Limitations And Advantages Of A Directional Antenna

Limitations And Advantages Of A Directional Antenna Abstract A discussion of directional antennas and performance, the limitations or drawbacks and advantages of using directional antennas compare to omnidirectional antennas. INTRODUCTION The definition for directional antennas is antennas which radiates in one or more directions that allowing to increases the performance on transmit, receive and reduce the interference from other sources, or in another way to say is the antennas that receives or sends signals most effectively in a particular. The Radio Frequency (RF) energy can be diverted in a particular direction to father distance. Therefore, it has long range coverage but the effective beam width decreases. Due to the size of directional antennas, the frequencies used are above 200 to 300 MHz. The antennas wideband property depends on the type of the antennas and the directional properties of the antennas are a function of their electrical size. Figure 1 : Directional Antenna with 6 zones. [6] Each zone is a wedge with radius r spanning à Ã¢â€š ¬/3 radians. Zone 1 always faces east. The dashed circle shows the omnidirectional communication radius. A few types of directional antennas are available. [5] Fixed Beam Fixed beam antenna has fixed gain profile with a primary lobe pointing in a single direction. We only can steering the beam by changing the orientation of the antenna physically , which permit relatively slow changes at best. This kind of antenna does provide high gain for their cost and are widely deployed in practice. Figure 2 : Fixed Beam antennas gain pattern Sector In sector antennas, there is multiple fixed beams antennas where each of these beam antennas aims in different direction. Each has covering different area and total 360 ° coverage. Packets may be sent on any sector. Switching between antennas is done electronically and allows the choice of sector to occur on a per packet basis. Figure 3 : Sector Antenna Gain Pattern Analog Phase Array Analog Phase Array antennas work by calculates phase shifts into the signal at antennas elements. There will be individual signals after from phase shifts interfere constructively and destructively with each other in order to form a particular gain pattern. Figure 4 : Analog Phase Array Antenna Gain Pattern Digital Phase Array Another description for Digital Phase Array is smart antenna uses digital signal to accomplish phase shifting. Even the additional power required to do this had increase the cost and complexity greater than the Analog Phase Array, but there is some significant function had been added. Lobes and nulls may be steered very precisely to amplify desired signals and eliminate extraneous ones and angle of arrival information for packets may be obtained as well. Multiple patterns may be realized simultaneously using the same set of elements. Figure 5 : Digital Phase Antenna Gain Pattern THE GAIN OF DIRECTIONAL ANTENNAS [1] The definition for directivity according to [7], The directivity of a wireless antenna is given by the ratio of maximum radiation intensity (power per unit solid angle) to the average radiation intensity (averaged over a sphere). The directivity of any source, other than isotropic, is always greater than unity. Both omnidirectional antennas and directional antennas have directivity but the difference between these two antennas is the coverage pattern. For omnidirectional antennas, the coverage pattern is torus-shaped. The directivity in directional antennas case in higher than the omnidirectional because of its ability to focus the beam. Because of the greater gain in the directional antennas, compare to onmidirectional, the signal transmitted with some power will be able to reach wider distance than the signal transmitted in the omnidirectional antennas. LIMITATION S OF DIRECTIONAL ANTENNAS Deafness [1] Deafness is one of the problems happen when using the directional antennas and it had limited the network performance. Deafness is the problem of failed to hearing from the others. In omnidirectional antennas, all neighboring node are capable of listening to all ongoing transmission but not in directional antennas. The node may be turned into particular sector while receiving and the node said to be locked. In this situation, all the signals that arrive in other sectors cannot be received by the nodes. The nodes said to be Deaf in all other sectors. Figure 6 : Deafness In the figure 2 above, it shows that Node A is communicating with Node B. During the communication, Node A is facing to Node B and turned away from Node C. When Node C is sending a transmission to node A, Node A failed to hear for the transmission unless it is available. Node A can be said Deaf towards Node C . The implement of directional antennas said to reduce the interference but it has increase the ratio of packet loss. Multiple retransmissions may also cause the node to misunderstanding that the connection is lost due to mobility and triggering for route discovering search. In another way to say, it causes the destructive interactions with the upper layers. Drawbacks Specific to Directional MAC (DMAC) The above layer in OSI model does not seem to harness the features of the model even there is some or specific changes in the physical layer. Reusing the same approaches as that omnidirectional MAC, DMAC has created or bring new problems which were not exists in omnidirectional MAC. There is a few drawbacks : Heightened hidden terminal When a node transmits a signal that may affect an ongoing transmission, the hidden terminal problem will be arise. The Ready to send and clear to send are not reaching all the neighbor nodes and this will cause those nodes unaware of ongoing transmission. Head of line blocking- The queuing mechanism used is the First-In-First-Out (FIFO). So the node with antennas will pick the first packet in the queues to transmit. The node will send the packets if the channel in the direction that the node wish to communicate with. If the channel is not idle, the node has to wait until the channel is idle and then transmit the packet. There is still has others packet in the queue waiting to transmit, and there is possible that the channel is not idle. Because of the first packet is still waiting for transmission, it blocks all the packets that can be transmitted. Imperfect virtual carrier sensing Nodes often do not listen to all the signals around them due to the deafness problem. This causes an incomplete Directional Network Allocation Vector (DNAV) table which doest not consistently store the state of the channel in different directions. This leads to imperfect virtual carrier sensing. Effect of mobility [1] Figure 7 : Effect of mobility The reach-ability due to higher range (Position 1) In the communication between two nodes, Node X to Node Y, the coverage using omnidirectional antennas is in circle pattern while the coverage pattern using directional antennas is in lobes pattern. If the Node Y moves out of the circle area, it will unable to receive any packet transmitted by Node X. Since the gain of directional gain is more higher, it is possible that Node Y is still in the directional range X and hence, Node Y still able to receive the packet transmitted. If not, Node Y still will be unable to receive the packet transmitted. Reach-ability in different sector (Position 2) In any area inside the circle area when using omnidirectional antennas, the Node X will be able to reach the Node Y. While using directional antennas with DMAC, Node X failed to reach the Node Y using the same sector. It is because Node Y has gone out of the range of the signal that is transmitted in that sector. Un-reach-ability due to omni-discovery (Position 3) Node X tries to send the packet in its old direction. After failing to reach it after Directional retransmit limit, Node Y will tries to send an omnidirectional signal. Since the Node Y is unreachable by directional signal, Node X cannot discover the Node Y and thus, Node X will assume that the Node Y is unreachable. Node X will never tries to reach the Node Y using different sector even though it is be done by transmitting directional signal in different sector. Node X will reports the error to the above routing layer and drops the packet due to no route. In fact this problem can be solved by transmitting the packet directionally in another sector. Totally unreachable (Position 4) This is another case where the Node Y moves to out of range for both and directional. Node X will be unable to reach the Node Y both in omnidirectional and directional. This case of mobility will lead to disconnection and cannot be recovered. ADVANTAGES OF USING DIRECTIONAL ANTENNAS Security Issue Use directional antennas to prevent Wormhole attack [6] Figure 8 : Wormhole attack where the adversary controls nodes X and Y and connects them through a low-latency link. Wormhole attack means that a forwarded packet from attackers through a high quality out-of-band link and replays those packet at another locations. The attackers will replay the packet received by node A at node B and vice versa. A more intelligent attacker may able to replace the wormhole endpoints at particular locations and this may disrupt nearly all communications to or from a certain node and to all the nodes in the communications. In directional antennas, based on the signal received, a node can get the approximate direction information. Thus, an attacker cannot execute the wormhole attack if the wormhole transmitter is recognized as a false neighbor, that is not the real neighbor and so ignore the messages. There are three increasingly affective protocols to help to prevent the wormhole attacks. As bidirectional information is added, it is more difficult to allot the attacker to launch the wormhole attack successfully. The three protocols are Directional neighbor discovery protocol, that is does not rely on any cooperation between nodes and cannot prevent many wormhole attacks. Verified neighbor discovery protocol, that is preventing wormhole attacks where the attacker control any two endpoints and the victim nodes are at least two hops distant. Strict neighbor discovery protocol where to prevent wormhole attacks even when the victim nodes are nearby. To Support Symmetric traffic services In Time Division Duplex (TDD) Code Division Multiple Access (CDMA) [2] Code Division Multiple Access comprises of two operations , that are Time Division Duplex and Frequency Division Duplex, which to provide two-way simultaneously. A pair of frequency bands is used for uplink and downlink transmissions in FDD. In TDD, the uplink sand downlink transmissions are multiplexed into time slots on the same frequency band, the system is its capability of flexibly to adjusting the uplink and downlink bandwidth by allocating different numbers of time slots. It is more suitable for applications with asymmetric traffic suck as Internet Browsing and file transfer compare to FDD. However, Cross-slot Interference which may seriously degrade the system capacity may happen in TDD-CDMA system during the transmission of asymmetric traffic from adjacent cells. Cross-slot interference is the interference due to opposite direction transmissions between two adjacent cell. In the [2], this paper has shown that the by applying developed interference analysis framework how the interference between virtual cells can be suppressed due to the directivity of directional antennas and thus proposed a virtual based interference resolving algorithm to support asymmetric traffic services in TDD-CDMA Systems. In this paper, it stated that how the directional antennas take effect in supporting the asymmetric system in TDD-CDMA. By using directional antennas in a trisector cellular system can restrict the strong base-base interference into a hexagon and consequently, it is possible by just coordinating the switching points of downlink and uplink bandwidth ratio in only three sectors for TDD-CDMA. The cross-slot-interference level in the omnidirectional case is larger if compare with the directional antennas case. This is due to the transmissions power from a mobile station in omnidirectional cellular system is greater than the trisector cellular system. The reason is because the smaller antennas gain. In ad hoc network Spatial reuse factor Figure 9 : Spatial reuse in directional antenna In figure 9, Node A want s to have communications with Node B , Node C and Node D. In omnidirectional case, the communication between Node C and Node D is not allowed if there is packet sending from Node A and Node B. This is to avoid that the packet from Node C to interfere with Node A to Node B communications. If we using directional antennas, then the sender may focus the beam towards to the receiver. It allows that the coomunications between Node A to Node B and Node C to Node D go on currently. As conclusion, if the nodes use directional antennasthen neighboring nodes that are not in the direction of the signal can go ahead with their transmission. Multiple transmissions can be initiated by different nodes instead of a single transmission if they are not interfere with one another. This increasing the spatial reuse factor. Extended Range and Energy Savings Figure 10 : Extended range in directional antenna In the figure 10, the Node A want to communicate with Node C. in omnidirectional case, the communications cannot reach in single hop. Node A has to transmit the packet to Node B and Node B will transmit the packet to Node C. When using directional antennas, there is larger directional gain. Hence, Node A is able to reach the Node C in single hop. With higher directional gain, focused beam can travel larger distance than those unfocused beam in omnidirectional beam. The sender can reach to receiver with farther away and this has increase the transmission range. Also with higher directional gain, the power required to reach a maximum distance is less than the power used in omnidirectional antennas. This reduce the energy spent by nodes for transmission and reception. Conclusion As conclusion, directional antennas have those benefits that is not exist or stronger or solve the problem exist in using omnidirectional antennas but there is also a few problem that occur only in using directional antennas. There is a few solution proposed to reduce the problem but there is still have a lot of space for improvement.

Ender’s Game Theme Essay Essay

Pressure, pain, corruption, and insecurity; imagine dealing with this every moment of your life. In The Ender’s Game by Orson Scott Card, a young boy genius must take on the weight of the world while dealing with these things. Ender, a nine year old boy, is chosen by the government to go to Battle School, where he must learn to fight and improve his army skills. While he’s there, he struggles with his own morality and insecurity, and tries to do what other people want him to do. Even though he is so smart that he beats every single challenge presented to him, he had to learn throughout the course of the novel to be self-reliant and try to figure out the truth about his whole training. Although Ender is a boy genius and master tactician, he is easily manipulated and has a tough time dealing with the pressure of the world. Ender’s clever genius and amazing military skills has made him become one of the most formidable opponents. His ability to use his genius in any situation combined with his great military skills makes him victorious in even some of the most impossible situations, such as when he had to battle against the humongous bugger army on the battle simulator. The bugger army had outnumbered him, â€Å"A thousand to one (696),† and he needed to think up of a plan. So Ender decided to do the unthinkable, to take out the enemy permanently. â€Å"Then he whispered a command and the ships dropped like rocks toward the planet’s surface. They were starships and fighters, completely unequipped to handle the heat of passage through an atmosphere. But Ender never intended them to reach the atmosphere. Almost from the moment they began to drop, they were focusing their Little Doctors on one thing only. The planet itself (701). † Ender, at first felt like he wouldn’t be able to win the battle with so many enemies against him. But he used his clever wit to think of the impossible and use his military skills to take action. He sent the ally ships as close to the enemy planet as possible and then used Little Doctors (Weapons of Mass Destruction) to nuke the whole planet. This decision eliminated the enemy, but it also killed Ender’s ally command fleet. Ender during the novel showed his great military strength and superior thinking to conquer many of his challenges. He was able to stand up and defeat any bullies who wanted to hurt him, and even with a seemingly useless army he was able to train them using new tactics to win every single battle with them. The final simulator test against the buggers was one of the greatest of his genius military wins, but little did he know that it was just a game. Although Ender is genius in many ways and has great military skills, he is still easily manipulated by adults and starts to crumble under the pressure of the world. Ender throughout the novel has very low self – esteem. He just views himself as a tool under other people’s hands. So, when he is given the chance of a two week break, he takes it and has a three month break. He was tired of being pressured to be the best military leader the human world had to offer. He didn’t believe he could keep enduring, and thought he would fail. On his break, the government got so desperate for Ender they sent his sister to go in and help persuade Ender to keep on fighting. â€Å"Ender insisted that his conversation with you should not be bugged. I promised him it wouldn’t be, and to help inspire confidence, the two of you are going out on a raft he built himself (546). † This scene of the book shows how Ender is still a human being, and everyone’s got a cracking point. In able to go on, many of us find it comforting and strengthening when someone says we can do it and inspires us to keep on fighting. Valentine was Ender’s inspiring push to keep him going, but even she was another tool the government used to manipulate Ender. Ender got manipulated a lot in the novel by adults, especially when he was training in the simulator. The adults acted like it was just a game or challenge, and that Ender was just practicing to face the buggers. But when the final test came and Ender won by destroying the whole bugger race, he realized that the adults lied to him, and it was never just a game. Orson Scott Card illustrated how even the strongest and best of us still has a limit and can crack. Ender proved how he was one of the smartest and most brilliant military leaders alive through his training and thought out decisions in Battle and Command School. He was a genius among geniuses, and always thought of something new and effective. But he too, succumbed under the pressure of the world, and needed inspiration and courage to push through. He became too easily manipulated by adults, which led him to a decision he wish he never made. Orson Scott showed how even the best of us, can give in to the dark and evil intentions of man.

Things You Wont Like About Pte Essay Samples and Things You Will

Things You Won't Like About Pte Essay Samples and Things You Will The Pain of Pte Essay Samples Marriage includes a lot of responsibilities where a practical approach to the relationships is of utmost importance. If you understand what you are writing about or have chosen the topic yourself, you want to do a little bit of research. Bear in mind an argumentative essay is based more on facts rather than emotion. Do your homework on the topic of your essay, while it is a part of literature or a function. Distinct kinds of essays need various kinds of research. Argumentative essays are also called position papers due to their justification of the side of the issue they are written in support of. Writing has existed for quite a lengthy moment. Writing an essay demands lots of steps to be made. Writing a persuasive essay can be complicated because you're not just presenting the research materials you've gathered but you're trying to influence your readers. It is a very important skill that will surely help you in your life. Things You Should Know About Pte Essay Samples Regardless of what you pick, you are to have a crystal clear knowledge of the subject described. Remember your analytical essay should contain talking points concerning the matter below your consideration. One of my favourite things about writing is that there isn't any correct or wrong answer. You're going to need to select a topic first, but your topic ought to be something that has two conflicting points or unique conclusions. Top Choices of Pte Essay Samples You may be asked about what you meant, so you've got to be ready for questions. Be cautious with the information that you pick. Furthermore, you've got to get prepared that you might find out you don't find all of the information that you demand. Don't attempt to operate with information you aren't really interested in. What You Should Do to Find Out About Pte Essay Samples Before You're Left Behind Tutorials are given to offer you detailed instructions on how best to use the templates. The words you opt to write about as your topics must be complex and abstract. Many people think that high school entrance essays are rather simpler to write than college entrance essays, that's the reason there are fewer places where you could get assistance with higher school entrance essays. Some people believe schools should select students based on their academic abilities, while some think that it's much better to have students with distinct abilities studying together. High school students need to compose essays on a number of topics which at first may appear to have nothing in common. Fully being a happy high school student wouldn't be possible without my loved ones. The Secret to Pte Essay Samples You may also have an indirect quotation if you want. An immediate quotation presents part of an original bit of text and ought to have a reference to the original source in light of the format required. An indirect quotation demands a reference to the original source also. Short essays, as its name implies, needs to be concise and succinct. High school essay examples incorporate a number of short essays like narrative, persuasive and analytical. Again, for more info about essay structure strategies, our PTE write essay' webinar is a good place to begin! To help you produce a productive essay outline here are tips that can assist you. Anyway, it has smart suggestions about how to compose an essay and the way to have it written. When selecting high school essay format, step one is to spot the sort of essay you want to write. Top Choices of Pte Essay Samples Most conclusions are just a paragraph in length as the conclusion is anticipated to be an overview of the whole essay. While the focus is principally on your side, there's also a discussion concerning the opposing side which goes far beyond a single sentence or a paragraph. Our very first trick is to attempt to select a topic accurately. Since you may see, essay writing involves plenty of things. First and foremost it's essential to be sure that you comprehend the essay question fully and your essay answers each part of the question adequately. The most important portion of a quick essay is known as the body. Your essay should reveal the things that are related to your audience.

The Goal Setting Theory Of Motivation - 1818 Words

In the 1960’s, Edwin Locke put forth the Goal-setting theory of motivation. This theory states that goal setting is fundamentally linked to task performance. It standardizes the idea that specific and challenging goals along with constructive feedback, contribute to enhanced task performance. Locke, one of the most notable contributors in goal setting theory, alongside Gary Latham have contributed to the history and evolution of goal setting while highlighting strengths and weaknesses of the theory in practice used by companies and making contributions to management. In Edwin Locke’s 1968 article Toward a Theory of Task Motivation and Incentives, he highlights that working towards a goal is a major source of motivation – which, in turn,†¦show more content†¦Participation of setting goal makes them more acceptable and leads to more involvement. Goal setting theory has certain eventualities such as self-efficiency is the individual’s self-confidence and faith that the individual has potential of performing the task. The higher the level of self-efficiency, than greater the efforts put in by the individual when they face challenging tasks. While, lower the level of self-efficiency, less will be the efforts put in by the individual or he might even quit while meeting challenges. Goal commitment- Goal setting theory assumes that the individual is committed to the goal and will not leave the goal. The goal commitment is dependent on the following factors: Goals are made open, known and broadcasted. Goals should be set-self by individual rather than designated. Individual’s set goals should be consistent with the organizational goals and vision. Goal setting is something that many of us recognize as a vital part of achieving success. By understanding goal-setting theory, you can apply Locke and Latham s principles to your goals. Their research confirms the usefulness of SMART goal setting, and their theory continues to influence the way that we measure performance today. Relevant additions have been made to Locke’s theory, which will be discussed further. As stated in the New Directions in Goal Setting Theory publication, â€Å"Goal theory is an ‘‘open’’ theory inShow MoreRelatedGoal-Setting Theory of Motivation2104 Words   |  9 PagesJOURNAL OF MANAGEMENT, BUSINESS, AND ADMINISTRATION VOLUME 15, NUMBER 1, 2011 Goal-Setting Theory of Motivation Fred C. Lunenburg Sam Houston State University ABSTRACT Locke and Latham provide a well-developed goal-setting theory of motivation. The theory emphasizes the important relationship between goals and performance. Research supports predictions that the most effective performance seems to result when goals are specific and challenging, when they are used to evaluate performance and linkedRead MoreGoal Setting Theory Of Motivation Essay877 Words   |  4 PagesEssay question: It is often claimed that goal-setting is a theory of motivation which works. Critically evaluate the evidence and discuss the extent to which it supports this claim. Introduction As element that drives the person to strive for the best within his or her own capacity, Guay et al. (2010) defined motivation as reasons that underlie behaviour. It is also interpreted by Huitt, W. (2011) cited Kleinginna and Kleinginna (1981) as an internal state or condition (sometimes described as aRead MoreMotivation Theory And The Goal Setting Theory1159 Words   |  5 Pages Essay 1 Content theories of motivation focus on the importance of work itself, challenges, growth opportunities and responsibilities that the work provides employees. Process theories of motivation focus on the cognitive processes that are part of employee’s decision making. It also deals with our thoughts and perceptions about our jobs. The decisions are made based on calculations of gains versus loses. Also, when it comes to process theories of motivation, how the work situation is perceivedRead MoreThe Goal Setting Theory for Employee Motivation1302 Words   |  6 PagesGoal setting theory can help motivate employees to do their job as managers can relate to Professor Edwin Locke goal theory. The underlying concept behind this theory is the belief that people’s goals play a vital part in deciding their behavior. People drive to satisfy these goals to help their emotions and desires. Goals guide people’s responses and actions. Goals command employee performance an d actions and this can call for action or feedback. The effort that individuals will exert in attemptingRead MoreGoal Setting Theory: Motivation, Stress, and Communication1278 Words   |  5 PagesMotivation, Stress, and Communication Motivation, Stress, and Communication Introduction Goal-setting has progressively become a prominent tool of performance utilized by individuals and business organizations. Companies attain their success by setting long and short-term targets which provide them with direction in productive channels economically. Some of the common attributed elements in goal setting include: sales, services, products, and customer relations in general. The setting of goalsRead MoreCompare and Contrast Expectancy and Goal Setting Theories of Work Motivation. Which Do You Find the More Useful and Why?1384 Words   |  6 Pagescontrast expectancy and goal setting theories of work motivation. Which do you find the more useful and why? Two of the best known approaches to work motivation are the expectancy theory introduced by Victor Vroom (1964) and the goal-setting theory introduced by Edwin A. Locke (1968). Both of these theories have garnered support from subsequent empirical research and have proved influential in how companies motivate their workers through incentive schemes and objective-setting exercises. As theirRead MoreBackground Of Id Medical Group1389 Words   |  6 Pagesbrand, motivation and engagement. The wellbeing is bound up flexibility, work-life balance, motivation, job-satisfaction and human research management. For this reason, the rank of giving something back and wellbeing is very high in 100 companies (high level means not good at about a topic). The two category have included a joint topic which is motivation. The company is not good at about motivation. Therefore, the company is not good financially. 3.0 Motivation and Theories 3.1 Motivation For motivationRead MoreHow Managers Motivate Employees And Helping Managers Keep Their Employees Motivation High Essay1492 Words   |  6 PagesMotivation in the workplace has been a frequently discussed subject for at least a century. Whether an employee is doing paperwork behind a desk, helping to put together a car on a conveyor belt, or trying to make a sale, motivation is essential in their job. The reason behind this is simple enough- the more motivated an employee is the more work they tend to get done. However, it can be a struggle for managers to keep their workers motivated. This struggle has led to the development of numerousRead MoreEssay on Reinforcement Versus Goal Theory724 Words   |  3 PagesReinforcement versus Goal Theory Lorraine Patterson OMM 625 Learning Organizations amp; Effectiveness Professor Renee Hill January 30, 2012 According to Edwin Locke the goal setting theory is a tool used for motivation. The theory states that goal setting is linked to task performance. The goal states â€Å"specifically challenging employees while using feedback will contribute to a higher and better performance while completing a task.†(Pane, S) The idea of workingRead MoreEssay on Insight on the Motivation of Workers596 Words   |  3 PagesMotivation has always been a subject of much research over the last fifty years however there have been many definitions and theories describing and analysing motivation but the research is never complete. Right from Robert Owen who described human beings to be like machines that need care and maintenance to work efficiently till Drucker (1999) who described them as the knowledge workers of the 21st century with different needs and therefore on what it is required I would like to elaborate on the