Penina Orenstein

Control Strategies for Dispersing Incident-Based Traffic Jams in Two-Way Grid Networks

Effective control strategies are required to disperse incident-based traffic jams in urban networks when dispersal cannot be achieved simply by removing the obstruction. This paper develops a selection of such control strategies and demonstrates their effectiveness in dispersing incident-based traffic jams in two-way rectangular grid networks. Using the spatial topology of traffic jam propagation, we apply the concept of vehicle movement ban, which is frequently adopted in real urban networks as a temporary traffic management measure. Four control strategies were developed, which are referred to as single-line control, multiline control, area control, and diamond control. We also explore a combination of these control strategies and evaluate the impact of these control strategies on the changes in traffic jam size and congestion delay. Finally, we simulate the processes of traffic jam formation and dissipation using the cell transmission model and demonstrate the performance of the proposed strategies. Simulation results show that the proposed strategies can indeed disperse incident-based traffic jams efficiently.

Maximizing the throughput of CDMA data communications

We analyze aggregate throughput as a function of the transmitter power levels and the number of terminals sending data to a CDMA base station. We find that when noise and out-of-cell interference are negligible, received power balancing maximizes the aggregate throughout of the base station, provided the population of active terminals does not exceed an optimum size. The optimum number of active terminals depends on the CDMA processing gain and the details of the physical layer and data link layer. These details are summarized in a univariate frame success function. When noise is present, power balancing is suboptimal mathematically but attractive for practical implementation.

An effective algorithm to simulate pedestrian flow using the heuristic force-based model

A heuristic method based on the concept of velocity obstacle has been included into the force-based model to describe the pedestrian dynamics. This paper has analysed the continuity and monotonicity of the heuristic function of finding the optimal direction of velocity, and proposed a heuristic detouring algorithm (HDA) to find approximate optimal solutions. In the cases of only one standing pedestrian in the vision field, the solutions calculated by the HDA are optimal; while in other cases, the solutions are near-optimal. To test the performances of HDA, numerical experiments are conducted by three other algorithms that are enumeration algorithm (EA), social force model (SFM), optimal reciprocal collision avoidance (ORCA). Results show that HDA is about 2 times faster than ORCA and 20 times faster than EA. HDA performs with higher efficiency than ORCA and EA, and the fundamental diagram obtained by HDA agrees with empirical data better than ORCA and SFM.

How Does Supply Network Evolution and Its Topological Structure Impact Supply Chain Performance

The idea of this research is to explore the evolution of a supply chain using an empirical approach. This can be achieved by harnessing the power of Bloomberg data with network visualization software. Such an investigation will help identify supply chain archetypes as well as lead to an understanding of how these supply chains might change over time. Coupled with additional secondary data sources, we could learn more about how these changes might be impacted by, and impact, firm performance. In this paper, we explore a number of supply networks and develop their associated supply chain maps. We use key metrics from social network analysis to quantify the nature of these networks and understand how they evolve. This empirical data is then used to create a paradigm which explains the structure of these supply networks. We use the maps and the metrics developed to describe them to draw preliminary conclusions about how supply network topology impacts its performance.

A Power Control Based Admission Algorithm for Maximizing Throughput in a CDMA Network

In this paper we examine the aggregate throughput of the uplink of a circuit switched CDMA data transmission system using a combination of theoretical and simulation techniques. The theoretical analysis determines the transmitter power levels and the number of active terminals that jointly maximize the throughput via standard optimization methods. We find that the terminal with the lowest path gain should transmit at maximum power and that all other terminals should aim for a common received power level that is higher than the received power from the terminal with lowest path gain. In addition we show that the system should admit the number of terminals that results in a target signal-to-interference-plus-noise ratio that depends on the processing gain and the noise power. A numerical example suggests that power control designed to achieve equal received power for all terminals results in aggregate throughput nearly as high as that obtained with optimum power control. This finding greatly simplifies the engineering problem from a network manager’s viewpoint.

Passenger Assignment Model Based on Common Route in Congested Transit Networks

AbstractIn this paper, the common line problem and passengers’ choice behaviors in transit networks are revisited and discussed. The concept of the common line problem is extended to represent a common route problem in transit networks. The transit routes are classified into various levels of attractive route sets according to route fixed costs and route frequencies. The transit passenger assignment problem on congested transit networks is defined to assign passenger flows on attractive route sets and is formulated as a variational inequality (VI) problem. In the proposed model, the effective frequency approach is applied to reflect the effects of passenger congestion on the waiting time at the stations. Compared with traditional models, the proposed passenger flow assignment model does not require a modification to the transit network nor a constant recomputation of the changing attractive line set. Finally, a simple example is used to illustrate the difference between common line and common route method...

Effects of additive noise on the throughput of CDMA data communications

We analyze the optimum transmitter power levels and the optimum number of active terminals sending data to a CDMA base station. The objective is to maximize the aggregate throughput of the base station. We find that in the presence of additive noise, received power balancing is suboptimal mathematically. We consider N terminals transmitting at the same data rate, with the power of the most distant terminal (terminal N), fixed at its maximum value, and the power of the other N-1 terminals varying. We conclude that the aggregate throughput at the base station is maximized or minimized (depending on the spreading gain G) when the receiver powers for the N-1 terminals operate at an identical receiver power, which is larger than that of the power-limited terminal. This finding reduces the complexity of the analysis to a univariate optimization problem. A numerical analysis indicates the extent to which additive noise reduces the optimum number of active terminals and the maximum base station throughput.

Getting the message about road safety

This paper reviews a range of problems in the road transport field and the potential role of vehicular ad-hoc network systems (VANETs) in helping to solve them. In reality, the communications requirements vary widely from one application to the next, in terms of range, latency, and connectivity together with vehicle and roadside hardware. Based on the nature of the wireless channel, this presents some challenges for communication to security. The paper concludes with a summary of the current state of VANET technology and presents a summary of the challenges to be found in each approach.

Understanding the Performance Limitations of a Simulated Large Scale Wireless Ad Hoc Network

We use a cellular automaton analogy to simulate a large scale wireless ad-hoc network. This approach combines mobility in its simplest form with some fundamental attributes of radio propagation and enables us to examine the communicative properties of the network which would not otherwise be accessible. The analysis shows that there is an optimal network density for which the throughput of the network is maximized. We examine this finding under a range of processing gain values and confirm (a) that both the maximum total network throughput and the networks sustainability increases proportionately with the processing gain and (b) that single-hop communication is always preferable to extended-hop communication. Furthermore we consider the performance of the system when communication is not limited to a single-hop. We show how processing gain can be used adaptively in order to control the transmission range and hence guarantee end-to-end connectivity in the network.

Information in motion: road vehicles as wireless relay stations for an ad hoc communications network

Abstract There is growing interest among automobile engineers and wireless communications researchers in the concept of a Vehicular Ad-hoc NETwork (VANET). Each motor vehicle on the road today provides a natural platform for mobile communications. When equipped with suitable on-board device, the population of vehicles in a busy area becomes a wireless network capable of relaying signals across considerable distances, without the need for a central transmitter. Among the applications so far suggested are the propagation of safety warnings such as icy road conditions, crime prevention, surveillance aimed at public security, together with less urgent passenger services, and even congestion management. To determine whether and how such a system would function, it is necessary to model two distinct kinds of network simultaneously—the road system and the wireless network. The challenge is signi-cant, not least because of the many factors involved. The authors have adapted a cellular automaton (CA) approach, which is used to investigate the relationship between communication, contention/interference and mobility. The results show how mobility a-ects network performance and how the processing gain G can be used to design e-ective coverage areas which maximize the total network throughput. Most important for safety-critical applications, a VANET can break down under congested road traffic conditions because of radio interference among the vehicles.