Link Performance Research Articles

Freeway Network Travel Time Reliability Analysis Methodology and Software Tool Development

Applications in the field often require analysis of freeway travel time reliability (TTR) at the network level. While micro-simulation is suitable for performing network-level analysis, the computational burden can become unreasonable when TTR analysis is factored in. As for macro-simulation, most network analysis studies often use simplified link performance functions to represent the travel time and flow relationship. Such functions are not generally sensitive to the range of geometric and traffic conditions that can influence freeway facility operations. This research extends the Highway Capacity Manual (HCM) freeway TTR analysis methodology to the network level. The proposed freeway network TTR analysis methodology generates scenarios that represent the impacts of origin–destination (OD) demand variations, weather events, incident events, and work zone events on freeway network travel time. For each scenario, the methodology performs user equilibrium (UE) traffic assignment and the HCM freeway facility core methodology is applied to represent the travel time and flow relationship. The method of successive average approach is applied to solve the UE traffic assignment. Finally, scenario travel times (and/or other performance measures) are aggregated into various distributions of interest, such as the network-, facility-, and OD-level distributions, and TTR performance measures are calculated at the three different levels. A software tool is developed using C# language on the .NET Framework. The software tool provides a convenient and efficient approach for transportation planners and researchers to conduct the freeway network TTR analysis, which helps to bridge the gap between research and practice.

Modeling and Spatial Diversity-Based Receiving Improvement of In-Flight UAV FSO Communication Links

An in-flight unmanned aerial vehicle (UAV) free-space optical (FSO) communication channel model is proposed by considering the beam deviation of the UAV under different motion states and the phase distortion caused by atmospheric turbulences. The influence of the different motion states and turbulences on the communication quality is evaluated through phase screen and Monte Carlo methods. When the average bit error rate (BER) is 10−5, the signal-to-noise ratio (SNR) should be increased from 13 dB to 20 dB when the tilt angle of the UAV increases from 0 to 5 mrad. An SNR of up to 20 dB is required when the variance of the wind σα2 is 2 mrad. The performance of the in-flight UAV FSO link can be effectively improved through spatial diversity receiving technology. The BER of lower than 10−5 can be obtained just with an SNR of 13 dB if the spatial diversity array with four receivers is used.

PCIE IP Validation Process Across Process Corner, Voltage and Temperature Conditions

IP validation has become more challenging for FPGA device as it supports high operating speed. PCIe is an IP used for high-speed data transfer. The link training and Initialization takes place at physical layer to initialize the link width and link data rate. The physical layer is getting more complex when it supports higher speed. The stability of link training is improved by optimizing the soft logic design in application layer. Two protocol tests usually validated in industry are link up testing and link & higher layer testing. Debugging tools supported by Quartus are fully utilized to detect any failure during link training. The characterization of link performance covers process corners, voltage and temperature conditions are hard to analyse. The H0 statement shows a significant difference for passing and failing case. The p-value is greater than 0.05 proved H0 statement is accepted. The difference on passing and failing percentage is insignificantly impacting overall link performance of PCIe. It concludes that the bug is random and not caused by any defects on the silicon layout of FPGA device. Thus, IP validation shows the robustness of the device and able to comply with base specification of PCIe.

Analysis of THz space communication link based on STK

The characteristics of terahertz communication technology, such as large capacity, high speed and high security, make it stand out among many wireless communication technologies. For future space communication application scenarios, the link performance and beam pointing accuracy of the terahertz communication system were analyzed. The beam adjustment angular acceleration index were analyzed through STK.

Performance of an Underwater Optical Wireless Link With a Randomly Placed or Moving Receiver

The current work investigates the outage probability of a vertical diffused line-of-sight underwater optical wireless communication link where a fixed transmitter at the sea surface communicates with a receiver floated below sea level, which may be still but randomly placed at a given location or moving following the random waypoint model. In both considered scenarios, the channel gain follows a random distribution making the problem mathematically challenging. Novel mathematical expressions are derived for the channel gain statistics for either random placement and mobility effects. Afterward, the signal-to-noise ratio statistics are extracted, assuming indirect modulation/direct detection at the receiver. Hence, the outage probability and the average bit-error-rate for on-off keying are readily calculated. Finally, some relevant numerical results are depicted in a series of figures to highlight the overall performance.

Meta Distributions—Part 1: Definition and Examples

Meta distributions (MDs) have emerged as a powerful tool in the analysis of wireless networks. Compared to standard distributions, they enable a clean separation of the different sources of randomness, resulting in sharper, more refined results. In particular, they capture the disparity of the performances of individual links or users. In this first part of a two-letter series, we start from first principles and give the formal definition of MDs and present several simple yet illustrative examples. Part 2 explores the properties of the MD in more depth and offers multiple interpretations and applications.

Adaptive optics model characterizing turbulence mitigation for free space optical communications link budgets.

Free-space optical communications (FSOC) is becoming an important option for both atmospheric and space-based high data rate networks. Long-range, mobile FSOC links in the former environments must mitigate the effects of turbulence if they are to provide reliable, high link availability under cloud-free atmospheric conditions. Adaptive optics (AO) has been proposed as one means of reducing link degradation in turbulence, but field validated AO performance models are few and not definitive. These models are important if credible FSOC high performance links are expected to be deployed using AO systems. This paper reviews the Strehl ratio for the Andrews AO model and provides comparisons between predicted AO-based FSOC link budgets and measured link performance derived from several field trials. These results suggest that AO systems perform well under weak turbulence or short range under 10 km, but only offer limited tip/tilt gain in moderate turbulence and no gain under high/saturation regime turbulence at longer ranges. Long range links close to the ground in high moderate turbulence may degrade AO performance further.

An experimental study on the seismic behavior and replaceability of the replaceable steel shear links

The reinforced concrete columns and steel beams (RCS) composite frames have received popularity in low to moderate seismic regions due to advantages of the system. However, the poor repairable capacity and deteriorating pinched hysteretic behaviour of the traditional RCS framed structure limit the application in practice under earthquakes. This study presents a modified RCS framed structure with replaceable members aiming to enhance the energy dissipation and resilience capability. The structural configuration character and the general predetermined levels of lateral response of the proposed RCS framed structure with replaceable members is first introduced. Seven quasi-static loading tests were subsequently conducted to evaluate the seismic behavior and replaceability of the replaceable shear links. Parameters including the link length ratio, stiffener configuration and link-to-column connection were examined. The test results depicted that the specimens exhibited the shear dominated behavior. The major failure features of the shear links included web-to-stiffener weld tear, web buckling and web fracture. All tested specimen showed a stable bearing strength, large inelastic rotation capacity and excellent energy dissipation behavior. The same link length ratio of the specimens with different specialized connections presented the similar behavior. Noted that end plate and web stiffeners connection can alleviate the stress concentration on the fillet weld of the flange-to-end plate weld and optimize the performance of the shear link. The average overstrength factor and inelastic rotation capacity of the test specimens were 1.9 and 0.087 rad significantly exceeding 1.5 and 0.08 rad provided by the AISC 341-16 provisions for the EBF links, respectively. In addition, the replaceability of the specimens was evaluated underwent the entire loading process. Compared with the T-shaped and Π-shaped plate connections, replacement of the shear link with the end plate demanded the least effort and time.

Using Machine Learning Algorithms for Accurate Received Optical Power Prediction of an FSO Link over a Maritime Environment

The performance prediction of an optical communications link over maritime environments has been extensively researched over the last two decades. The various atmospheric phenomena and turbulence effects have been thoroughly explored, and long-term measurements have allowed for the construction of simple empirical models. The aim of this work is to demonstrate the prediction accuracy of various machine learning (ML) algorithms for a free-space optical communication (FSO) link performance, with respect to real time, non-linear atmospheric conditions. A large data set of received signal strength indicators (RSSI) for a laser communications link has been collected and analyzed against seven local atmospheric parameters (i.e., wind speed, pressure, temperature, humidity, dew point, solar flux and air-sea temperature difference). The k-nearest-neighbors (KNN), tree-based methods-decision trees, random forest and gradient boosting- and artificial neural networks (ANN) have been employed and compared among each other using the root mean square error (RMSE) and the coefficient of determination (R2) of each model as the primary performance indices. The regression analysis revealed an excellent fit for all ML models, indicative of their ability to offer a significant improvement in FSO performance modeling as compared to traditional regression models. The best-performing R2 model found to be the ANN approach (0.94867), while random forests achieved the most optimal RMSE result (7.37).

Performance analysis of Terahertz communication link for cooperative Wireless Body Area Network

This paper presents performance analysis of Terahertz communication link for non-cooperative and cooperative Wireless Body Area Network (WBAN) considering a human model operating at Terahertz frequency (0.1–10.0 THz). Link parameter metrics like Signal to Noise ratio (SNR), Bit Error Rate (BER) and outage probability have been evaluated and revealed better performance of Terahertz link in cooperative WBAN compared to non-cooperative scenario by exhibiting better SNR, lower BER and lower outage probability. In the considered scenario for the cooperative link, amplify and forward (AF) scheme has been critically compared with decode and forward (DF) scheme and it has been observed that Terahertz link for decode and forward scheme exhibits better performance in terms of SNR, BER and outage probability by 5.68%, 24.51% and 80.9% respectively in comparison to amplify and forward scheme. By increasing the number of relays, a considerable decrease in outage probability has also been observed.

Research on Real-time and Reliability of Wireless Transmission of High-speed Train Control Data Based on Data Mining Technology

The informationization of high-speed railway is of great significance to the operation and maintenance of high-speed trains. Through the operation and maintenance data communication based on wireless public network, the ground monitoring system can know the real-time status of trains in time, which can facilitate the daily arrangement of inbound inspection and maintenance of trains and improve the operation and maintenance efficiency of high-speed trains. The reliability of data transmission in wireless sensor networks is low under the influence of resource constraints and environmental factors. However, the reliability of data transmission is an important index to evaluate the network performance in application fields such as national defense, military affairs and industrial control. Based on data mining technology, this paper analyzes the real-time, reliability and security of data transmission according to the characteristics of digital mobile communication used for data transmission in railway running and train automatic control. Combined with the characteristics of wireless channel in the environment of intelligent railway transportation system, this paper puts forward concrete measures to improve the performance of wireless link and concrete methods to judge whether wireless transmission can meet the requirements of IRTS environment.

Investigation of Underwater Wireless Optical Communications Links With Surface Currents and Tides for Oceanic Signal Transmission

This report investigated underwater wireless optical communication (UWOC) links in the presence of surface currents and tides. The scenario of surface currents and tides was generated by a sea water tank, a water pipe, and a water pump of different flow rates. It built the oceanic channel of UWOC varied with the salinity and flow rate in the UWOC transmission. The data rate of UWOC links based on a 520-nm laser diode and none-return-to-zero on-off keying (NRZ-OOK) modulation can achieve 3.4 Gb/s at a bit error rate (BER) of 3.78 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 10^{-4}$</tex-math></inline-formula> in 1.8 m long sea water tank when a flow rate reached 1.08 m/s. The BER, eye-diagrams, and received signal optical power measurements showed that both the increasing salinity and flow rate cause the UWOC channel attenuation, thus degrade the performance of UWOC links.

Distributed Resource Allocation for General Energy Efficiency Maximization in Offshore Maritime Device-to-Device Communication

In maritime scenario, the communication service, if any, is likely to be expensive due to the high-cost satellite transmissions or the very limited offshore coverage of terrestrial networks. Thus, how to achieve efficient radio resource management is one of the critical issues in maritime communication. In this letter, by exploiting the device-to-device (D2D) mechanism, we identify a general energy efficiency (GEE) optimization problem, which takes into account the physical link performance and the users’ pairing willingness (PW) quantified by a modified Jaccard coefficient metric. Then, we divide the GEE optimization problem into two sub-problems of user pairing and power allocation, and solve them by a distributed pairing method and by a new distributed resource allocation scheme, respectively. Simulation results demonstrate significant performance gains achieved by the proposed GEE maximization-based distributed D2D resource allocation (GEEM-DD2D-RA) algorithm over existing methods.

Achieving high budget classes in the downstream link of 50G-PON

With 50G passive optical networks (PONs) currently being standardized, we review the challenges of meeting the high loss budgets required in such high speed fiber access networks. Simulations of the 50 Gb/s link performance show the impact of critical parameters when using 25G-class avalanche photodiode receivers with digital signal processing. We describe how a 1342 nm electro-absorption modulated laser, with an external semiconductor optical amplifier, enables an E2-class, 20 km, downstream link for ITU-T, 50G-PON to be demonstrated. Using a 25G-class receiver and real-time equalization, a link budget of 35.6 dB was measured. With more powerful equalization performed offline, an increase in the link budget to 38.2 dB is also demonstrated.

Parameter Optimization for an Underwater Optical Wireless Vertical Link Subject to Link Misalignments

We consider transmitter–receiver (Tx–Rx) parameter optimization for a vertical underwater wireless optical communication link under misalignment conditions. The Tx is assumed to use a light-emitting diode, whereas the Rx uses a silicon photomultiplier that allows a high Rx sensitivity. We consider two typical application scenarios and investigate optimization of the Tx and Rx parameters to optimize the link performance in terms of outage probability. We derive accurate analytical expressions for the distribution of the channel attenuation accounting for link misalignments, which allows for the evaluation of the link performance in terms of bit-error-rate and outage probability without resorting to costly Monte Carlo simulations. Through numerical results, we show and discuss the impact of parameter optimization on the link performance in different link configurations and for various misalignment conditions. In particular, the presented results show the significant performance improvement resulting from optimizing the Tx beam divergence and the Rx field-of-view in the presence of pointing errors.

Analysis of Visible Light Communication Link’s Performance in Fire Smoke Environment

This paper mainly studies the communication performance of visible light communication link in fire smoke environment. Compared with the previous studies, this study no longer only considers a single wavelength and considers the influence of smoke and background light noise. Firstly, the variation of background light noise caused by sunlight during a day was analyzed, then signal-to-noise ratio (SNR) and bit error rate (BER) of the visible light communication link in fire smoke environment with different visibility were calculated, and finally, the variation of received power with the angle β between the LED optical axis and the communication link (from LED to receiver) was analyzed. The results show that, during a day from 07:00 to 18:30, background light noise first increases and then decreases, BER changes in the same trend and reaches the maximum at about 13:00, while SNR changes in the opposite trend and reaches the minimum at about 13:00. When visibility is 100 m, the maximum difference of SNR between 7:00 and 13:00 is about 19 dB, and the maximum difference of BER is about 5.3E-10. At 7:00, the maximum difference of SNR is about 13 dB between the visibility of 1 m and the visibility of 100 m, and the maximum difference of BER is about 1.44E − 11, and received power decreases with the increase of β. In addition, SNR increases with visibility of fire smoke environment, and BER changes in the opposite trend. Lastly, in order to enhance the performance of visible light communication in fire smoke environment, this paper gives the transmitting power scheme.

High-SFDR 100.8km ROF link with optical homodyne detection and genetic-algorithm-assisted digital demodulation.

Radio-over-fiber (ROF) link based on phase modulation and coherent detection has been widely proposed for linear transmission. Nowadays, there are increasing demands for long-distance analog radio-frequency (RF) signal transmission, as radars and broadcast systems. In this paper, a high spurious-free-dynamic-range (SFDR) analog coherent ROF link based on optical homodyne detection and genetic-algorithm-assisted digital demodulation is proposed and experimentally investigated. The ROF link is designed for transmitting RF signals ranging from 500 kHz to 100 MHz over a long-distance fiber under the environment of wide temperature. We test the link performance by transmitting different groups of two-tone signals (580 kHz and 600 kHz, 9 MHz and 10 MHz, 49 MHz and 50 MHz, 99 MHz and 100 MHz) over a 100.8-km single-mode fiber (SMF) under the temperature varying from -40°C to 70°C, the shot-noise-limited SFDR of the link are measured to be greater than 122 dB·Hz2/3.

A New Power Control Algorithm in MMSE Receiver for D2D Underlying Massive MIMO System

Device to device (D2D) underlying massive MIMO cellular network is a robust deployment which enables network to enhance its throughput. It also improves services and applications for the proximity-based wireless communication. However, an important challenge in such deployment is mutual interference. Interference, in the uplink spectrum, reusing the same resource with cellular user, is caused by D2D users. In this paper, we study a distributed power control (DPC) algorithm, using minimum mean square error (MMSE) filter in receiver, to mitigate the produced interference in this deployment scenario. For the DPC algorithm, employing the coverage probability of D2D links, an optimal power control approach is proposed, which maximizes the spectral efficiency of D2D links. Using this modeling approach, it is possible to derive closed-form analytical expressions for the coverage probabilities and ergodic spectral efficiency, which give insight into how the various network parameters interact and affect the link.‎ Also, the DPC algorithm is modeled by stochastic geometry and receiver filter is designed by estimation theory that a new structure in this robust network is an approach to improve spectral efficiency. Simulation results illustrate enhancing coverage probability performance of D2D links in term of the target (signal to interference ratio) SIR with respect to different receiver filter and other parameters which are existing in D2D links.

Evaluation of Misalignment Effect in Vehicle-to-Vehicle Visible Light Communications: Experimental Demonstration of a 75 Meters Link.

The use of visible light communications technology in communication-based vehicle applications is gaining more and more interest as the research community is constantly overcoming challenge after challenge. In this context, this article addresses the issues associated with the use of Visible Light Communications (VLC) technology in Vehicle-to-Vehicle (V2V) communications, while focusing on two crucial issues. On the one hand, it aims to investigate the achievable communication distance in V2V applications while addressing the least favorable case, namely the one when a standard vehicle rear lighting system is used as a VLC emitter. On the other hand, this article investigates another highly unfavorable use case scenario, i.e., the case when two vehicles are located on adjacent lanes, rather than on the same lane. In order to evaluate the compatibility of the VLC technology with the usage in inter-vehicle communication, a VLC prototype is intensively evaluated in outdoor conditions. The experimental results show a record V2V VLC distance of 75 m, while providing a Bit Error Ratio (BER) of 10−7–10−6. The results also show that the VLC technology is able to provide V2V connectivity even in a situation where the vehicles are located on adjacent lanes, without a major impact on the link performances. Nevertheless, this situation generates an initial no-coverage zone, which is determined by the VLC receiver reception angle, whereas in some cases, vehicle misalignment can generate a BER increase that can go up to two orders of magnitude.

Digital predistortion of radio over fiber (RoF) link using hybrid Memetic algorithm

Abstract Despite their many advantages over other communication links, radio over fiber (RoF) links also suffer from nonlinearity. This limits the dynamic range performance of the RoF link. Linearization techniques like digital predistortion can be explored for mitigating this nonlinearity. A hybrid optimization algorithm called hybrid Memetic algorithm, which uses the benefits of both Tabu search algorithm and Memetic algorithm, is used for parameter estimation of the digital predistorter. Simulation results demonstrate that the hybrid Memetic algorithm offers very promising outcomes.