Upstream Links Research Articles

Using temporal detrending to observe the spatial correlation of traffic.

This empirical study sheds light on the spatial correlation of traffic links under different traffic regimes. We mimic the behavior of real traffic by pinpointing the spatial correlation between 140 freeway traffic links in a major sub-network of the Minneapolis—St. Paul freeway system with a grid-like network topology. This topology enables us to juxtapose the positive and negative correlation between links, which has been overlooked in short-term traffic forecasting models. To accurately and reliably measure the correlation between traffic links, we develop an algorithm that eliminates temporal trends in three dimensions: (1) hourly dimension, (2) weekly dimension, and (3) system dimension for each link. The spatial correlation of traffic links exhibits a stronger negative correlation in rush hours, when congestion affects route choice. Although this correlation occurs mostly in parallel links, it is also observed upstream, where travelers receive information and are able to switch to substitute paths. Irrespective of the time-of-day and day-of-week, a strong positive correlation is witnessed between upstream and downstream links. This correlation is stronger in uncongested regimes, as traffic flow passes through consecutive links more quickly and there is no congestion effect to shift or stall traffic. The extracted spatial correlation structure can augment the accuracy of short-term traffic forecasting models.

Building information modeling-based model for calculating direct and indirect emissions in construction projects

The construction industry is considered as one of the most dynamic sectors that have upstream and downstream economic links and has been growing rapidly in the last few decades. On the other hand, it is considered as one of the main sources of greenhouse gases where construction projects represent a huge portion of sources producing carbon dioxide gases (CO2). Furthermore, greenhouse gases (GHG) are one of construction emissions that should be investigated to calculate the overall emissions. Therefore, estimating construction emissions is very important in order to keep emissions at an acceptable level. This paper presents a building information modeling (BIM)-based model that enables the estimation of six types of emissions including: greenhouse gases, sulfur dioxide, particular matter, eutrophication particles, ozone depleting particles and smog. As such, the total direct and indirect emissions can be calculated where these emissions are produced from construction activities during the overall project life cycle phases which are: manufacturing phase, transportation phase, construction phase, operation phase, maintenance phase, and deconstruction/demolition phase. The methods of calculating direct and indirect emissions are extensively described in the paper. A case study is presented to illustrate the use of the proposed BIM-based model.

Simulation method for stochastic generation of domestic wastewater discharges and the effect of greywater reuse on gross solid transport

Together with significant water saving, due to lower wastewater discharges, greywater reuse (GWR) may also increase the impacts of faecal matter and other gross solids (GS) on sewer systems (sedimentation, blocking). Modelling and assessments of these effects require detailed descriptions of individual domestic wastewater streams. A novel stochastic methodology to generate such streams was developed and validated. The generator was developed while considering dependencies between in-house water-use events, and their varying degree of elasticity. These generated streams served as input to a sewer model, where scenarios of GWR were simulated and their effects on GS transport were examined. Extensive GWR decreases GS movement mostly in upstream links. Nevertheless, transient high flows, characterising these links, may move stationary GS and prevent blockages. The developed generator can be adopted to other sewer-related studies. Intelligent implementation of the results can assist in introducing GWR, or other water saving measures to the urban sector.

Estimating the Effects of Urban Street Incidents on Capacity

The effect of incidents on capacity is the most critical parameter in estimating the influence of incidents on network performance. The Highway Capacity Manual 2010 (HCM 2010) provides estimates of the drop in capacity resulting from incidents as a function of the number of blocked lanes and the total number of lanes in the freeway section. However, there is limited information on the effects of incidents on the capacity of urban streets. This study investigated the effects on capacity of the interaction between the drop in capacity below demand at a midblock urban street segment location and upstream and downstream of signalized intersection operations. A model was developed to estimate the drop in capacity at the incident location as a function of the number of blocked lanes, the distance from the downstream intersection, and the green time–to–cycle length (g:C) ratio of the downstream signal. A second model was developed to estimate the reduction in the upstream intersection capacity resulting from the drop in capacity at the midblock incident location as estimated by the first model. The second model estimated the drop in capacity of the upstream links feeding the incident locations as a function of incident duration time, the volume-to-capacity (V/C) ratio at the incident location, and distance from an upstream signalized intersection. The models were developed on the basis of data generated with the use of a microscopic simulation model calibrated by comparison with parameters suggested in HCM 2010 for incident and no-incident conditions and by comparison with field measurements.

Upstream dispersion management of 25 Gb/s duobinary and PAM-4 signals to support 0–40 km differential reach

We extensively discuss 25 Gb/s per wavelength capacity in both IEEE and ITU-T standardization to support the increasing bandwidth requirement. In this Letter, we propose to use the optical dispersion compensation technique in an optical line terminal (OLT) combined with a bandwidth-limited electro-absorption modulated laser in an optical network unit to achieve 25 Gb/s capacity for the upstream link. We evaluate the positive and negative dispersion tolerances of 25 Gb/s electrical duo-binary (EDB) and pulse-amplitude modulation (PAM-4) signals. We achieve 39.5 and 31 dB upstream loss budgets for the 25 Gb/s EDB and PAM-4 signals by using −600 and −500 ps/nm optical dispersion compensation in OLT, respectively, both supporting 0–40 km differential reach.

A Riemann solver for a system of hyperbolic conservation laws at a general road junction

The kinematic wave model of traffic flow on a road network is a system of hyperbolic conservation laws, for which the Riemann solver is of physical, analytical, and numerical importance. In this paper, we present a new Riemann solver at a general network junction in the demand-supply space. In the Riemann solutions, traffic states on a link include the initial, stationary, and interior states, and a discrete Cell Transmission Model flux function in interior states is used as an entropy condition, which is consistent with fair merging and first-in-first-out diverging rules. After deriving the feasibility conditions for both stationary and interior states, we obtain a set of algebraic equations, and prove that the Riemann solver is well-defined, in the sense that the stationary states, the out-fluxes of upstream links, the in-fluxes of downstream links, and kinematic waves on all links can be uniquely solved. In addition, we show that the resulting global flux function in initial states is the same as the local one in interior states. Hence we presents a new definition of invariant junction models, in which the global and local flux functions are the same. We also present a simplified framework for solving the Riemann problem with invariant junction flux functions.

Single-source bidirectional free-space optical communications using reflective SOA-based amplified modulating retro-reflection

A novel amplified modulating retro-reflector (AMRR) based on a reflective semiconductor optical amplifier (RSOA) is proposed and a bidirectional free-space optical communication (FSO) system including both downstream and upstream links is experimentally demonstrated with only a single light source using this AMRR. The RSOA-based AMRR can provide a net gain more than 4dB and support the modulation bit rate up to 1.25Gbit/s. The bidirectional FSO transmission performance is evaluated by observing eye diagrams and measuring bit error rate (BER) results of both 10-Gbit/s DPSK downstream and 1.25-Gbit/s OOK upstream signals. The factors that limit the modulation bit rate and transmission quality are analyzed. The power penalties of both links are less than 0.69dB in the bidirectional FSO system at the BER of 1×10-3.

Efficient Upstream Bandwidth Multiplexing for Cloud Video Recording Services

The upsurge of cloud video recording (CVR) has gained increasing attention from the general public and entrepreneurs. With live video records archived in the cloud, the CVR paradigm enables various smart services by keeping track of activities in the monitored region from anywhere at any time. However, the limited upstream bandwidth affects the quality of surveillance when multiple distributed cameras share the same upstream link. To solve the problem, this paper proposes an efficient upstream bandwidth multiplexing algorithm to intelligently allocate upstream bandwidth for each live video stream while maximizing the overall utility from the perspective of a CVR user. Specifically, we formulate the upstream bandwidth multiplexing problem as a constrained stochastic optimization problem, and apply the technique of hierarchical approximation to solve it efficiently. Our algorithm can be extended to take the priority of video streams into account and allocate more upstream bandwidth to video streams with higher priorities. We explicitly prove the approximation ratio of the proposed algorithm. In addition, we also conduct extensive trace-driven simulations to verify the effectiveness of our algorithm. The simulation results show that our algorithm improves the overall CVR user utility by over 20% compared with other alternatives, and the average utility per bandwidth unit is guaranteed to be stable even when the number of video streams increases.

Estimating freeway route travel time distributions with consideration to time‐of‐day, inclement weather, and traffic incidents

SummaryThis paper develops an efficient probabilistic model for estimating route travel time variability, incorporating factors of time‐of‐day, inclement weather, and traffic incidents. Estimating the route travel time distribution from historical link travel time data is challenging owing to the interactions among upstream and downstream links. Upon creating conditional probability function for each link travel time, we applied Monte Carlo simulation to estimate the total travel time from origin to destination. A numerical example of three alternative routes in the City of Buffalo shows several implications. The study found that weather conditions, except for snow, incur minor impact on off‐peak and weekend travel time, whereas peak travel times suffer great variations under different weather conditions. On top of that, inclement weather exacerbates route travel time reliability, even when mean travel time increases moderately. The computation time of the proposed model is linearly correlated to the number of links in a route. Therefore, this model can be used to obtain all the origin to destination travel time distributions in an urban region. Further, this study also validates the well‐known near‐linear relation between the standard deviation of travel time per unit distance and the corresponding mean value under different weather conditions. Copyright © 2016 John Wiley & Sons, Ltd.

Gating Control for a Single Bottleneck Link Based on Traffic Load Equilibrium

The purpose of this paper is to improve the intelligence and universality of the classical method for gating control in the SCOOT system. First, we introduce a method to identify spillovers, and use the occupancy threshold for spillover recognition to trigger this special control logic. Second, the interrelationship of the traffic flows among adjacent traffic links is analyzed. Accordingly, we present an influence rate model for upstream links of the bottleneck link and a share ratio model for the downstream links. With known threshold values for the influence rate and share ratio, we propose a rule and process for selecting the intersections that should be included in the sub-area of the gating control. Third, we determine total capacity adjustments for the incoming and outgoing streams of bottleneck links. Under the measures, the queue can be dissipated to a permissible length within a given period of time. After that, the apportion models for the total adjustments among different paths and links are presented. Therefore, the correlation coefficients of the traffic flows are between the bottleneck link and the other links. Next, we ascertain the capacity decrements and increments for the gated and benefiting streams. The optimization schemes are defined so as to calculate splits for the gated and benefiting intersections. Finally, we evaluate the advanced method using a VISSIM simulation. The results show that a new control method brings significant and positive effects to the bottleneck link itself and to the entire test area.

Quantum networks

Researchers at University College Cork in Ireland have shown how the power budget of a passive optical network (PON) can be increased to support a higher number of customers and have longer reach without introducing active elements into the outside network plant. The bandwidth of upstream links in the PON is shared using time division multiplexing to allocate separate time-slots to the different users, which transmit bursts of data. Due to the non-uniform distribution of the outside network, plant loss, and differences in the user transmitters, the burst from the various users can present power levels with a high dynamic range. The burst-mode operation is ensured without the need to adopt additional high-speed electronic controls Optical fibre networks provide the backbone of today's global internet: the high bandwidth and long transmission reach of optical fibre make it the only technology capable of supplying the high speeds aggregate traffic capacities required for core and metro network links. As the bandwidth demand from end-users grows, optical fibre is becoming an economical solution for broadband access, where fibre-to-the-home solutions compete with other technologies, such as wireless and copper. To increase fibre efficiency and capability, various reach extenders can be used. These devices are available for passive optical networks including optical-electronic-optical repeaters and discrete optical amplifiers, based on either semiconductor optical amplifiers (SOA) or doped fibre amplifiers (xDFA). Unfortunately, they are usually placed in a powered enclosure or street cabinet, which increases installation and maintenance costs. Discrete amplifiers also need a high speed power control circuit for dealing with the upstream burst traffic. The solution proposed in the featured work maintains the passive structure of the network and does not need external control circuitry. It also offers a wider coverage of the optical spectrum used in PONs simply by changing the pump laser wavelength. Raman based reach extenders can also be used, and this method takes advantage of the Raman effect. The Raman effect is an inelastic scattering process in which an input optical photon is re-emitted at a different frequency with lower (or higher) energy, and the difference in energy is absorbed (or emitted) by molecular vibrations of the medium. In the silica optical fibre the Raman spectrum is broad due to the disorder of the silica molecules, and has a maximum at a frequency shift of 13.2 THz. Hence, if an intense optical pump source's frequency shifts by this amount when an optical data signal is introduced into the same optical fibre, stimulated Raman scattering will occur, effectively transferring part of the pump energy to the signal, leading to amplification. This can be used by reach extenders to amplify the signal. A number of factors have contributed to the recent development of compact reach extender modules that allow the network central office to extend the scale of already existing PON systems. These factors include the commercial availability of new high-power compact semiconductor quantum-dot lasers at the wavelengths of interest for this application, and the low-complexity structure of modern amplifiers. This opens up the possibility of compact reach extender modules for the network central office to extend the scale of already existing PON systems. Without such pump sources, more expensive and bulky fibre lasers would be required, and these offer lower potential for cost-effective integration. Increasing the span of fibre to home systems to 50 km opens the possibility of decreasing the number of electronic switching nodes in the network, thus reducing cost This technology is thus suitable for use in the public sphere, since the fabrication process of the employed pump lasers is established, making for reliable production. The 10 gigabit passive optical networks (XG-PON) standard is particularly suitable for this type of amplification, as only a relatively narrow spectral region is used for the upstream link, which can be covered by a single wavelength Raman pump module. Other standards, such as gigabit passive optical networks (G-PON), would require more stringent transmitter wavelength restrictions or the use of multiple wavelength Raman pump modules. This technology could be deployed by network operators and, if so, would benefit the general public through the wider availability of very high speed, fibre-enabled broadband.

Demonstration of Software-Reconfigurable Real-Time FEC-Enabled 4/16/64-QAM-OFDM Signal Transmission in an X-Band RoF System

In this paper, to the best of our knowledge, this is the first time that the generation and reception of online software-reconfigurable real-time 4/16/64-quadrature amplitude modulation (QAM)-encoded and forward error correction (FEC)-enabled orthogonal frequency-division multiplexing (OFDM) signals over X-band fiber-over-radio-based upstream links has been demonstrated. A Reed–Solomon code, i.e., RS (288, 256), with symbol interleaving/deinterleaving is applied to enhance bit-error-rate (BER) performance. The experimental results show that the 4/16/64-QAM-OFDM signals with net data rates of 1.6/3.2/4.8-Gb/s after 1.5-m wireless and 2.26-km SMF-28 transmission with BERs below the hard-decision FEC threshold of 3.8e-3 can be successfully achieved without using FEC. With the help of symbol-interleaved RS code, a post-FEC BER below 1e-8 can be observed when the pre-FEC BER is around 1e-3.

Country of origin labeling for complex supply chains: the case for labeling the location of different supply chain links

AbstractWe investigate the value of a country of origin label (COOL) that separately identifies the geographic location of different stages in a food product's supply chain. We estimate the willingness‐to‐pay (WTP) of U.S. consumers for a packaged cereal product where the key grain ingredient may be grown in one country and processed in a second country (multicountry supply chain) and compare it to equivalent products that have both stages located in a single country. We find consumer WTP for products with single‐country and multicountry supply chains are statistically different, meaning that simplifying a multicountry label by listing only the country where the ingredients are grown or only the country where the ingredients are processed can result in different consumer values. We also find that for countries with a poor quality reputation, consumers respond more negatively when that country has the “last touch” than when that country's involvement is limited to upstream supply chain links.

A link partitioning approach for real-time control of queue spillbacks on congested arterials

ABSTRACTIn oversaturated urban traffic conditions when traffic demand exceeds capacity at signalised intersections, queues fail to clear during the allocated green times. Once a queue reaches the upstream intersection in an arterial, a queue spillback occurs that reduces the upstream link capacity. To mitigate the negative impacts of spillbacks, this article introduces a real-time adaptive traffic signal control method for global management of spillbacks along signalised arterials. The key idea of the proposed method is to implement a real-time partitioning of the arterial to detect critical cluster(s) of consecutive links with oversaturated traffic conditions. The partitioning approach enables to develop locally smaller-sized decentralised signal control strategies operating on the most upstream and downstream intersections of each cluster. Micro-simulation investigations on a real-world arterial site demonstrate the benefits of the proposed approach compared to an existing pre-timed signal control strategy and a classical decentralised green extension strategy. Utilising an advanced queue length detection method and specific focus on queue spillbacks prevention, the control strategy leads to significant reduction of congestion, and arterial total delay.

Demonstration of the First Real-Time End-to-End 40-Gb/s PAM-4 for Next-Generation Access Applications Using 10-Gb/s Transmitter

We demonstrate the first known experiment of a real-time end-to-end 40-Gb/s pulse amplitude modulation (PAM)-4 system for next-generation access applications using 10-Gb/s class transmitters only. Based on the measurement of a real-time 40-Gb/s PAM system, low-cost upstream and downstream link power budgets are estimated. Up to 27 and 25 dB power budgets for 10- and 20-km standard single-mode fiber upstream links using erbium-doped fiber amplifiers (EDFA) preamplifiers are achieved. For downstream links using booster EDFAs and avalanche photodiode receivers, power budgets of 26.5 and 24.5 dB are feasible for 10- and 20-km SMFs, respectively. In addition, we show that colorless 40-Gb/s PAM-4 transmission over 20-km SMF in the C-band is achievable.

An Asymmetric High Serial Rate TDM-PON With Single Carrier 25 Gb/s Upstream and 50 Gb/s Downstream

We report a 2:1 rate asymmetric high serial rate time division multiplexing passive optical network (TDM-PON) with single carrier 25 Gb/s upstream and 50 Gb/s downstream. In the upstream, we present a first 25 Gb/s three-level modulated burst-mode receiver employing a ${1}/{4}$ -rate linear burst-mode avalanch photodiode transimpedance amplifier and a custom decoder IC. We successfully demonstrated burst-mode sensitivity of -20.4 dBm with 18 dB dynamic burst-to-burst for 25 Gb/s upstream links. In another direction, a downstream in upper O-band is proposed and demonstrated with three-level duo-binary modulation at 50 Gb/s in real time. The upstream and downstream transmission experiments show that the proposed asymmetric 50 G/25 G high serial rate TDM-PON can support $\ge$ 32 users while covering more than 20 km reach.

Optimal queue placement in dynamic system optimum solutions for single origin-destination traffic networks

The Dynamic System Optimum (DSO) traffic assignment problem aims to determine a time-dependent routing pattern of travellers in a network such that the given time-dependent origin-destination demands are satisfied and the total travel time is at a minimum, assuming some model for dynamic network loading. The network kinematic wave model is now widely accepted as such a model, given its realism in reproducing phenomena such as transient queues and spillback to upstream links. An attractive solution strategy for DSO based on such a model is to reformulate as a set of side constraints apply a standard solver, and to this end two methods have been previously proposed, one based on the discretisation scheme known as the Cell Transmission Model (CTM), and the other based on the Link Transmission Model (LTM) derived from variational theory. In the present paper we aim to combine the advantages of CTM (in tracking time-dependent congestion formation within a link) with those of LTM (avoiding cell discretisation, providing a more computationally attractive with much fewer constraints). The motivation for our work is the previously-reported possibility for DSO to have multiple solutions, which differ in where queues are formed and dissipated in the network. Our aim is to find DSO solutions that optimally distribute the congestion over links inside the network which essentially eliminate avoidable queue spillbacks. In order to do so, we require more information than the LTM can offer, but wish to avoid the computational burden of CTM for DSO. We thus adopt an extension of the LTM called the Two-regime Transmission Model (TTM), which is consistent with LTM at link entries and exits but which is additionally able to accurately track the spatial and temporal formation of the congestion boundary within a link (which we later show to be a critical element, relative to LTM). We set out the theoretical background necessary for the formulation of the network-level TTM as a set of linear side constraints. Numerical experiments are used to illustrate the application of the method to determine DSO solutions avoiding spillbacks, reduce/eliminate the congestion and to show the distinctive elements of adopting TTM over LTM. Furthermore, in comparison to a fine-level CTM-based DSO method, our formulation is seen to significantly reduce the number of linear constraints while maintaining a reasonable accuracy.

Modeling Freeway Work Zones with Mesoscopic Dynamic Traffic Simulator: Validation, Gaps, and Guidance

This study developed a validation procedure for a dynamic traffic assignment–based mesoscopic simulator and identified its relevant data requirements. Model inconsistencies at the network level can be detected through route-based validation with probe vehicle travel time data. Simultaneously, link-based validation uses point detector–based volume and speed data. A procedure for filtering the validation data set to make it consistent and comparable with the simulation results is outlined in the paper. Two assignment methods were tested with a detailed validation data set through a case study. The no-diversion assignment approach yielded higher travel time than the field-observed average time. In contrast, simulated travel time with the optimal diversion method implied a more rational behavior by drivers than was observed in the field, along with more diversion of trips on arterial routes in the vicinity of a work zone. Finally, a link-based performance comparison revealed worse queue spillback effects on the upstream links of the work zone than in reality.

Assessing spatial and temporal effects due to a crash on a freeway through traffic simulation

The focus of this paper is to simulate, evaluate and assess spatial and temporal effects in travel time variation and upstream distance or length of upstream links affected due to a crash. Traffic simulations were conducted for different conditions in VISSIM 5.30™ to obtain travel times at various points upstream of the crash location, over time, along a freeway corridor. Travel time variation between fatal crash condition and no crash condition (baseline condition) and between injury crash condition and no crash condition (baseline condition) were computed and compared to evaluate the effect of a crash on a freeway. Results obtained showed that fatal crash on freeways has an effect under low, moderate, and high traffic volume conditions, whereas injury crash has an effect only under moderate and high traffic volume conditions. The travel time variation and upstream distance affected due to a fatal crash on the right-most lane was generally higher than fatal crash on the left-most lane. The trends remained fairly consistent irrespective of the lane on which an injury crash occurred. The upstream distance affected due to a fatal crash varied from 1.5 miles to ∼7.5 miles based on traffic volume and lane on which the fatal crash occurred. It varied from ∼0.5 miles to 7 miles due to an injury crash and traffic condition. Queue may start dissipating at least 15min after blocked lanes are re-opened for normal traffic flow depending on the type of crash, traffic volume and lane in which the crash occurred. The results and findings from this research can be applied to emulate dynamic message signs over time and space so as to alert the motorists about the length and duration of congestion depending on the severity of crash and lane on which the crash occurred.

Design and Implementation of Path Failure Detection and Recovery Mechanism for Multihomed HIMALIS Network

We have designed the Heterogeneity Inclusion and Mobility Adaptation through Locator ID Separation (HIMALIS) network architecture to natively support sessions transfer from one link to another independently of the network and transport layer protocols. However, lack of a prompt path failure detection mechanism in HIMALIS cannot well utilize multiple links to protect against path failures. In this paper, we propose a complete path recovery mechanism that consists of path failure detection, lively path exploration, and path recovery processes. In particular, the failure detection mechanism is based on monitoring of data sending and receiving instances in end hosts by employing two timers, probe timer and keepalive timer. In case of path failure caused by gateway's upstream link down, the gateway provides the link failure notification to the host for expediting the detection process. We also present an overview of implementation of the mechanism. The implemented functions are verified by using both TCP and UDP applications and evaluated in a 21-node-scale network-emulation environment. The results show that the proposed mechanism provides fast failure detection, about 7 s which is much faster than the failure detection carried out based on TCP retransmission timeout which may take 5 min in the worst case, under both site- and host-multihoming configurations. The results also show that the proposed mechanism takes only about 200 ms to detect gateway's upstream link down.