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Since last two decades alot of work has been done on traffic security to reduce the number of accidents on roads. Traffic density is increasing everyday which demands more safe,fast and advance proactive safety system so number of accidents on roads can be reduced.
This real world is full of innumerable objects. Cars, trees, buildings and platoons of cars are some examples of objects. Objects can be divided between into two categories physical objects like cars, pedestrians, trees and buildings and conceptual objects like platoons of vehicles and virtual fences. Platoon of vehicles are physical object and are inferable from the environment, some conceptual objects like geo fences are artificially introduced. 
Objects can also be divided on behalf of cooperation. Objects which can communicate with each other are called cooperated Objects such as vehicles, beacons etc. Objects which cannot communicate or interchange information are called non-cooperative objects such as pedestrians, trees etc. Both physical and conceptual objects have properties such as identity, size, location, speed etc. Most important task in proactive safety system is that an object should collect correct information from other objects, interpret that information and warn driver about situation.
Classification of Cooperative objects
Vehicles observe their state, location, speed, direction and then pass that information to other cooperative objects which help other objects to take actions according to that information. Cooperative objects can further be divided in two categories.
A primary object to a vehicle is an object which does direct communication to that vehicle. Mostly primary objects are in short range of the vehicle. All observations which are received from a primary object are called primary observations. Primary observations always consist of that primary object's state, location, speed and direction.
A secondary object to a vehicle is an object which indirectly communicates to that vehicle. It means that secondary object communicates to the vehicle via some primary object to that vehicle. Secondary observations are observations received by secondary objects. It means that primary objects can also have information about more objects which are secondary observations but can be received and interpret the situation for that vehicle.
One of the most important tasks is to prioritize information received by other objects. Different objects have different priority of different information. When it's too much traffic on the road then every object will have a lot of information receiving from other objects. So to avoid overloading shared communication media, there should be a time period for each information according to their importance and system should remove information automatically if an object does not need that. Every object receives too many information from other objects so the receiving object should filter and select useful information. In form of updates receiving object should know how to prune and prioritize that information in an efficient way. To improve the handling of context information it is divided into two groups:
Primary context is defined by primary objects and their properties. And secondary context is defined by secondary objects and their properties.
Communication Types in Vehicular Networks
There are three main types of ranges which vehicles can deal with.
In short range vehicle sensors such as radars sense and aware situation which are just around them such as car in front of it or on back etc. Medium range means situation beyond line-of-sight but rapidly approaching, situation awareness rule out the sole use of in-vehicle sensors. Long range contains situations long away from vehicle. Centralized information system such as FM radio bulletins provides the driver long range situation awareness.
There are three types of communications vehicles can do on road:
Vehicle to Vehicle communication.
Vehicle to infrastructure communication.
Infrastructure to infrastructure communication
In vehicle to vehicle communications, vehicles communicate with each other to interchange information and in vehicle to infrastructure communication vehicles communicate with roadside units to get or send information. Infrastructure to infrastructure communication deals with information exchange between infrastructures.
There are three types of topologies:
In vehicle based networks all communications and decisions takes place in vehicles. There is no infrastrcture involved in that topology. Peers in the network takes decisions and send warnings within the network. The advantages of this topology is scalability, cost and robustness. But big problem in this topology is that information cannot be verified. Data sent or recieved by peers cannot be varified which is not secure.
In infrastructe based topology a sufficient amount of roadside unit are being deployed. Security issues in this topology can be handeled easily because authorized roadside units can be trusted. Because all data is passed by roadside units so control center can have more complete picture of the network. This topology is more authentic and secure. The main disadvantage of this topolgy is that deploying fixed infrastructure is highly cost.
Hybrid topology system achieves advantages of both vehicle based and infrastructure based topologies. In this topology vehicle based communication is used in areas where there is less risk such as we have straight and wide road, and roadside units are deployed in high risk areas such as intersections in urban areas and pedestrians on main roads etc. Hybrid topology is preffered on other two topologies because it has advantages of both topologies and it reduces the cost and make system more secure and safe.
Subject area and Motivation
The increase in the traffic density raises the crucial feature of traffic security to reducing the number of avoidable collisions. The communication between the vehicles on road is priority. There are two ways of communication between vehicles which are vehicle to vehicle and vehicle to infrastructure. Although the safety measures like seat belts, air bags and advance proactive safety systems helped in decreasing the number of fatalities and improving the road safety measures.
Our main focus in this thesis is to improve the advance proactive safety systems by improving the vehicle to vehicle communication in hinders environment.
Problem / Question to investigate
The increased density of traffic has increased probability of collisions, which may be controlled by improving space diversity. The advanced communication between the vehicle to vehicle and vehicle to wireless relay nodes may reduce the numeral collisions. Any node on the road can get trouble when other nodes are not in its line of sight, can be behind hinders or blind spots. This situation can increase the degree of risk of collisions. Our goal is to make a strategy and compare it to other possible strategies, in such a situation that how a node should select the best node for it to get the information about other nodes and reduce the probability of collisions. We have to see that how vehicle can get the information about the car with whom it can't communicate directly due some hazardous environment. Figure below elaborate the question to be investigated.
In this figure P, L, R and S are representing the vehicles carrying the information of vehicle ahead; as soon as they are moving in non hazardous environment they haven't any problem but when there occur some hazardous environment they have to develop some strategy that how and from whom they can get the information about vehicle behind the hazard. In this figure the Vehicle P reaching the Square can go possibly in three directions, there is no problem in getting the information of cars ahead if it goes straight or in left direction. The problem occurs when it wants to go in right direction and it can't communicate directly because the building on right is acting as hazard. There can be many other cases like this which we have to consider and have to make strategies according to that use case so that some simulation can be done according to those proposed strategies
We have divided the main thesis into two parts. First, Investigation and strategy development and second part is to develop a simulation based on that investigation and strategies.
Categorization of Add-Hoc Net works
Single Hop Network
Multiple Hops Network
When we talk about communication we discuss it with different aspect such as source-destination of communication which is Vehicle to Vehicle communication, Vehicle to Infrastructure communication and infrastructure to vehicle communication. Second aspect is direction of communication which can be either one way (Unidirectional) or two ways (Bi directional). Third aspect is source-reception which is point to point and point to multipoint.
There are different protocols used for wave communication in past like IEEE 1609 Protocol Suite which includes IEEE 1609.1, IEEE 1609.2, IEEE 1609.3, IEEE 1609.4 protocols and they were used in projects like VSC and VSC-A. IEEE 802.11 Protocol suites which include IEEE 802.11a, IEEE 802.11b, IEEE 802.11e, IEEE 802.11g, IEEE 802.11n and impending IEEE 802.11p which has also one modification known variant of IEEE 802.11p adapted according to European conditions. We will discuss these protocols in little detail in next report.
Vehicle to Vehicle Communication Protocol (802.11p)
IEEE 802.11p is a communication protocol which is designed for supporting communication of user having high mobility. It is the only standard which is supporting the V2V communication. The Operating bandwidth for 802.11p is reduced to 10MHZ from the 20MHZ which makes the communication more efficient at high mobility. The Physical and link layers are in the phase of standardization but still some improvements are needed for reliable communication, Right now MAC and Network layers are facing problem of instability of signal strength due to mobility. MAC procedure is facing one more setback of unbounded channel access delays which occurs with increase of network load
Enhanced Distributed Channel Access EDCA method is used by MAC protocol in the 802.11p, There are four types if data traffic defined in this protocol with default priorities and parameter settings of Arbitration Inter Frame Space (AIFS) and Contention Window (CW) background traffic (BK,15,1023,9), best effort traffic (BE,7,225,6), voice traffic (VO,3,7,3) and video traffic (VI,3,7,2). The voice and video traffic can have high priority if we select the window size of back off window smaller, which results in increasing the throughput.
A window based back off mechanism is used in MAC protocols named CSMA/CA in which the node want to transmit first sense the medium and if medium is not free to transmit it will pick up randomly back off time and the size of contention window CW become double if successive attempts of transmission failed unless the size of CW get equals to CWmax.
Transmission of data within a certain geographical region is transport of data from one node to one or all nodes in specific region depending on what forwarding mechanism adopted. Geographical region can be of either some circular or rectangular shape, there are two types of well know forwarding mechanism namely geounicast and geoanycast for car to car (C2C) or V2V communication.
Geographical Unicast (geounicast)
In geographical unicast transmission mode transport of data is meant from one source node to one destination node, this can be either by direct communication between source and destination or involved multiple hops to reach destination node depending on the scenario. Greedy forwarding technique is used without parameter routing. In this figure Yellow blocks shows Source and destination Vehicles, green blocks are mediator vehicles and blue blocks are neutral vehicles which have no contribute in communication
Geographical Anycast (geoanycast)
In geographical anycast transmission mode, transport of data is meant from one source node to any number of nodes within specific region for efficient flooding in that geographical area. When packet reached the area it is not forwarded inside geographic area.
Pre Crash Sensing
Position, Velocity, Deceleration, Heading
Position, Velocity, Acceleration, Heading
Turn Signal, Heading
V2V Communication in Hazardous environment
Our main goal to deal with communication between vehicles in hazardous environment, for that we will consider different situations and strategies to enable communication in most efficient way in hazardous environment. The basic target is to use network efficiently to provide information about hazardous location to vehicles in particular region. Information can be condition of road i.e. slippery patch, traffic jam, potholes (uncommon in Sweden), blind spots where driver can't see or communicate with traffic coming from other side, and merging vehicles with flowing traffic without disturbance
Vehicles that receive information about environment can either use the information to perform suitable action according to situation or pass it to vehicles coming after it to take necessary actions. There are also options to get this sort of information from the Road side units located in such area and propagate it in same manner either by Ad hoc network but we are focusing on getting the information by V2V communication. The things we have to consider is trust of vehicles on information provided by road side units and by other vehicles, ability of vehicles in region to share information to multiple hops and ability to track and evaluate information.
Components of V2V communication system
There are three basics components in the V2V communication namely Application unit (AU), on board unit (OBU) and road side Units. These components have there specific role in the system like Application Unit is responsible for running the applications that can use the OBU, The both can work either separate entities or together as one unit. OBU handles networking and mobility functions it is responsible for handling communication between V2V and V2I. OBU contains network device for SR communication based on IEEE 802.11p, it can also have network device for non safety communication based on IEEE 802.11 a/b/g/n. Road side units are devices located on highways, public places like parking area or fuel stations. RSU are also equipped with device capable of SR communication with IEEE 802.11p. RSU are responsible for extending the communication range of ad hoc network, running safety applications and in some cases providing internet communication.
Proposed Strategy and Future Study
We have made one strategy according to our scenario which is discussable and we have also some future goals and study which we want to include in our next report. Our next goal is to investigate about
Dynamic State map Information
Deep study of different communication protocol useful for short range communication and non safety communication.
Develop different scenarios and strategies accordingly.
Detection of hazard and actions
We have developed one strategy for on scenario which can be illustrated from figure below.
In this figure L, P, R, S are representing vehicles having the information of vehicle ahead. As far the vehicles move in non hazard environment it works fine but when it occur the hazard they need some vehicle other than vehicle ahead to have information of the vehicle behind the hazard. We propose that every vehicle should always keep the information of vehicle ahead and also information of any of on right or left.
In this case when vehicle reach on intersection and want to move on right direction but cant communicate directly to R due to hazard but it can get the information of that vehicle from the vehicle coming behind it before the intersection and it works fine for al 3 directions.
We planned to complete our thesis within the 5 months of specified schedule for the Master Thesis Work. Every numeric value represents one month. Our time plan for thesis will be:
Starting of report
First presentation about Introduction
Investigation about strategies
Second presentation about Thesis progress and findings
Compete drafting of Thesis
Reviewing of Final report
Final presentation of Thesis