p.p1 {font-kerning: none} P-OLSR Since FANETs have

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; text-align: justify; font: 12.0px ‘Times New Roman’; color: #000000; -webkit-text-stroke: #000000}
p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; text-align: justify; font: 12.0px ‘Times New Roman’; color: #000000; -webkit-text-stroke: #000000; min-height: 15.0px}
span.s1 {font-kerning: none}

P-OLSR

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

Since FANETs have  no central infrastructure, 
they are prone to isolated attacks and node failures. UAV move rapidly with high speeds hence the topology varies very rapidly. Nodes must react to this rapid change and be able to update their routing tables automatically. It can be achieved by using a fast and reactive algorithm. OLSR fails to track fast topology changes of a FANET. In P-OLSR routing algorithm relative speeds are used to calculate the weighted ETX factor that is expected transmission count. Consider node A and node B , ETX is used as measurement for quality of the wireless network link. It is defined as 
   formula:1 ETX ^A,B=1/r^f( put A,B instead of i,j)
where r^f is the probability that the data packet is successfully sent. r^r is probability that the acknowledgement packet is successfully sent. ETX of a particular route R is sum of ETX metrics of links composing the routes A,B.
formula :2 put A,B instead of i,j)

r^f , r^r(r is alfha)  are the receiving ratios which are measured using a link probe packet that is hello packet. The frequency in which hello messages are broadcasted is called Hello interval. A node takes a while before noticing that wireless link quality have reduced, and before realizing about the broken or a poor link it sends the data packets on a broken link causing interruption to the service. Relative speeds are used to learn how the link quality is going to change. By assuming that each node has knowledge about its neighboring nodes,   
formula :3 put A,B instead of i,j)

Where V(super script A,B subscript l) is relative speed between nodes A,B and BETA is a non negative value. If nodes moves towards each other relative speeds will be negative making ETX value less than 1 and vice versa if the nodes are moving away from each other.Hence the link between the nodes that are moving closing towards each other is preferred to that of the nodes moving away from each other. 

GPS information is collected by hello messages, each time ETX is calculated it will have its upgrade GPS information. Following is the formula to calculate instantaneous relative velocity between A,B 
formula :4 put A,B instead of i,j)
where t(sub script l) and t(sub script l-1) are time of arrival for last and second last hello messages respectively.
(figure 1
figure 2)
Implementation of P-OLSR is done through sharing hello messages through which each node will have to share GPS coordinates. Then each node uses its neighboring co-ordinates to calculate its relative speeds and share them through hello and TC messages. TC messages are topology control messages that are used to construct routing table. Figure1 is the structure of hello message in OLSR. It has the 1st block which is 8 bytes carries information about node. Where as in the figure2 which is format of modified P-OLSR hello message, have 16 bytes. It has 2 empty bytes that are used to communicate the relative speeds between the nodes. Similarly in TC message format the OLSR and P-OLSR differ by one byte which is used to communicate relative speeds between nodes.

x

Hi!
I'm Ethel!

Would you like to get a custom essay? How about receiving a customized one?

Check it out