Recently the advances of telecommunication systems and chip manufactures enable smart automobiles equipped with a variety of radios. For example, the Global Position System (GPS) has been widely deployed in vehicles for travel navigation and GPRS/3G cellular communication has be deployed in the buses of several public transportation system for tracking their locations. One promising new communication standard for such vehicular network is the IEEE 802.11p/1609 specification family, which is proposed for wireless access in vehicular environments based on DSRC (Dedicated Short Rang Communications) communication protocol. It aims to achieve the communications between vehicles and vehicles or vehicles and roadside units. The IEEE 802.11p/1609 network can be used to convey messages for applications for road safety, traffic condition report, traffic control, etc.
1.1. Motivation
There have been many papers that study how to minimize the preparing time of the medicine for patient. However, rare papers consider the time required by emergency vehicles for arriving at accident scenes. Reducing the arrival times of emergency vehicles to accident scenes allows emergency events to be properly processed before they cause more damage. For example, if an ambulance arrives at a traffic accident scene in a very short time, injured people can be taken care of before their body conditions get worse. Another example is that if a fire engine arrives at the fire scene in a very short time, the fire can be eliminated before it causes more damage.
To achieve this goal, we propose a traffic control mechanism based on the IEEE 802.11p/1609 radios technology. Because the IEEE 802.11p/1609 specification is still under development, it is difficult to evaluate the performances of our proposed mechanism with
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real 802.11p radios in the real world. Thus, in this thesis we use the simulation approach to evaluate the performances of the proposed mechanism.
1.2. Problem Description
In this thesis, a traffic control mechanism based on IEEE 802.11p/1609 is proposed.
Each intersection is installed with a RSU (Road-Side Unit) and each vehicle is equipped with an OBU (On-Board Unit). The traffic control center monitors the traffic condition and controls the traffic light signal.
Note that, although an emergency vehicle can move itself to the nearby lane, frequently altering its moving lane is dangerous for itself and may cause traffic accidents.
Especially, emergency vehicles such as ambulances, fire engines, and police cars may move at a high speed to save time to arrive at accident scenes. Therefore, evacuating vehicles for emergency vehicles on their way to the accident scenes not only saves the rescue time of injured people but also reduces the occurrences of accidents for emergency vehicles when they are moving to accident scenes.
The proposed traffic control mechanism uses three significant functions which are (1) Moving Path Arrangement, (2) Evacuation Message Delivery, and (3) Dynamic Traffic Lights Control. For moving path arrangement, the traffic control center will generate a shortest-time path to the accident scene for emergency vehicle to pass through so that the emergency vehicle will not waste too much time on choosing moving path. For evacuation message delivery, the traffic control center will send the evacuation message to a relevant RSU based on receiving the evacuation request sent from an emergency vehicle. The RSU will broadcast the evacuation message to nearby vehicles so that they can move themselves to other lanes and empty a lane in advance for facilitating emergency vehicles’ passing through. For dynamic traffic lights control, the traffic control center can dynamically switch
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the traffic lights into green to avoid the obstruction in the intersection so that the emergency vehicle will not be jammed when it approaches the intersection.
There are three interesting issues we will discuss in this thesis which are listed as follows.
(1) How will it affect the performance if we use different function combinations for the proposed traffic control mechanism: As described previously, there are three functions that can be used in the traffic control mechanism which are (1) moving path arrangement, (2) evacuation message delivery, and (3) dynamic traffic lights control.
How will it affect the performance if we use different function combinations for our traffic control mechanism?
(2) How will it affect the performance of the proposed mechanism if we deploy vehicles on the road map with different vehicle separation distances: The average vehicle separation distance (i.e., vehicle density) is different during day and night. Therefore, it is interesting for us to know how it affects the performance if we deploy vehicles on the road map with different vehicle separation distances.
(3) How will it affect the performance under different traffic lights periods: In the real world, traffic lights on a main lane may have longer green time than the less important lane. Due to this reason, we also interest in the effect of the performance when applying different traffic lights periods for each scenario.
1.3. Organization
The rest of this thesis is organized as follows. A brief overview of IEEE 802.11p/1609, A* algorithm, related work, and the NCTUns network simulator is described in Chapter 2.
In Chapter 3, the proposed design and implementation of the simulation environment is introduced. Using the module-based node location update and traffic signal control
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mechanism makes the NCTUns network simulator simulate much more nodes on the roadmap. In Chapter 4, the design and implementation of the proposed traffic control mechanism is depicted. The results of the proposed traffic control mechanism applying distinct schemes for each scenario are shown in Chapter 5. In Chapter 6, the future work is discussed. Finally, in Chapter 7, the conclusion of this thesis is described.
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