Enhancing AODV routing protocol using mobility parameters in VANET 任課教授:許子衡 教授 學生:王志嘉 Introduction Vehicular Ad-Hoc Networks (VANETs) are special type of Mobile ad Hoc Networks (MANETs). Direct wireless transmission from vehicle to vehicle make it possible to communicate even where there is no telecommunication infrastructure 2010/06/01 2 Introduction The USDOT and IEEE have taken up the standardization of the associated radio technology Wireless Access for Vehicular Environments (WAVE),now described as IEEE 802.11p. There are many challenges in VANETs. According to FCC frequency allocation we can categorize two main classes of applications for vehicular ad hoc networks. 2010/06/01 3 Introduction The first category which was mentioned above is to improve the safety level in roads, and the second predicted to grow very fast in the near future, is commercial services. There are many routing protocols for ad hoc networks. One of the most important of them is AODV. AODV is an on demand routing protocol. This protocol finds routes for a node only when it has data packet for transmission. 2010/06/01 4 Introduction AODV routing consists of three phases: route discovery, data transmission and route maintenance. Route discovery phase starts when a node wants to transmit data and has no route to destination. Now, AODV call route discovery process. 2010/06/01 5 Introduction In this phase,source node broadcasts a Route Request Packet(RREQ) to its neighbor. Nodes that receive RREQ packets divide into three categories: the receiver node is the destination of route, the node that has a route to destination or none of both. 2010/06/01 6 Introduction After routing phase, routing process calls data transmission phase, then it transmits data packets across selected route. In this phase, it is possible that a link is broken and results in route expiration. In this situation, the maintenance phase calls to repair broken route or find a new route to destination. 2010/06/01 7 Introduction One advantage of AODV is that for any pair of source and destination finds more than one route. Although this appears as advantage but more often this advantage acts as disadvantage. Finding several route need to exchange more control packet. This leads to increase routing overhead. 2010/06/01 8 Mobility model We want improve AODV as MANET routing protocol and make it useable for VANET with high performance. We must use one of VANET’s mobility models. Manhattan is one of the most important mobility models for VANET. In Manhattan mobility model, several horizontal and vertical streets co-exist in the simulation field and mobile nodes are moving on the lanes of the streets. 2010/06/01 9 Mobility model In figure 1, Manhattan has a vertical and a horizontal street with an intersection. Each street has two directions be made of a lane. 2010/06/01 10 Mobility model If one direction of a lane has positive value 1, then the lane on the opposite direction must have the negative value -1. Streets of each map have the maximum and minimum allowed velocity (Vmin, Vmax). 2010/06/01 11 Mobility model In this mobility model, acceleration is an input parameter. To calculate node’s next speed, model uses acceleration and current speed of node, relation 1 shows it: If β be less than zero, it means that the node is moving with de-acceleration (negative acceleration) Otherwise,it moves with positive acceleration. 2010/06/01 12 Mobility model If current speed of node is greater than the maximum allowed velocity for its lane, current speed decreases to Vmax. Otherwise, if current speed of nodeis less than minimum allowed velocity for its lane, current speed increases to Vmin. 2010/06/01 13 Method description In our method, we use node’s direction as most important parameter for next hop selection. Another parameter, which affects next hop selection, is node’s position, but importance of this parameter is less than direction. These mobility parameters have been obtained from GPS. 2010/06/01 14 Method description When a source node wants to send a packet to destination node, first, routing protocol gets direction of source node and destination node. Then, with respect to direction of source node and destination node, recognize intermediate node that can be participate in route between source and destination. 2010/06/01 15 Method description Because of using Manhattan mobility model, nodes can move in three situations: 1- Source node and destination node move in same direction. 2- Source node and destination node move in opposite direction. 3- Source node and destination are orthogonal. 2010/06/01 16 Method description In this paper we have only considered two first situations and have prolonged it to our future efforts. In supposed method, we also try to select intermediate nodes that are moving in suitable position between source and destination. Furthermore, their direction is important. 2010/06/01 17 Method description Corresponding pervious description, a node can be select as next hop in route between source and destination that has two conditions: A. It moves in same direction with source and/or destination. B. Intermediate node’s location is between source and destination. 2010/06/01 18 Method description Algorithm No.1 describes next hop selection according to the above criteria. The algorithm determines whether a candidate node can be an intermediate in route between source and destination. Get_Direction function returns direction of input node and Get_Position function returns location of any input nodes in network. 2010/06/01 19 2010/06/01 20 Method description Routes established by this way are more stable and have less overhead than original routing method. There is one problem : maybe we cannot find any intermediate node as next hop for routes having these restrictions. 2010/06/01 21 Method description For solving this problem, we change our strategy. Firstly, we put lower bound on number of discovered routes and then divide algorithm into two steps: In step one, protocol searches for nodes that have both condition of position and direction. If the results satisfy lower bound of routes, algorithm without doing anything will finish and do other routing phases such as route maintenance and data transmission. 2010/06/01 22 Method description In step2,algorithm removes position condition and all nodes that are in same direction with source and/or destination, can be selected as intermediate nodes for route. 2010/06/01 23 2010/06/01 24 Simulation environment Our simulation has been done in a 1000m×1000m area and for 700 second. Simulation area contains 3 horizontal streets, 3 vertical streets and 9 intersections. Each street has 2 lane and we do not supposed any traffic lights at intersections. Maximum speed when the number of nodes changes is 20m/s and acceleration is 5m/s2. Transmission range of each node is 250meters and 802.11 used as a MAC layer protocol. 2010/06/01 25 Simulation parameter A. Link Expiration Time (LET) We suppose that transmission range of every node is R. We also need node’s speed to calculate LET. Suppose we want calculate LET between node i and j. distance between them is |di,j| and velocity of each node is vi and vj. Base of these parameters and if nodes move in same direction, we have: 2010/06/01 26 Simulation parameter If two nodes are moving in opposite direction,equation 2 will be change to equation 3: After calculation of LET, we can obtain RET (Route Expiration Time). RET for a route is minimum LETs that make that route: 2010/06/01 27 Simulation parameter B. Broken links Route is more stable if it has less broken link in any connection. We use this parameter to show route stability. If the number of broken link per route is low,route is more stable. High broken link leads to exchange more control packet and have more packet loss than route with lower broken link. 2010/06/01 28 Simulation parameter C. Route length Route length determines by number of hops that every source nodes needs to traverse until reach a destination. 2010/06/01 29 Simulation results A. Link stability A link is stable if its nodes satisfying these three conditions; their moving directions are same, their positions are in acceptable states, and finally difference of their velocity is endurable with regard to their positions and direction 2010/06/01 30 Simulation results Figure 2, depicts number of broken links between source and destination with respect to change network density in our simulation environment. In this experiment, we have compared our method, DAODV, with original AODV. 2010/06/01 31 Simulation results As depicted in figure 3, DAODV behaves uniformly on changing of node’s speed. In AODV, number of broken links increase faster than DAODV in high velocities. 2010/06/01 32 Simulation results B. Route length Number of hops between source and destination determines route length. Our solution tries to reduce number of hops to shorten route lengths between source and destination. 2010/06/01 33 Simulation results Figure 4 demonstrates that in our method, route lengths are shorter than AODV routes. The improvement is about 30% in average. 2010/06/01 34 Simulation results As depicted in figure 5, our method is also sensitive to nodes velocities. It works well for the applications, which demands high-speed nodes, and selects shorter routes than AODV. 2010/06/01 35 Simulation results C. Route Expiration Time (RET) Figure 6 shows Route Expiration Time (RET) versus network density. As depicted in this figure,increasing the number of nodes leads to decrease RET. 2010/06/01 36 Simulation results Figure 7 shows that DAODV by changing speed of nodes is also more stable than AODV. 2010/06/01 37 Conclusion In this paper, we have proposed DAODV protocol that improves the performance issues on common AODV protocol. The main goal of DAODV is to establish more stable routes especially in the applications that demand high mobility of nodes such as VANETs. 2010/06/01 38 Conclusion The proposed method uses two important parameters of movement (direction and position) to select next hops during route discovery phase. Finally,our simulation experiments showed that DAODV protocol works well in various traffic situations. 2010/06/01 39