Idealistic Politics Essay

â€Å"The history of all hitherto existing society is the history of class struggles,† said Karl Marx, who is considered to be one of the world’s most seminal thinkers. Marx categorized these classes in two broad categories; the bourgeoisie versus the proletariats, the upper class opposed to the lower class and the caste that have access to the factors of production against everybody else who are compelled to sell their labor. In political terms the bourgeois were the â€Å"†¦committee for managing the common affairs of the whole bourgeoisie† (Marx, 20) and in order to reduce any friction, tension or resistance towards their supremacy they then laid down a set of ideals and values for all classes and citizens. The ultimate goal of having a monotonous set of principles was to disintegrate existing ideals and values by instigating the proletariats to fully accept the bourgeois’ set of principles by suspending their own. History, however, has yet to see such an outcome where the bourgeois triumph in instigating such circumstances successfully. What occurs in such circumstances instead is a conflict due to inconsistency that occurs between the dogmas of both classes; whereby the reality based ideals of the proletariats clashes with the idealistic values of the bourgeoisie. These conflicts in turn affect the political ideologies and actions since the politics is the arena where the battle of principles occurs, primarily due to two reasons. The first being that these conflicts will not surface in the first place except in the political arena due to the austere nature and secondly the outcomes will not be accepted unless at a level were they are made public and irreversible. Evidence of these conflicts exists in our texts and films, however in differing contexts. In Antigone, Creon represents the bourgeoisie and Antigone the proletariats; in A Discourse on the Moral Effects of the Arts and Sciences the arts and sciences were the corrupting vales instigated by the intellectuals whilst the savage being was the unlearned and naà ¯Ã‚ ¿Ã‚ ½ve proletariat, and finally in Marx’s Communist Manifesto where the distinctions are extremely clear among the two classes. In the course of my paper I wish to examine the strength and weakness of each of these ideal societies and their implications to political ideology and action. The values of Karl Marx’s idealist communist society â€Å"may be summed up in the single sentence: Abolition of private property† (Marx, 34). He believed that once private ownership was abolished people would change, and this would finally end the history of all class struggles. Communism to Marx was an extension or a purer form of socialism, whereby the people owned everything and everybody worked for the system, hence no form of personal interests was vested in the system. This assumption was made by placing a gamble on human behavior, probably the most unpredictable factor to place any form of wager on. Marx was assuming that among a whole class of people â€Å"no interests [were] separate and apart from those of the proletariat as a whole† (Marx, 33). The society that Marx visualized was one where all the citizens desired only the interests of the society by not desiring to satisfy their personal interests. History, however, does not have a basis for pure communism where a group of people have ceased to exist without any possessions and have lived only by the idea; the closest analogy one could give would be of hunter-gatherer societies. These societies, however, existed during the prehistoric times where human attitudes and behaviours were not being constantly reshaped by the changing economic systems in which people find themselves nowadays, which Marx himself mentions as there being no such thing as fixed â€Å"human nature.† Therefore, communism could never work because it goes against human nature. People are naturally more competitive than cooperative. Moreover, the possibility for revolution to occur where the bourgeoisie were to come down in their social status to the level of the proletariats and the proletariats rise to eminence of the bourgeoisies could only occur if human nature were to be dismantled, self memories be wiped out and in other words for the revolution to occur successfully in needs to be self induced. Marx in an indirect manner implies how one’s self worth has decreased with the current system when he discusses the dynamics of wage labour and whether it creates property for the laborer. He states that the system is self-defeating for the laborers, â€Å"which cannot increase except upon condition of begetting a new supply of wage-laborer for fresh exploitation† (Marx 34). If we were to refer back to the analogy hunter-gatherer societies the fruits of one’s labour were immediate; when an individual hunted his reward was immediate and did not wait for his fruits or â€Å"live only in so far as the interest of the ruling class requires it† (Marx. 35). In short man’s worth and dignity has been demoralized and â€Å"every individual has been converted in paid wage laborers†¦and has reduced†¦relations[s] to a mere money relations† (Marx, 21). Individuals were not bounded by the â€Å"social status† hunter-gatherer since everyone shared and everyone knew their worth. The advantage of this system is that it does not create any room for friction to occur because it does not include the idea of individuals desiring to wish to control the environment or vest any personal interests into the system. This can primarily be attributed to the value the system advocates of not wishing to differentiate people under any circumstances; the system does not know race, ethnicity and differences of age and sex no longer [have] any distinctive social validity (Marx, 26), a trait of hunter-gatherer societies, which Marx so dearly desires. These values would in turn affect the political ideologies of a system trying to covert to communism by picking on the one â€Å"essential condition for the existence†¦of the bourgeois class, the formation and the augmentation of capital: the condition for capital is wage labour† (Marx, 32). Therefore, the conflicts that would arise would be those that regarding wage labour and its supply; the bourgeoisie would advocate any action that would enhance the â€Å"competition between laborers† the key behind keeping a continuous supply of wage labour opposed to the proletariat’s immediate aim of cutting off this supply and by doing so ensuring its immediate aim of overthrowing the bourgeois supremacy. Any decline in wage labour would threaten the bourgeoisies’ capital by reducing its turnover, hence weakening their foothold in the marketplace in turn inhibiting their ability to â€Å"constantly revolutionize the instruments of production in order to exist and survive† (Marx, 21). The bourgeoisie quest to seek a continuous wage labour would see a shift in their political ideology; they would seek to manipulate cities, provinces and other nations that are weak cause them to become dependent on them. The consequence of such political centralization would lead to the â€Å"epidemic of overproduction,† whereby the only manner in which the crises can be overcome is â€Å"by the conquest of new markets, and by the and by the more through exploitation of the old ones† (Marx, 25). However, such exploitation of markets can occur only to a certain limit, until other nations impose regulations confiding the system to resort to desperate measures and turmoil, which occurred with China. Chinese products flooded the world market until recently and now they have been rejected entry into the World Trade Organization (WTO) and do not enjoy the benefits of free trade. Therefore, China have used â€Å"enforced destruction of a mass of productive forces† (Marx, 25) to decrease their output, which has lead to a lot of turmoil inside the country with dogmas of the government – political stability and international recognition – and the working class – subsistence and a better life – clashing against each other further depressing the situation. Like Karl Marx, J.J. Rousseau also painted a picture of ideal society. In his Discourse on the Moral Effects of the Arts and Sciences he condemns how societies have succumbed to arts and sciences that have â€Å"molded our behavior, and taught our passions to speak an artificial language† (Rousseau, 6) † with the desire to please one another with performances worthy of their mutual approbation (Rousseau, 4). He believed that individuals were imprisoned in the values and ideals of society that the arts and sciences strengthened, whereby everyone followed and nobody dared to be prompted by their inner selves in order not be seen as outcasts, resulting in man losing his individuality. In a nutshell, Rousseau believed that the arts and sciences had tainted origins and they reinforced our crimes by fostering our desire for comfort by transforming individuals into sugar coated pills, whereby â€Å"jealousy, suspicion, fear, coldness, reserve, hate and fraud lie constantly concealed under the uniform and deceitful veil of politeness† (Rousseau, 7). He in turn pictured a society were he believed man was innately pious was not restrained by society’s decorum therefore abandoning the possibilities o the vices that evolve in modern societies are nonexistent. He understood virtue in terms of bravery, courage and strength in other words he saw it in raw military power. The weaknesses in Rousseau’s painting of the ideal society are the assumptions that are embedded in the question that he was addressing – â€Å"Whether the restoration of the arts and sciences has had the effect of purifying or corrupting morals?† Rousseau has to assume that there has been a revival in the arts as well as assume a relationship between abstract and applied knowledge with morality that being the human behavior and customs a society embraces. Such assumptions lead Rousseau to base his argument on a set of contradictions. He idealized the values of the Persians, Germans and Spartans who had an unusual social structure where there was no study of abstract education, no accumulation of property and military virtues were emphasized. The idealizations of such societies contradicted his resentment for etiquette or what he referred to as the â€Å"veil of politeness†, since there exists no organization whereby more discipline, etiquette or order to our â€Å"rude but natural† morals is required than military organizations. Throughout the discourse the theme of man becoming corrupt once he enters society and losing his individuality because they â€Å"all act the same under the same circumstances alike† (Rousseau, 6) is repeatedly emphasized. This argument in itself is self-defeating because if it is the grouping of people that induces people to conceal themselves and live among uncertainty, Rousseau’s ideal society would truly only function for isolated individuals since such a level of purity could not occur in the â€Å"natural† dynamics of human societies. When individuals interact, the views and ideals of others will indeed affect the way the individual will live his life, since it is part of human nature to conform to the rules and regulations of others, which are a collection of ideals and values that compromise the principles of society. For a society to function in harmony there has to be some common ground whereby all the different members of that society must conform to and must sacrifice some of their individual ideals for the betterment of the society. Rousseau argues that man would not have to sacrifice his own ideals if he was not placed in the blasphemies of modern societies since he assumes humans are sincerely good and everyone would approve of the actions of others. This in itself breaks Rousseau’s argument since there is exists no yardstick to measure good and even if there were to exist such a measure, differences on which â€Å"good† is appropriate would in turn cause conflicts. The simplicity of the society Rousseau describes is its initial strength; the simpler ones life, the palette on which he is to express his bad perspectives becomes less like the â€Å"American savages†¦who live entirely on the products of the chase†¦[and] yoke, indeed, [cannot] be imposed on men who stand in need of nothing† (Rousseau,5). In a society where the needs do not exceed the basic physiological, safety and social needs and are readily satisfied the room for corruption becomes minimal. Therefore, I believe Rousseau’s attack on the arts and sciences is not so much on their origins or sources but more so on how it manages to widen our needs to include self-actualization and self-realization needs, which are needs that are satisfied by luxuries and how we appear in relation to the people surrounding us; a need where the veil and corruption required to have those needs satisfied. Rousseau’s painting of such an ideal society would not require a political system, however if all his assumptions were suspended the political implications would be drastic. In politics rarely is something said literally – and in a society where the members innately believe that everyone is sincerely good, would not be capable of reading between the lines and would end up in turmoil since other nations would manipulate their naivety. Furthermore, in a society where abstract knowledge such a geometry and economics is not taught the politicians will be incapable of drawing upon actions that will be favour their society, since politics is the evil of all sciences and without a good base in its basic terminology that being the abstract sciences one will be incapable of mastering it and using it to his advantage. Speak from their heart†¦Ã¢â‚¬ ¦Ã¢â‚¬ ¦offend someone†¦Ã¢â‚¬ ¦.do not take care In Antigone the Greek tragedy, morals, egos, and gender issues were the epics around which principles were based upon. Follow one man Harun Al Rashid†¦Ã¢â‚¬ ¦..Mamluks†¦Ã¢â‚¬ ¦..they use to be all loyal Lower class has less say in the political era in order to stop the formation of proletariats which is so important for the revolution to occur. Political laws that protect private property Enhance competitiveness (p.21) Dependence of poor countries on rich ([.23) Eradicate opposition immediately Strength of prletarits p.28 trade unions p.32 existence remains on capital 1) Basecaus they lay down ideals that seem utopian only to them, they forget 2) Might have noticed that there are more cons than pros Several of our texts paint images of ideal human society. Discuss the strengths and weaknesses of these imagined societies. How do these imagined ideal societies interact with political ideology and political action. Bibliography Marx, Karl and Friedrich Engels. The Communist Manifesto. New York: Bantam, 1992. Sophocles. The Three Theban Plays Antigone, Oedipus The King, Oedipus at Colonus. Trans. Robert Fagles. New York: Penguin, 1977. Communism Could Never work Because it goes against human nature. People are naturally more competitive than cooperative. http://www.wsu.edu/~brians/hum_303/nature.html

Mongols

In various times Mongols have been equated with the Scythians, the Magog and the Turkic peoples. Based on Chinese historical texts the ancestry of the Mongol peoples can be traced back to the Donghu, a nomadic confederation occupying eastern Mongolia and Manchuria. The identity of the Xiongnu is still debated today. Although some scholars maintain that they were proto-Mongols, the fact that Chinese histories trace certain Turkic tribes from the Xiongnu complicates the issue. 10] The Donghu, however, can be much more easily labeled proto-Mongol since the Chinese histories trace only Mongolic tribes and kingdoms (Xianbei and Wuhuan peoples) from them, although some historical texts claim a mixed Xiongnu-Donghu ancestry for some tribes (e. g. the Khitan). [11] The Donghu are mentioned by Sima Qian as already existing in Inner Mongolia north of the state of Yan in 699-632 BC. Mentions in the Lost Book of Zhou (Yizhoushu) and the Shanhaijing indicate the Donghu were also active during the Shang dynasty (1600–1046 BC).The Mongolic-speaking Xianbei formed part of the Donghu confederation, but had earlier times of independence, as evidenced by a mention in the Guoyu (â€Å" † section) which states that during the reign of King Cheng of Zhou (reigned 1042–1021 BC) the Xianbei came to participate at a meeting of Zhou subject-lords at Qiyang ( ) (now Qishan County) but were only allowed to perform the fire ceremony under the supervision of Chu (? ), since they were not vassals by covenant ( ).The Xianbei chieftain was appointed joint guardian of the ritual torch along with Xiong Yi. These early Xianbei came from the nearby Zhukaigou culture (2200-1500BC) in the Ordos Desert where maternal DNA corresponds to Mongolic Daurs and Evenks (Tungusified Xianbei). The Zhukaigou Xianbei (part of the Ordos culture of Inner Mongolia and northern Shaanxi) had trade relations with the Shang dynasty (1600-1046BC). The Zhou clan lived near the Beidi (who included the Xianbei) for 14 generations before moving to the Central Plains in middle Shaanxi under Gugong Danfu).Another closely connected core Mongolic Xianbei region was the Upper Xiajiadian culture (1000-600 BC) where the Donghu confederation was centered. After the Donghu were defeated by Modu Chanyu the Xianbei and Wuhuan survived as the main remnants of the confederation. Tadun Khan of the Wuhuan (died 207 AD) was the ancestor of the proto-Mongolic Kumo Xi. [12] In 49 AD the Mongolic Xianbei ruler Bianhe (Bayan Khan? ) raided and defeated the Xiongnu, killing 2000, after having received generous gifts from Emperor Guangwu of Han.The Xianbei reached their peak under Tanshihuai Khan (reigned 156-181) who expanded the vast, but short lived, Xianbei state. Xianbei Empire under Tanshihuai (141-181) Three prominent proto-Mongol groups split from the Xianbei, as recorded by the Chinese histories: the Nirun (claimed by some to be the Avars), the Khitan and the Shiwei (a sub-tribe called the â⠂¬Å"Shiwei Menggu† is held to be the origin of the Genghisid Mongols). [13] Besides these three Xianbei groups, there were other Xianbei groups with Mongolic affiliation such as the Murong, Duan and Tuoba.Their culture was nomadic, their religion Shamanism or Buddhism and their military strength formidable. There is still no direct evidence that the Nirun spoke a Mongolic language, although most scholars agree that they were proto-Mongolic. [14] The Khitan, however, had two scripts of their own and many Mongolic words are found in their half-deciphered writings that are usually found with a parallel Chinese text (for example, nair=sun, sair=moon, tau=five, jau=hundred, m. r=horse, im. a=goat, n. q=dog, m. ng=silver, ju. un=summer, n. m. ur=autumn, u. ul=winter, heu. ur=spring, tau. l. a=rabbit, t. q. a=hen and m. g. o=snake). [15] There is no doubt regarding the Khitan being proto-Mongol. [16] Asia in 500 AD, showing the Nirun (Juan-Juan) Empire and its neighbors Geographicall y the Tuoba Xianbei ruled Inner Mongolia and northern China, the Nirun (Yujiulu Shelun was the first to use the title Khagan in 402) ruled Outer Mongolia, the Khitan were concentrated in Southern Manchuria north of Korea and the Shiwei were located to the north of the Khitan.These tribes and kingdoms were soon overshadowed by the rise of the Gok-Turks in 555, the Uyghurs in 745 and the Yenisei Kirghizs in 840. The Tuoba were eventually absorbed into China. The Rouran fled west from the Gok-Turks and either disappeared into obscurity or, as some say, invaded Europe as the Avars under their Khan Bayan I. Some Rouran under Tatar Khan migrated east founding the Tatar tribes, who became part of the Shiwei. The Khitan, who were independent after their separation from the proto-Mongol Kumo Xi (ofWuhuan origin) in 388 AD, continued as a minor power in Manchuria until one of them, Abaoji (872-926), established the Khitan Liao Dynasty (907-1125). The Khitan fled west after their defeat by the Tungusic Jurchens (later known as Manchus) and founded the Kara-Khitan or Western Liao dynasty (1125–1218) in eastern Kazakhstan. In 1218 Genghis Khan destroyed the Kara-Khitan Kingdom after which the Khitan passed into obscurity. The modern-day minority of Mongolic-speaking Daurs in China are their direct descendants based on DNA evidence. [17][18] The Shiwei included a tribe called the Shiwei Menggu. 19] Bodonchar Munkhag (Chagatai tradition dates ‘Buzanjar Munqaq' to the rebellion of Abu Muslim or 747 AD. [20]) the founder of the House of Borjigin and the ancestor of Genghis Khan is held to be descended from the Shiwei Menggu. The early Shiwei paid tribute to the Tuoba Wei (386-534) and submitted to the Khitans. After the Khitans left Mongolia the Shiwei Mongols rose to prominence, when from the 1130s there were reciprocally hostile relations between the successive khans of the Khamag Mongol confederation (Khaidu, Khabul Khan and Ambaghai Khan) and the emperors of t he Jin dynasty.With the expansion of the Mongol Empire, the Mongols settled over almost all Eurasia and carried on military campaigns from the Adriatic Sea to Java and from Japan to Palestine. Mongols simultaneously became Padishahs of Persia, Emperors of China, Great Khans of Mongolia and one Mongol even became Sultan of Egypt (Al-Adil Kitbugha). The Mongols of the Golden Horde established themselves to govern Russia by 1240. [21] By 1279, the Mongols conquered the Song Dynasty and brought all of China under control of the Mongol Yuan Dynasty. 21] With the breakup of the Empire, the dispersed Mongols quickly adopted the mostly Turkic cultures surrounding them and were assimilated, forming parts of Tatars (not confused with a tribe in ancient Mongolia), Uzbeks, Kazakhs, Yugurs and Moghuls; linguistic and cultural Persianization also began to be prominent in these territories. However, most of the Mongols returned to Mongolia, retaining their language and culture. After the fall of t he Yuan Dynasty in 1368 the Mongols established their independent regime as Northern Yuan.However, the Oirads or Western Mongols began to challenge the Eastern Mongols under the Borjigin monarchs in the late 14th century. Present-day Khalkha Mongols and Inner Mongolians are the most prominent of the remaining Eastern Mongols while the Kalmyks (formerly Oirats) in Europe are the main descendants of the Western Mongols. The Khalkha emerged during the reign of Dayan Khan (1464–1543) as one of the six tumens of the Eastern Mongols. They quickly became the dominant Mongol clan in Outer Mongolia.

Democracy Remixed

If we take a look at American History, we see that many African Americans before us accomplished many things, in various disciplines, such as become the surgeon general of the United States, Win an Olympic Gold medal, Become a President of an Ivy League University, become CEO of a Fortune 500 company or even become President of the United States. These and the others on the extensive list of African American Firsts did not come easy or were given. In the words of Cohen, â€Å"They had to work hard, be respectful, and always have your superior humanity on display for whites to observe. With more and more 1st being accomplished, it has become more possible for many African Americans to reach hose same positions or go further. Today, in the year 2014, we also have new problems to face in terms of this new technology. Black twitter, for example, is an unofficial title for a community on twitter that has a huge impact online and in the media. Whether there is a primetimes television show or some breaking news story, Black twitter has you covered. Seemingly as a voice for all black Americans, this is heavily skewed by its demographic.Consisting of mainly young adults, this community becomes very negative and often creates moral panic and suppresses ACH other in the black community. The post-racial thesis suggests that in the post- civil rights era, material conditions have improved for Black Americans, but the conditions Black Americans face today are markedly better than the conditions that earlier generations had faced. As one example of many pressures black youth are facing, this shows that material conditions may have increased but the pressures are still prevalent In Democracy Remixed: Black Youth and the future of American Politics, a book by Cathy J.Cohen, discusses about the political life of young black people, not emitted to their relationship with the state and or government but between their peers, other members of the black community and the larger soci ety. In relation to the post-racial thesis, this book contains arguments that serve as a counter to the post-racial thesis by discussing many issues that young black people face. In chapter 2, she introduces the phenomenon called moral panics and how they affect the black community, especially black youth.In chapter 5, she discusses forms of alienation that black youth face and how they engage in the public sphere, attempting to voice heir own public agenda. In chapter 6, she engages the ideas that young black people develop in light of the election of the country 1st black president and what this means to them. Chapter 2, â€Å"Gangs Rap Made Me do it†, talks about moral panics and how Bill Cowboys and Don Emus are examples of creating such things. Earlier on in the chapter, they discuses some statistics developed by The Black Youth Project.These statistics showed results from surveys filled out by African Americans ages 30 and above and group based on levels of income The t opics of the survey included Rap Music's perceived Influence on Black Youth, The behavior of too many young black Americans threatens to progress of respectable black people who are trying to do the right things, and reasons young black Americans find it hard to get ahead. These topics were surprisingly posed to non-youth about three topics that involve black youth in America.Many of these adults had an opinion on all of these questions, because of moral panics. Cohen states that moral panic is a concept typically used by scholars to explain irrational and inflated reactions to lesser events that have been exaggerated by the media. Through the media, the crisis itself is shrouded by the massive uproar generated by the public. Bill Cowboys, known for his comedic background, spoke at Constitution Hall in Washington, D. C. Where they were commemoration the 50th anniversary of Brown v. Board of Education.The topics that he received fire from were the ones directed to poor black people a nd the black youth. From Cowboys perspective he is trying to let it be know that everything black people do, is a representation of all black Americans. His comments toward poor members in the black community included â€Å"These people are not parenting. They are buying things for kids, $500 sneakers for what? And wont spend $200 dollars for ‘Hooked on Phonics. ‘ † Here we have an older African American who is removed a generation from those parents he are addressing.This alone shows that there is a problem with the consecutive generation. This also highlights that the generation of parents who are buying the kids expensive sneakers are more worried about looks that education. We can infer that the kids wanted the expensive sneakers because of social pressures to be wealth. Also, His comments on Black Youth culture is that the out of today are uneducated when it comes to knowing about their African American and their African culture.He makes remarks about how bla ck males are putting on clothes backwards and sagging of pants, and women wearing short skirts and piercing. This is another example of pressure that the youth are facing because Bill Cowboys is probably not the only person making these remarks. The pressures of previous generations in its self are making it hard for the young black American to live. She introduces the 21st century, the average youth has a lot of things to deal with. Bullying, growing up, peer pressure, family, school

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Addressing Libya's Past Injustices - Essay Example As demonstrated by Kyriakakis (2009, p. 333), the provisions of the ICC laws include prosecution of persons who have committed crimes against humanity. Furthermore, according to article 5 of the Rome Statute of the International Criminal Court (1998), the international tribunal has jurisdiction to crimes of genocide, aggression and war crimes. BBC News Africa (2011) reported the capture of Gaddafi's son Saif al-Islam with the new prime minister of Libya saying that Saif will get a fair trial in Libya. Because Saif is accused of ordering killings during the regime of his slain father Muammar Gaddafi, it is therefore appropriate that the Libyan authorities hand him to the ICC for trial. Additionally the BBC News Africa, (2011) shows that the chief prosecutor of the International criminal court, Luis Moreno Ocampo promises a fair trial for Saif if he is submitted to the international tribunal. Moreover, Article 7 of the Rome Statute of the International Criminal Court (1998) provides ju risdiction of the court to the crimes of murder and torture which are parallel to the allegations against Saif al-Islam. According to Kyriakakis (2009, p. 336), the universality principle of the International Criminal Court as provided by the international law gives the ICC criminal jurisdiction regardless of country or nationality. Therefore despite the fact that Libya was opposed to the Rome treaty, the allegation that the ICC cannot claim jurisdiction of crimes committed outside the boundaries of the Rome treaty cannot prevent it from prosecuting people who commit crimes against humanity. However, the assertion of the new prime minister of Libya that Saif will be tried locally is not based on ICC jurisdiction. As a result, the ICC should provide the court trial for the Libyan leader. The ICC upholds human rights through its laws and its role is to protect the dignity of people through prosecution and punishment of individuals who commit dehumanizing crimes. The ICC claims that Sa if Gaddafi who was presumed to be the successor of his father played a leading role in organizing the killing of Libyan civilians as explained by the Asian News Monitor (2011). This amounts to genocide, which according to the laws of the ICC gives the international tribunal a mandate to prosecute Saif Gaddafi. Moreover, there could be political influence in local hearings of the Saif case, which could compromise the achievement of a fair trial. It should be noted that the ICC must have evidence to support its accusations against the Libyan leader before he is convicted of the alleged crimes. The arrest of Saif al-Islam by the militia force which is allied to NTC should therefore present the leader to the ICC to warrant the beginning of investigation by the international tribunal. This is because the ICC is described by the BBC News Africa (2011) as having reasons to belief that Saif al-Islam was involved in the alleged crimes through evidence material. Further investigation by the c ourt will back the current evidence of the crimes committed by the leader. Moreover, the trial at ICC is more likely to be unbiased and objective as compared to a local tribunal in Libya. Further support for the ICC hearing of the Saif case is demonstrated by the fact that the laws of the ICC provide for confirmation hearings before the actual court cases are heard. This means that if the arrested leader is submitted to the ICC, the international tribunal will thoroughly evaluate the prosecutor’s evidence to pave way for a fair trial. Trial will only occur if the evidence against the Libyan arrested leader meets the minimum threshold of crime beyond which ICC jurisdiction is justified. The need for an ICC trial for Saif al-Islam is

Reflective Questions Essay Example | Topics and Well Written Essays - 250 words

Reflective Questions - Essay Example how to use the camera in a professional way, how to film from different angle, how to avoid the camera shaking, how the lighting is important in the film process Etc. I enhanced this skill when we initialized our project and we put the outline, then we made the plan which we going to stick on, we organized the work and we divided the parts between our team members then we start doing our project based on that. We discovered later on that we should use just one voice instead of two voices in the narration because our subject was about sentence fluency. Moreover, when we divide our 10 min video after we found out that it would infects the audience bored. Honestly, I was not sure about our project subject (sentence fluency) in the beginning. You required an instructional video and this subject was teaching a grammar. Letter on I found that convert this subject to instructional video would be a challenge for me. Therefore, I decided to learn about sentence fluency and I face many problems because I am international student. I tried to beat this, I give all I have to present my work in great way, and I hope that what I did. My ability to persuasion other people improved. Once we were filming six volunteers and after we done we found that the camera was shaking. So I went to the writing center and I persuaded the 6 volunteers to re-film them again and I did that by show them the importance of the work we do and the importance of their role for the completion of this work. They agree and I did the re-filming process alone again. In addition, I persuaded ESL students to be filmed by explaining to them sentence fluency meaning and give them some advices so they can improve their writing skill. They agree and it was great experience and I am sure that my ability to communicate and persuasion others improved. How many hours have you spent on your project? Were there times when you worked long hours without noticing the passing of time? Give a number

Tropical rain forest Research Paper Example | Topics and Well Written Essays - 1250 words

Tropical rain forest - Research Paper Example Tropical rain forest Tropical rain forests are categorized into three: the monsoon, equatorial rain forests and the subtropical rainforests. They are characterized by very tall trees of different kinds and produce 40% of Earth’s oxygen. The trees form canopies which provide shelter to the plants and animals from the sun. Tropical rain forests host more than half of the estimated 10 million species of plants, animals and insects (Terashima, 49). The vegetation is ever green. The dominant species in the rain forests are plants, animals and insects. Location According to Newman (The Tropical rainforest), tropical rain forests are found on the earth’s surface between the tropic of cancer in the North and the tropical of cancer in the south around 23.5 degrees north and south of the equator. Areas around the equator receive a constant amount of sunlight and rainfall which favours the growth of rainforest. Tropical rain forests are mainly found in central and South America, South East Asia and is lands near it and in West Africa. The largest tropical rainforest across the globe is the Amazon rainforest. Climate According to Terashima (52), ecosystem is usually very wet with the total rainfall between 1500 and 2500 mm per year. Most of the rains stays on the rain forest, evaporates, cools to form clouds and fall again. The rainforest soils are infertile since the nutrients are washed away by the rains. There are usually no dry seasons and the day temperatures are around 30-35 Degree Celsius (Terborgh, The midday sun is always near the vertical and is overhead twice a year at the equinoxes. This means there is more direct sunlight hitting the ground and the sea and much water evaporates into the air (Newman, 2002). At night the temperatures range between 20-25 degrees Celsius. Little difference exists between the warmest and coolest months. Tropical rainforests have a high humidity and the type of climate is known as the equatorial climate. Tropical rainforest climate is found at latitudes within five degrees North and South of the equator. The high humidity is due to the warm sunlight, rainfall and the tree canopies which help retain the moisture. Major interactions Among the Organisms that live in the Tropical rain forests Competition According to University of Michigan (The Tropical Rainforest) there is a wide diversity of animals in the tropical rain forests. The tropical birds such as Costa Rica, parrots, macaws and hornbills eat fruits, nuts insects, seeds and nectar. Monkeys such as gorilla and the Lar gibbon feed on leaves, fruits, leaves and bark while the orang-utan and spider monkey feed on leaves fruits, nuts, seeds and insects. Also in Whitemore (195), spiders which live on the canopies eat fruits and leaves hence competing with the birds and some mammal for food in the ecosystem. Both the birds, monkeys and spiders compete for the same food in the ecosystem. Predation The bats also prey on frogs which also prey on insects. Jaguar feeds on r odents and frogs the bats and the jaguar are the predators whereas the frogs and other rodents are the prey. Snakes which are also predators feed on other rodents (Terborgh, 121). Predators use poison, camouflage and strength to kill their prey. Man is another predator whose prey is edible animals and plants. Men use the animals and plant

Education Assignment 1 Example | Topics and Well Written Essays - 1250 words

Education 1 - Assignment Example The majorities of the schools have deserted conventional means of exchange of ideas and made to order techniques that are based on knowledge and technology. Nearly every one of the schools has made use of network based exchange of ideas systems. In these circumstances, the schools make use of computers and sets of connections to be in touch with families. The schools also use constituency web sites to be linked with families and other citizens (Kowalski, 2010). In addition, the schools have employed electronic newsletters to help improve communication with other people in the society. Like other schools, my school uses different types of technologies to communicate with families. First, the school uses district web sites to communicate with families (Kowalski, 2010). The district administrators have developed a wide range of web sites that schools and families can use to interact. The schools post information on the websites and then the families access the information. The websites have been created well to let families and society members browse the sites. In addition, the sites make available areas where the families can mail their commentary. With the exception of using websites, the school makes use of electronic newsletters to make a statement with them. The school managers and administrators send electronic messages to parents. The school makes cards which are forwarded to parents. The techniques mentioned have been successful as indicated by good association between the school and parents. The school has been capable to work mutually with the parents to make better learners’ performance and the general presentation of the education (Kowalski, 2010). Computer technology associations are significant to schools and regions as they assist in making accurate announcement to parents and the society. Schools require directing the produce, media outlets and electronic messages so as to advertisement positive relationships. Technology association procedur e assists schools in the progress of their technology associations and improves their association with people and parents. Majority of the schools have not adopted good technology associations and this has interfered with communication with parents and society. Schools can make use of different methods to better their media associations and the school system (Kowalski, 2010). The specialized discipline of planned public associations offers a lot of remuneration to organizations. It assists them avoid and alleviate crises. Additionally, it also permits them to recognize and direct issues that may get in the way with their goals. It also allows them in structuring and maintaining quality associations with planned societies. 3. School administrators ought to encourage exposed announcement so as to be capable of developing constructive relations and improving partnerships. Most of the education centers are not capable to uphold open exchange of ideas, and this affects media relationship deficiently. The administrators of these schools should hold up free communication so as to develop high-quality relationship with press journalists (Kowalski, 2010). The managers and administrators of the schools should support empowerment. They must approve the press personnel and extra people involved. Through motivating the press, human resources and other community members assist in easing the association betwe

Professional Application Essay Example | Topics and Well Written Essays - 2250 words

Professional Application - Essay Example Some of the best practice and ideas are looked into and the essential settlement of ideas is brought to the fore. A variety of communication objectives are provided. The research also analyzes the targeted market audience. In a nutshell the research paper in depth talks about the marketing strategies that could be employed by the Steve Marden footwear company that aims to break the barriers in its line of business and enjoy a more market base unlike its rivals. Introduction Marketing communication involves bringing the products of a firm to the market and creating awareness that the product exists. It also involves other relevant information by the suppliers to the consumers that could be improvements on quality or branding. Marketing communication consists of the place, price promotion and the product. Methods and techniques of promotion differ with the product and the number of people targeted. It considers the types or groups of people the advertisement is reaching out to, their a ge gap, the kind of media they are most likely to come into contact with most of the time. Steve Marden limited which is a recognized footwear brand aims to make use of the integrated marketing campaign technique so as to rise above their competitors and to also maximize their sales and realize better revenue. One of the most common issues that affect product marketing is the message relay technique. This is an Achilles heel in the Steve Marden limited company. Once a technical team is tasked with the aim of marketing a product, they have to give it an appealing marketing message that will bring out the curiosity effect amongst the targeted market. Here are a number of the technical techniques employed by the marketing team. Steve Marden Limited is aiming to break the barriers in terms of marketing its footwear products. It first needs to re-strategize the marketing department of the company so as to bring in the people who will drive the sales of the company upwards. The marketing team will need to come up with a theme or logo that defines Steve Marden Limited and defines the company amongst its competitors. These is a major step in allowing Steve Marden Limited to be the major footwear brand it aims to be. Brochures hold a lot of information that needs to be passed onto the targeted audience, and also they are easy to fold and pass around. Many can be created at the same time and provide for large coverage without being bulky. Direct mailing gives promotion a sense of personal touch. Mail can also be customized for different people accordingly so as to meet their needs and motivate them. Newsletters contain useful organizational information that needs to be communicated appropriately. Posters and bulletins as well provide a means to reach consumers. However they are often not paid attention and are effective when you place them strategically where the customers are likely to see and notice them. Posters should also be kept neat and made attractive to be noti ced. Social networks that involve discussion groups are effective methods of promoting and advertising products. The social network is cheap to operate with and very fast media. It would involve sites like Facebook alongside company blogs and websites. (Belch & Belch, 2012) Television can sometimes be quite expensive; however, it is a very effective medium as it reaches a very extensive population and grows in popularity with time. Radio on the other hand is also an effective tool of advertisement as it reaches a good population. Even so,

Zha Scapegoat Assignment Example | Topics and Well Written Essays - 2500 words

Zha Scapegoat - Assignment Example ReneÃŒ  Girard’s theory of scapegoat is a theory based on the origins of sacrifice. The theory advocates that historical collective murders arise at the commencement of primitive ritual sacrifice. Rituals and myths memorize and disguise these distressing, violent origins (Girard 92). A fundamental concept in the thought of Girard is that of contagion. Markedly, both the mythic falsification of collective murder and contagious transfer are well illustrated in Girard’s scrutiny of the symbol of Oedipus. According to ReneÃŒ  Girard, the attribution of evil and crime to an innocent individual is neither motiveless nor arbitrary, but is a reaction to the actual social risk. However, in the collective murder, the instantaneous cause is the breakdown of the social order. The breakage is provoked by famine, war, plague, or any other major social disaster. During this situation, every person turn out to be the enemy of all: the rich against the poor, neighbour against neighbour, brother against brother. According to ReneÃŒ  Girard the scapegoat comes in as a safety value in the condition of spiralling violence whereby every person resorts to retribution so as to attain what is rightfully theirs. The conflict of all against all, the violence that looms to pouch t he community, is revolutionized to a war against one person. ReneÃŒ  Girard denotes that with the death of the scapegoat, the violence cycle ends. The title of the film ‘The Wrong Man’ recognizes one of the main persistent themes in Hitchcock’s work that is the theme of the innocent man or the mistakenly accused. The film tells a story of the erratic arrest and incarceration of Balestrero. This occurred after he was wrongly identified as the thief of an insurance company office aside from other several stores. The basis of the film is on a true story, the factual life case of Christopher Balestrero. As evident

Use of Ace Inhibitors for Treatment of Hypertension Essay Example for Free

Use of Ace Inhibitors for Treatment of Hypertension Essay The prevalence of hypertension globally has sparked much research on medications and ways to cure it. Although there are varieties of medications available in the market to control hypertension, there are still none that can actually cure it. Until the time a drug to cure hypertension emerges, hypertension will be controlled by the use of antihypertensive drugs. Among the few well known classes of antihypertensive drugs is a group of angiotensin converting enzyme inhibitors or ACE inhibitors. ACE inhibitors are a fairly recent addition to the antihypertensive drug class and have been widely used since then due to its many potential benefits. ACE inhibitors are indicated for many conditions which include hypertension, prevention and treatment of cardiovascular disorders, and prevention of nephropathy in diabetes mellitus. When used in hypertension, it is done so in combination with diuretics with fairly good results. (Merck, 2003)   Ã‚  Ã‚  Ã‚  Ã‚   The use of ACE inhibitors is especially useful for congestive heart failure patients. Therefore, it is indicated in cases where hypertension exists in correlation with congestive heart failure. There has been a significant decrease in the overall morbidity and mortality rates of patients suffering from both the conditions when using ACE inhibitors.   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   The mode of action of these drugs is many fold, and for that reason very effective in the treatment of hypertension. For instance, it acts on the vascular system to reduce vascular pressure, which allows for less arterial pressure, combined with more venous capacity, thus immediately reducing the blood pressure. Alongside, it increases cardiac output and cardiac index and stroke volume. The main function of the ACE inhibitors, however, is the inhibition of the ACE enzyme, which is responsible for increased vascular pressure, ventricular remodeling, production of aldosterone and vasopressin respectively. (Katzung, 2004)   Ã‚  Ã‚  Ã‚  Ã‚   Such drugs however, require careful dosage regimes based on extensive studying of the case, as there are many side effects associated with these drugs. The most common of these include hypotension, due to the vasodilator effect of the drugs.(Merck, 2003)   The second most common problem is the development of persistent cough in such patients, which leads to reduction in patient compliance. The bid and tid dosage regimes also reduce the patients’ compliance. Due to its renal effects, ACE inhibitors must be used carefully in cases where damage to the kidney is expected or the kidneys are functionally impaired. For example, in patients with renal artery stenosis, the use of these drugs can lead to renal impairment. The prevention of release of aldosterone caused by these drugs impairs excretion of potassium in the body, which can lead to hyperkalemia. Increased levels can also lead to the development of angioedema, which can be life threatening. ACE inhibitors are also contraindicated in patients who are pregnant as it is teratogenic in nature. (Kaplan and Rose, 2007)   Ã‚  Ã‚  Ã‚   Due to the mode of activity of these drugs, the ACE inhibitors become contraindicated in cases of history of angioedemas or renal artery stenosis, compromised renal functioning capacities, aortic valve stenosis and in patients suffering from hypovolumia. (Klabunde, 2007)   Ã‚  Ã‚  Ã‚  Ã‚   Many drugs now belong to this category, however, the paper will discuss three of these, captopril, enalapril and lisinopril.   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   Captopril main mode of action lies in the suppression of the renin-angiotensin-aldosterone system. By inhibiting the ACE inhibitor, angiotensin I is prevented from converting into angiotensin II.   Captopril enjoys universal attention due to the fact that it is the first ACE inhibitor introduced. Its mode of action and its effect were considered a breakthrough at the time of its conception. Its action is two fold. Firstly, it helps in dilating the vessels, thereby helping reduce blood pressure. Secondly, it has shown very good performance in the cases of myocardial infarction and congestive heart failure. And thirdly, it has shown good results in the prevention of diabetic nephropathy. (www.rxlist.com)   Ã‚  Ã‚  Ã‚   There is very little difference in the working of all the ACE drugs, however, captopril differs in this respect due to its shorter duration of action and increased chances of adverse effects.   This intensity of side effects potentiated further research, the result of which was the introduction of enalapril in the market, and still further drugs subsequently. Regardless of the drug, the ACE inhibitors generally take several weeks of administration to give full effectiveness and results. When used with thiazide diuretics, the results achieved are even more.(Merck, 2003)   Ã‚  Ã‚  Ã‚   Captopril is administered one hour before meals to achieve maximum peak volume concentration, which is reached within an hour of ingestion of drug. Initial dosage may be as low as 25 mg bid or tid, and gradually can be increased to double dose bid or tid. The addition of thiazide diuretics is usually carried out when using captopril alone at 50 mg alone does not sufficiently control blood pressure.(Katzung, 2004) This range can be increased to 150 mg per day, provided the use of a thiazide diuretic is also carried out. The administration of drug results in the lowering of blood pressure within one hour. Renal blood flow is increased; however, the GFR remains unchanged. When used with digitalis, captopril shows good efficacy in the treatment of congestive heart failure. Its use has been very favorable in patients who had previously suffered from myocardial infarction, or those with left ventricular dysfunction. In case of LVD and CHF or MI, the usual starting dose is 50 mg target dose. (Kaplan and Rose, 2007)   Ã‚  Ã‚     Captopril has shown to increase the risk of developing neutropenia and agranulocytosis and therefore, full blood picture is mandatory for patients using captopril for a prolonged period. Also, since mode of elimination from the body is through the kidneys, the use of captopril becomes contraindicated or at least under observation in cases of renal impairment or dysfunction. (Katzung, 2004)   Ã‚  Ã‚  Ã‚  Ã‚   Enalapril is the second drug introduced in the ACE inhibitor series. The main reason for its production was to eliminate the problems seen with the use of captopril. As in captopril, the drug utilizes the renin-angiotensin-aldosterone system. Production of enalapril involved changing the molecular constitution of captopril, and therefore, the final result was the first dicarboxylate- containing ACE inhibitor, or enalaprilat. However, this modification limited the use of this drug as intravenous injection only. Further modifications in this structure led to the oral form by the name enalapril. (www.rxlist.com)   Ã‚  Ã‚  Ã‚   Enalapril works by converting itself through hydrolysis into enalaprilat in the body. Enalaprilat then inhibits the ACE enzyme. The peak serum levels are reached within an hour of administration of the drug. As opposed to captopril, enalapril absorption is independent of gastric contents; rather it is dependant on the urinary recovery. In hypertensive patients, the dosage of enalapril results in both supine and standing but not orthostatic hypotension. This effect is not seen in case of captopril. The antihypertensive activity becomes visible within one hour of administration of the drug. This effect then remains for around 24 hours. Similar to captopril, enalapril shows improved hypertensive control when administered with a thiazide diuretic. it is also indicated for cases suffering from heart failure, and asymptomatic left ventricular dysfunction. (Kaplan and Rose, 2007)   Ã‚  Ã‚  Ã‚  Ã‚   Unlike captopril, which can be administered simultaneously with a preceding diuretic, enalapril can only be started after cessation of the diuretic after two to three days. This is essential to minimize the risk of developing hypotension. If this is not possible a test dose of 2.5 mg is given for at least two hours under observation, and the drug administered accordingly. The usual dosage regime may vary from 10 to 40 mg per day, and that is if the patient is not on a diuretic. Dose adjustment becomes necessary for patients who have impaired renal function, which may require reduction of the dose to almost half of the average 5 mg. this dosage is amenable to changes based on the blood pressure response seen. (www.rxlist.com)   Ã‚  Ã‚  Ã‚  Ã‚   Enalapril is highly favored over captopril as it has lesser side effects than its predecessor. It has a well toleration response, and the adverse effects are very mild in nature. Patients may complain of fatigue, asthenia, diarrhea and nausea, headache and dizziness, cough and skin rash. These symptoms can be present with varying degrees according to the reason why the drug is being administered. For example in heart cases, it can also lead to syncope symptoms and some differences in the special sensory perceptions. Angioedema is perhaps the most serious side effect of enalapril, with severity seen more in blacks than in non-black populations. This can be very fatal should laryngeal angioedema ensue. Initial doses can lead to fall of blood pressure and hypotension, which must be monitored very closely. Hyperkalemia, increase in blood urea nitrogen and serum creatinin levels, and decrease in hematocrit and hemoglobin can also be seen. Liver enzymes can also become elevated. (Merck manual, 2003)   Ã‚  Ã‚  Ã‚  Ã‚   The effects of enalapril were much improved and effective with lesser side effects when compared to captopril, however, the speed of effect was still high in the case of captopril. The third drug to get introduced in the series of ACE inhibitors became lisinopril. The drug was important as it was the first hydrophilic ACE inhibitor introduces, with longer half life and penetration in the tissue. The drug remains the same even after excretion from the body, and is indicated for all the conditions mentioned above for which ACE inhibitors are introduced. While captopril and enalapril were made for bid and tid dosages, lisinopril, due to its longer half life, is generally administered once a day, helping aid patient compliance.   Ã‚  Ã‚  Ã‚  Ã‚   The mode of action is similar to its sister drugs, that is the drug acts by inhibiting the ACE enzyme. The peak serum concentration of this drug however, is reached after 7 hours, compared to one hour of both captopril and enalapril. When used for hypertension, it results in the reduction of both standing and supine hypertension, with â€Å"no compensatory tachycardia†(Rx list, 2007)   Ã‚  Ã‚  Ã‚  Ã‚   The dosage of lisinopril is given according to the drug history of the patient. Patients with no use of diuretics are given 10 mg per day as initial dose. This can be increased from 20 to 40 mg as the case may need. In diuretic using patients, the protocol for the administration of lisinopril is the same as for enalapril. The diuretic is stopped two to three days prior to the administration of lisinopril, and observed for signs of hypotension. Dosage is then adjusted according to the body response of the patient. This drug should not be given along with any potassium supplements as it can lead to hyperkalemia. Renal status similarly, addresses the dosage of the drug, with 10 mg as standard for normal kidney function, 5 mg for moderate to severe renal impairment, and 2.5 mg or so for dialysis patients after proper observation and blood pressure response. (Klabubde, 2007)   Ã‚  Ã‚  Ã‚   Side effects of lisinopril are not so different from the side effects seen in the case of enalapril and captopril. However, cough becomes the primary side effect of this drug along with fatigue and asthenia etc. In all cases of ACE inhibitors, the side effects must be monitored closely and managed accordingly should the need arise. (ACE Inhibitors, 2004)   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   In conclusion, the introduction of ACE inhibitors has been a welcome addition in the antihypertensive drug family and is now used widely due to its excellent prognosis in patients with concurrent heart conditions. Its use with thiazide diuretics has been widely documented and further studies will help in the introduction of much improved brands of ACE inhibitors. References ACE inhibitor drugs. Site last accessed on August 5, 2007 from www.rxlist.com ACE inhibitors, 2004. Site last accessed on August 5, 2007 from http://www.chfpatients.com/ace_old.htm Norman A Kaplan and Burton D Rose, 2007. ACE inhibitors in the Treatment of Hypertension. Site last accessed on August 5, 2007 from http://patients.uptodate.com/topic.asp?file=hyperten/10107#1 Richard E. Klabunde, 2007. Angiotensin Converting Enzyme Inhibitors. Site last accessed on August 5, 2007 from http://cvpharmacology.com/vasodilator/ACE.htm Bertram G. Katzung, 2004. Basic and Clinical Pharmacology, ninth edition. The Merck Manual of Medical Information. Second Home Edition. Section III, Heart and Blood Vessel Disorders.

High Performance Wireless Telecommunications Modulation

High Performance Wireless Telecommunications Modulation Introduction The primary goal of the project is to analyze of OFDM system and to assess the suitability of OFDM as a modulation technique for wireless communications. In the part of project is covered two leading successfully implementation of OFDM based technologies are Digital Video Broadcasting (DVB-T and DVB-H) and Long Term Evolution (LTE advanced for 4G). Wireless communications is an emerging field, which has seen enormous growth in the last several years. The huge uptake rate of mobile phone technology, Wireless Local Area Networks (WLAN) and the exponential growth of the Internet have resulted in an increased demand for new methods of obtaining high capacity wireless networks. For cellular mobile applications, we will see in the near future a complete convergence of mobile phone technology, computing, Internet access, and potentially many multimedia applications such as video and high quality audio. In fact, some may argue that this convergence has already largely occurred, with the advent of being able to send and receive data using a notebook computer and a mobile phone. The goal of third and fourth generation mobile networks is to provide users with a high data rate, and to provide a wider range of services, such as voice communications, videophones, and high speed Internet access. The higher data rate of future mobile networks will be achieved by increasing the amount of spectrum allocated to the service and by improvements in the spectral efficiency. OFDM is a potential candidate for the physical layer of fourth generation mobile systems. Basic Principles of OFDM OFDM overview The Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique where multiple low data rate carriers are combined by a transmitter to form a composite high data rate transmission. The first commercial use of OFDM in the communication field was in the 1980s, and it was later widely used in the broadcast audio and video field in the 1990s in such areas as, ADSL, VHDSL, ETSI standard digital audio broadcast (DAB), digital video broadcast (DVB), and high-definition digital TV (HDTV). Digital signal processing makes OFDM possible. To implement the multiple carrier scheme using a bank of parallel modulators would not be very efficient in analog hardware. However, in the digital domain, multi-carrier modulation can be done efficiently with currently available DSP hardware and software. Not only can it be done, but it can also be made very flexible and programmable. This allows OFDM to make maximum use of available bandwidth and to be able to adapt to changing system requirements. Figure 1 is illustrated, Instead of separate modulators; the outgoing waveform is created by executing a high-speed inverse DFT on a set of time-samples of the transmitted data (post modulation). The output of the DFT can be directly modulated onto the outgoing carrier, without requiring any other components. Each carrier in an OFDM system is a sinusoid with a frequency that is an integer multiple of a base or fundamental sinusoid frequency. Therefore, each carrier is like a Fourier series component of the composite signal. In fact, it will be shown later that an OFDM signal is created in the frequency domain, and then transformed into the time domain via the Discrete Fourier Transform (DFT). Two periodic signals are orthogonal when the integral of their product, over one period, is equal to zero. This is true of certain sinusoids as illustrated in Equation 1. Definition of Orthogonal The carriers of an OFDM system are sinusoids that meet this requirement because each one is a multiple of a fundamental frequency. Each one has an integer number of cycles in the fundamental period. [2, 145-153; 6] The importantance of being orthogonal The main concept in OFDM is orthogonality of the sub-carriers.Since the carriers are all sine/cosine wave, we know that area under one period of a sine or a cosine wave is zero. Lets take a sine wave of frequency m and multiply it by a sinusoid (sine or a cosine) of a frequency n, where both m and n are integers. The integral or the area under this product is given by These two components are each a sinusoid, so the integral is equal to zero over one period. When we multiply a sinusoid of frequency n by a sinusoid of frequency m/n the area under the product is zero. In general for all integers n and m , sin(mx), cos(mx), cos(nx) , sin(nx) are all orthogonal to each other. These frequencies are called harmonics. Making the subcarriers mathematically orthogonal was a breakthrough for OFDM because it enables OFDM receivers to separate the subcarriers via an FFT and eliminate the guard bands. As figure 3 shows, OFDM subcarriers can overlap to make full use of the spectrum, but at the peak of each subcarrier spectrum, the power in all the other subcarriers is zero. OFDM therefore offers higher data capacity in a given spectrum while allowing a simpler system design. Creating orthogonal subcarriers in the transmitter is easy using an inverse FFT. To ensure that this orthogonality is maintained at the receiver (so that the subcarriers are not misaligned), the system must keep the transmitter and receiver clocks closely synchronizedwithin 2 parts per million in 802.11a systems. The 802.11a standard therefore dedicates four of its 52 subcarriers as pilots that enable phase-lock loops in the receiver to track the phase and frequency of the incoming signal. The 802.11a standard therefore dedicates four of its 52 subcarriers as pilots that enable phase-lock loops in the receiver to track the phase and frequency of the incoming signal. This method also eliminates low-frequency phase noise.Separating the subcarriers via an FFT require about an order of magnitude fewer multiply-accumulate operations than individually filtering each carrier. In general, an FFT implementation is much simpler than the RAKE receivers used for CDMA and the decision-feedback equalizers for TDMA.This idea are key to understanding OFDM. The orthogonality allows simultaneously transmission on a lot of sub- carriers in a tight frequency space without interference form each other. In essence this is similar to CDMA, where codes are used to make data sequences independent (also orthogonal) which allows many independent users to transmitin same space successfully.[2, 153-154; 6 ; 7] OFDM Operation Preliminary Concepts When the DFT (Discrete Fourier Transform) of a time signal is taken, the frequency domain results are a function of the time sampling period and the number of samples as shown in Figure 4. The fundamental frequency of the DFT is equal to 1/NT (1/total sample time). Each frequency represented in the DFT is an integer multiple of the fundamental frequency. Parameter Mapping from Time to Frequency for the DFT The maximum frequency that can be represented by a time signal sampled at rate 1/T is fmax = 1/2T as given by the Nyquist sampling theorem. This frequency is located in the center of the DFT points. All frequencies beyond that point are images of the representative frequencies. The maximum frequency bin of the DFT is equal to the sampling frequency (1/T) minus one fundamental (1/NT).The IDFT (Inverse Discrete Fourier Transform) performs the opposite operation to the DFT. It takes a signal defined by frequency components and converts them to a time signal. The parameter mapping is the same as for the DFT. The time duration of the IDFT time signal is equal to the number of DFT bins (N) times the sampling period (T).It is perfectly valid to generate a signal in the frequency domain, and convert it to a time domain equivalent for practical use (The frequency domain is a mathematical tool used for analysis. Anything usable by the real world must be converted into a real, time domain signal). This is how modulation is applied in OFDM. In practice the Fast Fourier Transform (FFT) and IFFT are used in place of the DFT and IDFT, so all further references will be to FFT and IFFT.[1 ,118 ; 4] Definition of Carriers The maximum number of carriers used by OFDM is limited by the size of the IFFT. This is determined as follows in Equation 2. OFDM Carrier Count In order to generate a real-valued time signal, OFDM (frequency) carriers must be defined in complex conjugate pairs, which are symmetric about the Nyquist frequency (fmax). This puts the number of potential carriers equal to the IFFT size/2. The Nyquist frequency is the symmetry point, so it cannot be part of a complex conjugate pair. The DC component also has no complex conjugate. These two points cannot be used as carriers so they are subtracted from the total available. If the carriers are not defined in conjugate pairs, then the IFFT will result in a time domain signal that has imaginary components. This must be a viable option as there are OFDM systems defined with carrier counts that exceed the limit for real-valued time signals given in Equation 2.In general, a system with IFFT size 256 and carrier count 216. This design must result in a complex time waveform. Further processing would require some sort of quadrature technique (use of parallel sine and cosine processing paths). In this report, only real-value time signals will be treated, but in order to obtain maximum bandwidth efficiency from OFDM, the complex time signal may be preferred (possibly an analogous situation to QPSK vs. BPSK). Equation 2, for the complex time waveform, has all IFFT bins available as carriers except the DC bin. Both IFFT size and assignment (selection) of carriers can be dynamic. The transmitter and receiver just have to use the same parameters. This is one of the advantages of OFDM. Its bandwidth usage (and bit rate) can be varied according to varying user requirements. A simple control message from a base station can change a mobile units IFFT size and carrier selection.[2,199-206; 4] Modulation Binary data from a memory device or from a digital processing stream is used as the modulating (baseband) signal. The following steps may be carried out in order to apply modulation to the carriers in OFDM: combine the binary data into symbols according to the number of bits/symbol selected convert the serial symbol stream into parallel segments according to the number of carriers, and form carrier symbol sequences apply differential coding to each carrier symbol sequence convert each symbol into a complex phase representation assign each carrier sequence to the appropriate IFFT bin, including the complex conjugates take the IFFT of the result OFDM modulation is applied in the frequency domain. Figure 5 and Figure 6 give an example of modulated OFDM carriers for one symbol period, prior to IFFT. OFDM Carrier Magnitude prior to IFFT For this example, there are 4 carriers, the IFFT bin size is 64, and there is only 1 bit per symbol. The magnitude of each carrier is 1, but it could be scaled to any value. The phase for each carrier is either 0 or 180 degrees, according to the symbol being sent. The phase determines the value of the symbol (binary in this case, either a 1 or a 0). In the example, the first 3 bits (the first 3 carriers) are 0, and the 4th bit (4th carrier) is a 1. OFDM Carrier Phase prior to IFFT Note that the modulated OFDM signal is nothing more than a group of delta (impulse) functions, each with a phase determined by the modulating symbol. In addition, note that the frequency separation between each delta is proportional to 1/N where N is the number of IFFT bins. The frequency domain representation of the OFDM is described in Equation 3. OFDM Frequency Domain Representation (one symbol period) After the modulation is applied, an IFFT is performed to generate one symbol period in the time domain. The IFFT result is shown in 7. It is clear that the OFDM signal has varying amplitude. It is very important that the amplitude variations be kept intact as they define the content of the signal. If the amplitude is clipped or modified, then an FFT of the signal would no longer result in the original frequency characteristics, and the modulation may be lost. This is one of the drawbacks of OFDM, the fact that it requires linear amplification. In addition, very large amplitude peaks may occur depending on how the sinusoids line up, so the peak-to-average power ratio is high. This means that the linear amplifier has to have a large dynamic range to avoid distorting the peaks. The result is a linear amplifier with a constant, high bias current resulting in very poor power efficiency. OFDM Signal, 1 Symbol Period Figure 8 is provided to illustrate the time components of the OFDM signal. The IFFT transforms each complex conjugate pair of delta functions (each carrier) into a real-valued, pure sinusoid. Figure 8 shows the separate sinusoids that make up the composite OFDM waveform given in Figure 7. The one sinusoid with 180 phase shift is clearly visible as is the frequency difference between each of the 4 sinusoids. Transmission The key to the uniqueness and desirability of OFDM is the relationship between the carrier frequencies and the symbol rate. Each carrier frequency is separated by a multiple of 1/NT (Hz). The symbol rate (R) for each carrier is 1/NT (symbols/sec). The effect of the symbol rate on each OFDM carrier is to add a sin(x)/x shape to each carriers spectrum. The nulls of the sin(x)/x (for each carrier) are at integer multiples of 1/NT. The peak (for each carrier) is at the carrier frequency k/NT. Therefore, each carrier frequency is located at the nulls for all the other carriers. This means that none of the carriers will interfere with each other during transmission, although their spectrums overlap. The ability to space carriers so closely together is very bandwidth efficient. OFDM Time Waveform Figure 9 shows the OFDM time waveform for the same signal. There are 100 symbol periods in the signal. Each symbol period is 64 samples long (100 x 64 = 6400 total samples). Each symbol period contains 4 carriers each of which carries 1 symbol. Each symbol carries 1 bit. Note that Figure 9 again illustrates the large dynamic range of the OFDM waveform envelope. OFDM Spectrum Figure 10 shows the spectrum for of an OFDM signal with the following characteristics: 1 bit / symbol 100 symbols / carrier (i.e. a sequence of 100 symbol periods) 4 carriers 64 IFFT bins spectrum averaged for every 20 symbols (100/20 = 5 averages) Red diamonds mark all of the available carrier frequencies. Note that the nulls of the spectrums line up with the unused frequencies. The four active carriers each have peaks at carrier frequencies. It is clear that the active carriers have nulls in their spectrums at each of the unused frequencies (otherwise, the nulls would not exist). Although it cannot be seen in the figure, the active frequencies also have spectral nulls at the adjacent active frequencies. It is not currently practical to generate the OFDM signal directly at RF rates, so it must be up converted for transmission. To remain in the discrete domain, the OFDM could be upsampled and added to a discrete carrier frequency. This carrier could be an intermediate frequency whose sample rate is handled by current technology. It could then be converted to analog and increased to the final transmit frequency using analog frequency conversion methods. Alternatively, the OFDM modulation could be immediately converted to analog and directly increased to the desired RF transmits frequency. Either way, the selected technique would have to involve some form of linear AM (possibly implemented with a mixer). [1, 122-125; 6] Reception and Demodulation The received OFDM signal is down converted (in frequency) and taken from analog to digital. Demodulation is done in the frequency domain (just as modulation was). The following steps may be taken to demodulate the OFDM: partition the input stream into vectors representing each symbol period take the FFT of each symbol period vector extract the carrier FFT bins and calculate the phase of each calculate the phase difference, from one symbol period to the next, for each carrier decode each phase into binary data sort the data into the appropriate order OFDM Carrier Magnitude following FFT Figure 11 and Figure 12 show the magnitude and spectrum of the FFT for one received OFDM symbol period. For this example, there are 4 carriers, the IFFT bin size is 64, there is 1 bit per symbol, and the signal was sent through a channel with AWGN having an SNR of 8 dB. The figures show that, under these conditions, the modulated symbols are very easy to recover. OFDM Carrier Phase following FFT In Figure 12 that the unused frequency bins contain widely varying phase values. These bins are not decoded, so it does not matter, but the result is of interest. Even if the noise is removed from the channel, these phase variations still occur. It must be a result of the IFFT/FFT operations generating very small complex values (very close to 0) for the unused carriers. The phases are a result of these values. [1, 125 -128; 3] OFDM transceiver OFDM signals are typically generated digitally due to the difficulty in creating large banks of phase lock oscillators and receivers in the analog domain. Figure 13 shows the block diagram of a typical OFDM transceiver. The transmitter section converts digital data to be transmitted, into a mapping of subcarrier amplitude and phase. It then transforms this spectral representation of the data into the time domain using an Inverse Discrete Fourier Transform (IDFT). The Inverse Fast Fourier Transform (IFFT) performs the same operations as an IDFT, except that it is much more computationally efficiency, and so is used in all practical systems. In order to transmit the OFDM signal the calculated time domain signal is then mixed up to the required frequency. Block diagram showing a basic OFDM transceiver [3] The receiver performs the reverse operation of the transmitter, mixing the RF signal to base band for processing, then using a Fast Fourier Transform (FFT) to analyze the signal in the frequency domain. The amplitude and phase of the subcarriers is then picked out and converted back to digital data. The IFFT and the FFT are complementary function and the most appropriate term depends on whether the signal is being received or generated. In cases where the Signal is independent of this distinction then the term FFT and IFFT is used interchangeably. [1, 125 -128, 3] Analysis of OFDM characteristics Guard Period OFDM demodulation must be synchronized with the start and end of the transmitted symbol period. If it is not, then ISI will occur (since information will be decoded and combined for 2 adjacent symbol periods). ICI will also occur because orthogonality will be lost (integrals of the carrier products will no longer be zero over the integration period), To help solve this problem, a guard interval is added to each OFDM symbol period. The first thought of how to do this might be to simply make the symbol period longer, so that the demodulator does not have to be so precise in picking the period beginning and end, and decoding is always done inside a single period. This would fix the ISI problem, but not the ICI problem. If a complete period is not integrated (via FFT), orthogonality will be lost. The effect of ISI on an OFDM signal can be further improved by the addition of a guard period to the start of each symbol. This guard period is a cyclic copy that extends the length of the symbol waveform. Each subcarrier, in the data section of the symbol, (i.e. the OFDM symbol with no guard period added, which is equal to the length of the IFFT size used to generate the signal) has an integer number of cycles. Because of this, placing copies of the symbol end-to-end results in a continuous signal, with no discontinuities at the joins. Thus by copying the end of a symbol and appending this to the start results in a longer symbol time. Addition of a guard period to an OFDM signal [3] In Figure 14, The total length of the symbol is Ts=TG + TFFT, where Ts is the total length of the symbol in samples, TG is the length of the guard period in samples, and TFFT is the size of the IFFT used to generate the OFDM signal. In addition to protecting the OFDM from ISI, the guard period also provides protection against time-offset errors in the receiver. For an OFDM system that has the same sample rate for both the transmitter and receiver, it must use the same FFT size at both the receiver and transmitted signal in order to maintain subcarrier orthogonality. Each received symbol has TG + TFFT samples due to the added guard period. The receiver only needs TFFT samples of the received symbol to decode the signal. The remaining TG samples are redundant and are not needed. For an ideal channel with no delay spread the receiver can pick any time offset, up to the length of the guard period, and still get the correct number of samples, without crossing a symbol boundary. Function of the guard period for protecting against ISI [3] Figure 15 shows this effect. Adding a guard period allows time for the transient part of the signal to decay, so that the FFT is taken from a steady state portion of the symbol. This eliminates the effect of ISI provided that the guard period is longer than the delay spread of the radio channel. The remaining effects caused by the multipath, such as amplitude scaling and phase rotation are corrected for by channel equalization. In order to avoid ISI and ICI, the guard period must be formed by a cyclic extension of the symbol period. This is done by taking symbol period samples from the end of the period and appending them to the front of the period. The concept of being able to do this, and what it means, comes from the nature of the IFFT/FFT process. When the IFFT is taken for a symbol period (during OFDM modulation), the resulting time sample sequence is technically periodic. This is because the IFFT/FFT is an extension of the Fourier Transform which is an extension of the Fourier Series for periodic waveforms. All of these transforms operate on signals with either real or manufactured periodicity. For the IFFT/FFT, the period is the number of samples used. Guard Period via Cyclic Extension With the cyclic extension, the symbol period is longer, but it represents the exact same frequency spectrum. As long as the correct number of samples are taken for the decode, they may be taken anywhere within the extended symbol. Since a complete period is integrated, orthogonality is maintained. Therefore, both ISI and ICI are eliminated. Note that some bandwidth efficiency is lost with the addition of the guard period (symbol period is increased and symbol rate is decreased) [2,154-160, 3] Windowing The OFDM signal is made up of a series of IFFTs that are concatenated to each other. At each symbol period boundary, there is a signal discontinuity due to the differences between the end of one period and the start of the next. These discontinuities can cause high frequency spectral noise to be generated (because they look like very fast transitions of the time waveform). To avoid this, a window function (Hamming, Hanning, Blackman, ) may be applied to each symbol period. The window function would attenuate the time waveform at the start and the end of each period, so that the discontinuities are smaller, and the high frequency noise is reduced. However, this attenuation distorts the signal and some of the desired frequency content is lost.[1, 121;2 154] Multipath Characteristics OFDM avoids frequency selective fading and ISI by providing relatively long symbol periods for a given data rate. This is illustrated in Figure 17. For a given transmission channel and a given source data rate, OFDM can provide better multipath characteristics than a single carrier. OFDM vs. Single Carrier, Multipath Characteristic Comparison However, since the OFDM carriers are spread over a frequency range, there still may be some frequency selective attenuation on a time-varying basis. A deep fade on a particular frequency may cause the loss of data on that frequency for a given time, but the use of Forward Error Coding can fix it. If a single carrier experienced a deep fade, too many consecutive symbols may be lost and correction coding may be ineffective. [8] Bandwidth A comparison of RF transmits bandwidth between OFDM and a single carrier is shown in Figure 18 (using the same example parameters as in Figure 17). OFDM Bandwidth Efficiency In Figure 18, the calculations show that OFDM is more bandwidth efficient than a single carrier. Note that another efficient aspect of OFDM is that a single transmitters bandwidth can be increased incrementally by addition of more adjacent carriers. In addition, no bandwidth buffers are needed between transmit bandwidths of separate transmitters as long as orthogonality can be maintained between all the carriers.[2, 161-163; 8; 9] Physical Implementation Since OFDM is carried out in the digital domain, there are many ways it can be implemented. Some options are provided in the following list. Each of these options should be viable given current technology: ASIC (Application Specific Integrated Circuit) ASICs are the fastest, smallest, and lowest power way to implement OFDM Cannot change the ASIC after it is built without designing a new chip General-purpose Microprocessor or MicroController PowerPC 7400 or other processor capable of fast vector operations Highly programmable Needs memory and other peripheral chips Uses the most power and space, and would be the slowest Field-Programmable Gate Array (FPGA) An FPGA combines the speed, power, and density attributes of an ASIC with the programmability of a general purpose processor. An FPGA could be reprogrammed for new functions by a base station to meet future (currently unknown requirements).This should be the best choice.[9] OFDM uses in DVB (Digital Video Broadcasting) DVB (Digital Video Broadcast) is a set of standards for the digital transmission of video and audio streams, and also data transmission. The DVB standards are maintained by the DVB Project, which is an industry-led consortium of over 260 broadcasters, manufacturers, network operators, software developers, regulatory bodies and others in over 35 countries. DVB has been implemented over satellite (DVB-S, DVB-S2), cable (DVB-C), terrestrial broadcasting (DVB-T), and handheld terminals (DVB-H). the DVB standard following the logical progression of signal processing steps, as well as source and channel coding, COFDM modulation, MPEG compression and multiplexing methods, conditional access and set-top box Technology. In this project is presented an investigation of two OFDM based DVB standards, DVB-T and DVB-H. DVB-T (Digital Video Broadcasting Terrestrial) The first Terrestrial Digital Video Broadcasting pilot transmissions were started in the late 90s, and the first commercial system was established in Great Britain. In the next few years the digital broadcasting system has been set up in many countries, and the boom of the digital terrestrial transmission is estimated in the next few years, while the analogue transmission will be cancelled within about 15 years. The greatest advantage of the digital system is the effective use of the frequency spectrum and its lower radiated power in comparison with the analogue transmission, while the covered area remains the same. Another key feature is the possibility of designing a so-called Single Frequency Network (SFN), which means that the neighboring broadcast stations use the same frequency and the adjacent signals dont get interfered. The digital system transmits a data stream, which means that not only television signals but data communication (e.g. Internet service) may be used according to the demands. The data stream consists of an MPEG-2 bit stream, which means a compression is used, enabling the transfer of even 4 or 5 television via the standard 8 MHz wide TV channel. For the viewer, the main advantages are the perfect, noise-free picture, CD quality sound, and easier handling, as well as services like Super Teletext, Electronic Programme Guide, interactivity and mobility.[11, 251-253] Modulation technique in DVB-T The DVB-T Orthogonal Frequency Division Multiplexing (OFDM) modulation system uses multi-carrier transmission. There are 2 modes, the so-called 2k and 8k modes, using 1705 and 6817 carriers respectively, with each carrier modulated separately and transmitted in the 8 MHz TV channel. The common modulation for the carriers is typically QPSK, 16-QAM or 64-QAM. Each signal can be divided into two, so-called „In Phase (I) and „Quadrature Phase components, being a 90Â ° phase shift between them. The constellation diagram and the bit allocation is shown in bellow 16-QAM constellation diagram and bit allocation [6] This modulation can be demonstrated in the constellation diagram, where the 2 axes represent the 2 components (I and Q). In case of using 16-QAM modulation, the number of states is 16, so 1 symbol represents 4 bits. [11, 255; 6; 14] Bir errors If we simulate all the carriers in the constellation diagram we get not just 1 discrete point, but many points, forming a „cloud and representing each state. In case of additive noise the „cloud gets bigger and the receiver may decide incorrectly, resulting in bit errors. Figure 2 shows the measured constellation diagram without and with additive noise. Measured 16-QAM constellation diagram a) without additive noise b) with additive noise [6] To ensure perfect picture quality, the DVB-T system uses a 2 level error correction (Reed-Solomon and Viterbi). This corrects the bad bits at an even 10-4 Bit Error Rate (BER) and enables error-free data transmission. [13, 32-36] The multi-carrier structure The structure of carriers can be illustrated also in the function of time (Figure 20). The horizontal axis is the frequency and the vertical axis is the time. The 8 MHz channel consists of many carriers, placed 4462 Hz or 1116 Hz far from each other according to the modulation mode (2k or 8k). Structure of OFDM carriers [13] There are some reserved, so-called Transmission Parameter Signalling (TPS) carriers that do not transfer payload, just provide transmission mode information for the receiver, so the total number of useful carriers is 1512 and 6048 respectively in the two transmission modes, and the resultant bit rate is between 4,97 and 31,66 Mbit/s, depending on the modulation (QPSK, 16-QAM or 64-QAM), the transmission mode (2k or 8k), the Code Rate (CR) used for error correction and the selected Guard Interval (GI). This guard interval means that there is a small time gap between each symbol, so the transmission is not continuous. This guarding time enables perfect reception by eliminating the errors caused by multipath propagation.[4, 79-90; 13] Frequency spectrum In 2k mode, 1705 carriers are modulated in the 8 MHz TV channel, so each carrier is 4462 Hz far from its neighbor, while in 8k mode this distance is 1116 Hz. In digital broadcasting, there are no vision and sound carriers, so the power for each carrier is the same. This mean High Performance Wireless Telecommunications Modulation High Performance Wireless Telecommunications Modulation Introduction The primary goal of the project is to analyze of OFDM system and to assess the suitability of OFDM as a modulation technique for wireless communications. In the part of project is covered two leading successfully implementation of OFDM based technologies are Digital Video Broadcasting (DVB-T and DVB-H) and Long Term Evolution (LTE advanced for 4G). Wireless communications is an emerging field, which has seen enormous growth in the last several years. The huge uptake rate of mobile phone technology, Wireless Local Area Networks (WLAN) and the exponential growth of the Internet have resulted in an increased demand for new methods of obtaining high capacity wireless networks. For cellular mobile applications, we will see in the near future a complete convergence of mobile phone technology, computing, Internet access, and potentially many multimedia applications such as video and high quality audio. In fact, some may argue that this convergence has already largely occurred, with the advent of being able to send and receive data using a notebook computer and a mobile phone. The goal of third and fourth generation mobile networks is to provide users with a high data rate, and to provide a wider range of services, such as voice communications, videophones, and high speed Internet access. The higher data rate of future mobile networks will be achieved by increasing the amount of spectrum allocated to the service and by improvements in the spectral efficiency. OFDM is a potential candidate for the physical layer of fourth generation mobile systems. Basic Principles of OFDM OFDM overview The Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique where multiple low data rate carriers are combined by a transmitter to form a composite high data rate transmission. The first commercial use of OFDM in the communication field was in the 1980s, and it was later widely used in the broadcast audio and video field in the 1990s in such areas as, ADSL, VHDSL, ETSI standard digital audio broadcast (DAB), digital video broadcast (DVB), and high-definition digital TV (HDTV). Digital signal processing makes OFDM possible. To implement the multiple carrier scheme using a bank of parallel modulators would not be very efficient in analog hardware. However, in the digital domain, multi-carrier modulation can be done efficiently with currently available DSP hardware and software. Not only can it be done, but it can also be made very flexible and programmable. This allows OFDM to make maximum use of available bandwidth and to be able to adapt to changing system requirements. Figure 1 is illustrated, Instead of separate modulators; the outgoing waveform is created by executing a high-speed inverse DFT on a set of time-samples of the transmitted data (post modulation). The output of the DFT can be directly modulated onto the outgoing carrier, without requiring any other components. Each carrier in an OFDM system is a sinusoid with a frequency that is an integer multiple of a base or fundamental sinusoid frequency. Therefore, each carrier is like a Fourier series component of the composite signal. In fact, it will be shown later that an OFDM signal is created in the frequency domain, and then transformed into the time domain via the Discrete Fourier Transform (DFT). Two periodic signals are orthogonal when the integral of their product, over one period, is equal to zero. This is true of certain sinusoids as illustrated in Equation 1. Definition of Orthogonal The carriers of an OFDM system are sinusoids that meet this requirement because each one is a multiple of a fundamental frequency. Each one has an integer number of cycles in the fundamental period. [2, 145-153; 6] The importantance of being orthogonal The main concept in OFDM is orthogonality of the sub-carriers.Since the carriers are all sine/cosine wave, we know that area under one period of a sine or a cosine wave is zero. Lets take a sine wave of frequency m and multiply it by a sinusoid (sine or a cosine) of a frequency n, where both m and n are integers. The integral or the area under this product is given by These two components are each a sinusoid, so the integral is equal to zero over one period. When we multiply a sinusoid of frequency n by a sinusoid of frequency m/n the area under the product is zero. In general for all integers n and m , sin(mx), cos(mx), cos(nx) , sin(nx) are all orthogonal to each other. These frequencies are called harmonics. Making the subcarriers mathematically orthogonal was a breakthrough for OFDM because it enables OFDM receivers to separate the subcarriers via an FFT and eliminate the guard bands. As figure 3 shows, OFDM subcarriers can overlap to make full use of the spectrum, but at the peak of each subcarrier spectrum, the power in all the other subcarriers is zero. OFDM therefore offers higher data capacity in a given spectrum while allowing a simpler system design. Creating orthogonal subcarriers in the transmitter is easy using an inverse FFT. To ensure that this orthogonality is maintained at the receiver (so that the subcarriers are not misaligned), the system must keep the transmitter and receiver clocks closely synchronizedwithin 2 parts per million in 802.11a systems. The 802.11a standard therefore dedicates four of its 52 subcarriers as pilots that enable phase-lock loops in the receiver to track the phase and frequency of the incoming signal. The 802.11a standard therefore dedicates four of its 52 subcarriers as pilots that enable phase-lock loops in the receiver to track the phase and frequency of the incoming signal. This method also eliminates low-frequency phase noise.Separating the subcarriers via an FFT require about an order of magnitude fewer multiply-accumulate operations than individually filtering each carrier. In general, an FFT implementation is much simpler than the RAKE receivers used for CDMA and the decision-feedback equalizers for TDMA.This idea are key to understanding OFDM. The orthogonality allows simultaneously transmission on a lot of sub- carriers in a tight frequency space without interference form each other. In essence this is similar to CDMA, where codes are used to make data sequences independent (also orthogonal) which allows many independent users to transmitin same space successfully.[2, 153-154; 6 ; 7] OFDM Operation Preliminary Concepts When the DFT (Discrete Fourier Transform) of a time signal is taken, the frequency domain results are a function of the time sampling period and the number of samples as shown in Figure 4. The fundamental frequency of the DFT is equal to 1/NT (1/total sample time). Each frequency represented in the DFT is an integer multiple of the fundamental frequency. Parameter Mapping from Time to Frequency for the DFT The maximum frequency that can be represented by a time signal sampled at rate 1/T is fmax = 1/2T as given by the Nyquist sampling theorem. This frequency is located in the center of the DFT points. All frequencies beyond that point are images of the representative frequencies. The maximum frequency bin of the DFT is equal to the sampling frequency (1/T) minus one fundamental (1/NT).The IDFT (Inverse Discrete Fourier Transform) performs the opposite operation to the DFT. It takes a signal defined by frequency components and converts them to a time signal. The parameter mapping is the same as for the DFT. The time duration of the IDFT time signal is equal to the number of DFT bins (N) times the sampling period (T).It is perfectly valid to generate a signal in the frequency domain, and convert it to a time domain equivalent for practical use (The frequency domain is a mathematical tool used for analysis. Anything usable by the real world must be converted into a real, time domain signal). This is how modulation is applied in OFDM. In practice the Fast Fourier Transform (FFT) and IFFT are used in place of the DFT and IDFT, so all further references will be to FFT and IFFT.[1 ,118 ; 4] Definition of Carriers The maximum number of carriers used by OFDM is limited by the size of the IFFT. This is determined as follows in Equation 2. OFDM Carrier Count In order to generate a real-valued time signal, OFDM (frequency) carriers must be defined in complex conjugate pairs, which are symmetric about the Nyquist frequency (fmax). This puts the number of potential carriers equal to the IFFT size/2. The Nyquist frequency is the symmetry point, so it cannot be part of a complex conjugate pair. The DC component also has no complex conjugate. These two points cannot be used as carriers so they are subtracted from the total available. If the carriers are not defined in conjugate pairs, then the IFFT will result in a time domain signal that has imaginary components. This must be a viable option as there are OFDM systems defined with carrier counts that exceed the limit for real-valued time signals given in Equation 2.In general, a system with IFFT size 256 and carrier count 216. This design must result in a complex time waveform. Further processing would require some sort of quadrature technique (use of parallel sine and cosine processing paths). In this report, only real-value time signals will be treated, but in order to obtain maximum bandwidth efficiency from OFDM, the complex time signal may be preferred (possibly an analogous situation to QPSK vs. BPSK). Equation 2, for the complex time waveform, has all IFFT bins available as carriers except the DC bin. Both IFFT size and assignment (selection) of carriers can be dynamic. The transmitter and receiver just have to use the same parameters. This is one of the advantages of OFDM. Its bandwidth usage (and bit rate) can be varied according to varying user requirements. A simple control message from a base station can change a mobile units IFFT size and carrier selection.[2,199-206; 4] Modulation Binary data from a memory device or from a digital processing stream is used as the modulating (baseband) signal. The following steps may be carried out in order to apply modulation to the carriers in OFDM: combine the binary data into symbols according to the number of bits/symbol selected convert the serial symbol stream into parallel segments according to the number of carriers, and form carrier symbol sequences apply differential coding to each carrier symbol sequence convert each symbol into a complex phase representation assign each carrier sequence to the appropriate IFFT bin, including the complex conjugates take the IFFT of the result OFDM modulation is applied in the frequency domain. Figure 5 and Figure 6 give an example of modulated OFDM carriers for one symbol period, prior to IFFT. OFDM Carrier Magnitude prior to IFFT For this example, there are 4 carriers, the IFFT bin size is 64, and there is only 1 bit per symbol. The magnitude of each carrier is 1, but it could be scaled to any value. The phase for each carrier is either 0 or 180 degrees, according to the symbol being sent. The phase determines the value of the symbol (binary in this case, either a 1 or a 0). In the example, the first 3 bits (the first 3 carriers) are 0, and the 4th bit (4th carrier) is a 1. OFDM Carrier Phase prior to IFFT Note that the modulated OFDM signal is nothing more than a group of delta (impulse) functions, each with a phase determined by the modulating symbol. In addition, note that the frequency separation between each delta is proportional to 1/N where N is the number of IFFT bins. The frequency domain representation of the OFDM is described in Equation 3. OFDM Frequency Domain Representation (one symbol period) After the modulation is applied, an IFFT is performed to generate one symbol period in the time domain. The IFFT result is shown in 7. It is clear that the OFDM signal has varying amplitude. It is very important that the amplitude variations be kept intact as they define the content of the signal. If the amplitude is clipped or modified, then an FFT of the signal would no longer result in the original frequency characteristics, and the modulation may be lost. This is one of the drawbacks of OFDM, the fact that it requires linear amplification. In addition, very large amplitude peaks may occur depending on how the sinusoids line up, so the peak-to-average power ratio is high. This means that the linear amplifier has to have a large dynamic range to avoid distorting the peaks. The result is a linear amplifier with a constant, high bias current resulting in very poor power efficiency. OFDM Signal, 1 Symbol Period Figure 8 is provided to illustrate the time components of the OFDM signal. The IFFT transforms each complex conjugate pair of delta functions (each carrier) into a real-valued, pure sinusoid. Figure 8 shows the separate sinusoids that make up the composite OFDM waveform given in Figure 7. The one sinusoid with 180 phase shift is clearly visible as is the frequency difference between each of the 4 sinusoids. Transmission The key to the uniqueness and desirability of OFDM is the relationship between the carrier frequencies and the symbol rate. Each carrier frequency is separated by a multiple of 1/NT (Hz). The symbol rate (R) for each carrier is 1/NT (symbols/sec). The effect of the symbol rate on each OFDM carrier is to add a sin(x)/x shape to each carriers spectrum. The nulls of the sin(x)/x (for each carrier) are at integer multiples of 1/NT. The peak (for each carrier) is at the carrier frequency k/NT. Therefore, each carrier frequency is located at the nulls for all the other carriers. This means that none of the carriers will interfere with each other during transmission, although their spectrums overlap. The ability to space carriers so closely together is very bandwidth efficient. OFDM Time Waveform Figure 9 shows the OFDM time waveform for the same signal. There are 100 symbol periods in the signal. Each symbol period is 64 samples long (100 x 64 = 6400 total samples). Each symbol period contains 4 carriers each of which carries 1 symbol. Each symbol carries 1 bit. Note that Figure 9 again illustrates the large dynamic range of the OFDM waveform envelope. OFDM Spectrum Figure 10 shows the spectrum for of an OFDM signal with the following characteristics: 1 bit / symbol 100 symbols / carrier (i.e. a sequence of 100 symbol periods) 4 carriers 64 IFFT bins spectrum averaged for every 20 symbols (100/20 = 5 averages) Red diamonds mark all of the available carrier frequencies. Note that the nulls of the spectrums line up with the unused frequencies. The four active carriers each have peaks at carrier frequencies. It is clear that the active carriers have nulls in their spectrums at each of the unused frequencies (otherwise, the nulls would not exist). Although it cannot be seen in the figure, the active frequencies also have spectral nulls at the adjacent active frequencies. It is not currently practical to generate the OFDM signal directly at RF rates, so it must be up converted for transmission. To remain in the discrete domain, the OFDM could be upsampled and added to a discrete carrier frequency. This carrier could be an intermediate frequency whose sample rate is handled by current technology. It could then be converted to analog and increased to the final transmit frequency using analog frequency conversion methods. Alternatively, the OFDM modulation could be immediately converted to analog and directly increased to the desired RF transmits frequency. Either way, the selected technique would have to involve some form of linear AM (possibly implemented with a mixer). [1, 122-125; 6] Reception and Demodulation The received OFDM signal is down converted (in frequency) and taken from analog to digital. Demodulation is done in the frequency domain (just as modulation was). The following steps may be taken to demodulate the OFDM: partition the input stream into vectors representing each symbol period take the FFT of each symbol period vector extract the carrier FFT bins and calculate the phase of each calculate the phase difference, from one symbol period to the next, for each carrier decode each phase into binary data sort the data into the appropriate order OFDM Carrier Magnitude following FFT Figure 11 and Figure 12 show the magnitude and spectrum of the FFT for one received OFDM symbol period. For this example, there are 4 carriers, the IFFT bin size is 64, there is 1 bit per symbol, and the signal was sent through a channel with AWGN having an SNR of 8 dB. The figures show that, under these conditions, the modulated symbols are very easy to recover. OFDM Carrier Phase following FFT In Figure 12 that the unused frequency bins contain widely varying phase values. These bins are not decoded, so it does not matter, but the result is of interest. Even if the noise is removed from the channel, these phase variations still occur. It must be a result of the IFFT/FFT operations generating very small complex values (very close to 0) for the unused carriers. The phases are a result of these values. [1, 125 -128; 3] OFDM transceiver OFDM signals are typically generated digitally due to the difficulty in creating large banks of phase lock oscillators and receivers in the analog domain. Figure 13 shows the block diagram of a typical OFDM transceiver. The transmitter section converts digital data to be transmitted, into a mapping of subcarrier amplitude and phase. It then transforms this spectral representation of the data into the time domain using an Inverse Discrete Fourier Transform (IDFT). The Inverse Fast Fourier Transform (IFFT) performs the same operations as an IDFT, except that it is much more computationally efficiency, and so is used in all practical systems. In order to transmit the OFDM signal the calculated time domain signal is then mixed up to the required frequency. Block diagram showing a basic OFDM transceiver [3] The receiver performs the reverse operation of the transmitter, mixing the RF signal to base band for processing, then using a Fast Fourier Transform (FFT) to analyze the signal in the frequency domain. The amplitude and phase of the subcarriers is then picked out and converted back to digital data. The IFFT and the FFT are complementary function and the most appropriate term depends on whether the signal is being received or generated. In cases where the Signal is independent of this distinction then the term FFT and IFFT is used interchangeably. [1, 125 -128, 3] Analysis of OFDM characteristics Guard Period OFDM demodulation must be synchronized with the start and end of the transmitted symbol period. If it is not, then ISI will occur (since information will be decoded and combined for 2 adjacent symbol periods). ICI will also occur because orthogonality will be lost (integrals of the carrier products will no longer be zero over the integration period), To help solve this problem, a guard interval is added to each OFDM symbol period. The first thought of how to do this might be to simply make the symbol period longer, so that the demodulator does not have to be so precise in picking the period beginning and end, and decoding is always done inside a single period. This would fix the ISI problem, but not the ICI problem. If a complete period is not integrated (via FFT), orthogonality will be lost. The effect of ISI on an OFDM signal can be further improved by the addition of a guard period to the start of each symbol. This guard period is a cyclic copy that extends the length of the symbol waveform. Each subcarrier, in the data section of the symbol, (i.e. the OFDM symbol with no guard period added, which is equal to the length of the IFFT size used to generate the signal) has an integer number of cycles. Because of this, placing copies of the symbol end-to-end results in a continuous signal, with no discontinuities at the joins. Thus by copying the end of a symbol and appending this to the start results in a longer symbol time. Addition of a guard period to an OFDM signal [3] In Figure 14, The total length of the symbol is Ts=TG + TFFT, where Ts is the total length of the symbol in samples, TG is the length of the guard period in samples, and TFFT is the size of the IFFT used to generate the OFDM signal. In addition to protecting the OFDM from ISI, the guard period also provides protection against time-offset errors in the receiver. For an OFDM system that has the same sample rate for both the transmitter and receiver, it must use the same FFT size at both the receiver and transmitted signal in order to maintain subcarrier orthogonality. Each received symbol has TG + TFFT samples due to the added guard period. The receiver only needs TFFT samples of the received symbol to decode the signal. The remaining TG samples are redundant and are not needed. For an ideal channel with no delay spread the receiver can pick any time offset, up to the length of the guard period, and still get the correct number of samples, without crossing a symbol boundary. Function of the guard period for protecting against ISI [3] Figure 15 shows this effect. Adding a guard period allows time for the transient part of the signal to decay, so that the FFT is taken from a steady state portion of the symbol. This eliminates the effect of ISI provided that the guard period is longer than the delay spread of the radio channel. The remaining effects caused by the multipath, such as amplitude scaling and phase rotation are corrected for by channel equalization. In order to avoid ISI and ICI, the guard period must be formed by a cyclic extension of the symbol period. This is done by taking symbol period samples from the end of the period and appending them to the front of the period. The concept of being able to do this, and what it means, comes from the nature of the IFFT/FFT process. When the IFFT is taken for a symbol period (during OFDM modulation), the resulting time sample sequence is technically periodic. This is because the IFFT/FFT is an extension of the Fourier Transform which is an extension of the Fourier Series for periodic waveforms. All of these transforms operate on signals with either real or manufactured periodicity. For the IFFT/FFT, the period is the number of samples used. Guard Period via Cyclic Extension With the cyclic extension, the symbol period is longer, but it represents the exact same frequency spectrum. As long as the correct number of samples are taken for the decode, they may be taken anywhere within the extended symbol. Since a complete period is integrated, orthogonality is maintained. Therefore, both ISI and ICI are eliminated. Note that some bandwidth efficiency is lost with the addition of the guard period (symbol period is increased and symbol rate is decreased) [2,154-160, 3] Windowing The OFDM signal is made up of a series of IFFTs that are concatenated to each other. At each symbol period boundary, there is a signal discontinuity due to the differences between the end of one period and the start of the next. These discontinuities can cause high frequency spectral noise to be generated (because they look like very fast transitions of the time waveform). To avoid this, a window function (Hamming, Hanning, Blackman, ) may be applied to each symbol period. The window function would attenuate the time waveform at the start and the end of each period, so that the discontinuities are smaller, and the high frequency noise is reduced. However, this attenuation distorts the signal and some of the desired frequency content is lost.[1, 121;2 154] Multipath Characteristics OFDM avoids frequency selective fading and ISI by providing relatively long symbol periods for a given data rate. This is illustrated in Figure 17. For a given transmission channel and a given source data rate, OFDM can provide better multipath characteristics than a single carrier. OFDM vs. Single Carrier, Multipath Characteristic Comparison However, since the OFDM carriers are spread over a frequency range, there still may be some frequency selective attenuation on a time-varying basis. A deep fade on a particular frequency may cause the loss of data on that frequency for a given time, but the use of Forward Error Coding can fix it. If a single carrier experienced a deep fade, too many consecutive symbols may be lost and correction coding may be ineffective. [8] Bandwidth A comparison of RF transmits bandwidth between OFDM and a single carrier is shown in Figure 18 (using the same example parameters as in Figure 17). OFDM Bandwidth Efficiency In Figure 18, the calculations show that OFDM is more bandwidth efficient than a single carrier. Note that another efficient aspect of OFDM is that a single transmitters bandwidth can be increased incrementally by addition of more adjacent carriers. In addition, no bandwidth buffers are needed between transmit bandwidths of separate transmitters as long as orthogonality can be maintained between all the carriers.[2, 161-163; 8; 9] Physical Implementation Since OFDM is carried out in the digital domain, there are many ways it can be implemented. Some options are provided in the following list. Each of these options should be viable given current technology: ASIC (Application Specific Integrated Circuit) ASICs are the fastest, smallest, and lowest power way to implement OFDM Cannot change the ASIC after it is built without designing a new chip General-purpose Microprocessor or MicroController PowerPC 7400 or other processor capable of fast vector operations Highly programmable Needs memory and other peripheral chips Uses the most power and space, and would be the slowest Field-Programmable Gate Array (FPGA) An FPGA combines the speed, power, and density attributes of an ASIC with the programmability of a general purpose processor. An FPGA could be reprogrammed for new functions by a base station to meet future (currently unknown requirements).This should be the best choice.[9] OFDM uses in DVB (Digital Video Broadcasting) DVB (Digital Video Broadcast) is a set of standards for the digital transmission of video and audio streams, and also data transmission. The DVB standards are maintained by the DVB Project, which is an industry-led consortium of over 260 broadcasters, manufacturers, network operators, software developers, regulatory bodies and others in over 35 countries. DVB has been implemented over satellite (DVB-S, DVB-S2), cable (DVB-C), terrestrial broadcasting (DVB-T), and handheld terminals (DVB-H). the DVB standard following the logical progression of signal processing steps, as well as source and channel coding, COFDM modulation, MPEG compression and multiplexing methods, conditional access and set-top box Technology. In this project is presented an investigation of two OFDM based DVB standards, DVB-T and DVB-H. DVB-T (Digital Video Broadcasting Terrestrial) The first Terrestrial Digital Video Broadcasting pilot transmissions were started in the late 90s, and the first commercial system was established in Great Britain. In the next few years the digital broadcasting system has been set up in many countries, and the boom of the digital terrestrial transmission is estimated in the next few years, while the analogue transmission will be cancelled within about 15 years. The greatest advantage of the digital system is the effective use of the frequency spectrum and its lower radiated power in comparison with the analogue transmission, while the covered area remains the same. Another key feature is the possibility of designing a so-called Single Frequency Network (SFN), which means that the neighboring broadcast stations use the same frequency and the adjacent signals dont get interfered. The digital system transmits a data stream, which means that not only television signals but data communication (e.g. Internet service) may be used according to the demands. The data stream consists of an MPEG-2 bit stream, which means a compression is used, enabling the transfer of even 4 or 5 television via the standard 8 MHz wide TV channel. For the viewer, the main advantages are the perfect, noise-free picture, CD quality sound, and easier handling, as well as services like Super Teletext, Electronic Programme Guide, interactivity and mobility.[11, 251-253] Modulation technique in DVB-T The DVB-T Orthogonal Frequency Division Multiplexing (OFDM) modulation system uses multi-carrier transmission. There are 2 modes, the so-called 2k and 8k modes, using 1705 and 6817 carriers respectively, with each carrier modulated separately and transmitted in the 8 MHz TV channel. The common modulation for the carriers is typically QPSK, 16-QAM or 64-QAM. Each signal can be divided into two, so-called „In Phase (I) and „Quadrature Phase components, being a 90Â ° phase shift between them. The constellation diagram and the bit allocation is shown in bellow 16-QAM constellation diagram and bit allocation [6] This modulation can be demonstrated in the constellation diagram, where the 2 axes represent the 2 components (I and Q). In case of using 16-QAM modulation, the number of states is 16, so 1 symbol represents 4 bits. [11, 255; 6; 14] Bir errors If we simulate all the carriers in the constellation diagram we get not just 1 discrete point, but many points, forming a „cloud and representing each state. In case of additive noise the „cloud gets bigger and the receiver may decide incorrectly, resulting in bit errors. Figure 2 shows the measured constellation diagram without and with additive noise. Measured 16-QAM constellation diagram a) without additive noise b) with additive noise [6] To ensure perfect picture quality, the DVB-T system uses a 2 level error correction (Reed-Solomon and Viterbi). This corrects the bad bits at an even 10-4 Bit Error Rate (BER) and enables error-free data transmission. [13, 32-36] The multi-carrier structure The structure of carriers can be illustrated also in the function of time (Figure 20). The horizontal axis is the frequency and the vertical axis is the time. The 8 MHz channel consists of many carriers, placed 4462 Hz or 1116 Hz far from each other according to the modulation mode (2k or 8k). Structure of OFDM carriers [13] There are some reserved, so-called Transmission Parameter Signalling (TPS) carriers that do not transfer payload, just provide transmission mode information for the receiver, so the total number of useful carriers is 1512 and 6048 respectively in the two transmission modes, and the resultant bit rate is between 4,97 and 31,66 Mbit/s, depending on the modulation (QPSK, 16-QAM or 64-QAM), the transmission mode (2k or 8k), the Code Rate (CR) used for error correction and the selected Guard Interval (GI). This guard interval means that there is a small time gap between each symbol, so the transmission is not continuous. This guarding time enables perfect reception by eliminating the errors caused by multipath propagation.[4, 79-90; 13] Frequency spectrum In 2k mode, 1705 carriers are modulated in the 8 MHz TV channel, so each carrier is 4462 Hz far from its neighbor, while in 8k mode this distance is 1116 Hz. In digital broadcasting, there are no vision and sound carriers, so the power for each carrier is the same. This mean