Compare and Contrast Essay Example | Topics and Well Written Essays - 1500 words

Compare and Contrast - Essay Example This paper thus helps to provide a clear and concise understanding on the basis of these three short stories and poem in order to compare and contrast the same on various levels as is further discussed within the scope of this paper. ‘My Last Duchess’ by Robert Browning is an excellent example of a dramatic monologue which appeared first in the year 1842 in the poet’s ‘Dramatic Lyrics’. The poem has been written about the fifth Duke of Ferrara who was married to Lucrezia di Cosimo de Medici and talks about the kind of influence that wealth, power, as well as pure aristocracy had on the life of the duke. Furthermore, written and composed by Richard Wright, ‘Big Black Good Man’ is a story that first appeared in the story collection of ‘Eight Men’ which was one of the last works of the author. It is about a man by the name of Olaf, who finds himself providing room one fine afternoon, in his office, to a big black man for the sub sequent five or six nights. The third story discussed is ‘Cathedral’ written by Raymond Carver in the year 1983 and was included in his anthology in the same year as well. It is about the spiritual houses of God, on a broad basis of a theme and the theme of blindness and sight prevails throughout the course of the story as the author tries to explain the kind of faith that most people have on God. My Last Duchess has been set during the Italian Renaissance period and reeks of aristocracy and how the rich survived during the time. It mainly talks about how marriage, power and wealth influence a man’s life and how when these factors are involved in play, a man ceases to think about emotions like love, desire and death. In the poem, the Duke does not seem to be in love with his dead wife or even lament about her death. Instead, he enjoys the fact that he narrates to the messenger, how he had had her killed and experiences a sense of joy in doing the same. As compare d to this, Big Black Good Man talks mainly about differences on the basis of colour as the black man asks for lodgings to Olaf and the former gets scared of the consequences of sheltering a man who was so different from the rest of society. Thus it mainly seeks to talk about the period of apartheid that the world faced and how the same was countered in different countries, especially in America. Cathedral aims to discuss the spirituality and oneness that a man can develop with God however, how the same may be based on blind faith at times, without understanding the true consequences of a situation. However, the narrator narrates a story about a blind man, who is later able to open his eyes due to finding sight because of the gift of God and understanding and knowledge of the ways of the world. All three have been written in the form of a dramatic prose or a short story, including Browning’s My Last Duchess, even though it is a poem. However, it is regarded as more of a short dramatic monologue or piece of writing and retains a certain rhyme scale by an iambic parameter and may be read as a story which is being narrated on the basis of certain emotions and feelings. The other two are short stories and have been published in anthologies. All three have wide appreciation regarded all over the world because of their broad themes which has helped readers in an understanding of these different eras. My Last Duchess has a historical background attached to it and talks about the way the Duke

Witness Memory as Evidence in Criminal Trials

Witness Memory as Evidence in Criminal Trials 1. When, and why, are witnesses’ memories unreliable as evidence in criminal trials in England and Wales? Memory Memory is one’s ability to recall the past events. Memory let us explain our personal experiences and perception about anything which is occurred in past. Types Of Memory There are three types of memory Episodic Memory Episodic memory refers to our memory of special event like accident, death etc. Semantic Memory There are too many general knowledge is stored in one’s mind which comes under the semantic memory type. It also refers to the information which is stored in our mind to perform any skill. It also tells us how to perform in some repeated situation. Procedural Memory Understanding the procedural memory is rather difficult to understand and contains different kind of information. Generally it refers to series of events which occurred on numerous times. Importance Of Witness Memory Witness memory is a fuel of any investigation because it let investigator to collect information about incident but human memory is too fragile to exactly remember every moment. There are also numerous factors involved which affect witness memory that is environment factors, witness factors, stress levels of the witness/victim, weapon focus. When Witness Memory Is Unreliable As Evidence? Witnesses memories are unreliable as evidence in criminal trials in England and Wales when there is a â€Å"TurnBull† direction indicated the state of witness at the time of incident happened because so many researches has found the massive impression on the quality of information. What Is TurnBull? There are too many environmental factors which affect the memory of witness and can damage the quality and quantity of information. R. V. Turnbull guidance proposed a term ADVOKATE Amount of time one observed Distance – What was the distance between event and witness Visibility – How much the scene was clear? Obstruction – Was there anything obscuring the view? Known or seen before – If the situation was familiar? Any reason to remember – What is the reason behind to remember. Time lapse – How long the exposure of event? Error or material discrepancy – Is there any discrepancy between the fact and the description (Booklet). Why Witness State Is Unreliable In England and Wales, Evidence is not reliable, when there is a Turnbull direction in a state of witness because sometime witness rely on external help to recall the incident or he may have perceived wrongly due to distance or visibility or both (Bull, 1999) Generally people under the investigation are not ready to recall the incident currently. Many factors like fear, stress and nervousness can affect their quality of information. Sometimes they rely on external resources to feed them and they wrongly perceive the series of happening occurred at TBR events. Sometimes witness may lie for any previous dispute or grudge. Witness may be biased and can provide wrong information to affect the investigation Conclusion Since witness memory depends on lots of factors which are indicated through the famous term ADVOKATE therefore investigation should be taken with caution and every term of ADVOKATE should be properly and clearly note down. To gather worthy information from the witness, should check the witness personal preference of biasness or favoritism. It should also be checked that whether the witness is pressurized by the culprit to speak lie. What changes should be made, to the procedures for identifying suspects in criminal investigations in England and Wales, according to psychological research? Human memory is too fragile to exactly remember the incident which happened that is why interviewing the witness to identifying the suspect is rather difficult task. It can also affect by the â€Å"Turnbull† directions. Usually witness replies the interviewer in broad term and can only describe six or seven characteristics of suspect like age (Between 20-30) or height (between 5’6’’ – 5’8’’) that is why it is always difficult to get accurate knowledge about victim. The accurate information may be collected through cognitive interview but this type of interview demands too much time to conclude things. These re the reasons for which psychological research stress on the identification parade to identify the culprit. (Kapardis ebrary, 2010) Why Should Be Identification Parade Arranged? Identification parade are arranged to avoid two hurdles of identifying the culprit. Verbal Overshadowing In most of crime, during the investigation, witness is interviewed by more than one officer and provided stream of information due to which he can mix up the details which is stored in witnesses’ mind and the information he is provided by the officers about culprit. If identification parade is arranged then a witness can easily identify the suspect or the person who is somehow linked with the crime. Information To The Public Some crimes are needed to announce in public through media and police shows the picture, video or sketch of suspect in public. Sometimes a totally innocent person can be suspected and shown to public. Witnesses, after seeing the police announcement about suspect can to mix-up the faces of suspect with actual culprit. In that case, after the identification parade, officers are directed to ask witnesses whether they have seen any broadcast on media or not? Asking directly to the witness is rather strange. According to researchers, it is more appropriate to ask logically by the witness rather than directly. Changing Facial Expressions. Facial expressions of people are changed with the passage of time due to weight, tiredness, hair color or culprit can deliberately change it to be hidden from the police but if culprit is arrested for identification parade then he cannot change his facial expression and can be identified by the witness. Conclusion Investigation with witness should be deal with cautious and interviewer should know the art of interviewing to get accurate information. Investigator should avoid direct questions like was that man wearing black shirt? Or did you see blood spot on right side of window? It is recommended to ask series of questions to grab the fact like the series below. What have you seen at spot? Can you tell us the gender of person you have seen? What was he wearing? It is also recommended to setup interview as soon as possible because there is margin of memory fail. Describe the extent to which offender profiling is relied upon both in criminal investigations and in criminal trials in England and Wales.? Offender Profiling Offender profiling is a tool of investigation about the culprit with the help of evidences. Offender profiling is commonly perceive as a magical ability of investigator to put hands on the culprit. It is also called psychological profiling, criminal personality profiling, profile analysis and the offender profiling is carried by the profilers or offender profilers. Offender profiling is a psychological assessment of evidence which is collected from the crime scene. Offender profiler collects evidence from the crime scene and assess assumes the personality type which usually exhibits similar patterns (Jackson Bekerian, 1997). Aims Of Profiling The aim of profiling is to get closer to suspect and get the answer of three questions What happened at the spot of incident? What personality type can be involved in it? What personality traits can be possessed by that personality type? These questions are generally analyzed by the psychologist who are expert of their field and are outside of the police department. Limitations Of Offender Profiling Although the crime scene can reflect the personality of offender and psychiatrist put insights on it but sometimes searching the link between the crime and mental state of offender is not cleared or understandable. It is also criticized that psychologist are helpful only in the crime which are committed in extreme cases of mental illness. They are not much useful in the crimes which are not committed due to mental illness. One more criticism is usually done on clinical approach that psychologists works according to science of psychology which is remain ambiguous and has flaws in it. Understanding and evaluating complex human psyche is rather difficult task and sometimes it is understood completely wrong Conclusion Offender profiling is no doubt a significant part of crime investigation but it is also limited in a way. It restricts psychiatrist to some specific pattern of personality traits while human behavior is always complex and cannot read accurately always. It is not necessary that crime scene always show the exact pattern of behavior which culprit exhibit. Identify the key ways in which the research, into common forms of decision-error, might inform and improve practice in criminal investigations and trials? Deception Identifying someone’s lie is not easy according to research reaching correct result is tending to fall between 50 to 60 percent. The more common reason of this trend is over confidence of people in their ability to judge others. Detection Of Deception Despite of fact that deception cannot be easily caught, people also make some basic judgment errors. These judgment errors are categorized in five types. Pinocchio’s Nose There is indeed some universal signs of lying like stammering, avoid eye contact, blushing but it cannot equally apply to everybody on the earth. So these universal signals may guide to wrong direction. Erroneous Assumptions Some people thing that deception can easily be caught by facial expression or they are the master of face reading. Some people do have the ability of face reading but in general this ability is over estimated. Othello Error This type of error is actually comes in existence due to Shakespeare’s drama where Othello achieved his target by accusing Desdemona but in modern criminal justice system this error misleads because most of people became nervous and feared when the feel that they are under observation. The Plausibility Problem Plausible and implausible problems have problem to judge right because we do not believe implausible event if it is reported by some old man. Countermeasures A natural liar can deceive the interviewer after noticing the interviewer suspicion and can adjust his/her behavior accordingly. Techniques To Improve Decision Errors Scholars and researchers proposed three techniques of improving decision errors. Un- spoken deeds Lying can be judged by the entire body language which includes gestures, postures, facial expressions, voice quality etc. Some common proposed techniques of judging un spoken deeds are: Decrease in movement of entire legs till feet Decrease in hand movements Sudden increase and decrease in voice. These all assumed signs should be deal with cautious because it cannot be true in every situation like deception errors and may lead to in accurate judgment. Spoken Deeds Numerous techniques are used to judge the â€Å"REAL† of words that are written or spoken. The two most famous techniques of read between the lines are: Statement Validity Analysis (SVA) which is developed by Steller and Kohnken in 1997 which is then incorporated by Criteria Based Content Analysis (CBCA). It implies that our account is different in content and quality in case of reality or imagination. This techniques uses nineteen criteria to judge a statement. This technique is not commonly use in U.K. Physiological Methods The most common technique of physiological method is Polygraph, which measures physiological reaction like heart beat, sweating etc to check the deception. The polygraph is conducted through different sensors that are attached to the body and every physiological reaction recorded as a graphical presentation. Although polygraph is considered as very effective tool of detecting deception and has been used in different countries but it is not used in U.K. criminal justice system due to complex human nature and the fact that human behavior and their psychological reactions are vary from person to person. Conclusion To improve decision making process in U.K spoken deeds and physiological test should be considered because these two techniques have been using in different countries and showing successful results to some extent but these techniques should be used with the caution and must not be rated overly. It should be used with the understanding that human nature varies from person to person and same reactions cannot be equally applied to everybody Bibliography Booklet. (n.d.). Retrieved from Police Service Of Northern Ireland: http://www.psni.police.uk/de/public_order_8th_edition.pdf Milne, R. and Bull, R. (1999).Investigative interviewing: Psychology and practice. Chichester: Wiley.† Kapardis, A., ebrary, I. (2010). Psychology and law: a critical introduction. New York: Cambridge University Press 2010. 1 | Page

Hamlet Analysis :: essays research papers

In Act 1 Scene 5 of Shakespeare’s Hamlet, the ghost of King Hamlet can be portrayed as either, a harsh, mean, and demanding father or a caring, nice, and understanding dad. This depends on how you manipulate the lighting, actions, which includes speech, and other special effects. By manipulating the lighting on the ghost of King Hamlet, he can be presented as either a demanding and harsh father or a caring and understanding dad. To present the ghost as a demanding and harsh father you could use a bright red light shining on him. Using a red light would portray him as evil because the color red is associated with such things as fire and hell, both which have negative connotations. For example, at the beginning of the scene a single red light can shine down on the ghost from behind casting a dark shadow onto Hamlet. When the ghost says, “Revenge his foul and most unnatural murder.'; The single light from behind could move to directly over the ghost casting a shadow onto his face to make him look even more menacing. Also, lights all over the stage would begin at a low red glow and slowly rise to a bright red engulfing the whole stage when the ghost finishes off the quote saying, “murder';. If you manipulate the light in another way the ghost can be p resented as a caring father. By using a white or a blue light would portray him as good because the colors of white and blue are connected with things such as heaven and angels, both of which have good connotations. For example, when showing the ghost, a white light could be coming at him from all angles, following wherever he goes. When the ghost of King Hamlet says, “Taint not thy mind…aught.'; A white light could be coming from under the stage shining up onto the ghost, and also from all other angles. This would cause the ghost to shine brightly from the light bouncing off his armor. Saying this quote while having white light surround him would further portray him as caring. This is because he is telling Hamlet not to harm, or even think of harming his mother. Not only does lighting show how the ghost of King Hamlet can be portrayed in two different ways, but it can also be displayed by his actions and speech.

Body Ritual Among the Nacirema

Connor Doyle Summary of Body Ritual among the Nacirema 10/20/2012 Introduction to Sociology The Nacirema Horace Miner depicted this cultural group located in Northwest America â€Å"living in the territory between the Canadian Cree, the Yaqui and Tarahumare of Mexico, and the Carib and Arawak of the Antilles† (Miner 503). Closely imitating the United States of America. If you take a look at the Nacirema's name spelled backwards, its American. The concept behind this is that Miner wanted to describe American's rituals in a way that people would deem crazy.But in all actuality, it's what us humans do everyday and never think twice of it. For if we forgot to do one of these things, we would feel uncomfortable all day long. â€Å"According to Nacirema mythology, their nation was originated by a culture hero, Notgnihsaw,† Hines describes that, â€Å"he was known for two great feats of strength—the throwing of a piece of wampum across the river Pa-To-Mac and the chopp ing down of a cherry tree in which the Spitit of Truth resided† (Miner 503). This is referring to, what many religions call, God. It's a universal feeling that everyone wants to encounter, that their is a higher power somewhere.He then goes on to say the â€Å"Nacirema culture is charecterized by a highly developed market economy which has evolved in a rich natural habitat† (Miner 503). This is refering to our Free Market Economy. The way we evolved in a â€Å"rich natural habitat†, is that we've always been prosepering since our birth as a country. With the exceptions of some down falls, we have been the world's leading power. It states that the Nacirema focus a lot of activity on the human body and its appearance. He states that it is a dominate concern, making every other aspect in life second best.Though many cultures have similar rituals to this, regarding the body, these aspects on society are quite unique. They even believe that their own human body is ugl y making it a natural reaction to try and improve your situation. They also acknowledge the fact that the human body deterioates and attracts disease. Since man knows these facts, the only option left is to perform rituals regarding the improvement of your body. He says that in every Nacirema's house their is at lease one shrine devoted mainly to the self-improvement of the people. This is refering to what we commonly know as a bathroom.If you really come to think about it, the bathroom is almost souly used for self-improvement. Every action from shaving, to brushing your teeth is preconcieved and is subconcsiously telling you that you need these things everyday. He goes on to say that â€Å"the rituals associated with it are not family ceremonies but are private and secret. † Then he states that the only time you really talk about these rituals are to your children, and only telling them the basics while they are still growing up. Another big part of the Nacirema culture is the medicine man.He is the only one that knows what is in the secret potion. Every Nacirema believes that if they are to go without these magic potions, they would cease to live. It goes hand in hand with the culture of our society. If people don't have a cure for the smallest thing, they still feel vulnerable. We rely on so many perscriptions, medications, and cure-alls for a quick fix. Without these things, we as a society would feel completely weak. They say that the medicine man can only work if they recieve â€Å"substantial gifts† (Miner 504), which is the same for our doctors as well.Even when the Nacirema have been done with the charms, they still keep the expired remains in their drawer just for safety. In fear that without these charms, they would remain vulnerable. The medicine man is even able to make a women's breast larger or smaller, depending on the request. The holy man, refered to in the Nacirema culture, is what we commonly know as the Dentist. Miner says t hat in addition to brushing and maintaing their teeth, they visit a â€Å"holy-mouth-man once or twice a year. They refer to a Dentist tool's as â€Å"paraphernalia, consisting of a variety of augers, awls, probes, and prods† (Miner 504). To the untrained eye that's what it looks like. Not many other cultures around the world, that are not as prosperous, ever make visits to a Dentist. They go on to say that â€Å"these objects in the exorcism of the evils of the mouth involves almost unbelievable ritual torture of the client† (Miner 505). Their has always been a fear of pain when attending the Dentist. Young children dread going every year, but to their parents and their society it is standard to have a high maintance mouth.

Emotional Intelligence and Athletic Performance - 1744 Words

According to Salovey and Mayer (1990), â€Å"understanding emotions involves comprehension of how basic emotions are blended to form complex emotions, how emotions are affected by events surrounding experiences, and whether various emotional reactions are likely in given social settings. Regulating emotions encompasses the control of emotions in oneself and in others. An individual’s emotional intelligence is an indication of how he or she perceives, understands, and regulates emotions. In sum, emotional intelligence is a form of intelligence that involves â€Å"the ability to monitor one’s own and others’ feelings and emotions, to discriminate among them and to use this information to guide one’s thinking and actions† (Salovery and Mayer, 1990,†¦show more content†¦Research has pointed out the importance for us to develop a clear perspective on the theoretical development of EQ. Moreover, how this theory may or may not overlap with tradit ional forms of intelligence and with psychological skills and strategies as they relate to athletic performance. In the Lane et al. (2010) study, the researchers have explored the findings of how emotional intelligence is related to emotions experienced before successful and unsuccessful performances and how certain emotions are correlated with successful performances and poor performances. Previous research has shown that emotional intelligence is correlated positively with pleasant emotions and negatively with unpleasant emotions. Further, Lane et al. (2009c) found emotional intelligence scores correlated with frequent use of psychological skills. Athletes reporting frequent use of psychological skills (Thomas et al., 1999) also appear to report high scores on the self-report emotional intelligence scales. B. Comparison of the purposes posed by the studies The purpose of the Zizzi et al. (2003) study was to find a relationship between emotional intelligence and athletic performance in a sample of Division I baseball players. This study explored the relationships between emotional intelligence and the global measures of baseball performance in a sample of college baseball players. More specifically, aShow MoreRelatedThe Theory Of Ei As A Mental Ability861 Words   |  4 Pagesreferring to an individual’s tendency to manage his or her emotions and is usually measured using self-report style questionnaires (Laborde, Brà ¼ll, Weber Anders, 2011) such as the Trait Emotional Intelligence Questionnaire (TEIQue; Petrides, 2009). The EI as a mental ability approach considers EI as a form of intelligence. 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Radio resource management in relay enhanced ofdma based networks - Free Essay Example

Sample details Pages: 29 Words: 8556 Downloads: 6 Date added: 2017/06/26 Category Statistics Essay Did you like this example? 1 Introduction The convenience and popularity of wireless technology has now extended into multimedia communications, where it poses a unique challenge for transmitting high rate voice, image, and data signals simultaneously, synchronously, and virtually error-free . That challenge is currently being met through Orthogonal Frequency Division Multiplexing (OFDM), an interface protocol that divides incoming data streams into sub-streams with overlapping frequencies that can then be transmitted in parallel over orthogonal subcarriers [2,3]. To allow multiple accesses in OFDM , Orthogonal Frequency Division Multiple Access (OFDMA) was introduced. Don’t waste time! Our writers will create an original "Radio resource management in relay enhanced ofdma based networks" essay for you Create order Relaying techniques, along with OFDMA, are used to achieve high data rate and high spectral efficiency. 1.1 Orthogonal Frequency Division Multiple Access OFDMA, an interface protocol combining features of OFDM and frequency division multiple access (FDMA)., was developed to move OFDM technology from a fixed-access wireless system to a true cellular system with mobility with same underlying technology, but more flexibility was defined in the operation of the system [1,8]. In OFDMA, subcarriers are grouped into larger units, referred to as sub-channels, and these sub-channels are further grouped into bursts which can be allocated to wireless users [4]. 1.2 Relay-Enhanced Networks In cellular systems, a way to achieve remarkable increase in data rate, but without claiming for more bandwidth, is to shrink cell sizes, however, with smaller cells more base stations (BSs) are needed to cover a same area due to which deployment and networking of new BSs acquire significant costs [5]. An alternative solution to this problem is to deploy smart relay stations (RSs), which can communication with each other and with BSs through wireless connections reducing systems cost. A relay station (RS), also called repeater or multi-hop station, is a radio system that helps to improve coverage and capacity of a base station (BS) and the resulting networks employing relay stations are sometimes called cooperative networks [6]. 1.3 Technological Requirement The continuously evolving wireless multimedia services push the telecommunication industries to set a very high data rate requirement for next generation mobile communication systems. As spectrum resource becomes very scarce and expensive, how to utilize this resource wisely to fulfil high quality user experiences is a very challenging research topic. Orthogonal frequency-division multiple access (OFDMA)-based RRM schemes together with relaying techniques allocate different portions of radio resources to different users in both the frequency and time domains and offers a promising technology for providing ubiquitous high-data-rate coverage with comparatively low cost than deploying multiple base stations [5]. Although wireless services are the demand of future due to their mobility and low cost infrastructure but along with this they suffer serious channel impairments. In particular, the channel suffers from frequency selective fading and distance dependent fading (i.e., large-scale fading) [1, 8]. While frequency selective fading results in inter-symbol-interference (ISI), large-scale fading attenuates the transmitted signal below a level at which it can be correctly decoded. Orthogonal Frequency-Division Multiple Access (OFDMA) relay-enhanced cellular network, the integration of multi-hop relaying with OFDMA infrastructure, has become one of the most promising solutions for next-generation wireless communications. 1.3.1 Frequency Selective Fading In wireless communications, the transmitted signal is typically reaching the receiver through multiple propagation paths (reflections from buildings, etc.), each having a different relative delay and amplitude. This is called multipath propagation and causes different parts of the transmitted signal spectrum to be attenuated differently, which is known as frequency-selective fading. In addition to this, due to the mobility of transmitter and/or receiver or some other time-varying characteristics of the transmission environment, the principal characteristics of the wireless channel change in time which results in time-varying fading of the received signal [9]. 1.3.2 Large Scale Fading Large scale fading is explained by the gradual loss of received signal power (since it propagates in all directions) with transmitter-receiver (T-R) separation distance. These phenomenonss cause attenuation in the signal and decrease in its power. To overcome this we use diversity and multi-hop relaying. 1.3.3 Diversity Diversity refers to a method for improving the reliability of a message signal by using two or morecommunication channelswith different characteristics. Diversity plays an important role in combatingfadingandco-channel interferenceand avoidingerror bursts. It is based on the fact that individual channels experience different levels of fading and interference. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver [10]. 1.4 Proposed Simulation Model We developed a simulation model in which each user-pair is allocated dynamically a pair of relay and subcarrier in order to maximize its achievable sum-rate while satisfying the minimum rate requirement. The algorithm and the results of the simulation model are given in chapter 4. 1.5 Objectives The objective of our project is to have a detail overview of the literature regarding Orthogonal Frequency Division Multiple Access (OFDMA), Radio Resource Management (RRM) and Relaying techniques. After literature review we developed a simulation framework in which we will try to use minimum resources to get maximum throughput by using dynamic resource allocation. 1.6 Tools For the design and implementation of proposed Algorithm, we have used the following tools MATLAB Smart Draw Corel Draw 1.7 Overview Chapter 2 contains the literature review. It explains the basic principles of OFDMA, Radio Resource Management (RRM) and the relaying techniques. Chapter 3 explains the implementation of OFDM generation and reception that how an OFDM signal is generated and transmitted through the channel and how it is recovered at the receiver. Chapter 4 could be considered as the main part of thesis. It focuses on the simulation framework and the code. We have followed the paper Subcarrier Allocation for multiuser two-way OFDMA Relay networks with Fairness Constraints. In this section we have tried to implement the Dynamic Resource Allocation algorithm in order to achieve the maximum sum rate. Results are also discussed at the end of the end of the chapter. 2 Literature Review Introduction: First section of this Chapter gives a brief overview about OFDMA.OFDMA basically is the combination of Orthogonal Frequency Division Multiplexing (OFDM) and Frequency Division Multiplexing Access (FDMA).OFDMA provides high data rates even through multipath fading channels. In order to understand OFDMA, we must have brief introduction to Modulation, Multiple Access, Propagation mechanisms, its effects and its impairments while using OFDMA. 2.1 Modulation Modulation is the method of mapping data with change in carrier phase, amplitude, frequency or the combination [11]. There are two types of modulation techniques named as Single Carrier Modulation (SCM) Transmission Technique or Multicarrier Modulation (MCM) Transmission Technique. [12] Single Carrier Modulation (SCM) In single carrier transmission modulation (SCM) transmission, information is modulated using adjustment of frequency, phase and amplitude of a single carrier [12]. Multi Carrier Modulation (MCM) In multicarrier modulation transmission, input bit stream is split into several parallel bit streams then each bit stream simultaneously modulates with several sub-carriers (SCs) [12]. 2.2 Multiplexing Multiplexing is the method of sharing bandwidth and resources with other data channels. Multiplexing is sending multiple signals or streams of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end [13]. 2.2.1 Analog Transmission In analog transmission, signals are multiplexed using frequency division multiplexing (FDM), in which the carrier bandwidth is divided into sub channels of different frequency widths,and each signal is carried at the same time in parallel. 2.2.2 Digital Transmission In digital transmission, signals are commonly multiplexed using time-division multiplexing (TDM), in which the multiple signals are carried over the same channel in alternating time slots. 2.2.3 Need for OFDMA General wireless cellular systems are multi-users systems. We have limited radio resources as limited bandwidth and limited number of channels. The radio resources must be shared among multiple users. So OFDM is a better choice in this case. OFDM is the combination of modulation and multiplexing. It may be a modulation technique if we analyze the relation between input and output signals. It may be a multiplexing technique if we analyze the output signal which is the linear sum of modulated signal. In OFDM the signal is firstly split into sub channels, modulated and then re-multiplexed to create OFDM carrier. The spacing between carriers is such that they are orthogonal to one another. Therefore there is no need of guard band between carriers. In this way we are saving the bandwidth and utilizing our resources efficiently. 2.3 Radio Propagation Mechanisms There are 3 propagation mechanisms: Reflection, Diffraction and Scattering. These 3 phenomenon cause distortion in radio signal which give rise to propagation losses and fading in signals [14]. 2.3.1 Reflection Reflection occurs when a propagating Electro-Magnetic (EM) wave impinges upon an object which has very large dimensions as compared to the wavelength of the propagating wave. Reflections occur from the surface of the earth and from buildings and walls. 2.3.2 Diffraction When the radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities (edges), diffraction occurs. The secondary waves resulting from the obstructing surface are present throughout the space and even behind the obstacle, giving rise to a bending of waves around the obstacle, even when a line-of-sight path does not exist between transmitter and receiver. At high frequencies, diffraction, like reflection, depends on the geometry of the object, as well as the amplitude, phase and polarization of the incident wave at the point of diffraction. 2.3.3 Scattering When the medium through which the wave travels consists of objects with dimensions that are small compared to the wavelength, and where the number of obstacles per unit volume is large. Scattered waves are produced by rough surfaces, small objects or by other irregularities in the channel. In practice, foliage, street signs and lamp posts produce scattering in a mobile radio communications system. 2.4 Effects of Radio Propagation Mechanisms The three basic propagation mechanisms namely reflection, diffraction and scattering as we have explained above affect on the signal as it passes through the channel. These three radio propagation phenomena can usually be distinguished as large-scale path loss, shadowing and multipath fading [14][15]. 2.4.1 Path Loss Path Lossis the attenuation occurring by an electromagnetic wave in transit from a transmitter to a receiver in a telecommunication system. In simple words, it governs the deterministic attenuation power depending only upon the distance between two communicating entities. It is considered as large scale fading because it does not change rapidly. 2.4.2 Shadowing Shadowingis the result of movement of transmitter, receiver or any channel component referred to as (obstacles). Shadowing is a statistical parameter. Shadowing follows a log-normal distribution about the values governed by path loss. Although shadowing depends heavily upon the channel conditions and density of obstacles in the channel, it is also normally considered a large scale fading component alongside path loss. 2.4.3 Multipath Fading Multipath Fadingis the result of multiple propagation paths which are created by reflection, diffraction and scattering. When channel has multiple paths. Each of the paths created due to these mechanisms may have its characteristic power, delay and phase. So receiver will be receiving a large number of replicas of initially transmitted signal at each instant of time. The summation of these signals at receiver may cause constructive or destructive interferences depending upon the delays and phases of multiple signals. Due to its fast characteristic nature, multipath fading is called small scale fading. 2.5 Orthogonal Frequency Division Multiplexing (OFDM) Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multicarrier modulation that is robust to multi-path radio channel impairments [15]. Now-a-days it is widely accepted that OFDM is the most promising scheme in future high data-rate broadband wireless communication systems. OFDM is a special case of MCM transmission. In OFDM, high data rate input bit stream or data is first converted into several parallel bit stream, than each low rate bit stream is modulated with subcarrier. The several subcarriers are closely spaced. However being orthogonal they do not interfere with each other. 2.5.1 Orthognality Signals are orthogonal if they are mutually independent of each other. Orthogonality is a property that allows multiple information signals to be transmitted perfectly over a common channel and detected, without interference. Loss of orthogonality results in blurring between these information signals and degradation in communications. Many common multiplexing schemes are inherently orthogonal. The term OFDM has been reserved for a special form of FDM. The subcarriers in an OFDM signal are spaced as close as is theoretically possible while maintain orthogonality between them.In FDM there needs a guard band between channels to avoid interference between channels. The addition of guard band between channels greatly reduces the spectral efficiency. In OFDM, it was required to arrange sub carriers in such a way that the side band of each sub carrier overlap and signal is received without interference. The sub-carriers (SCs) must be orthogonal to each other, which eliminates the guard band and improves the spectral efficiency . 2.5.2 Conditions of orthogonality 2.5.2.1 Orthogonal Vectors Vectors A and B are two different vectors, they are said to be orthogonal if their dot product is zero 2.6 OFDM GENERATION AND RECEPTION OFDM signals are typically generated digitally due to the complexity of implementation in the analog domain. The transmission side is used to transmit digital data by mapping the subcarrier amplitude and phase. It then transforms this spectral representation of the data into the time domain using an Inverse Discrete Fourier Transform (IDFT) but due to much more computational efficiency in Inverse Fast Fourier Transform (IFFT), IFFT is used in all practical systems. The receiver side performs the reverse operations of the transmission side, mixing the RF signal to base band for processing, and then a Fast Fourier Transform (FFT) is employed to analyze the signal in the frequency domain. The demodulation of the frequency domain signal is then performed in order to obtain the transmitted digital data. The IFFT and the FFT are complementary function and the most suitable term depends on whether the signal is being recovered or transmitted but the cases where the signal is independent of this distinction then these terms can be used interchangeably [15]. 2.6.1 OFDM Block Diagram 2.6.2 Implementation of OFDM Block Diagram 2.6.2.1 Serial to Parallel Conversion: In an OFDM system, each channel can be broken down into number of sub-carriers. The use of sub-carriers can help to increase the spectral efficiency but requires additional processing by the transmitter and receiver which is necessary to convert a serial bit stream into several parallel bit streams to be divided among the individual carriers. This makes the processing faster as well as is used for mapping symbols on sub-carriers. 2.6.2.2 Modulation of Data: Once the bit stream has been divided among the individual sub-carriers by the use of serial to parallel converter, each sub-carrier is modulated using 16 QAM scheme as if it was an individual channel before all channels are combined back together and transmitted as a whole. 2.6.2.3 Inverse Fourier Transform: The role of the IFFT is to modulate each sub-channel onto the appropriate carrier thus after the required spectrum is worked out, an inverse Fourier transform is used to find the corresponding time domain waveform. 2.6.2.4 Parallel to Serial Conversion: Once the inverse Fourier transform has been done each symbol must be combined together and then transmitted as one signal. Thus, the parallel to serial conversion stage is the process of summing all sub-carriers and combining them into one signal 2.6.2.5 Channel: The OFDM signal is then transmitted over a channel with AWGN having SNR of 10 dB. 2.6.2.6 Receiver: The receiver basically does the reverse operations to the transmitter. The FFT of each symbol is taken to find the original transmitted spectrum. The phase angle of each transmission carrier is then evaluated and converted back to the data word by demodulating the received phase. The data words are then combined back to the same word size as the original data. 2.7 OFDMA in a broader perspective OFDM is a modulation scheme that allows digital data to be efficiently and reliably transmitted over a radio channel, even in multipath environments [17]. OFDM transmits data by using a large number of narrow bandwidth carriers. These carriers are regularly spaced in frequency, forming a block of spectrum. The frequency spacing and time synchronization of the carriers is chosen in such a way that the carriers are orthogonal, meaning that they do not interfere with each other. This is despite the carriers overlapping each other in the frequency domain [18]. The name OFDM is derived from the fact that the digital data is sent using many carriers, each of a different frequency (Frequency Division Multiplexing) and these carriers are orthogonal to each other [19]. 2.7.1 History of OFDMA The origins of OFDM development started in the late 1950s with the introduction of Frequency Division Multiplexing (FDM) for data communications. In 1966 Chang patented the structure of OFDM and published the concept of using orthogonal overlapping multi-tone signals for data communications. In 1971 Weinstein introduced the idea of using a Discrete Fourier Transform (DFT) for Implementation of the generation and reception of OFDM signals, eliminating the requirement for banks of analog subcarrier oscillators. This presented an opportunity for an easy implementation of OFDM, especially with the use of Fast Fourier Transforms (FFT), which are an efficient implementation of the DFT. This suggested that the easiest implementation of OFDM is with the use of Digital Signal Processing (DSP), which can implement FFT algorithms. It is only recently that the advances in integrated circuit technology have made the implementation of OFDM cost effective. The reliance on DSP prevented the wide spread use of OFDM during the early development of OFDM. It wasnt until the late 1980s that work began on the development of OFDM for commercial use, with the introduction of the Digital Audio Broadcasting (DAB) system . 2.7.2 Advantages using OFDMA There are some advantages using OFDMA. OFDM is a highly bandwidth efficient scheme because different sub-carriers are orthogonal but they are overlapping. Flexible and can be made adaptive; different modulation schemes for subcarriers, bit loading, adaptable bandwidth/data rates possible. Has excellent ICI performance because of addition of cyclic prefix. In OFDM equalization is performed in frequency domain which becomes very easy as compared to the time domain equalization. Very good at mitigating the effects of delay spread. Due to the use of many sub-carriers, the symbol duration on the sub-carriers is increased, relative to delay spread. ISI is avoided through the use of guard interval. Resistant to frequency selective fading as compared to single carrier system. Used for high data rate transmission. OFDMA provides flexibility of deployment across a variety of frequency bands with little need for modification is of paramount importance. A single frequency network can be used to provide excellent coverage and good frequency re-use. OFDMA offers frequency diversity by spreading the carriers all over the used spectrum. 2.7.3 Challenges using OFDMA These are the difficulties we have to face while using OFDMA [20][21][22], The OFDM signal suffers from a very high peak to average power ratio (PAPR) therefore it requires transmitter RF power amplifiers to be sufficiently linear in the range of high input power. Sensitive to carrier frequency offset, needs frequency offset correction in the receiver. Sensitive to oscillator phase noise, clean and stable oscillator required. The use of guard interval to mitigate ISI affects the bandwidth efficiency. OFDM is sensitive to Doppler shift frequency errors offset the receiver and if not corrected the orthogonality between the carriers is degraded. If only a few carriers are assigned to each user the resistance to selective fading will be degraded or lost. It has a relatively high sensitivity to frequency offsets as this degrades the orthogonality between the carriers. It is sensitive to phase noise on the oscillators as this degrades the orthogonaility between the carriers. 2.7.4 Comparison with CDMA in terms of benefits 2.7.4.2 CDMA Advantages: CDMA has some advantages over OFDMA [22], Not as complicated to implement as OFDM based systems. As CDMA has a wide bandwidth, it is difficult to equalise the overall spectrum significant levels of processing would be needed for this as it consists of a continuous signal and not discrete carriers. Not as easy to aggregate spectrum as for OFDM. 2.7.5 OFDMA in the Real World: UMTS, the European standard for the 3G cellular mobile communications, and IEEE 802.16, a broadband wireless access standard for metropolitan area networks (MAN), are two live examples for industrial support of OFDMA. Table 1 shows the basic parameters of these two systems. UMTS(Cellular ) IEEE IEEE 802.16 ( Wireless I IEEE 802.16 ( Wireless MAN ) System bandwidth 100kHz-1.6MHz (Flexible) 6Mhz Number of subcarriers 240 / 100kHz 2048 Subcarrier spacing 4.16kHz 3.35kHz n Subcarriers / Band-unit 24 Subcarrier/Bandslot 53 Subcarrier/Subchannel Modulation time 240 s 298 s Guard time 38 s (pre-) and 8 s (post-guard) 38 s Symbol time 288 s 340 s Resource allocation unit 1 bandslot, 1 timeslot (1 symbol) 1 Subchannel, 1 timeslot Modulation QPSK , 8-PSK QPSK, 16-QAM, 64-QAM (differential and coherent) Channel coding Convolutional (1/3, 2/3) Turbo (1/2) Opt. Outer Reed-Solomon (4/5) Frequency hopping 1 hop/burst, 876 hop/sec, 1.6MHz NA (Flexible) Max. Data throughput 11 Table 1. OFDMA system parameters in the UMTS and IEEE 802.16 standards 2.8 Radio Resource Management In second section of this chapter we will discuss radio resource management schemes, why we need them and how they improve the efficiency of the network. Radio resource management is the system level control of co-channel interference and other radio transmission characteristics in wireless communication systems. Radio resource management involves algorithms and strategies for controlling parameters such as Transmit power Sub carrier allocation Data rates Handover criteria Modulation scheme Error coding scheme, etc 2.8.1 Study of Radio Resource Management End-to-end reconfigurability has a strong impact on all aspects of the system, ranging from the terminal, to the air interface, up to the network side. Future network architectures must be flexible enough to support scalability as well as reconfigurable network elements, in order to provide the best possible resource management solutions in hand with cost effective network deployment. The ultimate aim is to increase spectrum efficiency through the use of more flexible spectrum allocation and radio resource management schemes, although suitable load balancing mechanisms are also desirable to maximize system capacity, to optimize QoS provision, and to increase spectrum efficiency. Once in place, mobile users will benefit from this by being able to access required services when and where needed, at an affordable cost. From an engineering point of view, the best possible solution can only be achieved when elements of the radio network are properly configured and suitable radio resource m anagement approaches/algorithms are applied. In other words, the efficient management of the whole reconfiguration decision process is necessary, in order to exploit the advantages provided by reconfigurability. For this purpose, future mobile radio networks must meet the challenge of providing higher quality of service through supporting increased mobility and throughput of multimedia services, even considering scarcity of spectrum resources. Although the size of frequency spectrum physically limits the capacity of radio networks, effective solutions to increase spectrum efficiency can optimize usage of available capacity. Through inspecting the needs of relevant participants in a mobile communication system, i.e., the Terminal, User, Service and Network, effective solutions can be used to define the communication configuration between the Terminal and Network, dependent on the requirements of Services demanded by Users. In other words, it is necessary to identify proper communications mechanisms between communications apparatus, based on the characteristics of users and their services. This raises further questions about how to manage traffic in heterogeneous networks in an efficient way. 2.8.2 Methods of RRM 2.8.2.1 Network based functions Admission control (AC) Load control (LC) Packet scheduler (PS) Resource Manager (RM) Admission control In the decision procedure AC will use threshold form network planning and from Interference measurements. The new connection should not impact the planned coverage and quality of existing Connections. (During the whole connection time.) AC estimates the UL and DL load increase which new connection would produce. AC uses load information from LC and PC. Load change depends on attributes of RAB: traffic and quality parameters. If UL or DL limit threshold is exceeded the RAB is not admitted. AC derives the transmitted bit rate, processing gain, Radio link initial quality parameters, target BER, BLER, Eb/No, SIR target. AC manages the bearer mapping The L1 parameters to be used during the call. AC initiates the forced call release, forced inter-frequency or intersystem handover. Load control Reason of load control Optimize the capacity of a cell and prevent overload The interference main resource criteria. LC measures continuously UL and DL interference. RRM acts based on the measurements and parameters from planning Preventive load control In normal conditions LC takes care that the network is not overloaded and remains Stable. Overload condition . LC is responsible for reducing the load and bringing the network back into operating area. Fast LC actions in BTS Lower SIR target for the uplink inner-loop PC. LC actions located in the RNC. Interact with PS and throttle back packet data traffic. Lower bit rates of RT users.(speech service or CS data). WCDMA interfrequency or GSM intersystem handover. Drop single calls in a controlled manner. 2.8.2.3 Connection based functions Handover Control (HC) Power Control (PC) Power control Uplink open loop power control. Downlink open loop power control. Power in downlink common channels. Uplink inner (closed) loop power control. Downlink inner (closed) loop power control. Outer loop power control. Power control in compressed mode. Handover Intersystem handover. Intrafrequency handover. Interfrequency handover. Intersystem handover. Hard handover (HHO). All the old radio links of an MS are released before the new radio links are established. Soft handover (SHO) SMS is simultaneously controlled by two or more cells belonging to different BTS of the same RNC or to different RNC. MS is controlled by at least two cells under one BTS. Mobile evaluated handover (MEHO) The UE mainly prepares the handover decision. The final decision is made by SRNC. Network evaluated handover (NEHO) The SRNC makes the handover decision. 2.8.3 Why we need RRM or Purpose of RRM? The rapid increase in the size of the wireless mobile community and its demands for high-speed multimedia communications stands in clear contrast to the rather limited spectrum resources that have been allocated in international agreements. Efficient spectrum or radio resource management (RRM) is of paramount importance due to these increasing demands. Purposes of RRM are as: Ensure planned coverage for each service. Ensure required connection quality. Ensure planned (low) blocking. Optimise the system usage in run time. 2.8.4 Joint Radio Resource Management (JRRM) In designing wireless systems, typical problems are encountered, such as the signal attenuation, terminal noise, fast fading due to the multipath phenomenon, shadowing, Multiple Access Interference (MAI) and other typical system related features, e.g. the mutual relation between interference strength and duration period given by link adaptation. These typical problems challenge the communication systems from using radio resources efficiently. The radio resources not only, by definition, the radio spectrum, but also realized in the real radio networks, access rights for individual mobile users, time period a mobile user being active, channelization codes, transmission power, connection mode, etc., that require the management functions being designed in different time scales. Furthermore, radio resources from different radio networks can be managed jointly in order to solve the encountered problems more effectively. The term Joint Resource Management (JRRM) is therefore generalized as: JRRM are the controlling mechanisms that support intelligent admission of calls and sessions for a set of networks or cell layers. They control the distribution of traffic, power and the variances of them, thereby aiming at an optimized usage of radio resources and maximized system capacity. JRRM mechanisms work over multiple radio networks or cell layers with the necessary support of reconfigurable/multi-mode terminals. JRRM is operated in a network which consists of several subnetworks or cell layers of a single radio network. The term subnetwork is defined in Definition I-2. The High Performance Radio Local Area Network Type 2 (H/2) as a typical WLAN RAT specified by ETSI (European Telecommunications Standards Institute) BRAN (Broadband Radio Access Networks) and UMTS/FDD specified by the 3rd Generation Partnership Project (3GPP) are two subnetworks studied in this thesis. 2.8.5 Sub-Carrier Allocation We have analyzed the Dynamic sub-carrier allocation algorithm the main of which is to allocate dynamically a pair of relay and subcarrier to each user-pair in order to minimize the achievable sum rate of each user-pair while satisfying the minimum rate requirement for every user-pair. 2.9 Relay Station and Relay Enhanced Systems A relay basically is a transceiver which creates a communication link between the source and destination [23]. It virtually can be considered as another transmitter. In third section of this chapter we will be discussing basic idea about Relay, Relay stations, Relaying and its strategies, Co-operative and non-cooperative relaying. But in order to understand these terms one must have idea about Cellular networks, their demand for coverage and capacity and the benefit of using relay station in order to increase the capacity [24]. 2.9.1 Cellular Networks Cellular networks are radio networks made up of a number of non-overlapping cells, each served by at least one base station, that cover a wide geographic area. Several frequencies are assigned to each cell, which can be reused in other cells. Cellular networks mainly consist of two parts: the radio access network or base station subsystem (BSS) and the core network, which are connected through a backhaul connection [24]. 2.9.1.1 Analog Transmission to Digital Transmission Cellular networks appeared in the 1960s and used analog communications. Second generation systems moved from analog to digital due to its many advantages. The components are cheaper, faster, smaller, and require less power. Voice quality is improved due to error correction coding. Digital systems also have higher capacity than analog systems since they can use more spectrally-efficient digital modulation and more efficient techniques to share the cellular spectrum. They can also take advantage of advanced compression techniques and voice activity factors. In addition, encryption techniques can be used to secure digital signals against eavesdropping. Digital systems can also offer data services in addition to voice, including short messaging, e-mail, Internet access, multimedia capabilities, etc [24]. 2.9.1.2 Base Station Subsystem The base station subsystem is responsible for handling traffic and signaling between the core network and the user. It consists of a network of base station transceivers (called nodes) grouped under several base station controllers (BSC or Radio Network Controllers (RNC)) which are connected to the core network. A single BSC can have tens or even hundreds of BTSs under its control. The BSC handles allocation of radio channels, is in charge of admission control, receives measurements from the mobile phones, controls handovers from BTS to BTS, etc. The BSC can route voice calls through the public switched telephone network (PSTN) or provide Internet access. It also acts as a concentrator of low capacity connections to and from the BTS into a high capacity connection to and from the core network. The Base Station is in charge of the radio interface: scrambling, modulation, scheduling, adaptative coding, link quality measurements, soft handovers, etc[24]. 2.9.2 Core Network The core network is in charge of routing and forwarding the user data, handovers between different technologies, it manages the databases with the user and terminals information, security issues, etc. The core network in cellular networks has suffered several changes over the last decade. For example, in the GSM second generation networks a new packet commuting network was added later to give support to GPRS technology which included gateways to external IP networks. Later on, with third generation networks like UMTS and its several releases, the core network was expanded to support soft switching (release 4) or multimedia transmissions (release 5 with the multimedia subsystem). Presently, the core network is evolving to an all-IP network in future generation networks [24]. 2.9.4 Coverage Area The coverage area of a cell is the expected percentage of the cells area where the received power is greater than a certain minimum, given that the user terminals require a minimum received SNR for acceptable performance. 2.9.5 Capacity Capacity refers to the theoretical maximum transmission rate that can be achieved over a wireless channel. 2.9.6 Need of using Relay Technology Presently, the amount of free spectrum is decreasing, and future networks will have to use the available bands at higher frequencies, meaning a decrease in coverage and an increase in base station density. Moreover, next generation cellular networks are expected to support different types of services including web browsing, FTP, video streaming, VoIP, online gaming, real time video, etc., therefore require even higher transmission rates. Physical layer technologies such as OFDM, smart antennas and Multiple Input Multiple Output (MIMO) systems are being designed to achieve this goal. Relay technology can be used both to increase capacity and coverage, as many papers have proved thus far [24]. 2.10 Relay A relay is a node that receives information from the source and forwards it to the destination, so it can assist in a transmission to improve performance. Relays can have many applications, like capacity enhancement, load balancing or coverage extension of cells, which is what we are interested in. SOURCE RELAY DESTINATION 2.10.1 Why to use Relay Some reasons which become the reason of deploying relays [25], Mobile stations can transmit at lower power. Transmission at higher frequencies is more vulnerable to non LOS conditions. The transmission power required for high data rates at large distances is very high Increasing the base station density is one option A relay acts as a helper node to increase coverage and throughput. Relay is connected to the base station through wireless channel. Relays are much closer to the mobile stations than the base station; hence high data rates are possible. 2.10.2 Cooperative relaying In general, every communicating system has a source node that broadcast the signal towards the multiple/helping relays in the network, which in turn re transmits the processed version towards the destination [26]. 2.10.2.1 Benefits of using Cooperative Relaying Cooperative relaying provides [27], Better BER performance due to spatial diversity Higher efficiency due to spatial multiplexing 2.10.2.2 Two methods of Cooperative Relaying There are two phases through which a signal have to move in order to reach the destination utilizing cooperative environment, Broadcasting Mode (BA) When the source broadcasts the signal towards multiple relays present in between destination and source. Multiple Access Mode (MA) When different relays transmits their data towards a single destination. This mode of transferring info from multiple relays to single destination is multiple access mode. 2.10.3 Multihop Communication Multi-hop communication occurs when data travel from the source to the destination node via more than two hops. This could be achieved without need of other costly BSs. The maximum allowed number of hops must be carefully considered (higher number of hops increases a transmission time). Multi-hop based network may also improve system performance thanks to cooperative relay technique. This is accomplished by sending information simultaneously via multiple different paths and combining the received information at the side of receiver [28]. 2.10.4 Relay Station A relay station is an intermediate station/node that passes information between terminals or other relay stations and is used to help a base station to improve its coverage and capacity. Relay station has other names such as repeater, or multi-hop station and the networks that use relay stations are sometimes called cooperative networks [29]. The notion of relay channel appeared in the late 60s. E. C. van der Meulen introduced the idea of a three-terminal communication channel consisting of a source, a destination and a relay. T. M. Cover and A. El Gamal later published a paper where they computed upper and lower bounds for the capacity of the single relay channel and give an exact expression for the Gaussian degraded case. Given the complexity of the relay channel, it hasnt been until the exhaustive research on MIMO channels over the last decade that relay networks have been on the spot again, and recently there have been many publications on the topic [24]. 2.10.4.1 Concept of Relay Figure 2.3 Relaying System RS will typically cover a region up to 300 miles in diameter and transmit at lower power level than BS. Relays do not have wired connection to backhaul. Cooperative diversity is additional advantage of relaying [25]. 2.10.4.2 Relay station vs. Base Station The primary advantage of deploying relay stations in terms of the cost is expected to come from the differences in the cost of the backhaul. When a relay station is deployed, instead of a Base Station with a wired backhaul connection, there are no direct backhaul costs. There is no cost for provisioning the wired connection, and there are no monthly charges for the backhaul. Similarly, when a relay station is deployed, instead of a Base Station with wireless backhaul, the use of a relay station eliminates the need to purchase, set up, and maintain microwave link equipment, and to purchase the rights to additional spectrum in which this equipment operates. Relay Stations are also expected to be less costly to deploy because they do not require line of sight channel conditions on the relay link, allowing greater flexibility in site selection than for a Base Stations with wireless backhaul. The idea behind a relay channel is to use the relay to create spatial diversity sending the same signal through independent fading paths. This can be done in two steps. Firstly, the source broadcasts the signal both to the relay and the destination. In the second step, the relay transmits the received signal to the destination, so the destination ends up with two different independent versions of the same signal. The way in which the relay processes and retransmits the received signal to the destination has given rise to several strategies which have been deeply analyzed in the literature [24]. 2.10.5 Relaying Strategies There are many relaying strategies; three of them are discussed below 2.10.5.1 Amplify-and-Forward (AF) This is the simplest strategy that can be used at the relay because it acts as a dummy with a constraint on the maximum power. The relay amplifies the received signal from the source and transmits it to the destination without doing any decision. The main drawback of this strategy is that the relay terminal is also amplifying the received noise to the destination. When this strategy is applied to the cooperative communication, it is able to obtain a better uncoded bit error rate (BER) than direct transmission [5]. Additionally, the outage probability of the cooperative communication is also derived, demonstrating that a diversity order of two is obtained for two cooperative users. When the relay is equipped with multiple antennas and there is channel state information (CSI) of the source-relay and relay destination links, the AF strategy can attain significant gains over the direct transmission by means of optimum linear filtering the data to be forwarded by the relay [30]. In AF strategy, the relay simply amplifies the noisy version of the signal it has received in the first step and retransmits this noisy version. The destination then combines both signals to decide the transmitted bit. More generally, AF refers to any strategy where the relay linearly transforms the received signal. Although noise is also amplified in the relay, this strategy produces two independent versions of the same signal at the destination which allow for a better detection of the information sent. It has been proved that this strategy is optimal at high SNR, achieving diversity of order two [24]. 2.10.5.2 Decode-and-Forward (DF) In DF strategies, the relay tries to detect the received information, re-encodes and retransmits the signal after detection. If detection is unsuccessful the relaying can be harmful when detecting at the destination, therefore the strategy should be implemented such that the relay only retransmits the information when detection is successful. DF requires more complex devices than AF methods, but the noise at the receiver is much lower [24]. The RS decodes the signal and performs error correction. The decoded data is encoded using the same or different codebook before transmitting to the destination. The two phases need not be of same duration [25]. 2.10.5.3 Compress-and-Forward (CF) In this case, the relay performs a non-linear transformation on the received signal and then retransmits to destination. In this way, the relay station can compress the received signal and forward it to destination without the need to decode it. Some typical examples of CF strategies are Estimate and Forward or Quantize and Forward [24]. The relay compresses the received signal by using Wyner-Ziv lossy source coding and forwards it to the destination [25]. 2.10.5.4 Relaying Techniques (Some Facts) DF performs well only when the channel quality between BS and the RS is good. Only advantage of AF is that it is computationally less intensive at the relay. CF technique performs better than direct transmission in all channel conditions even if channel between BS and RS is degraded. CF is computationally intensive. CF is not considered for Wimax relaying [31]. 2.10.6 Relay usage Scenarios These are the Relay usage scenarios created for IEEE 802.16j. 2.10.6.1 Fixed Infrastructure Fixed-infrastructure relays, like BSs, are to be deployed by the service provider in stationary areas to serve general traffic. They are intended to increase both throughput and coverage because they are likely to be placed above roof tops to allow an LOS with the BS, but this may not always be the case. This category also may include commercial relays purchased by a subscriber, which may leave and enter the network at any time [31]. Fixed Infrastructure is to improve coverage in shadow areas and increase throughput due to LOS communication [25]. 2.10.6.2 In-Building Coverage Even with the relatively small demands of voice service, current mobile phones often perform poorly inside buildings. Relays are expected to be placed both by the service provider and by the end user near the shell, or just inside, of the building to fill the coverage hole inside. This type of relay also can be deployed near tunnels or subways to provide coverage where there is otherwise none. These relays can be nomadic and likely will operate with NLOS channels. Intriguingly, they may operate on battery power and probably will have low complexity [31]. In-Building coverage scenario is to fill the coverage hole inside the building [25]. 2.10.6.3 Temporary Coverage Events where a large group of people are densely packed into a small area form a unique opportunity for relays. The multihop capability of 802.16j will enable some of the traffic generated by this dense population to be routed to BSs in adjacent cells. Near stadiums, this infrastructure can be placed by the service provider as a permanent solution. Temporary relays also can be deployed in emergencies where some BSs may have been damaged. For this reason, temporary coverage relays may be required to run on batteries and will range from small and simple to large and complex [31]. Temporary coverage is for the stadiums or gatherings of people during an event. It is also temporary replacement to a damaged relay [25]. 2.10.6.4 Coverage on Mobile Vehicle A mobile vehicle, such as a train or bus, presents unique challenges to communications engineers. Usually, there are several people located very closely together, and the vehicle is moving, sometimes very quickly, through cells. To provide reliable coverage to such users, a complex relay may be deployed on the vehicle and obviously, will be highly mobile [31]. A complex relay is required that can handle quick handoffs while providing coverage in train or bus [25]. 2.10.7 Diversity Multipaths in certain scenarios create fading in the received signal. Due to the high possibility of the multipaths and fading nature of the channel, Diversity technique is being organized which can effectively reduce that fading effects and provides much better reception at the receiver side by achieving same signal trough different channels which in turn with some appropriate combining scheme decreasing probability of BER of the signal and provides better communication result [32]. There are three ways of achieving diversity. Transmit Diversity Receive Diversity MIMO Diversity 2.10.7.1 Cooperative Diversity Cooperative diversityis a cooperative multiple antenna technique for improving or maximising total networkchannel capacitiesfor any given set of bandwidths which exploits userdiversityby decoding the combined signal of the relayed signal and the direct signal in wireless multihop networks. 2.10.7.2 Spatial Diversity Spatial diversityis one of several wirelessdiversity schemesthat use two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clearline-of-sight(LOS) between transmitter and receiver. Instead the signal is reflected along multiple paths before finally being received. Multiple paths created by use of relay can be used to exploit spatial diversity. 3 OFDM Simulation and Results In this chapter, we will discuss about simulation model of OFDM transceiver developed in MATLAB and will be discussing the simulation results. 3.1 OFDM Transceiver implementation Simulation for implementation of basic OFDM transceiver is divided into three portions: OFDM Transmitter Channel OFDM Receiver 3.2 OFDM Transmitter OFDM Transmitter simulation consists of the following steps as shown is Figure 5.1. Binary Data Generation Conversion of Serial input data into Parallel format Modulation of each symbol using 16 QAM IFFT block of each modulated symbol Generation of OFDM signal by combining symbols in serial fashion 3.3 Channel Channel that we implement in simulation is AWGN with 10 dB SNR 3.4 OFDM Receiver OFDM Receiver simulation consists of the following steps as shown in Figure 5.2. Reception of Signal through channel and converting into parallel fashion FFT of each symbol QAM demodulation Parallel to Serial Conversion to recover the transmitted data 3.5 Results of Simulation Model 3.5.1 Message Signal A random Signal is generated using MATLAB built-in function binornd and is plotted as shown in Figure 5.3 Modulated Signal Each symbol is passed through the QAM modulator using qammod built-in function in MATLAB and the scatter plot is obtained as shown in figure 5.4 Signal through Channel The signal is passed through the channel which is considered as Additive White Gaussian Noise and its scatter plot is given in the Figure 5.5. Demodulation The received signal is converted into parallel format and then each symbol is demodulated using MATLAB built-in function qamdemod. The scatter plot obtained is shown in the Figure 5.6 Recovered Signal The demodulated symbols are then combined together in order to have the data transmitted data as shown in Figure 5.7 3.6 Conclusion We have analyzed that how an OFDM signal is generated typically digitally and found that with 10dB SNR signal can be recovered easily but below that SNR there are chances of error in the recovered signal 4 Implementation of Dynamic Subcarrier Allocation ( DSA) Algorithm In this chapter, we will discuss about the research paper we followed during our final year project and the implementation of the algorithm Dynamic Subcarrier Allocation (DSA) proposed in the research paper followed. 4.1 Introduction to Research Paper During our final year project we have studied many research papers and selected Subcarrier Allocation for Multiuser Two-Way OFDMA Relay Networks with Fairness Constraints by Hanmok Shin and Jae Hong Lee, Seoul National University, Korea, published at VTC. In this paper we analyzed an adaptive subcarrier allocation scheme for a multiuser two-way OFMDA relay network having multiple user-pairs and multiple relays. 4.1.1 One-way versus Two-way Half duplex relaying systems 4.1.1.1 One-way Half duplex relaying Systems In one-way half-duplex mode relays dont transmit and receive simultaneously at same time and frequency as shown in Figure 6.1. The main disadvantage of these relaying systems is a loss in throughput compared with full-duplex relaying. 4.1.1.2 Two-way Half duplex relaying Systems In two-way half-duplex relaying systems two users communicate with each other in two phases: Phase 1 Phase 1 is the Multiple Access (MA) phase in which all users transmit their information simultaneously to relays. Phase 2 Phase 2 is the Broadcast (BC) phase in which the relay amplifies the received signal and then broadcast it to all the users using same sub-carrier. Both these phases are shown in Figure 6.2. Compared with traditional one-way half-duplex relaying systems, these systems achieve higher power and spectral efficiencies by allowing simultaneous message exchange between a BS and the users [1]. In two-way half-duplex relaying both Amplify and Forward (AF) and Decode and Forward (DF) protocols can be used but AF protocol due to its simple transceiver design is more appealing in practice and is also considered in the paper followed. 4.2 Dynamic Sub-carrier Allocation (DSA ) Algorithm We have analyzed the Dynamic sub-carrier allocation algorithm the main aim of which is to allocate dynamically a pair of relay and subcarrier to each user-pair in order to maximize the achievable sum-rate of each user-pair while satisfying the minimum rate requirement for every user-pair. The algorithm is divided into three main steps given below: Step 1 In the first step, all sets and subcarrier assignment indicator variables are initialized, where the set of user-pairs, relays, and subcarriers are denoted by K , M , and N , respectively. Set: K={1,2,.,K} M = {1, 2, . . .,M} N={1,2,,N} k,m(n)= 0 Step 2 In the second step, one relay-subcarrier pair (m*,n*) which maximizes the instantaneous rate (rk,m(n)) is allocated to one user-pair for all user-pairs. for k = 1 : K do (m*,n*) = arg max rk,m(n) , m M, n N k,m*(n*) = 1 , N = N {n*}; Update rk end where rk is achievable rate of the kth user-pair. Step 3 In the third step, remaining subcarriers are allocated to the user-pairs and relays under the maximum transmit power constraints of the users and relays. while N do k*=arg min rk , k K if rk* rmin then (m*,n*) = arg max rk*,m(n) , m M, n N k*,m*(n*) = 1 , N = N {n*}; If n=1NpAk*(n)=n=1NpBk*(n)PU then K = K {k*} ; end If n=1NpRm*(n)PR then M = M {m*}; end else n* = rand (N); (k*,m*) = arg max rk,m n* , m M, k K k,m*(n*)=1, N = N { n* }; If n=1NpAk*(n)=n=1NpBk*(n)PU then K = K {k*} ; end If n=1NpRm*(n)PR then M = M {m*}; end end Update rk end Where PU and PR denote the maximum transmit power of each of users and relays, respectively. pAk(n) and pBk(n) denote the transmit power of the user Ak and Bk on the subcarrier n, respectively. 4.3 Simulation Framework and Results 4.3.1 Simulation Parameters We considered the values of parameter in our simulation framework as shown in Table 6.1 Parameter Value No. of User-pairs 8 No. of Relays 3 No. of Sub-carriers 128 Minimum rate requirement 2.5 Mbps Maximum Transmitting power of each user 100 mWatts Maximum Transmitting power of relay 3000 mWatts Table 4.1 4.3.2 Simulation Results We developed the simulation framework to implement the DSA algorithm in MATLAB by employing the above parameters and found the results as shown in Figure 6.3. Results shows that subcarriers are allocated to each user-pair unless each user-pair or each relay meets its maximum power constraint else all the subcarriers will be allocated to all the user-pairs while satisfying the minimum rate requirement for every user-pair. 5 Conclusions Future Work 5.1 Conclusion: Our work basically involved study of relaying and OFDMA technologies. We analyzed adaptive subcarrier allocation algorithm for a multiuser two-way OFDMA relay network. In the DSA algorithm, subcarriers are allocated to the user-pairs with lowest achievable rate to satisfy the minimum rate requirement .We have developed its simulation framework by assigning the subcarriers and relays to the user-pairs depending upon their transmitting powers. 5.2 Future Work: Working on OFDMA technology to enhance its role in its competitive market is of great importance due to its high data rate feature.

The Rwandan Genocide Began On April 6Th 1994 Culminating

The Rwandan Genocide began on April 6th 1994 culminating in the killing of an estimated 800,000 Hutus and their sympathizers. After it became apparent that the Rwandan government was not willing or able to protect it s citizens, the question became why did the international community do nothing to intervene. Rwandan citizens’ lived under the premise, that their rights are protected under UN accords and treaties. The Genocide Convention of 1948, outlined the responsibilities of the participating countries under. However, the International community did not abide by the Convention. In Article 3 of the convention, it states that it is a punishable crime to commit genocide, plan or conspire to commit genocide, incite or cause other†¦show more content†¦The UN s lack of intervention, was based mainly on economics and conflict avoidance. The UNAMIR was an understaffed peacekeeping force which was ill-equipt intentionally, to keep costs low. With that in mind, the UN simply didn t want the added expense of sending extra troops to Rwanda.[7] An example of this mindset was evident in the actions of the United States. After suffering recent losses in Somalia, the United States was not interested in being involved in another costly conflict.[8] However, as the atrocities in Rwanda escalated, the UN had no choice but to act. On May 17, 1994, the UN finally agreed on the deployment of 5,000 to Rwanda, but their departure was delayed due to arguments regarding who will pay for them.[9] The UN had a legal and moral obligation to intervene sooner. As a former colony, the presence of colonialism in a country, will impose values and rule of law onto the culture. Some would say, former colonizing nations have legal reparative obligations, to their former colony when the colony is in transition to Nationhood. There is an argument to be made as to the damage done to a culture by being colonized. Before German colonization of Rwanda, the Tutsi-Hutu were divided by socioeconomic class, not ethnicity.[10] The Tutsi reigned peacefully over theShow MoreRelatedOutline of the Rwandan Genocide2079 Words   |  9 PagesOutline of the Rwandan Genocide: Draft Introduction Rwanda is a small land-locked nation, about 26,338 square kilometres in size, bordered by Burundi, Democratic Republic of Congo, Uganda and Tanzania. Though mainly flat, the country has a large mountain range on its northwest coast – the Virunga Mountains – that are home to the famous Rwandan Mountain Gorillas. In 1994, this seemingly insignificant country put itself on the world map, but for all the wrong reasons. Over a period of just one hundredRead MoreOne Significant Change That Has Occurred in the World Between 1900 and 2005. Explain the Impact This Change Has Made on Our Lives and Why It Is an Important Change.163893 Words   |  656 Pagesdepression from the late 1860s to the 1890s, as well as the social tensions and political rivalries that generated and were in turn fed by imperialist expansionism, one cannot begin to comprehend the causes and consequences of the Great War that began in 1914. That conflict determined the contours of the twentieth century in myriad ways. On the one hand, the war set in motion transformative processes that were clearly major departures from those that defined the nineteenth-century world order