Spectrum Sensing and Spectrum Sensing Techniques

Spectrum Sensing and Spectrum Sensing Techniques Chapter 1.Introduction In recent years there has been an enormous growth in wireless communication devices and wireless users. The ever increasing demand for higher speed and reliability made researchers think about intelligent radios like Cognitive Radios (CR). But major amount of spectrum is available for licensed users. There are various communication bodies like the International Telecommunication Union (ITU), European Conference of Postal and Telecommunications Administrations (CEPT) also European Telecommunications Standards Institute (ETSI) who works on standards of communication that defines the use of spectrum for licensed and unlicensed users. 1.1 Background Spectrum is a valuable resource in communication. Over the past few years as the use of various wireless technology is increasing rapidly so we either need more spectrum or make efficient use of current spectrum to satisfy their needs. One way of making efficient use of spectrum is employing spectrum sharing technique. There are many spectrum sharing techniques available like energy detection, cyclostationary feature detector, and matched filter. Of the above technique matched filter and cyclostationary gives more accurate result but they are bit complex and computationally harder as compared to energy detection technique. Energy detection is the simplest of above three and computationally less complex. 1.2 Motivation Survey has shown that at any given time only portion of spectrum is utilized. According to a report published by FCC (Federal Communications Commission America) in 2003 has set a set of rule for efficient use of spectrum for licensed and unlicensed users. Also OFCOM (Office of Communications United Kingdom) has noticed the underutilization of spectrum. At any given time only portion of spectrum is utilized. Even if the system says there are no frequencies available, there is still some frequency available. These available frequencies are known as spectrum holes or white spaces. Some of the bands are completely occupied by users while some bands go unutilized. And that is inefficient use of spectrum. We must have noticed that in cases of emergencies like the train bomb blast in July 2006 in Mumbai, India cellular network actually failed to support huge amount of customer at the same time, this was also the case during 9/11 in USA. If we were having cognitive radios at that time peop les would have been able to talk to their families and inform about their safety. As we are moving from 3G (Third generation) to 4G (Fourth Generation) we need to make certain changes in our wireless technologies. Below shown is the measurement of 0 GHz to 6 GHz at Berkley Wireless Research Center (BWRC). 1.3 Aim and Objective This thesis emphasises on understanding Cognitive radios, the importance of spectrum sensing for todays world, the issues regarding the same. A simplified Matlab code is used to support our thesis. As the thesis follows you will find more about cognitive radios and spectrum sensing with a technique to generate white space at a specific frequency. The main objective of the thesis is to do survey on spectrum sensing and spectrum sensing techniques. Then do plan a model for the same. A model can be supported by a Matlab code. And after all this we need to analyse the model we suggested and further improvements that can be done in that. 1.4 Thesis Organisation Our thesis is organised as follows: Chapter.2 Literature Review This chapter begins with a brief history about cognitive radios .Which is followed by a detail explanation of Cognitive radios and spectrum sensing and some of the spectrum sensing techniques used. At the end of this chapter a business model for spectrum sensing and multi resolution of CR is given. Chapter.3 System Description This chapter basically deals with sampling and its importance to us. Also you will find technique to get your spectrum at specific center frequency under â€Å"generation of White Spaces†. Chapter.4 Simulation/Design Analysis As the name suggests, this chapter deals with simulation model and detail explanation of the code used for spectrum sensing using energy detection. In this chapter we have shown the output of the simulation used. Chapter.6 Future Work This chapter suggests some of the future work to be done with this thesis which could be useful for further research in this field. Chapter.7 Conclusion This gives the concluding part of the thesis. Chapter 2 Literature Review In this chapter we are going to discuss about the cognitive radios, like what are they and why are they so important to us. The chapter begins with a short history of cognitive radios, which is followed by a general discussion on OFDM, some of the challenges faced by cognitive radios in real environment, and also some of the applications of cognitive radios. We have tried to explain spectrum sensing in brief and the techniques used for spectrum sensing in todays world. Finally a business model for spectrum sensing is showed which is preceded by multi-resolution of Cognitive radios. 2.1 History of cognitive radios Dr. Joseph Mitola III was the first to introduce or propose the theory of Cognitive radios in 1999. According to Dr. Joseph Mitola Cognitive radios will be the radios that are smart and intelligent enough to find the available bandwidth in a spectrum. It will also have knowledge of right information that has to be passed to the user. And user does not have to take some extra effort for that. It is supposed to do this automatically. He has also mentioned in his PhD dissertation that CR is natural extensions of software defined radios. In 2002 the FCC published a report prepared by Spectrum Policy Task Force [SPTF] which says that majority of spectrum is underutilized. And there is actually is not shortage of spectrum but rather we need to make efficient use of the current spectrum. Also in same year 2002 Professor Cave from UK presented a report which speaks of the possibility of selling bandwidth to the user depending on their requirement. But it would not be fair to give unlicensed user allow to use licensed spectrum. So in December 2002 FCC issued a Notice of Enquiry (NOI) to see TV channel bands can be made available to unlicensed users. Then in 2003 FCC forms a set of rules and proposed interference temperature model for keep track of interference. Later in the same year Notice of Proposed Rulemaking (NPRM) tried to see into issues related to cognitive radio technology where it also pointed out Cognitive radios is a advanced technology which could help efficient use of spectrum by licensed users in own network and by sharing spectrum and with unlicensed users by negotiating when required. This encouraged many researchers in the field of cognitive radios. Major progress in cognitive radios took place in the year 2004, where FCC published NRPM which showed possibility of allowing secondary users to use licensed spectrum. FCC opened three bands for unlicensed users which are 6525 to 6700 MHz, 12.75 to 13.15 GHz and 13.2125-13.25 GHz. This allowed cognitive dev ices to transmit six times more. Also IEEE standards are working parallel to the FCCs. Spectrum pooling system by Professor Timo A Weiss from Karlsruhe University Germany), OFDM based Cognitive radios by professor Ian F Akyildiz et al from GIT (USA) are some of the promising works in Cognitive radios. there are many researches are done, many still going on in Europe, Asia, and America, exploring various aspects of cognitive radios. In Jan 2010 first call over a CR network was made in university of Oulu using CRAMNET (Cognitive Radio Assisted Mobile Ad Hoc Network). 2.2 Cognitive radio With the development of wireless communication devices and technologies in WLAN and WAN spectrum is becoming scarcer. Low frequency bands which are near few GHz are very scarce and highly congested. In current wireless system we are using fixed spectrum allocation scheme. In fixed spectrum allocation scheme a part of spectrum is owned by an operator. Unlicensed users are not allowed to use that spectrum. This leads to the problem of spectrum scarcity. Survey has shown that more than 50% of the spectrum is underutilized. This is where Cognitive Radio (CR) is comes into picture. CR is introduced to solve the problem of spectrum sharing. Cognitive Radios actually scans the spectrum and during scanning it looks for spectrum holes. The main objective of the cognitive radios is to look for opportunities or white spaces in spectrum band as quickly and as much as possible. And when we say opportunity, opportunity could be in time or frequency domain. Also when we locate this spectrum holes opportunistically we also need to vacant the occupied spectrum as soon as primary user comes back. Here primary user means the users whose spectrum we are using (licensed user) and secondary means the unlicensed users. Cognitive radio is a pattern for wireless communication technology in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. These altered parameters are associated with the active monitoring of several factors in the external and internal radio environment e.g. radio frequency spectrum, user behaviour. Cognitive radio can be said as next generation of software defined radio (SDR). They are flexible in terms of their transmission characteristics in terms of frequency, bandwidth, ISP which makes smart decisions to configure the SDR at any point in time to achieve a particular goal. By combining these two technologies makes a radio intelligent and flexible and which helps to adapt it to the variations in the environment, user requirements as per the other radio users. Adaptation to changes and requirements should lead to highly reliable communication whenever and wherever required, while making efficient use of spectrum. Good cognitive radio uses analysis done for long period to know about the environment and also his own behaviour. There are various parameters taken into account to decide transmission and reception changes, we can distinguish certain types of cognitive radio. The main two are as follow: Full Cognitive Radio : It is also known as Mitola radio in which every possible parameter which can be observed by a wireless node is taken into consideration to take decision Spectrum Sensing Cognitive Radio: It is the type in which only the radio frequency spectrum is considered. And Depending on the parts of the spectrum available for cognitive radio, we can distinguish as: Licensed Band Cognitive Radio: It is the type in which cognitive radio is capable of using bands assigned to licensed users, apart from unlicensed bands, such as U-NII band or ISM band. Unlicensed Band Cognitive Radio: This can only utilize unlicensed parts of radio frequency spectrum only or the bands which are free to use. 2.3 About OFDM OFDM stands for Orthogonal Frequency Division Multiplexing. It is generally a type of Frequency Division Multiplexing (FDM) rather a special case in FDM. What makes it special is its orthogonal behaviour. Now the word orthogonal basically means mutually independence. When we say A is orthogonal to B, we mean that A has no vector in direction of B and vice versa or in other words A and B is mutually independent. Or the integral of two signals over one period is 0. In OFDM a single signal is first multiplexed and modulated independently to create orthogonal signals. This means the signal is first divided into number of smaller streams and then modulated further before transmission. For example imagine a slicing of cheese and grilling or cheese. Slicing is like FDM where whole data is sent in a bunch and grilling is like OFDM where the data to be sent is first divided into smaller data and then processed to transmit further like OFDM. Figure shown below is one more way to understand the concept of OFDM. On the left hand side is a big container which carry whole bunch of data at one time and take it to the destination. And on right hand side is four smaller containers where each carry smaller portion of data and take it to the destination. These smaller containers can be assumed as sub-carriers. And in case of OFDM they are orthogonal sub-carriers. The main advantage over here is that even if some of the cheese is lost during grilling, still we have not lost all the cheese. In OFDM input data with high data rate is first passed thorough serial to parallel converter. This parallel divided data is then modulated on individually. And parallel to serial conversion is done before transmission. This parallel divided data is our sub-carriers. These sub-carriers must be orthogonal. 2.4 Cognition cycle Above figure shows the rough model of Cognition Cycle. It reads the surrounding environment and makes decision accordingly. When we say decision we mean cognitive radio sense the requirement or urgency that may be in terms of changing a channel or churning from one technology to another depending upon the scenario. There are different stages where it observes the environment, learns it and then plans its action make required decision and then execute its plans. It is much like a radio with a power of thinking which was not been able before. The figure below shows the cognitive radio architecture suggested by Dr. Mitola. 2.4.1 Some important terms 2.4.1.1Wireless Environment/Outside world- It refers to a communication environment that includes any communication devices and the frequency bands they are working in. 2.4.1.2 Spectrum sensing- It is the technique used by cognitive radios to sense the spectrum. This action involves finding availability of white spaces or spectrum holes in the spectrum. 2.4.1.3 Spectrum Management- It involves catching the best spectrum available so as to satisfy user communication requirements. Cognitive radios should decide on the best spectrum band so that it can meet the Quality of service required for all available frequency bands, therefore these functions are necessary for Cognitive radios. These management functions can be classified as: Spectrum analysis Spectrum decision Spectrum Mobility: It is defined as the process when a cognitive radio device exchanges its frequency of operation. Cognitive radio networks target to use the spectrum in a dynamic manner by allowing the radio terminals to operate in the best available frequency band, maintaining seamless communication requirements during the transition to better spectrum. Spectrum Sharing: providing the fair spectrum scheduling method. One of the major challenges in open spectrum usage is the spectrum sharing. It can be regarded to be similar to generic media access control MAC problems in existing systems 2.5Cognitive Radio Challenges Three main problems experienced by CR are as follows: Interference (Mainly because of Hidden Nodes). Security. Control. They are described as follows: 2.5.1 Interference and the Hidden Node Problem Ideally while designing a CR we should consider that it does not have any impact on existing radio users, but in practically some impact is expected. If a particular user have non-cognitive radios, it is essential to study and make a note that how they would be affected by the interference of CR, mainly with respect to sharing resources such as spectrum, time, space etc. CR adaptive nature could be difficult to predict and thus making it hard to control the behaviour of a CR which will concern for user who faces CR interference issue. In communication industry the main concern about CR is the hidden node problem. This scenario arises when a CR is not capable to detect an interference with any of non-cognitive radios within its range, not only because of CRs own spectrum sensing is ineffective but also due to some non-cognitive radios are hidden. For example, if a transmitting contemporary user is not in the range from the CR, its transmission power may not be strong enough at the CRs location, it may be reduce than the noise floor which makes it more difficult to get detected. As the CR might not be able to detect a transmission by a contemporary user and similarly unaware of availability of the receiving by a contemporary user. Consequently, if it is confirmed as safe to use the contemporary users frequency and CR starts transmitting, at the contemporary receiving end it will create interference. The CR may have a limited view of spectrum provided from wide spectrum measurements which may cause interference with the receiving user. The localised spectrum view denotes that a CR should be potential to find transmitting user those are communicating below the noise level, since the strength of the received signal is very weak at the CRs location. Similarly a situation can occur where the signal attenuate by distance, thus user transmission is blocked by obstacles such as buildings, towers, hills or mountains. For example consider a CR in a valley would have a limi ted picture of the surrounding radio environment, as compared to that if it were located on top of a hill. 2.5.2 Security Concerns CR may be vulnerable to malicious effect, resulting into unexpected or problematic behaviour of individual CRs or complete networks. This problem springs up from the potential to re-program CRs in an unauthorized way. Hacking or placing a vulnerable code, virus on a network might enable criminals to steal valuable information from a CR through electronically, fool a network operator into charging others for services or achieve potentially widespread denial-of-service. A considerable amount of regulatory work will require to be done to clarify who would be responsible for the various security areas of CR, software developers, manufacturers, network operators and CR users themselves may all have a role to play. The CR security issue is closely related to that of SDR, which already discussed and hence not repeated here. Instead, a brief summary of the issues is given. Downloading software updates over an air interface poses some specific problems for security. Several digital signatures will be required for each piece of downloaded software in order to meet likely regulatory requirements. Exactly who is necessary to authorize software downloads must be standardized before any large scale deployment of over-the-air updates can be realized. 2.5.3 Burden of Control and Regulatory challenges A CR in reality will have some effect on different spectrum users the compliance of these new radios is likely to focus on a Policy module defined within a CR, which will determine the boundaries of CR behaviour. It is important while studying CR; to consider how users would not be affected by interference from CR devices and the exact operation and nature of a proposed CR policy system must be understood carefully. It is likely to include a detail case study of the specifications and characteristics of all the contemporary users for a specific CR or complete network of CRs may share the resources. The effort in controlling CR devices, it is necessary to ensure their behaviour is properly or not, even in the case of faulty or tampered devices, that measures are quickly implemented to intense problems. This will involve policies and standards which are created in a universal digitally interpretable policy, so that all CRs can understand the same. Monitoring techniques and powerful alg orithms are required to enable detection and identification of bad CRs and in this way it provides traceability to find or determine who is responsible for the issue. In addition to these challenges, spectrum regulators and spectrum managers will require providing access to licensed spectrum in such a way that is traceable, transparent and highly dynamic. If CRs are allowed to cover international territory additional effort will be required, due to the necessity to provide and collaborate cooperation with other countries. Assuming that acceptable control of CR policy behaviour is technically possible and feasible, it may turn out to be such a great burden that it will be simply not economically viable and the benefits of CR are outweighed by this burden. 2.6 Important Applications for Cognitive Radio are Downloading of audio and video files on mobile handsets. This application requires moderate data rates and near-ubiquitous coverage. Emergency services communications: It requires interoperability and a moderate data rate with local coverage. Broadband wireless networking: Very high data rate required but CR users have option to accept limited coverage, e.g. hot spots. Multimedia wireless and sensor networking: Broad range of data rates may be required. 2.7 Spectrum Sensing Spectrum sensing is the process performing measurements on the part of spectrum and on the basis of measured data making a decision related spectrum usage. As the requirement and quantity of users is getting increased day by day, it is necessary for ISPs to have large amount of spectrum in order to achieve the QOS (Quality of Service). This leads the interest in unlicensed spectrum access and spectrum sensing is vital concept of this. In a situation where there are licensed user and any unlicensed exists, licensed user (primary user) is to be protected and no unlicensed user can interfere any licensed users operation and such cases Spectrum sensing is also useful to detect the existence or non existence of a primary user. Spectrum sensing is an important concept for exploring spectrum opportunities for the secondary spectrum usage in real-time. It detects the unused spectrum and shares it without any noticeable interference with other users. It is an important requirement of the Cogn itive Radio in order to sense spectrum holes. Detecting primary users is the most efficient way to detect spectrum holes. 2.8 Spectrum Sensing Techniques Available Spectrum sensing plays a vital role in cognitive radios. And the type of spectrum sensing techniques to choose more or less depends upon the spectrum sensing technique. A method such as energy detection proves to be one of the simplest of all, but it doesnt works well at low SNR, varying noise levels, fading. On the other hand technique such as Matched filters shows better performance, but they comes complex receiver design. We are going to discuss some of these techniques as we proceed further. 2.8.1 Matched Filter Technique This is the technique which takes minimum amount of sensing time. In this method of spectrum detection, receiver receives a pilot signal along with the data that is sent by the transmitter. A pilot signal is a single frequency that is used for synchronisation. All the secondarys those are struggling for spectrum should have knowledge of this pilot signal. There should` be tight timing synchronisation between primary and secondary. They are also required to know about the kind of modulation being used, pulse shaping. Also secondarys must have another receiver for every primary. This kind of techniques also fails when there is frequency offset. Examples of this technique are TV signals, CDMA with pilot, also used in OFDM. 2.8.2 Energy Detection technique This is the most simples of all techniques. In this the receiver has no knowledge of the transmitted signal. The receivers need not to have knowledge about the modulation type or any kind of pilot signal. Earlier energy detection was done with the help of a LPF (Low Pass Filter), Digital to Analog converter (D/A), and square law device that used to calculate the energy of the signal. Later it is done by making use of fast Fourier transform (FFT). This is known as periodogram method in energy detection. 2.8.2 Cyclostationary Feature Detection Signals are modulated with sine waves or cyclic prefix as in OFDM. And they are periodic. This periodic property of a signal helps it to be cyclostationary. This technique basically uses this principle of spectral correlation to detect the spectrum. Even if signals have similar PSD (Power Spectral Density) but they have do not have similar spectral correlation. 2.9 Multi-resolution for Cognitive Radio Sensing The concept of multi-resolution for Cognitive Radio can be applied with different methods but, the basic idea is the same. The whole spectrum is first sensed by using a coarse resolution. After this first step fine resolution sensing is done on a part of interested bands. In this way CR avoids itself from sensing the spectrum at one time and thus saving time and power. In this way, the sensing time is reduced and the power also been saved from unrequited computations. Also the multiple antenna architecture helps parallel processing and enables to reduce the sensing time. But, it increases the chip area and consumption of power which is not desirable. Also for coarse resolution sensing the mixer has to produce many frequencies and Also it should switch to one frequency for beginning the fine resolution sensing. If the signal is low pass signal then we can use fine resolution to scan the whole spectrum. Because low pass signal has low center frequencies and its sampling is doable. But for pass band signals it is not feasible to scan the whole spectrum. Because, for example say if we have some signal with center frequency of 850 MHz, it is not practically possible to do sample that signal. As according to Nyquist theorem sampling rate should be at least twice that of center frequency. Therefore it is practically not possible to sample a signal at 1600 Mega Hertz. 2.10 Business Model for Spectrum Sensing So far we have discussed about Cognitive radios and spectrum sensing in details. Since this is telecom, and telecom involves huge capital investment. One of the most costly things in telecom is getting the license itself and then comes the infrastructure and installations etc. Currently most of countries work on static spectrum allocation basis. For spectrum sensing to work we need some kind of regulation or set of rules that all will be ready to work with. A team from Brussels University has suggested a model for the same. The same model is discussed in brief below. This model is divided into four main categories. i. Ownership- Ownership simply means the ownership of license. One who has license is authorized to use particular band of spectrum. And if another licensee wants to share a spectrum then it will depends on parameters discussed below. If the operator is unlicensed then there is now issue of ownership. ii. Exclusivity- Exclusivity means whether or not a particular operator is exclusively assigned a band of spectrum. That will be issue of regulator to decide to exclusively assign a spectrum to a specific user. If it is assigned exclusively then nobody can access that band of frequency, and if not then those bands of frequencies will be available for sharing. iii. Tradability- Tradability means whether or not a terminal is allowed to switch between frequencies from different operators. If tradability is permitted frequency band or bands can be auctioned for sale or given on lease. iv. Neutrality- It is possible that some of frequency bands can be accessed by number of RATs (radio Access Technology) or may be limited to a particular RAT. If frequency bands are not available to number of RATs then that band need to address more issues, such as setting technical conditions to access the band and coordinating the cooperation between multiple technologies. Unlicensed: Unlicensed deals with the band of frequencies which are free to use, like ISM band. Common example for this is Wi-Fi which operates in 2.4GHz. This band of frequency is available to all and there is special condition to access this band. Single RAT Pool: This pool is related to a group of licensees which are not exclusively assigned any band of frequency and using same RAT. Multi RAT Pool: It is similar to Single RAT Pool except that it has multiple RATs. Single RAT Market: In this each operator is assigned with a separate frequency, but that can be accessed by the conditionally secondarys. Multi RAT Market: In this the operator is a licensee and is exclusively assigned with a band of frequency, and also with tradability. Flexible Operator and Static Spectrum: If a particular band of spectrum is exclusively assigned to an operator and without tradability. And if there is only one RAT, then it is known as Static Spectrum else Flexible Operator. 2.11 Survey outcome As per the literature review we concludes to use Energy detection technique for spectrum sensing as it is the fastest spectrum detection technique available and also it is simpler as compared to other techniques. There are many researches done in this field and many are still doing. Because of the survey we get knowledge about various techniques available in market. This led us to do a simulation model with one of the spectrum sensing technique. Now as far as selection of spectrum sensing technique is concerned, we selected Energy detection technique. The same could be seen in next part of the thesis which includes its design and implementation in simulation model. Chapter 3 Simulation Design 3.1 Sampling and Its Importance Sampling is a process of converting the continuous analog signal to a discreet analog signal and the samples signal is the discreet time representation of the original signal. If the message is coming from a digital source, then it is in the form to be processed by digital communication systems. But in real life not every signal is digital, message signal can be analog. In situation like these, we have to first convert the analog signal into discreet time signal, this is sampling. For this process to work well, sampling rate should be selected carefully or in other words it should satisfy Nyquist criterion. And Nyquist Criterion says that the sampling frequency should be at least twice the maximum frequency in signal. Fs ≠¥ 2fmax or T=1/ fmax Where â€Å"Fs† is sampling frequency, fmax is maximum frequency in the signal. T=Sampling period. Sampling is like reading a signal in analog form and taking its value at that instant of time. So more the samples we take better the resolution of the signal and, signal can be recovered more accurately. But if we take less number of samples, then resolution of the signal decreases. If we go on reducing the sampling rate, then times comes when it is difficult to recover the original signal from the sampled signal or in other words original information in the signal is lost. This is also known as aliasing. Aliasing is the effect which takes place if the signal is sampled less than twice the maximum frequency. 3.2 Types of Signal 3.2.1 Time limited signal- It is a signal which exists for only certain duration of time. Out of this duration, signal does not exist. A rectangular pulse of duration â€Å"T† seconds can be considered as time limited signal. x(t)=A †¦ for 0 3.2.2 Band Limited signals- It is a signal which has a frequency spectrum which exists only over a certain range of frequency. The value of signal outside this range of frequency is zero. Mod(X(f))=A †¦.-B 3.3 Sampling Of Low pass and Band Pass signal Low pass sampling theorem states that- a) A band limited signal of finite energy, which has no frequency components higher than W Hertz, is c

Comparing Hamlet by William Shakespeare and The Killings by Andre Dubus

Comparing Hamlet by William Shakespeare and The Killings by Andre Dubus Losing a loved one to tragedy, especially two most brutal and malicious tragedies as these, will torture the minds of any and all men. Terrifying thoughts, even carefully planned acts of revenge will plow themselves into your brain. It is how we react to these situations that can and will forever define that man, his life, and his actions. In these two stories, Hamlet's father and Matt Fowler's son are murdered with jealous motives of romance, ambition, betrayal and rage. Revenge captures the hearts of both characters, but in different forms. Hamlet sees his fathers ghost and is told if he ever loved his father he is to ?[revenge his foul and most unnatural murder]?. The brutal slayer of Fowler?s son is out on bail and faces minimal jail time for the life of Frank Fowler, Matt?s youngest son. Matt decides to take the law into his own hands and with the help of a friend, plans and executes the murder of Richard Strout. With the killer of his son bar-hopping around town and his wife broken apart with grief, Matt Fowler loses himself in revenge. He begins to carry an unregistered gun hoping to confront Strout and kill him in ?self-defense?. He is defeated in his professional life, losing his nerve as a hard-working bank manager, unable to look his customers in the eye without shying away in fear and grief. Finally confessing himself to a poker buddy, his murderous intentions rush out onto the table. His friend, who?s sympothy and loyalty may be excessive, agrees to help Matt take his revenge on Strout. Hamlet, instead, seeks his revenge alone. When Horatio, Marcellus, and Bernardo take Hamlet to see the ghost of his father, he follows the ghost... ...n a dish served cold. Though he found the nerve to seek his revenge, I doubt he ever stopped replaying the events of that night in his head, wondering if he did the right thing, and if the pricetag for it was going to be hell or prison. Neither Hamlet nor Fowler forgive the men who wronged them, and their lives, consumed with the idea of injustice, were ruined along with almost everyone else?s. For Fowler, the answer was easy: Kill and don?t get caught. He thought only of the best way to get away with it, forgetting his morals and judgement. I question how hard he thought if he should do it or not. His instincts told him to kill, and that is what he did. Hamlet, on the other hand, fought with himself over and over about how to appropriatly handle his revenge, and opportunity presented itself, as it always does, with time. Regretfully, he was mortally wounded.

Adolescent Psychological Disorder: Depression Essay

Depression is a common psychological disorder which is more likely to be experienced by young people. Although this psychological disorder could be manifested in all age range, studies show that individuals who are in their adolescence to early adulthood stage have greater tendency to feel depress (Costell, Swendsen & Rose, 173, 2008). This disorder is often accompanied by feelings of sadness, despair or hopelessness which eventually causes a person to become isolated among the other individuals. Several issues regarding the frequency of depression occurrence had been studied by researchers. It is said that the rate of depression is determined by the differences in gender, race and ethnicity. This claim suggests that women are more likely to experience depression than men and the same holds regarding the issue of ethnicity and race. Thus, the whites were less to experience depression than the minority (Brown, Meadows & Elder, 1300, 2007). Most of the time sadness and depression is interchangeably used. While it is true that depression is a product of intense sadness, one must know the distinction between these two. As to elaborate a little, the feeling of sadness has less damaging effect and usually last within a short period of time. Individuals learn to let go of this feeling at a much faster phase while people who embrace this feeling for a long time would eventually develop the depression disorder. Two types of depression basically arise, that is, major depression and minor depression (dysthymia). The degree or state of depression varies as an individual ages. The major depression disorder usually last in a short period of time but is basically more severe than the other type. The consequences that depression posed on one’s individuality are essential consideration to be reflected on. Most of these consequences are harmful and can bring damaging effect to the life of an individual thus thorough understanding of this psychological disorder would impose a great advantage. Causes of Depression Occurrence of depression is brought by numerous factors. Events, people, the environment as well as genetic factors contribute to the incidence of depression. In this paper, three causes of depression from different studies conducted would be discussed. Some of these causes of can eventually be modified while some are not liable to change. Nutrition was viewed to have a vital contribution to depression. (Shariatpanaahi et al, 532, 2007). It is established that the mental and cerebral mechanisms are being affected due to nutrient deficiencies therefore resulting to mood disorders including depression. Prevalence of Iron deficiency anemia was viewed to have certain contribution to depression. The study conducted by Shariatpanaahi and his colleagues looked at the association between serum ferritin level and depression. Their study resulted that students who are experiencing depression have lower serum ferritin level than the healthy ones (Shariatpanaahi et al, 534, 2007). With reference to the result generated, lower serum ferritin level which indicates minimal presence of iron in the body was viewed to have a vital role in the brain function and in the establishment of depression. The stressful experience of college freshmen to their new environment inside the learning place could also trigger depression. Being in an unfamiliar environment is a stressful event that brings a sense of discomfort (Dyson and Renk, 1231, 2006). Accompanying this feeling of discomfort is the change on depression symptomatology that they experience. Being in their transition stage towards adulthood, stress and depression were showed to be greatly triggered. Race and ethnicity is also viewed for depressive symptoms to occur. The study conducted by Brown and his colleagues (2007) resulted that different race-ethnic groups (including Hispanics, Asians, Blacks and whites) shows different level of depressive symptoms. In their study, the whites showed the lowest level of such symptoms while the Hispanics and Asians showed the highest. The level of depressive symptoms among the blacks falls between the whites and the two other race-ethnic groups (1300). Explanation for the occurrence of such depressive symptoms are said to be interconnected with the mental health and stressful experiences of these different minority groups. The location or condition of the Hispanics, Asians and Blacks in the society greatly contributes to their depression. Most of these groups, as well as their family, belongs to the lower class in the society thus receiving minimal benefits in terms of health care and tends to dwell in neighborhoods which are characterized as unsafe (Brown, Meadows & Elder, 1298, 2007). Upon the exposure of these race-ethnic groups to these conditions, the depression disorder develops and is heightened. Symptoms of Depression Basically the most obvious symptom of depression is an intense feeling of sadness manifested most of the time. Different symptoms are expressed by individuals in different age brackets as well as different instances or conditions of these individuals in the society. Taking in consideration the study conducted by Brown and his colleagues, symptoms of depression manifested by the race-ethnic minority includes anxiety and a sense of inferiority (Brown, Meadows & Elder, 1307, 2007). For new colleges trying to be familiar and adapting to their new environment, behaviors including a depressed mood or sadness most of the time (being away from their parents), irritability, inability to enjoy things and inability to concentrate are apparent (Dyson and Renk, 1234, 2006). Other symptoms that are most likely associated with depression includes withdrawal from friends and family, significant weight loss or gain, change in sleep patterns, pessimism and indifference, feeling tired, feeling numb emotionally and the worst is entertaining the thought of death or suicide. Effects of the Disorder Depression, if not given thorough attention could bring the worst effect to an individual. How an individual responds to the feeling of depression determines the effect of the disorder in his actions (Nolen-Hoeksema, 569, 1991). The feeling of depression is more likely to bring about negative thoughts in an individual’s mind. With these thoughts in mind, negative emotions would also be triggered. Entertaining such thoughts and emotions would bring distraction in one’s health, education, work and relationship with other people. Adolescence performance in school tends to decline as a result of depression (Dyson and Renk, 1234, 2006). Because of their inability to concentrate or focus on the lessons being thought in the learning place, their grades used to decline. Academic failures, school dissatisfaction as well as negative relationship with teachers and other students may take place. Depressed individuals seem to be pre-occupied with their thought of being depressed therefore interfering with their capability to think critically, perform well and socialized with other individuals in the learning place. Such scenario is true in the work place. Because of the disorder, individuals are more likely to be out of focus on their work thus they are more likely to accomplish lesser job (or they do not accomplish anything at all) within a given period. This type of behavior in the workplace would bring unwanted effects on the part of the individual as well as in the company. This could also lead to an individual’s dismissal in the job. Again, such dismissal would only trigger further depression and could bring forth to a worst event. Depressed individuals also shows attitude of wanting to be alone. Sharing one’s frustration (which eventually causes the prevalence of depression) with his family is sometimes hard to do. This ultimately contribute to a reduce interaction and may develop poor family relationship. Sometimes, depressed adolescent causes negative confrontation between parents as well as between siblings. Psychiatric hospitalization can also occur among adolescence if the level of depression is severe (Herman and Ostrander, 484, 2007). Some depressed individuals tend to be engaged in accidents in roads. They tend to drive recklessly thus resulting to several body impairments (Nolen-Hoeksema, 570, 199). Such action of reckless and violent driving is a means to pour out the feeling of depression. However, Nolen-Hoeksema argued that the relief from depression through this action is only for a short run. Coping up with Depression Several therapies and combination of these therapies are being suggested by psychologists as well as doctors to cope up with depression. In the study conducted by Nolen-Hoeksema, 570, 1991), she suggested the used of distractive response as a way to cope up with depression. In this response, adolescence experiencing depression are encourage to draw their attention to other things such as engaging in activity with friends or doing a hobby. In this way, Nolen-Hoeksema hypothesized that an individual would tend be distracted and would somehow overcome his feeling of depression. Guidance and support of family members (especially support from mothers) is also a means to help adolescence to cope up with depression. The multi family group approach (Lemmmens et al, 51, 2007) is greatly encouraged. This approach is concern to provide the needs of the patient and also guides the family to stand the difficulties of depression that are experience by the family as a whole. Fostering interaction between the patient and members of his family would put the patient at ease. Recognizing the fact that his family is there to support him and guide him all through out would lessen his burden and would therefore aid in treating depression. Cognitive therapy was also studied to aid in the treatment of depression (Beevers and Miller, 68, 2005). The result of there study shows that the used of mentioned therapy ‘may help patients to deal more functionally to their negative thoughts. ’ As stated on the discussion regarding the effects of depression, negative thoughts are said to be the driving force in which depression arises. Effectively managing these negative would lessen the occurrence of the disorder. This type of approach or therapy is basically more of prevention rather than treatment. Nevertheless, its efficiency in the control of depression is noteworthy. Conclusion  Depression is brought about by several factors faced by an individual in the society. Although this psychological disorder is somewhat inevitable and is said to be a common disorder, prevention and treatments should be provided. As to any other physical or psychological diseases, severe state of depression could bring unwanted and detrimental effect to the individual himself as well as to other people. Manifestation of symptoms of this psychological disorder must be taken in deep consideration. The stage of adolescence undeniably entails a lot of stress that could somehow cause an individual to incur depression. Adolescents are vulnerable to changes because different emotional as well as physiological activities are happening within their body. It is therefore important to be considerate and out lay the necessary actions to guard the adolescents to the threats of depression. Involvement of parents and other family members in preventing and treating the said disorder is greatly encourage. Other therapies should also be considered as a treatment for this disorder. Thorough understanding of the causes, symptoms and treatments of depression would be of great significant. The harm that this disorder imposes to adolescents is truly alarming. Its effects on the individual’s well-being and activities are disturbing. Psychologists together with other medical researchers are continuously finding ways to lessen the occurrence of this disorder. Thus, in order for their efforts to efficiently work, a collaborative support from the society is needed. The society should not undermine the effects of depression but instead thorough knowledge regarding this disorder as well as the harm that accompanies it must be explained and made clear.

Essay about Taking a Look Back at the Black Death - 755 Words

Who knew that in the 1300s, plague would strike along the trade routes (Doc 1) to the Middle East, North Africa, and Europe, killing nearly one-third of the population it exposed to it in just five short years? Many during this time period would say that God, not only knew, but also was the one responsible for bringing the plague known as the â€Å"Black Death, Great Pestilence, or even the Great Plague;† it was a combination of three different plagues from three different bacterial strains: bubonic, pneumonic, and septicemic (Background Essay). No matter which type one was affected by, it almost always led to a death, agonizing death. When Europe and the Middle East were struck with the Black Death in the mid-14th century, religion was the†¦show more content†¦In addition, the Muslims never blamed anyone for the plague (Doc 10). Although they were not as common, there were non-religious opinions about the cause of the plague, and European Christians and the Middl e Eastern Muslims agreed on many of them. The miasma, impure air, carried by the wind (Doc 5) was one possible cause that seemed logical. However, there were a few that did not seem as believable: the conjunction of Saturn, Jupiter, and Mars, excessive clothing and outrageous fashion, etc (Doc 5). Due to the plague, Christians and Muslims led different lives and their lifestyles began to change. Not only is this due to the magnitude (â€Å"The hand of the Almighty strikes repeatedly, to greater and greater effect. The terrible judgment gains in power as time goes by.† (Doc 4)) and swiftness of death (â€Å"The maximum of survival after the spitting of blood was fifty hours.† (Doc 3)) but also to the horrifying nature of death. â€Å"They died by the hundreds, both day and night, and all were thrown in those ditches and covered with earth†¦And so many died that all believed it was the end of the world.† (Doc 3) As a result, Christians became more inclin ed than before to evil and wickedness (Doc 6). Priests even became more concerned with themselves, and they went to other benefices where they would receive larger stipends (Doc 6). Therefore, many parishes became unserved (Doc 6). The number of moreShow MoreRelatedThe Language Of Contemporary Art1729 Words   |  7 PagesPlayful In this image the children appear playful and in a relaxed environment surrounded by adults taking care of them. They appear to be in the age range of 3 to 6 years old. 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