In this work, an improved low-power encoding algorithm for serial links is proposed to reduce switching transition for any random data pattern making them more suited to real-time applications. The proposed encoding algorithm is coded, simulated and verified its area and power performance using Synopsys tools utilizing UMC 90 nm technology. Experimental results have shown that it provides on average 48.83% of switching activity reduction for any real-time applications.

Crosstalk Limitations due to Intercore Coupling on the BER Performance of an Optical Communication System with Homogeneous Multi-core Fiber

Abstract The effect of crosstalk due to inter-core coupling on the bit error rate (BER) performance of a fiber optic communication link with a homogeneous multi-core optical fiber (MCF) and a direct detection receiver with optical preamplifier is analytically evaluated and presented in this paper. Coupling coefficients due to inter-core coupling in a 7-core MCF is evaluated numerically with as a function of core-to-core distance (pitch) and relative refractive index contrast. Coupling length is determined against various index contrasts and at different core pitches. Crosstalk power, Signal to Crosstalk plus Noise Ratio (SCNR), BER and power penalty at any output core with light launched into other core of a 7-core MCF are determined analytically. The results show that there is mentionable deterioration in BER performance due to coupling induced crosstalk, and system suffers distinct power penalty at a given BER. For example, power penalty at BER of 10e-9 is found to be 4.0 dB and 4.3 dB for a MCF link of 10 km corresponding to relative refractive index difference of 0.0036 and 0.0030, respectively, for a pitch value of 30 µm and core radius of 4.5 µm.

Performance Analysis of a STBC FDM FSO Communication System with Direct Detection Receiver under Turbulent Condition

Abstract Weather conditions are severely degraded the performance of FSO communication link. Atmospheric turbulence is one of the important weather conditions that degrade the performance even under clear sky condition. In this paper, we provide a noble analytical approach to evaluate the performance of STBC coded FDM FSO communication system with direct detection optical receiver under turbulent condition. Analysis is carried out to find the channel capacity of RF subcarrier modulation taking into consideration the effect of strong atmospheric turbulence which is modeled as gamma-gamma distribution and the probability density function of the conditional CNR, conditioned on a given turbulence-induced fading is derived considering equal gain receive diversity combining technique with direct detection optical receiver followed by RF synchronous demodulation. Results are evaluated numerically in terms of average CNR, BER and channel capacity for several system parameters like turbulence variance, link distance, data rate, etc.

Bridging the Gap Between CP-OFDM and ZP-OFDM for the Provision of Ultra-Low Latency Services in 5G

In this paper, we introduce and characterize a new filter bank multicarrier (FBMC) architecture, based on flexible zero padding (FZP), suitable for applications obeying stringent latency requirements. FZP conveniently distributes zeros between transmit (Tx) and receive (Rx) waveforms, and covers cyclic prefix (CP) and zero padding (ZP) as special extremal cases, providing, in this way, a bridge between classical CP-orthogonal frequency division multiplexing (OFDM) and ZP-OFDM. It has the merit of being the only possible architecture that guarantees optimum confined and autonomous transmission and reception of each OFDM symbol within the symbol period, leading to a minimized latency. We assess the best achievable signal-to-interference-plus-noise-ratio (SINR) performances, of all possible FBMC configurations, obeying the FZP architecture, through a systematic optimization of their Tx and Rx waveforms, using the ping-pong optimized pulse shaping (POPS) algorithm. We also assess the whole communication link performance, in terms of raw and coded bit error rate (BER), for several representative FZP configurations. It turns out that the medium alternative between CP and ZP, which evenly distributes FZP between the Tx and Rx waveforms, does not provide a significant improvement in signal-to-interference ratio (SIR) and BER, for slightly time dispersive channels, but brings more robustness to time synchronization errors. The conducted study shows that conventional CP-OFDM remains an interesting alternative since it leads to an insignificant degradation in SIR, compared to the optimal FZP configuration, while providing a decorrelated noise at the receiver, beneficial for short coded packets.