Emergency Communication in VANET Using GPSR
R. Chitra Pooja Sri Nithyasri Ravi Abigail Judith Peter
2015503510 2015503537 2015503534 2015503002
Computer Technology Computer Technology Computer Technology Computer Technology
MIT MIT MIT MIT
Abstract—
Vehicular Ad Hoc Network(VANET) is a form of MANET where vehicles act as a router or host. VANET has been designed to offer a high level of safety for the drivers in order to minimize the number of road accidents. VANET, are implemented so that vehicles will be able to exchange information between them and with the road side units. This proposed work focuses on the wireless communications that are more reliable and faster that is used to connect the vehicles with each other and with the outside. Routing is most challenging issue in VANET, which requires high efficient broadcast schemes. In this paper, Greedy Perimeter Stateless Protocol(GPSR) is used to send message by a vehicle to its neighbors when any emergency situation occurs. The main feature of our proposed work is to detect the direction of the moving vehicle before forwarding the packet to its destination in order to prevent packet loss.

Index Terms—Emergency message, GPSR, direction, packet loss.

INTRODUCTION
With the number of cars rapidly growing, Ad Hoc network technology applied to vehicle traffic system has became an research area of transportation system. VANET is a kind of self-organized network specially designed for the vehicle to vehicle (V2V) communication. The traffic messages can be obtained by building the vehicle communication network utilizing the wireless communication systems, the GPS system and intelligent computer system on board. In VANET,the communication performance of the entire network greatly depends on the efficiency and effectiveness of the routing protocol. The pros and cons of routing protocol strategies largely decide the link quality in wireless communication. Therefore, routing protocol is one of the key technologies in VANET. Safety communication in VANET is made by two means:Periodic safety messages and event-driven messages. Beacon messages are safety messages containing sender status information such as position, speed etc using IEEE 802.11p broadcast mode. On the other hand, Event-driven messages also known as Emergency messages sent by a vehicle when dangerous situation happens on the road and it can be im-plemented using Greedy Perimeter Stateless Routing(GPSR)

protocol. In this paper , we firstly make an introduction of the stateless routing based on the GPSR routing protocol and then a corresponding improvement has been taken on account of the time delay problem which caused by mobility in GPSR routing protocol in VANET environment. Finally, experiments are made aiming at the enhanced GPSR routing protocol in NS2 simulation, the analysis of its performance proves that the enhanced GPSR routing protocol in the vehicles environment has lower packet loss rate and less time delay than the traditional GPSR routing protocol.

A. GPSR
GPSR (Greedy Perimeter Stateless Routing) is a typical position based routing protocol which is suitable for VANET network. GPSR obtains neighbor vehicles node information by GPS positioning equipment etc rather than getting a large number of routing information in order to maintain the infor-mation in neighbor table as well as the information in routing table . In GPSR routing protocol, each node periodically broadcasts its own location information to the neighbor node (the next-hop node), the information is stored in neighbor table after neighbor information has been received. The forwarding node chooses the next-hop forwarding node according to both neighbor location information and destination location. Before sending data packets, first the ID of destination node is inquired through location-based service information in order to get the location of the destination node. In GPSR, there are two methods – Greedy Forwarding and Perimeter Forwarding. In Greedy Forwarding, it will find the neighbor node and transmit the data. In Perimeter forwarding is used when greedy forwarding cannot find the node and this method will choose one of the nodes within a void area to continue transmitting the packet to its destination.

Advantages:
Message received by all nodes in very short time
GPSR protocol are very scalable for medium to large size networks
GPSR protocol have reduced the network congestion.

GPSR protocol have high packet delivery rate.

Maintain vehicle location information for better and fast routing.

It is very beneficial to reduce road accidents.

Link is established when required.

B. Components of VANET
The ID of destination node is identified through location-based service information in order to get the location of the destination node.

TA: Trusted Authority(TA) acts as the registry center of RSU’s and vehicles, is trusted by all entities in the VANET and responsible for distributing key materials to all entities. And the TA has the ability to trace the real identity of the vehicle if necessary. For secure communication, a wired secure transport protocol such as Transport Layer Security (TLS) is used between TA and RSU. In order to avoid the formation of performance bottlenecks and improve reliability, redundant TA is usually set.

RSU: : Road Side Unit(RSU) is located on the roadside and can communicate directly with the vehicle as a bridge between the TA and vehicles. The RSU can authenticate its received messages, and if necessary, process the results locally, or send the results to the traffic management center for data analysis. In order to ensure that RSU can help the vehicle to carry out message authentication, RSUs computation performance should be far greater than the vehicle.

Vehicle: The OBU mounted on the vehicle periodically broadcast the traffic related information to improve the oper-ation efficiency of regional traffic and traffic security. Each vehicle has a tamper-proof device (TPD) to store received key material securely .

RELATED WORKS
Shivashankar, B.Hanisha Chowdary, Gagandeep kaur, Archana kumari, Chethan kumar reddy proposed DRIFT, a protocol for VANET to work in a very high environment with different traffic conditions using the technology of vehicle to vehicle communication. The transmission of information should be done by the vehicles which are present inside that area. With that we can increase the data dissemination with the place of concern with low cost and less delay.

Radityo Anggoro, Muchammad Husni, Randy Bastian proposed DSR protocol with the help of intersection node at GPSR protocol to increase the data transmission reliability on VANET. The result shows that the implementation of source route with the help of intersection node was able to increase the reliability of data transmission on VANET.

Yao-Hsin Chou, Ting-Hui Chu, Shu-Yu Kuo, and Chi-Yuan Chen proposed Appropriate Vehicular Emergency Dissemination (AVED) strategy based on the WAVE/DSRC standard for improving broadcast mechanisms including reception rate, forwarding counts, packet loss rate and End-to-End delay time in V2V communication. In AVED, each vehicle collects accident information of other vehicles in the same hop and establishes a routing table. By this information, the sender can determine which forwarder is the most reliable. In addition, the back-off procedure assigns

an appropriate back-off time to forwarders, so as ensure the reception rate and to reduce redundant broadcasts and medium contention.

Jia Li, Ping Wang, Cha Wang proposed the scheme which reduces beacon interval overhead and data collision in high density. It mainly focuses on successful data rate and routing overhead to decide whether the performance is satisfying or not. This proposal decreases the routing overhead under the same successful data rate performance, thus leaves enough bandwidth resources for data transmitting.

Chunlin Wang, Quanrun Fan, Xiaolin Chen, Wanjin Xu proposed Prediction based Greedy Perimeter Stateless
Routing Protocol which detects the speed and direction of moving vehicle to adapt to the high speed mobility of vehicles.

Neha, Isha proposed GPSR that uses the location information for routing packets, to find the exact destination position the packet is send to the old destination position and from that old position location request send to get back the exact position. In this HLS and GLS algorithms are altered by HRHLS and HRGLS in which old position is use to forward data packets then intermediate node send location request to find new destination.

Haojun Yang, Ming Yu, and Xuming Zeng proposed Greedy Perimeter Stateless Routing(GPSR) is implemented with Link Available Time(LAT) which predicts the next hop selection of GPSR, instead of simply using a greedy forwarding algorithm. LAT is decided by the measurable variables within a predefined time interval. Matrix based LAT is implemented to predict the next hop to decide which node should be the next hop for relaying.

Aji Setiabudi, Amalia Ayu Pratiwi, Ardiansyah, Doan.Perdana, Riri Fitri Sari compared the Greedy Perimeter Stateless Routing(GPSR) Protocol is compared with Zone Routing Protocol(ZRP) based on parameter metrics such as average throughput,packet delivery ratio,end-to-end delay and packet loss in VANET environment. ZRP routing protocol is sensitive to the number of nodes that exist in the area. Meanwhile, even though GPSR is less reliable to transmit data packets to the destination, GPSR has the advantage with a low delay and high throughput, either in sparse area or dense area. Both routing protocols do not particularly affected by the speed of the node.

Yu Wang,1 Zhizhong Ding,2 Fei Li, Xue Xia and Zhentao Li illustrates the functional design of the application including the synchronization between the WAVE devices, channel allocation under different conditions and WSMP transmission. In addition, sub-applications and Task Manager have been developed for the program optimization and resource management. The WAVE protocol is well suited for wireless communication in the VANET and a well-performed application layer program design is essential for the low-latency and low-overhead in VANET.

PROPOSED WORK
The existing works focuses on sending a message to its neighbors when emergency situation occurs. The proposed system focus on sending a message to its neighbors by detect-ing the direction of moving vehicle using GPSR protocol. It prevents packet loss and also it can be able to send emergency message within its beacon interval
A. Architecture Diagram
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D. Algorithm for Enhanced GPSR Protocol
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Algorithm 1 Enhanced GPSR
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Step 1 : Periodically broadcast its own location to the neighboring node
Step 2 : Maintain neighbor table
Step 3 : In case of Emergency, calculate the Euclidean distances from each of its neighbors
Step 4 : Choose the one with smallest distance
Step 5 : If the direction of moving vehicle and its neighbor vehicle is same, then send a packet
Step 6 : Else go to step 3, and choose another neighbor
Step 7 : After receiving packet, stop the vehicle
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IV. PERFORMANCE AND RESULT ANALYSIS
Fig 1. System model
B. Enhanced GPSR
In this paper, an enhanced GPSR approach is proposed. The nodes will periodically broadcast its own location infor-mation to its neighbors(V2V). When an emergency situation occurs, a node should calculate euclidean distance to all its neighbors through neighbor information table and choose the one with smallest distance. If the direction of source vehicle and destination vehicle is same then send the packet. Else choose another neighbor and send an emergency message. On receiving emergency packet, the destination should take necessary measures.

C. Flowchart for Enhanced GPSR
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Fig 2. Enhanced GPSR

We use NS-2 to simulate the Enhanced GPSR protocol, and compare it with GPSR. The throughput of GPSR and Enhanced GPSR is compared.

Throughput: Throughput is used to evaluate the per-formance of the network. It is the amount of data received by the destination node in the unit time without packet lost. As shown in fig 2, the Enhanced GPRS throughput is much higher than GPSR at a fixed transmission rate. This is because the next hop routing selected by GPRS protocol is not all the best routing, or even because the node moves quickly to select the wrong route, resulting in a large number of packet losses, affecting its throughput. Enhanced GPRS uses node direction to predict node location, and combines greedy forwarding, which is more effective, reliable in selecting next hop routing, reducing loss rate and improving throughput. The experiment shows that Enhanced GPSR has a higher spit amount than GPSR, almost 2 times as much as GPSR.

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Fig 2. Throughput
End to End Delay: It is the amount of time taken by the packet to reach the target node. The smaller the transmission delay, the more effective the packet forwarding path thus it the lowers the packet loss rate. An Enhanced GPSR has a smaller transmission delay than the GPSR, and the performance is better than that of GPSR. This is mainly because Enhanced GPSR is more effective than GPSR routing path even though enhanced GPSR need to detect the direction of moving nodes.

V. CONCLUSION
In vehicle ad hoc network(VANET), there is a chance for high-speed mobility and hence it changes network topology which results in packet loss and time delay. Proposed En-hanced GPSR uses the nodes direction to predict the position of next hop node and uses greedy algorithm to select the next hop, the throughput and transmission delay performance are better than the GPSR protocol. It also proves that our idea is effective and suitable for high speed mobile ad hoc network. In this paper, simulation is done only on vehicle to vehicle(v2v). In future, vehicle to infrastructure(v2i) can also be utilized to simulate experiment.

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