Sharif Digital Repository

This paper presents an ITS project in Iran, as the first intelligent tunnel management system to be deployed in support of urban traffic management. It aims to protect highway users from possible hazards, provide them travel information and support traffic controllers in efficient and effective exercise of daily works. The project concerns a high trafficked tunnel which has been inaugurated in July 2006 to connect two parts of a highway in Tehran, linking the northwest districts to northeast ones. This corridor was selected as a good candidate, due in particular, to the variety of problems encountered [1]. In order to launch the project a co-operation has been negotiated in late 2005 between... 

This work investigates the application of Dependency Structure Matrix (DSM) to problems with fast dynamics, such as airspace sectorization. The aim of this paper is to use a powerful mathematical tool to distinguish relevant agents in a busy airspace with a logical and meaningful distribution of the workload among air traffic controllers. This approach will help prevent controllers from getting exhausted in busy airspaces and increase the overall capacity of the airspace. It could also serve as a logical interface to simulate the chance of human error in a controlled aerodrome. Different case-studies by the authors reveal that adding realtime capabilities to the existing platform can be very... 

Self-adaptation is a well-known technique to handle growing complexities of software systems, where a system autonomously adapts itself in response to changes in a dynamic and unpredictable environment. With the increasing need for developing self-adaptive systems, providing a model and an implementation platform to facilitate integration of adaptation mechanisms into the systems and assuring their safety and quality is crucial. In this paper, we target Track-based Traffic Control Systems (TTCSs) in which the traffic flows through pre-specified sub-tracks and is coordinated by a traffic controller. We introduce a coordinated actor model to design self-adaptive TTCSs and provide a general... 

Over the last decade, there has been an increase in air transportation, which has raised awareness to provide necessary procedures to respond to air transportation demands and reduce delay costs. One such procedure, 'performance-based navigation (PBN),' currently studied, is expected to increase the airspace capacity based on aircraft's individual performances. This research describes an efficient and expandable model for allocating standard terminal arrival route during continuous descent approach (CDA) that effectively uses PBN requirements. As a case study, we have considered the 'Atlanta International Airport' and verified the model's accuracy using real-time traffic data. The model is... 

Autonomous traffic control systems are large-scale systems with critical goals. To satisfy expected properties, these systems adapt themselves to possible changes in their environment and in the system itself. The adaptation may result in further changes propagated throughout the system. For each change and its consequent adaptation, assuring the satisfaction of properties of the system at runtime is important. A prominent approach to assure the correct behavior of these systems is verification at runtime, which has strict time and memory limitations. To tackle these limitations, we propose Magnifier, an iterative, incremental, and compositional verification approach that operates on an... 

Transit assignment is an important problem in the literature of transportation. Almost all competitive algorithms in this area are strategy based. For uncongested transit networks, the problem may be formulated into an optimization problem for which good solution algorithms exist. A variational inequality formulation of the problem with several solution methods is also presented in the literature for congested networks. This paper is devoted to solving a transit assignment problem based on complementarity formulation using path flows. The solution algorithm exploits the three concepts of decomposition, path generation, and linearization. The procedure has been applied on a large-scale... 

Transmission Control Protocol (TCP) uses multiple timers to do its work. The most important of these is the retransmission timer. In this paper, the TCP retransmission timer adjustment mechanism is approached from a system point of view and a new mechanism is proposed. A simple recursive system identification algorithm is used to capture both time variant and time invariant Internet behavior. Also a dynamic model-based Round-Trip Time (RTT) predictor was provided. Based on network simulation and real Internet data collection, it was observed that when the retransmission timer is adjusted by the proposed predictor instead of the traditional RTT estimator, performance increased significantly  

Self-adaptive systems are systems that automatically adapt in response to environmental and internal changes, such as possible failures and variations in resource availability. Such systems are often realized by a MAPE-K feedback loop, where Monitor, Analyze, Plan and Execute components have access to a runtime model of the system and environment which is kept in the Knowledge component. In order to provide guarantees on the correctness of a self-adaptive system at runtime, the MAPE-K feedback loop needs to be extended with assurance techniques. To address this issue, we propose a coordinated actor-based approach to build a reusable and scalable model@runtime for self-adaptive systems in the... 

The time headway of vehicles is an importan microscopic traffic flow parameter which affects the safety and capacity of highway facilities such as freeways and multi-lane highways. The present paper intends to provide a report on the results of a study aimed at investigating the effect of the lane position on time headway distributions within the high levels of traffic flow. The main issue of this study is to assess the driver's behavior at different highway lanes based on a headway distribution analysis. The study was conducted in the city of Isfahan, Iran. Shahid Kharrazi six-lane highway was selected for collecting the field headway data. The under-study lanes consisted of passing and... 

This paper presents an ITS pilot project in a developing country, Iran, as a way to foster to the development of ITS national strategic plan. The pilot project concerns a high trafficked road corridor, linking the capital Tehran to the largest city in the suburb: Karaj, This corridor was selected among others, by the end of 2002 as a good candidate, due in particular to the variety of problems encountered [1] In order to launch the pilot project a co-operation was set up in 2004 between ISIS, Groupe EGIS, France and Metra Consulting Engineers Co, Iran and several ITS experts were sent to Iran for two missions in June and July 2004. The mission consisted of detailed on-site visits, interviews... 

The evermore widespread use of microscopic traffic simulation in the analysis of road systems has refocused attention on sub models, including car-following and lane-changing models. In this research a microscopic model is developed which combines car-following and lane-changing models and describes driver behaviour as a crash risk reduction process of drivers. This model has been simulated by a cellular automata simulator and compared with the real data. It has been shown that there is no reason to consider the model invalid for drivers' behaviour in the basic segments of freeways in Iran, during not-congested conditions. Considering that uncertainty of position of vehicles is caused by... 

Autonomous traffic control systems are large-scale systems with critical goals. To satisfy expected properties, these systems adapt themselves to possible changes in their environment and in the system itself. The adaptation may result in further changes propagated throughout the system. For each change and its consequent adaptation, assuring the satisfaction of properties of the system at runtime is important. A prominent approach to assure the correct behavior of these systems is verification at runtime, which has strict time and memory limitations. To tackle these limitations, we propose Magnifier, an iterative, incremental, and compositional verification approach that operates on an... 

The use of traffic information in the form of radio reports, as a solution to the problem of congestion, is one of the issues, which are of particular importance for large cities like Tehran. In this study, factors affecting the use of traffic information in the context of a developing country are examined for commuters in the city of Tehran using ordered logit models. Results based on the particular survey designed for this purpose are compared to those of a developed country. Regarding the use of information in the form of listening to the radio traffic reports, the models show that older commuters, commuters who adjust their departure time according to traffic conditions (those who are... 

This paper proposes a new medium-access control (MAC) protocol designed for wireless sensor networks. A wireless sensor network is an array of large number of sensors interconnected by a multi-hop ad-hoc network. The primary objective for the sensor network is achieving to low-power consumption while latency is usually less important compare to traditional wireless networks. This characteristic of sensor network motivates the design of new MAC layer so that power consumption is reduced. In this paper, a novel traffic-aware algorithm based on distributed node schedule management (DMD) protocol is introduced that utilizes distributed dynamic node scheduling strategy to dramatically increase... 

We propose a general mobility model based on region splitting and mapping each subregion on a multi-server node. By using the theory of multi-class Jackson queueing network with multiserver nodes and employing the product-form solution for such queueing networks, we obtain an analytical form for the spatial traffic distribution in a typical region with specific number of users. To this end, we consider the spatial statistical pattern for new and handoff call arrivals and the ratio between these two types of arrivals. At last, we apply our new model to some simple mobility scenarios and compute the resultant active user's location densities. © 2003 IEEE  

One of the most prominent features of code division multiple-access (CDMA) cellular networks is their ability for applying soft-handoff. This type of handoff results in a better supporting of seamless communication services, capacity enhancement, QoS improvement, etc. Because of existence of more parameters and flexibilities compared to hard-handoff, an optimum solution for soft-handoff management and admission control for new and handoff calls is necessary. In this paper we propose a new algorithm with two thresholds for admission of new and handoff calls, and with two decision boundaries for controlling of handoff traffic. We compare this algorithm with a simpler one with only one decision... 

A wireless network with beamforming capabilities at the receiver is considered that allows two or more transmitters to share the same channel to communicate with the base station. A novel approach is introduced, which combines the effects of the digital signal processing (adaptive beamforming) at the physical layer with the traffic policies at the network layer on the overall queuing model of a cell. The effect of signal processing on the queuing model of the cell is represented by a parameter in the final cell model. Each cell is modeled by a multiuser/multiserver service facility, where each server is a beamformed channel formed by the cell's base station. From this effective cell model,...