Digital Signal Processing (DSP) and CDMA Advantages

Digital Signal Processing (DSP) and CDMA Advantages INTRODUCTION ANALOG AND DIGITAL SIGNALS The signal is initially generated is in the form of an analog electrical voltage or current, produced for example by a microphone or some other type of transducer. The output from the readout system of a CD (compact disc) player, the data is already in digital form. An analog signal must be converted into digital form before DSP techniques can be applied. An analog electrical voltage signal, for example, can be digitized using an electronic circuit called an analog-to-digital converter or ADC. This generates a digital output as a stream of binary numbers whose values represent the electrical voltage input to the device at each sampling instant. Digital signal processing (DSP)-digital representation of signals and the use of digital processors to analyze, modify, or extract information from signals. Many signals in DSP are derived from analogue signals which have been sampled at regular intervals and converted into digital form. The key advantages of DSP over analogue processing are Guaranteed accuracy (determined by the number of bits used) Perfect reproducibility No drift in performance due to temperature or age Takes advantage of advances in semiconductor technology Greater flexibility (can be reprogrammed without modifying hardware) Superior performance (linear phase response possible, and filtering algorithms can be made adaptive) Sometimes information may already be in digital form. There are however (still) some disadvantages Speed and cost (DSP design and hardware may be expensive, especially with high bandwidth signals) Finite word length problems (limited number of bits may cause degradation). Application areas of DSP are considerable: Image processing (pattern recognition, robotic vision, image enhancement, facsimile, satellite weather map, animation) Instrumentation and control (spectrum analysis, position and rate control, noise reduction, data compression) Speech and audio (speech recognition, speech synthesis, text to speech, digital audio, equalisation) Military (secure communication, radar processing, sonar processing, missile guidance) Telecommunications (echo cancellation, adaptive equalisation, spread spectrum, video conferencing, data communication) Biomedical (patient monitoring, scanners, EEG brain mappers, ECG analysis, X-ray storage and enhancement). INTRODUCTION TO CDMA Code Division Multiple Access (CDMA) is a radically new concept in wireless communications. It has gained widespread international acceptance by cellular radio system operators as an upgrade that will dramatically increase both their system capacity and the service quality. It has likewise been chosen for deployment by the majority of the winners of the United States Personal Communications System spectrum auctions. It may seem, however, mysterious for those who arent familiar with it. CDMA is a form of spread-spectrum, a family of digital communication techniques that have been used in military applications for many years. The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for simple point-to-point communication at the same data rate. Originally there were two motivations: either to resist enemy efforts to jam the communications (anti-jam, or AJ), or to hide the fact that communication was even taking place, sometimes called low probability of intercept (LPI). It has a history that goes back to the early days of World War II. The use of CDMA for civilian mobile radio applications is novel. It was proposed theoretically in the late 1940s, but the practical application in the civilian marketplace did not take place until 40 years later. Commercial applications became possible because of two evolutionary developments. One was the availability of very low cost, high density digital integrated circuits, which reduce the size, weight, and cost of the subscriber stations to an acceptably low level. The other was the realization that optimal multiple access communication requires that all user stations regulate their transmitter powers to the lowest that will achieve adequate signal quality. CDMA changes the nature of the subscriber station from a predominately analog device to a predominately digital device. Old-fashioned radio receivers separate stations or channels by filtering in the frequency domain. CDMA receivers do not eliminate analog processing entirely, but they separate communication channels by means of a pseudorandom modulation that is applied and removed in the digital domain, not on the basis of frequency. Multiple users occupy the same frequency band. This universal frequency reuse is not fortuitous. On the contrary, it is crucial to the very high spectral efficiency that is the hallmark of CDMA. Other discussions in these pages show why this is true. CDMA is altering the face of cellular and PCS communication by: Dramatically improving the telephone traffic capacity Dramatically improving the voice quality and eliminating the audible effects of multipath fading Reducing the incidence of dropped calls due to handoff failures Providing reliable transport mechanism for data communications, such as facsimile and internet traffic Reducing the number of sites needed to support any given amount of traffic Simplifying site selection Reducing deployment and operating costs because fewer cell sites are needed Reducing average transmitted power Reducing interference to other electronic devices Reducing potential health risks Commercially introduced in 1995, CDMA quickly became one of the worlds fastest growing wireless technologies. In 1999, the International Telecommunications Union selected CDMA as the industry standard for new third-generation (3G) wireless systems. Many leading wireless carriers are now building or upgrading to 3G CDMA networks in order to provide more capacity for voice traffic, along with high-speed data capabilities. DS_CDMA Multiple access systems based on DS CDMA have achieved increasing significance for mobile communications applications. A promising concept is based on DS_CDMA applying MRC at the receiver. MRC takes advantage of the channel diversity to combat the multipath fading. However the capacity of a DS_CDMA system is limited by both multi-user interference and inter symbol interference ISI in high data rate applications. OFDM is applied to combat the frequency selectivity of the channel using a simple one tap equalizer Further more OFDM prevents the ISI and inter carrier interference ICI by inserting a guard interval between adjacent OFDM symbols OFDM is typically used for audio TV and HDTV transmission over terrestrial channels and achieves high spectral efficiency. The CMDA Technology overview FDMA In Frequency Division Multiple Access, the frequency band is divided in slots. Each user gets one frequency slot assigned that is used at will. It could be compared to AM or FM broadcasting radio where each station has a frequency assigned. FDMA demands good filtering. TDMA In Time Division Multiple Access, the frequency band is not partitioned but users are allowed to use it only in predefined intervals of time, one at a time. Thus, TDMA demands synchronization among the users. CDMA CDMA, for Code Division Multiple Access, is different from its traditional ways in which it does not allocate frequency or time in user slots but gives the right to use both to all users simultaneously. To do this, it uses a technique known as Spread Spectrum . In effect, each user is assigned a code,which spreads its signal bandwidth in such a way that only the same code can recover it at the receiver end. This method has the property that the unwanted signals with different codes get spread even more by the process, making them like noise to the receiver . Spread Spectrum Spread Spectrum is a mean of transmission where the data occupies a larger bandwidth than necessary. Bandwidth spreading is accomplished before the transmission through the use of a code, which is independent of the transmitted data. The same code is used to demodulate the data at the receiving end. The following figure illustrate the spreading done on the data signal x(t) by the spreading signal c(t) resulting in the message signal to be transmitted, m(t). Originally for military use to avoid jamming (interference created on purpose to make a communication channel unusable), spread spectrum modulation is now used in personal communication systems for its superior performance in an interference dominated environment . Definition of Spread Spectrum: A transmission technique in which a pseudo-noise code, independent of the information data, is employed as a modulation waveform to â€Å"spread† the signal energy over a bandwidth much greater than the signal information bandwidth. At the receiver the signal is â€Å"despread† using a synchronized replica of the pseudo-noise code. Basic Principle of Spread Spectrum System: The Principal types of Spread Spectrum are Direct Sequence (DS), and Frequency Hopping (FH). An over view of these systems is hereby given: Pseudo shift of the phase pseudo shift of the frequency Coherent demodulation noncoherent Direct Sequence Spread Spectrum (DSSS) A pseudo-noise sequence pnt generated at the modulator, is used in conjunction with an M-ary PSK modulation to shift the phase of the PSK signal pseudo randomly, at the chipping rate Rc (=1/Tc) a rate that is integer multiple of the symbol rate Rs (=1/Ts). The transmitted bandwidth is determined by the chip rate and by the base band filtering. The implementation limits the maximum chip rate Rc (clock rate) and thus the maximum spreading. The PSK modulation scheme requires a coherent demodulation. PN code length that is much longer than a data symbol, so that a different chip pattern is associated with each symbol. Frequency Hopping Spread Spectrum A Pseudo-noise sequence pnt generated at the modulator is used in conjuction with an M-ary FSK modulation to shift the carrier frequency of the FSK signal pseudurandomly, at the hopping rate Rh. The transmitted signal occupies a number of frequencies in time, each for a period of time Th (= 1/Rh), referred as dwell time. FHSS divides the available bandwidth into N channels and hops between these channels according to the PN sequence. At each frequency hop time the PN generator feeds the frequency synthesizer a frequency word FW (a sequence of n chips) which dictates one of 2n frequency position fhl . Transmitter and receiver follows the same frequency hop pattern. The transmitted bandwidth is determined by the lowest and highest hop position by the bandwidth per hop position (à ¢Ã‹â€ Ã¢â‚¬  fch). For a given hop, instantaneous occupied bandwidth is the conventional M-FSK, which is typically much smaller than Wss. So the FHSS signal is a narrowband signal, all transmission power is concentrated on one channel. Averaged over many hops, the FH/M-FSK spectrum occupies the entire spread spectrum bandwidth. Because the bandwidth of an FHSS system only depends on the tuning range, it can be hopped over a much wider bandwidth than an DSSS system. Since the hops generally result in phase discontinuity (depending on the particular implementation) a noncoherent demodulation is done at receiver. With slow hopping there are multiple data symbol per hop and with fast hopping there are multiple hops per data symbol. 3.3 Basic principle of Direct Sequence Spread Spectrum For BPSK modulation the building blocks of a DSSS system are: Input: Binary data dt with symbol rate Rs = 1/Ts (=bitrate Rb for BPSK) Pseudo-noise code pnt with chip rate Rc = 1/Tc (an integer of Rs) Spreading: In the transmitter, the binary data dt (for BPSK, I and Q for QPSK) is ‘directly multiplied with the PN sequence pnt , which is independent of the binary data, to produce the transmitted baseband signal txb: txb = dt . pnt The effect of multiplication of dt with a PN sequence is to spread the baseband bandwidth Rs of dt to a baseband bandwidth of Rc. Despreading: The spread spectrum signal cannot be detected by a conventional narrowband receiver. In the receiver, the baseband signal rxb is multiplied with the PN sequence pnr . If pnr = pnt and synchronized to the PN sequence in the received data, than the recovered binary data is produced on dr. The effect of multiplication of the spread spectrum signal rxb with the PN sequence pnt used in the transmitter is to despread the bandwidth of rxb to Rs . If pnr ≠  pnt , than there is no dispreading action. The signal dr has a spread spectrum. A receiver not knowing the PN sequence of the transmitter can not reproduce the transmitted data. Performance in the presence of interference: To simplify the presence of interference, the spread spectrum system is considered for baseband BPSK communication (without filtering). The received signal rxb of the transmitted signal txb plus an additive inteferance i (noise, other users, jammer,†¦Ã¢â‚¬ ¦): rxb = t xb + i = dt . pnt + i To recover the original data dt the received signal rx0 is multiplied with a locally generated PN sequence pnr that is an exact replica of that used in the transmitter (that is pnr = pnt and synchronized) The multiplier output is therefore given by: dr = rxb . pnt = dt . pnt . pnt + i . pnt The data signal dt is multiplied twice by the PN sequence pnt , where as the unwanted inteferance i is multiplied only once. Due to the property of the PN sequence: pnt + pnt = +1 for all t The multiplier output becomes: dr = dt + i . pnt The data signal dr is reproduced at the multiplier output in the receiver, except for the inteferance represented by the additive term i . pnt . Multiplication of the inteferance by the locally generated PN sequence, means that the spreading code will affect the inteferance just as it did with the information bearing signal at the transmitter. Noise and inteferance, being uncorrelated with the PN sequence, becomes noise-like, increase in bandwidth and decrease in power density after the multiplier. After dispreading, the data component dt is narrow band (Rb) whereas the inteferance component is wideband (Rc). By applying the dr signal to a baseband (low-pass) filter with a band width just large enough to accommodate the recovery of the data signal, most of the inteferance component i is filtered out. The effect of inteferance is reduced by processing gain (Gp). Narrowband inteferance: The narrowband noise is spread by the multiplication with the PN sequence pnr of the receiver. The power density of the noise is reduced with respect to the despread data signal. Only 1/Gp of the original noise power is left in the information baseband (Rs). Spreading and dispreading enables a bandwidth trade for processing gain against narrow band interfering signals. Narrow band inteferance would disable conventional narrow band receivers. The essence behind the inteferance rejection capability of a spread spectrum system: the useful signal (data) gets multiplied twice by the PN sequence, but the inteferance signal get multiplied only once. Wideband interference: Multiplication of the received signal with the PN sequence of the receiver gets a selective despread of the data signal (smaller bandwidth, higher power density). The inteferance signal is uncorrelated with the PN sequence and is spread. Origin of wideband noise: Multiple Spread Spectrum user: multiple access mechanism. Gaussian Noise: There is no increase in SNR with spread spectrum: The large channel bandwidth (Rc instead of Rs) increase the received noise power with Gp: Ninfo = N0 . BWinfo à   Nss = N0 . BWss = Ninfo .Gp The spread spectrum signal has a lower power density than the directly transmitted signal. Code division multiple access (CDMA) is a methode of multiplexing (wireless) users distinct (orthogonal) codes. All users can transmit at the same time, and each is allocated the entire available frequency spectrum for transmission. CDMA is also known as Spread-Spectrum multiple access (SSMA). CDMA dose not require the bandwidth allocation of FDMA, nor the time synchronization of the individual users needed in TDMA. A CDMA user has full time and full bandwidth available, but the quality of the communication decreases with an increasing number of users (BER ). In CDMA each user: Has its own PN code Uses the same RF bandwidth Transmits simultaneously (asynchronous or synchronous) Correlation of the received baseband spread spectrum signal rxb with the PN sequence of user 1 only despreads the signal of user 1. The other user produces noise Nu for user 1. ACCESS SCHEMES For radio systems there are two resources, frequency and time. Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access (FDMA). Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access (TDMA). In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections. MULTIPATH AND RAKE RECEIVERS One of the main advantages of CDMA systems is the capability of using signals that arrive in the receivers with different time delays. This phenomenon is called multipath. FDMA and TDMA, which are narrow band systems, cannot discriminate between the multipath arrivals, and resort to equalization to mitigate the negative effects of multipath. Due to its wide bandwidth and rake receivers, CDMA uses the multipath signals and combines them to make an even stronger signal at the receivers. CDMA subscriber units use rake receivers. This is essentially a set of several receivers. One of the receivers (fingers) constantly searches for different multipaths and feeds the information to the other three fingers. Each finger then demodulates the signal corresponding to a strong multipath. The results are then combined together to make the signal stronger. Difference between TDMA vs CDMA. TDMA is Time Division Multiple Access, while CDMA is Code Division Multiple Access. Both technologies achieve the same goal of better utilization of the radio spectrum by allowing multiple users to share the same physical channel, but by using different methods and that is why the three of the four words in each acronym are identical. Both allow more than one person to carry out a conversation on the same frequency without causing interference. The two technologies differ in the way in which users share the common resource. In TDMA the channel is chopped up into sequential time slices. The data of each user is put on the channel in a round-robin fashion. In reality, only one user actually uses the channel at any given point of time, but he uses it only for short bursts. He then gives up the channel for a short duration to allow the other users to have their turn. This is similar to how a computer with just one processor runs multiple applications simultaneously. CDMA on the other hand allows everyone to transmit at the same time. With conventional methods of modulation techniques it would hav been simply not possible. What makes CDMA to allow all users to transmit simultaneously is a special type of digital modulation called Spread Spectrum. In this modulation technique users stream of bits is taken and splattered them across a very wide channel in a pseudo-random fashion. The pseudo part is very important here as at the receiver end the randomization must be undone in order to collect the bits together in a coherent order. For example consider a room full of couples, and each couple trying to carry on one-on-one conversations. In TDMA each couple takes their turn for talking and they keep their turns short by speaking only one sentence at a time. As there is always more one person speaking in the room at any given point of time, no one has to worry about being heard over the background din. In CDMA assume each couple talks simultaneously, but they all use different languages. The background din doesnt cause any real problem as none of the listeners understand any language other than that of the individual to whom they are listening. Voice Encoding At this point many people confuse two distinctly different issues involved in the transmission of digital audio. The first is the WAY in which the stream of bits is delivered from one end to the other. This part of the air interface is what makes one technology different from another. The second is the compression algorithm used to squeeze the audio into as small a stream of bits as possible. This latter component is known at the Voice Coder, or Vocoder for short. Another term commonly used is CODEC, which is a similar word to modem. It combines the terms COder and DECoder. Although each technology has chosen their own unique CODECs, there is no rule saying that one transmission method needs to use a specific CODEC. People often lump a technologys transmission method with its CODEC as though they were single entities. Voice encoding schemes differ slightly in their approach to the problem. Because of this, certain types of human voice work better with some CODECs than they do with others. The point to remember is that all PCS CODECs are compromises of some sort. Since human voices have such a fantastic range of pitch and tonal depth, one cannot expect any single compromise to handle each one equally well. This inability to cope with all types of voice at the same level does lead some people to choose one technology over another. All of the PCS technologies try to minimize battery consumption during calls by keeping the transmission of unnecessary data to a minimum. The phone decides whether or not you are presently speaking, or if the sound it hears is just background noise. If the phone determines that there is no intelligent data to transmit it blanks the audio and it reduces the transmitter duty cycle (in the case of TDMA) or the number of transmitted bits (in the case of CDMA). When the audio is blanked your caller would suddenly find themselves listening to dead air, and this may cause them to think the call has dropped. To avoid this psychological problem many service providers insert what is known as Comfort Noise during the blanked periods. Comfort Noise is synthesized white noise that tries to mimic the volume and structure of the real background noise. This fake background noise assures the caller that the connection is alive and well. However, in newer CODECs such as EVRC (used exclusively on CDMA systems) the background noise is generally suppressed even while the user is talking. This piece of magic makes it sound as though the cell phone user is not in a noisy environment at all. Under these conditions, Comfort Noise is neither necessary, nor desirable. DS-CDMA-INTRODUCTION While multiple access interference (MAI) by other users has been recognized as the capacity-limiting factor in direct sequence code-division multiple-access (DS-CDMA)-based cellular communication systems, multiuser approaches have largely alleviated the problem when the noise process is additive Gaussian. With the availability of multiuser detectors, inaccurate or inappropriate noise modelling assumptions seem to have become the issue again. Whereas multiuser detection has much to offer in the mobile- to-base station uplink, it does not at present appear to be feasible for the downlink due to the complexity involved and the lack of resistance against adjacent cell interference. Moreover, the few multiuser proposals for the downlink require the knowledge of all spreading codes, which is not possible in the tactical military environment, for instance. Enhanced single-user receivers equipped with adaptive filter banks deliver promising performance with reasonable complexity, especially in slowly varying channels. Thus, the performance of single-user detectors is still of interest, particularly in the presence of non-Gaussian noise. In both urban outdoor and indoor mobile radio environments, electromagnetic interference generated by man-made sources such as factories or power lines causes the noise to be of non-Gaussian nature. Large noise magnitudes are deemed very improbable by linear receivers, and consequently performance deterioration is experienced. It is therefore desirable to build systems that can maintain respectable functionality under a broad class of noise distributions, rather than strictly optimizing for the unrealistic Gaussian assumption. Such is the goal of robust detection and estimation theory, which aims to design systems that are suboptimal under nominal channel conditions (e.g., Gaussian channel) and yet do not face catastrophy when the noise distribution is not nominal (e.g., unlike linear schemes). Note that suboptimality here refers to very good performance that is slightly worse than that of the nominal-optimal detector/estimator. The direct sequence code division multiple access (DS-CDMA) technique has been favourably considered for application in digital mobile cellular networks due to its potential to provide higher system capacity over conventional multiple access techniques. Unlike FDMA and TDMA capacities which are mostly limited by the bandwidth, the capacity of a CDMA system is mainly restricted by its interference level. Any reduction in interference produces a direct and linear increase in system capacity. Multiple access interference (MAI) caused by non-zero cross-correlation between different spreading sequences is the major type of interference limiting the CDMA system capacity. Much work has been done to characterize MAI, and to analyze and evaluate the CDMA system performance in the presence of MAI. Since the cross-correlation properties of most sets of spreading codes are either too complex to analyze or very difficult to compute when different transmissions are not synchronized, a random seque nce model. In the case of moderate to large processing gains, Gaussian distribution with variable variance is a good approximation for the MAI distribution. One of the approaches to reduce MAI is to employ orthogonal spreading sequences, and try to synchronize the transmissions at the chip level (quasi-synchronization). However, this is generally difficult to achieve in multipoint-to-point systems, such as the reverse link (mobile-to-base) of a cellular system, due to a lack of synchronization of the various mobile terminals, and the variable transmission delays. In this paper, a multi-carrier DS-CDMA (MCDS-CDMA) scheme is employed to facilitate the synchronization process, and thus reduce MAI. SYSTEM MODEL A model of the MS-DS-CDMA system for the kth user of a CDMA system is shown in the figure 1. TRANMSITTER MODEL At the transmitter the user‘s data stream dk(t) is divided into M interleaved sub streams and spread by a spreading sequence ck(t) to a fraction 1/M of the entire transmission bandwidth W. The resultant chip sequences are then used to modulate M carrier. The carrier frequencies ωm,m=1,2,M are equally spaced by the chip rate so that they are mutually orthogonal over one channel symbol interval T. Let R be the information rate and Rc be the carrier control code rate then the channel symbol interval is BER PERFORMANCE: MC-DS-CDMA system performance measured by bit error rate through analysis and simulation. Analysis: The BER is analysed based on the following: Ortoganal spreading sequences with rectangular pulse shape are applied. ÃŽ ¶k,k=1†¦K are independent of random variables distributd in (-ÃŽ ¶D,ÃŽ ¶D) WHERE ÃŽ ¶D=ÃŽ µD+Ï‚D.Given W and ÃŽ ¶D,M is chosen so that ÃŽ ¶D It is assumed that the fading parameters of the desired user . It is perfectly estimated so that the coherent detection and optimum soft decision decoding could be carried out at the receiver to make the problem analytically tractable. The fading amplitudes as independent Rayleigh random variables with equal second moments. The model is MATLAB INTRODUCTION: Matlab is a commercial Matrix Laboratory package which operates as an interactive programming environment. It is a mainstay of the Mathematics Department software lineup and is also available for PCs and Macintoshes and may be found on the CIRCA VAXes. Matlab is well adapted to numerical experiments since the underlying algorithms for Matlabs builtin functions and supplied m-files are based on the standard libraries LINPACK and EISPACK. Matlab program and script files always have filenames ending with .m; the programming language is exceptionally straightforward since almost every data object is assumed to be an array. Graphical output is available to supplement numerical results. IMREAD Read image from graphics file. A = IMREAD(FILENAME,FMT) reads a grayscale or color image from the file specified by the string FILENAME. If the file is not in the current directory, or in a directory on the MATLAB path, specify the full pathname. The text string FMT specifies the format of the file by its standard file extension. For example, specify gif Digital Signal Processing (DSP) and CDMA Advantages Digital Signal Processing (DSP) and CDMA Advantages INTRODUCTION ANALOG AND DIGITAL SIGNALS The signal is initially generated is in the form of an analog electrical voltage or current, produced for example by a microphone or some other type of transducer. The output from the readout system of a CD (compact disc) player, the data is already in digital form. An analog signal must be converted into digital form before DSP techniques can be applied. An analog electrical voltage signal, for example, can be digitized using an electronic circuit called an analog-to-digital converter or ADC. This generates a digital output as a stream of binary numbers whose values represent the electrical voltage input to the device at each sampling instant. Digital signal processing (DSP)-digital representation of signals and the use of digital processors to analyze, modify, or extract information from signals. Many signals in DSP are derived from analogue signals which have been sampled at regular intervals and converted into digital form. The key advantages of DSP over analogue processing are Guaranteed accuracy (determined by the number of bits used) Perfect reproducibility No drift in performance due to temperature or age Takes advantage of advances in semiconductor technology Greater flexibility (can be reprogrammed without modifying hardware) Superior performance (linear phase response possible, and filtering algorithms can be made adaptive) Sometimes information may already be in digital form. There are however (still) some disadvantages Speed and cost (DSP design and hardware may be expensive, especially with high bandwidth signals) Finite word length problems (limited number of bits may cause degradation). Application areas of DSP are considerable: Image processing (pattern recognition, robotic vision, image enhancement, facsimile, satellite weather map, animation) Instrumentation and control (spectrum analysis, position and rate control, noise reduction, data compression) Speech and audio (speech recognition, speech synthesis, text to speech, digital audio, equalisation) Military (secure communication, radar processing, sonar processing, missile guidance) Telecommunications (echo cancellation, adaptive equalisation, spread spectrum, video conferencing, data communication) Biomedical (patient monitoring, scanners, EEG brain mappers, ECG analysis, X-ray storage and enhancement). INTRODUCTION TO CDMA Code Division Multiple Access (CDMA) is a radically new concept in wireless communications. It has gained widespread international acceptance by cellular radio system operators as an upgrade that will dramatically increase both their system capacity and the service quality. It has likewise been chosen for deployment by the majority of the winners of the United States Personal Communications System spectrum auctions. It may seem, however, mysterious for those who arent familiar with it. CDMA is a form of spread-spectrum, a family of digital communication techniques that have been used in military applications for many years. The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for simple point-to-point communication at the same data rate. Originally there were two motivations: either to resist enemy efforts to jam the communications (anti-jam, or AJ), or to hide the fact that communication was even taking place, sometimes called low probability of intercept (LPI). It has a history that goes back to the early days of World War II. The use of CDMA for civilian mobile radio applications is novel. It was proposed theoretically in the late 1940s, but the practical application in the civilian marketplace did not take place until 40 years later. Commercial applications became possible because of two evolutionary developments. One was the availability of very low cost, high density digital integrated circuits, which reduce the size, weight, and cost of the subscriber stations to an acceptably low level. The other was the realization that optimal multiple access communication requires that all user stations regulate their transmitter powers to the lowest that will achieve adequate signal quality. CDMA changes the nature of the subscriber station from a predominately analog device to a predominately digital device. Old-fashioned radio receivers separate stations or channels by filtering in the frequency domain. CDMA receivers do not eliminate analog processing entirely, but they separate communication channels by means of a pseudorandom modulation that is applied and removed in the digital domain, not on the basis of frequency. Multiple users occupy the same frequency band. This universal frequency reuse is not fortuitous. On the contrary, it is crucial to the very high spectral efficiency that is the hallmark of CDMA. Other discussions in these pages show why this is true. CDMA is altering the face of cellular and PCS communication by: Dramatically improving the telephone traffic capacity Dramatically improving the voice quality and eliminating the audible effects of multipath fading Reducing the incidence of dropped calls due to handoff failures Providing reliable transport mechanism for data communications, such as facsimile and internet traffic Reducing the number of sites needed to support any given amount of traffic Simplifying site selection Reducing deployment and operating costs because fewer cell sites are needed Reducing average transmitted power Reducing interference to other electronic devices Reducing potential health risks Commercially introduced in 1995, CDMA quickly became one of the worlds fastest growing wireless technologies. In 1999, the International Telecommunications Union selected CDMA as the industry standard for new third-generation (3G) wireless systems. Many leading wireless carriers are now building or upgrading to 3G CDMA networks in order to provide more capacity for voice traffic, along with high-speed data capabilities. DS_CDMA Multiple access systems based on DS CDMA have achieved increasing significance for mobile communications applications. A promising concept is based on DS_CDMA applying MRC at the receiver. MRC takes advantage of the channel diversity to combat the multipath fading. However the capacity of a DS_CDMA system is limited by both multi-user interference and inter symbol interference ISI in high data rate applications. OFDM is applied to combat the frequency selectivity of the channel using a simple one tap equalizer Further more OFDM prevents the ISI and inter carrier interference ICI by inserting a guard interval between adjacent OFDM symbols OFDM is typically used for audio TV and HDTV transmission over terrestrial channels and achieves high spectral efficiency. The CMDA Technology overview FDMA In Frequency Division Multiple Access, the frequency band is divided in slots. Each user gets one frequency slot assigned that is used at will. It could be compared to AM or FM broadcasting radio where each station has a frequency assigned. FDMA demands good filtering. TDMA In Time Division Multiple Access, the frequency band is not partitioned but users are allowed to use it only in predefined intervals of time, one at a time. Thus, TDMA demands synchronization among the users. CDMA CDMA, for Code Division Multiple Access, is different from its traditional ways in which it does not allocate frequency or time in user slots but gives the right to use both to all users simultaneously. To do this, it uses a technique known as Spread Spectrum . In effect, each user is assigned a code,which spreads its signal bandwidth in such a way that only the same code can recover it at the receiver end. This method has the property that the unwanted signals with different codes get spread even more by the process, making them like noise to the receiver . Spread Spectrum Spread Spectrum is a mean of transmission where the data occupies a larger bandwidth than necessary. Bandwidth spreading is accomplished before the transmission through the use of a code, which is independent of the transmitted data. The same code is used to demodulate the data at the receiving end. The following figure illustrate the spreading done on the data signal x(t) by the spreading signal c(t) resulting in the message signal to be transmitted, m(t). Originally for military use to avoid jamming (interference created on purpose to make a communication channel unusable), spread spectrum modulation is now used in personal communication systems for its superior performance in an interference dominated environment . Definition of Spread Spectrum: A transmission technique in which a pseudo-noise code, independent of the information data, is employed as a modulation waveform to â€Å"spread† the signal energy over a bandwidth much greater than the signal information bandwidth. At the receiver the signal is â€Å"despread† using a synchronized replica of the pseudo-noise code. Basic Principle of Spread Spectrum System: The Principal types of Spread Spectrum are Direct Sequence (DS), and Frequency Hopping (FH). An over view of these systems is hereby given: Pseudo shift of the phase pseudo shift of the frequency Coherent demodulation noncoherent Direct Sequence Spread Spectrum (DSSS) A pseudo-noise sequence pnt generated at the modulator, is used in conjunction with an M-ary PSK modulation to shift the phase of the PSK signal pseudo randomly, at the chipping rate Rc (=1/Tc) a rate that is integer multiple of the symbol rate Rs (=1/Ts). The transmitted bandwidth is determined by the chip rate and by the base band filtering. The implementation limits the maximum chip rate Rc (clock rate) and thus the maximum spreading. The PSK modulation scheme requires a coherent demodulation. PN code length that is much longer than a data symbol, so that a different chip pattern is associated with each symbol. Frequency Hopping Spread Spectrum A Pseudo-noise sequence pnt generated at the modulator is used in conjuction with an M-ary FSK modulation to shift the carrier frequency of the FSK signal pseudurandomly, at the hopping rate Rh. The transmitted signal occupies a number of frequencies in time, each for a period of time Th (= 1/Rh), referred as dwell time. FHSS divides the available bandwidth into N channels and hops between these channels according to the PN sequence. At each frequency hop time the PN generator feeds the frequency synthesizer a frequency word FW (a sequence of n chips) which dictates one of 2n frequency position fhl . Transmitter and receiver follows the same frequency hop pattern. The transmitted bandwidth is determined by the lowest and highest hop position by the bandwidth per hop position (à ¢Ã‹â€ Ã¢â‚¬  fch). For a given hop, instantaneous occupied bandwidth is the conventional M-FSK, which is typically much smaller than Wss. So the FHSS signal is a narrowband signal, all transmission power is concentrated on one channel. Averaged over many hops, the FH/M-FSK spectrum occupies the entire spread spectrum bandwidth. Because the bandwidth of an FHSS system only depends on the tuning range, it can be hopped over a much wider bandwidth than an DSSS system. Since the hops generally result in phase discontinuity (depending on the particular implementation) a noncoherent demodulation is done at receiver. With slow hopping there are multiple data symbol per hop and with fast hopping there are multiple hops per data symbol. 3.3 Basic principle of Direct Sequence Spread Spectrum For BPSK modulation the building blocks of a DSSS system are: Input: Binary data dt with symbol rate Rs = 1/Ts (=bitrate Rb for BPSK) Pseudo-noise code pnt with chip rate Rc = 1/Tc (an integer of Rs) Spreading: In the transmitter, the binary data dt (for BPSK, I and Q for QPSK) is ‘directly multiplied with the PN sequence pnt , which is independent of the binary data, to produce the transmitted baseband signal txb: txb = dt . pnt The effect of multiplication of dt with a PN sequence is to spread the baseband bandwidth Rs of dt to a baseband bandwidth of Rc. Despreading: The spread spectrum signal cannot be detected by a conventional narrowband receiver. In the receiver, the baseband signal rxb is multiplied with the PN sequence pnr . If pnr = pnt and synchronized to the PN sequence in the received data, than the recovered binary data is produced on dr. The effect of multiplication of the spread spectrum signal rxb with the PN sequence pnt used in the transmitter is to despread the bandwidth of rxb to Rs . If pnr ≠  pnt , than there is no dispreading action. The signal dr has a spread spectrum. A receiver not knowing the PN sequence of the transmitter can not reproduce the transmitted data. Performance in the presence of interference: To simplify the presence of interference, the spread spectrum system is considered for baseband BPSK communication (without filtering). The received signal rxb of the transmitted signal txb plus an additive inteferance i (noise, other users, jammer,†¦Ã¢â‚¬ ¦): rxb = t xb + i = dt . pnt + i To recover the original data dt the received signal rx0 is multiplied with a locally generated PN sequence pnr that is an exact replica of that used in the transmitter (that is pnr = pnt and synchronized) The multiplier output is therefore given by: dr = rxb . pnt = dt . pnt . pnt + i . pnt The data signal dt is multiplied twice by the PN sequence pnt , where as the unwanted inteferance i is multiplied only once. Due to the property of the PN sequence: pnt + pnt = +1 for all t The multiplier output becomes: dr = dt + i . pnt The data signal dr is reproduced at the multiplier output in the receiver, except for the inteferance represented by the additive term i . pnt . Multiplication of the inteferance by the locally generated PN sequence, means that the spreading code will affect the inteferance just as it did with the information bearing signal at the transmitter. Noise and inteferance, being uncorrelated with the PN sequence, becomes noise-like, increase in bandwidth and decrease in power density after the multiplier. After dispreading, the data component dt is narrow band (Rb) whereas the inteferance component is wideband (Rc). By applying the dr signal to a baseband (low-pass) filter with a band width just large enough to accommodate the recovery of the data signal, most of the inteferance component i is filtered out. The effect of inteferance is reduced by processing gain (Gp). Narrowband inteferance: The narrowband noise is spread by the multiplication with the PN sequence pnr of the receiver. The power density of the noise is reduced with respect to the despread data signal. Only 1/Gp of the original noise power is left in the information baseband (Rs). Spreading and dispreading enables a bandwidth trade for processing gain against narrow band interfering signals. Narrow band inteferance would disable conventional narrow band receivers. The essence behind the inteferance rejection capability of a spread spectrum system: the useful signal (data) gets multiplied twice by the PN sequence, but the inteferance signal get multiplied only once. Wideband interference: Multiplication of the received signal with the PN sequence of the receiver gets a selective despread of the data signal (smaller bandwidth, higher power density). The inteferance signal is uncorrelated with the PN sequence and is spread. Origin of wideband noise: Multiple Spread Spectrum user: multiple access mechanism. Gaussian Noise: There is no increase in SNR with spread spectrum: The large channel bandwidth (Rc instead of Rs) increase the received noise power with Gp: Ninfo = N0 . BWinfo à   Nss = N0 . BWss = Ninfo .Gp The spread spectrum signal has a lower power density than the directly transmitted signal. Code division multiple access (CDMA) is a methode of multiplexing (wireless) users distinct (orthogonal) codes. All users can transmit at the same time, and each is allocated the entire available frequency spectrum for transmission. CDMA is also known as Spread-Spectrum multiple access (SSMA). CDMA dose not require the bandwidth allocation of FDMA, nor the time synchronization of the individual users needed in TDMA. A CDMA user has full time and full bandwidth available, but the quality of the communication decreases with an increasing number of users (BER ). In CDMA each user: Has its own PN code Uses the same RF bandwidth Transmits simultaneously (asynchronous or synchronous) Correlation of the received baseband spread spectrum signal rxb with the PN sequence of user 1 only despreads the signal of user 1. The other user produces noise Nu for user 1. ACCESS SCHEMES For radio systems there are two resources, frequency and time. Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access (FDMA). Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access (TDMA). In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections. MULTIPATH AND RAKE RECEIVERS One of the main advantages of CDMA systems is the capability of using signals that arrive in the receivers with different time delays. This phenomenon is called multipath. FDMA and TDMA, which are narrow band systems, cannot discriminate between the multipath arrivals, and resort to equalization to mitigate the negative effects of multipath. Due to its wide bandwidth and rake receivers, CDMA uses the multipath signals and combines them to make an even stronger signal at the receivers. CDMA subscriber units use rake receivers. This is essentially a set of several receivers. One of the receivers (fingers) constantly searches for different multipaths and feeds the information to the other three fingers. Each finger then demodulates the signal corresponding to a strong multipath. The results are then combined together to make the signal stronger. Difference between TDMA vs CDMA. TDMA is Time Division Multiple Access, while CDMA is Code Division Multiple Access. Both technologies achieve the same goal of better utilization of the radio spectrum by allowing multiple users to share the same physical channel, but by using different methods and that is why the three of the four words in each acronym are identical. Both allow more than one person to carry out a conversation on the same frequency without causing interference. The two technologies differ in the way in which users share the common resource. In TDMA the channel is chopped up into sequential time slices. The data of each user is put on the channel in a round-robin fashion. In reality, only one user actually uses the channel at any given point of time, but he uses it only for short bursts. He then gives up the channel for a short duration to allow the other users to have their turn. This is similar to how a computer with just one processor runs multiple applications simultaneously. CDMA on the other hand allows everyone to transmit at the same time. With conventional methods of modulation techniques it would hav been simply not possible. What makes CDMA to allow all users to transmit simultaneously is a special type of digital modulation called Spread Spectrum. In this modulation technique users stream of bits is taken and splattered them across a very wide channel in a pseudo-random fashion. The pseudo part is very important here as at the receiver end the randomization must be undone in order to collect the bits together in a coherent order. For example consider a room full of couples, and each couple trying to carry on one-on-one conversations. In TDMA each couple takes their turn for talking and they keep their turns short by speaking only one sentence at a time. As there is always more one person speaking in the room at any given point of time, no one has to worry about being heard over the background din. In CDMA assume each couple talks simultaneously, but they all use different languages. The background din doesnt cause any real problem as none of the listeners understand any language other than that of the individual to whom they are listening. Voice Encoding At this point many people confuse two distinctly different issues involved in the transmission of digital audio. The first is the WAY in which the stream of bits is delivered from one end to the other. This part of the air interface is what makes one technology different from another. The second is the compression algorithm used to squeeze the audio into as small a stream of bits as possible. This latter component is known at the Voice Coder, or Vocoder for short. Another term commonly used is CODEC, which is a similar word to modem. It combines the terms COder and DECoder. Although each technology has chosen their own unique CODECs, there is no rule saying that one transmission method needs to use a specific CODEC. People often lump a technologys transmission method with its CODEC as though they were single entities. Voice encoding schemes differ slightly in their approach to the problem. Because of this, certain types of human voice work better with some CODECs than they do with others. The point to remember is that all PCS CODECs are compromises of some sort. Since human voices have such a fantastic range of pitch and tonal depth, one cannot expect any single compromise to handle each one equally well. This inability to cope with all types of voice at the same level does lead some people to choose one technology over another. All of the PCS technologies try to minimize battery consumption during calls by keeping the transmission of unnecessary data to a minimum. The phone decides whether or not you are presently speaking, or if the sound it hears is just background noise. If the phone determines that there is no intelligent data to transmit it blanks the audio and it reduces the transmitter duty cycle (in the case of TDMA) or the number of transmitted bits (in the case of CDMA). When the audio is blanked your caller would suddenly find themselves listening to dead air, and this may cause them to think the call has dropped. To avoid this psychological problem many service providers insert what is known as Comfort Noise during the blanked periods. Comfort Noise is synthesized white noise that tries to mimic the volume and structure of the real background noise. This fake background noise assures the caller that the connection is alive and well. However, in newer CODECs such as EVRC (used exclusively on CDMA systems) the background noise is generally suppressed even while the user is talking. This piece of magic makes it sound as though the cell phone user is not in a noisy environment at all. Under these conditions, Comfort Noise is neither necessary, nor desirable. DS-CDMA-INTRODUCTION While multiple access interference (MAI) by other users has been recognized as the capacity-limiting factor in direct sequence code-division multiple-access (DS-CDMA)-based cellular communication systems, multiuser approaches have largely alleviated the problem when the noise process is additive Gaussian. With the availability of multiuser detectors, inaccurate or inappropriate noise modelling assumptions seem to have become the issue again. Whereas multiuser detection has much to offer in the mobile- to-base station uplink, it does not at present appear to be feasible for the downlink due to the complexity involved and the lack of resistance against adjacent cell interference. Moreover, the few multiuser proposals for the downlink require the knowledge of all spreading codes, which is not possible in the tactical military environment, for instance. Enhanced single-user receivers equipped with adaptive filter banks deliver promising performance with reasonable complexity, especially in slowly varying channels. Thus, the performance of single-user detectors is still of interest, particularly in the presence of non-Gaussian noise. In both urban outdoor and indoor mobile radio environments, electromagnetic interference generated by man-made sources such as factories or power lines causes the noise to be of non-Gaussian nature. Large noise magnitudes are deemed very improbable by linear receivers, and consequently performance deterioration is experienced. It is therefore desirable to build systems that can maintain respectable functionality under a broad class of noise distributions, rather than strictly optimizing for the unrealistic Gaussian assumption. Such is the goal of robust detection and estimation theory, which aims to design systems that are suboptimal under nominal channel conditions (e.g., Gaussian channel) and yet do not face catastrophy when the noise distribution is not nominal (e.g., unlike linear schemes). Note that suboptimality here refers to very good performance that is slightly worse than that of the nominal-optimal detector/estimator. The direct sequence code division multiple access (DS-CDMA) technique has been favourably considered for application in digital mobile cellular networks due to its potential to provide higher system capacity over conventional multiple access techniques. Unlike FDMA and TDMA capacities which are mostly limited by the bandwidth, the capacity of a CDMA system is mainly restricted by its interference level. Any reduction in interference produces a direct and linear increase in system capacity. Multiple access interference (MAI) caused by non-zero cross-correlation between different spreading sequences is the major type of interference limiting the CDMA system capacity. Much work has been done to characterize MAI, and to analyze and evaluate the CDMA system performance in the presence of MAI. Since the cross-correlation properties of most sets of spreading codes are either too complex to analyze or very difficult to compute when different transmissions are not synchronized, a random seque nce model. In the case of moderate to large processing gains, Gaussian distribution with variable variance is a good approximation for the MAI distribution. One of the approaches to reduce MAI is to employ orthogonal spreading sequences, and try to synchronize the transmissions at the chip level (quasi-synchronization). However, this is generally difficult to achieve in multipoint-to-point systems, such as the reverse link (mobile-to-base) of a cellular system, due to a lack of synchronization of the various mobile terminals, and the variable transmission delays. In this paper, a multi-carrier DS-CDMA (MCDS-CDMA) scheme is employed to facilitate the synchronization process, and thus reduce MAI. SYSTEM MODEL A model of the MS-DS-CDMA system for the kth user of a CDMA system is shown in the figure 1. TRANMSITTER MODEL At the transmitter the user‘s data stream dk(t) is divided into M interleaved sub streams and spread by a spreading sequence ck(t) to a fraction 1/M of the entire transmission bandwidth W. The resultant chip sequences are then used to modulate M carrier. The carrier frequencies ωm,m=1,2,M are equally spaced by the chip rate so that they are mutually orthogonal over one channel symbol interval T. Let R be the information rate and Rc be the carrier control code rate then the channel symbol interval is BER PERFORMANCE: MC-DS-CDMA system performance measured by bit error rate through analysis and simulation. Analysis: The BER is analysed based on the following: Ortoganal spreading sequences with rectangular pulse shape are applied. ÃŽ ¶k,k=1†¦K are independent of random variables distributd in (-ÃŽ ¶D,ÃŽ ¶D) WHERE ÃŽ ¶D=ÃŽ µD+Ï‚D.Given W and ÃŽ ¶D,M is chosen so that ÃŽ ¶D It is assumed that the fading parameters of the desired user . It is perfectly estimated so that the coherent detection and optimum soft decision decoding could be carried out at the receiver to make the problem analytically tractable. The fading amplitudes as independent Rayleigh random variables with equal second moments. The model is MATLAB INTRODUCTION: Matlab is a commercial Matrix Laboratory package which operates as an interactive programming environment. It is a mainstay of the Mathematics Department software lineup and is also available for PCs and Macintoshes and may be found on the CIRCA VAXes. Matlab is well adapted to numerical experiments since the underlying algorithms for Matlabs builtin functions and supplied m-files are based on the standard libraries LINPACK and EISPACK. Matlab program and script files always have filenames ending with .m; the programming language is exceptionally straightforward since almost every data object is assumed to be an array. Graphical output is available to supplement numerical results. IMREAD Read image from graphics file. A = IMREAD(FILENAME,FMT) reads a grayscale or color image from the file specified by the string FILENAME. If the file is not in the current directory, or in a directory on the MATLAB path, specify the full pathname. The text string FMT specifies the format of the file by its standard file extension. For example, specify gif

The Pearl

Assignment 1 † Money is the root of all evil†. To what extend is this one of the themes of the novel you studied. The Pearl by John Steinbeck – The theme of Greed Nurain Ariff This theme emerges the moment the people of La Paz get to know about Kino's pearl and we begin to see changes in the characters. All of them have their own selfish schemes when they learn about Kino's pearl. When they know that Kino has the pearl the village of La Paz is alive with avarice. Everyone wants something from Kino. Everyone was affected and wanted something from the pearl.Kino was the only one in the way. The doctor wanted money for â€Å"curing† the child. The priest wanted money to fix the church. The shopkeepers, the pearl buyers, and the rest of the town wanted money for their own purposes. The pearl was a poison that ruined many good people and made the evil people worst. The doctor is pure evil. He would not treat Kino's baby because Kino had nothing to pay him with. W hen the doctor heard of Kino's sudden wealth, he said Kino was his client. As he visualized life back in Paris all he could think of was getting enough money to be able to go back again.When he went to see Kino, he even made up a fake symptom of death to scare Kino into letting him â€Å"treat† the baby. Instead, he poisoned the baby and cured him of the poison he had given the baby himself. This horrible doctor is filled with avarice. He did not care who he had to harm to get more money. All he cares about is money. The priest wanted money to fix the church. Even the priest, a person who is highly regarded in the community, has some plans on how to use the money from the sale of the pearl. It is only after this that he thinks how the pearl will affect Kino's personal life.The priest is nearly as bad as the doctor. He also wanted money from Kino. He thinks  of certain repairs necessary for the church. He wondered what the pearl would be worth. And he wondered if he had bapt ized Kino’s baby, or married him for that matter. He thought if he did these things he was more likely to get money to fix the church. The priest calls on Kino and his family. He reminds them that they should show their gratitude to God for this unexpected gain and to pray for guidance in the future. Juana agrees and says that they will be married in the church.The priest is also a horrid person; he is supposed to be a holy figure, but he was poisoned by the thought of riches. These hopes caused him to lie. The new riches also affected the townspeople. The shop keepers hear about Kino's wealth and hope to sell their clothes. They knew that an indigent man that becomes rich by luck knows how it feels to be poor. Therefore, they would get money too. The pearl buyers were also full of avarice for the pearl. They wanted to buy the pearl for a very low price so they were cheating Kino. They hoped that if they bought the pearl, the boss would promote them and they would make more m oney.Everyone wanted something from the pearl. Kino became the whole town's enemy because of that. The effects of greed  after Kino finds the pearl are he learns how far others will go, including committing murder to gain wealth and the power that it brings. All those who hear about the pearl, even his neighbours  Ã¢â‚¬Å"suddenly became related to pearl, and pearl went into the dreams, the speculations, the schemes, the plans, the futures, the wishes, the needs, the lusts, the hungers, of everyone. † And since Kino stood in their way, â€Å"he became curiously every man's enemy. Kino recognizes this desire in himself, not for wealth, but for the power the pearl can grant him. He says the pearl is his soul. Comments: Good elaboration of points. However, do you actually know the meaning of the word ‘avarice’ you use in the essay? Why don’t you just stick to the common word ‘greed’? Just in case you use it in the wrong context? Overall, good attempt 😉 Taufiq In the novel The Pearl written by John Steinback, one of the themes is money is the root of all the evil because when Kino found the pearl everyone has a bad idea on how to manipulate Kino and become rich such as the doctor who is greedy.Before Kino had money to treat his son ,Coyotito, he was very evil and later when Kino found the Pearl he took the advantage of Kino to take the pearl that Kino would sell and poisoned his son to convince Kino to let him treat Coyotito . The priest is also evil when he needs the money to repair the church. He used the tactics so that he could have that money by saying that Coyotito should be baptised in the church and Juana and Kino should marry legally in the church. The pearl buyers are also evil when they know that Kino has found the greatest pearl that is also their source of income.They became very greedy and offered the lowest price to Kino so that they will get more income. Comments: A lot of grammatical errors can be found in your answer. Most of your sentences are also confusing and the meaning is not clear. Try to write simple and short sentences with less error. Make sure you organize your ideas before writing them. Faiqa From the novel that I studied, The Pearl by John Steinbeck, the phrase â€Å"Money is the root of all evil† is shown in the theme of greed. The doctor in this novel is an example of a greedy person.In the beginning of the novel, the doctor refused to treat Kino's son, Coyotito, who had been stung by a scorpion as he knows Kino will not be able to pay him for the service. To him, the natives or the ‘Indians' are nothing more than animals. However, after the discovery of the Pearl of the World, the doctor suddenly becomes concerned about Coyotito's health. He even goes as far as to visit the sick baby at Kino's brush house. All this is done purely because of his greed. He is hoping that by doing this, Kino will feel indebted to him. He is also certain that Kino w ill be able to pay him now.The priest is also a greedy person. Before the discovery of the pearl, the priest does not seem to be too interested in the affairs of the natives. However, after the discovery of the pearl the priest makes the effort of visiting Kino to remind him of his duties. The priest's visit is actually to ensure that Kino will donate some money so that repair works can be carried out at the church. To a certain extent, I think this phrase is exposes the fact that greed brings out the worst in man. It can also be used to describe Kino's characteristic.Before the pearl was found, Kino was contented with his life. The scene at the beginning of the novel shows how Kino's life is peaceful. Kino is also protective over his family before he found the pearl. The description of him killing the scorpion shows how protective he is to his son. Not only is he caring and gentle with his family, he also takes good care of his belongings, for example, his canoe. But, after the dis covery of the pearl, Kino becomes as cold and deadly as steel. He is willing to kill, first the attacker and then the trackers, in order to guard his pearl from falling into their hands.Kino's character in the novel slowly changes and the author likens his behaviour to that of animals'. He is suddenly described as a snake after he hits and kicks Juana when the latter tries to throw the pearl back into the sea. Later, he is described as a lizard as he edges his way closer to the trackers before killing all of them. Finally, Kino becomes fierce and violent as the story progresses. He is ultimately described as a terrible killing machine before he kills all the trackers. Comment: Good elaboration. Some minor grammatical error can be found in the essay. Nur AliaThis theme emerges the moment the people of La Paz get to know about Kino's pearl and we begin to see changes in the characters. All of them have their own selfish schemes when they learn about Kino's pearl. Even the priest, a pe rson who is highly regarded in the community, has some plans on how to use the money from the sale of the pearl. It is only after this, that he thinks how the pearl will affect Kino's personal life. Since Kino is the only one who stands in the way of the others by possessing the pearl, he becomes every man's enemy. The doctor makes Coyotito ill so that he can then ‘treat' Coyotito and ask for payment from Kino.Out of greed, he has betrayed the nobility of his profession. The pearl buyers conspire to cheat Kino so that they can make bigger profits. Unidentified people, envious of Kino's pearl, attack him physically and damage his possessions. His house is ransacked and burnt down. This leaves him no choice but to abandon the safety of his community and travel into the unknown. Even Kino himself is affected by the pearl, although he plans to use it to better himself and his family's situation, he becomes obsessed with it and turns violent, even against Juana.He becomes a changed person. He is filled with anger, turning animal-like and â€Å"hissed at Juana like a snake†, when she tried to throw the pearl he beats her up and kicks her. Comment: A lot of spelling error found in your answer. Please make sure that you recheck your essay before submitting it next time. Syazwan Based on the novel that I had studied, money is the root of all evil. Kino had found the big pearl when his son Coyotito was bitten by the scorpion. The theme of greed can be seen when the villagers knew about the big pearl.Kino tried to find good treatment for his son. The greedy doctor only wants the money as he is a selfish person. Kino tried to sell the pearl at town. The dealers only offer him a low price although they know the pearl is of a good quality. Kino was attacked by the attacker Kino saved himself when he killed the attacker. The pearl gives many problems to Kino and his family. Lastly, Coyotito was killed and Kino throws back the pearl into the sea. Comment: Your an swer does not really fulfil the requirement of the question. The ideas are there but you did not explain them clearly.Please refer to your friends’ answer which received good comments from me. Ayuni In the Pearl, â€Å"Money Is the root of all evil† represents the theme of greed. The doctor refused to treat Coyotito for the scorpion’s sting as Kino has no money. After Kino’s discovery of the pearl the doctor claims that Coyotito is his patient and pretended to ‘ treat' the baby . The doctor was just only thinking about money. The Pearl buyers planned to cheat Kino. They offer Kino a very low price for the pearl. They say that the pearl is too soft and chalky and will lose its colour.They only want to get more profit. The priest came to Kino after knowing about the discovery of the great pearl. He always thought of the church, and used religion for selfish ends. The thief and trackers tried to steal the pearl from Kino until violence happens. Kino ha s also become a greedy person. He does not listen to Juana when she asked him to throw back the pearl before many evil happened to them. Comment: Your answer is quite okay. Make sure you elaborate a little bit more in your exam so that your ideas will be more organized. Fatin NabilaMoney is the root of all evil. The theme greed and selfishness is the theme that is extended to it. The doctor in the novel is an example of a greedy person. The doctor refused to treat Coyotito because he will not work for free. The doctor is only interested in treating Coyotito after he knows about great pearl that Kino has discovered. Moreover, the attackers and trackers are also greedy. They attempt to steal the pearl from Kino. The priest is also a greedy person. Before the discovery of the pearl, the priest does not seem to be too interested in the affair of the natives.However, after the discovery of the pearl the priest’s visit is actually to ensure that Kino will donate some money so that repair works can be carried out at the church. Comment: Your ideas are largely organized and supported. However, your answer would be more solid if you include more examples as there are a lot of characters which portrayed greed in the novel. Faris One of the themes represented in the novel The Pearl is greed. It can corrupt people. Kino found a strange pearl, and this is a good thing for Kino and his family. He hopes for a quality treatment for his son, Coyotito who was stung by an evil scorpion.He wanted to marry Juana in a church and give education to his son when he grows up. The news about it was heard by the villagers including the doctor, the priest, and the pearl buyers. At first the pearl symbolizes hope and triumph but at last it showed how men were overcame by greed when the pearl was known by the villagers. They wanted the pearl for their own use. Because they wanted the power and have the power, they would do anything to get the pearl because it is a great pearl. The pe arl made them become so greedy. It shows that the money is the root of all evil.It can be seen when Kino killed the trackers who wanted to steal it. At last, Coyotito died when the tracker shot him thinking he was a coyote pup. Comment: Quite good. Please pay more attention to grammar and sentence structure. Fatin Inani One of the themes represented in The Pearl is greed. It corrupts people. Kino finds a rare pearl, and this is a good thing for him. He hopes for quality treatment for his baby who had been stung by a scorpion. He hopes that he and Juana will now be able to afford a proper wedding, as well as a better quality of life.He hopes for power and respect from others, too, as seen in his desire to get a rifle. Most of all, he hopes to give his son a good education that will ensure him a good future and enable him to look after the interests of the simple village folk. The pearl is at first, a symbol of hope and triumph, but because of the greed of men, it soon becomes a symbo l of corruptibility and evil desires of man. In itself, it is not an evil thing, but the evil, selfish desire of greedy men turn into an ugly thing. Even the kind, noble, well-liked Kino falls under the power of the pearl.Here, we see a related theme, the theme of the corruptibility of man. Kino becomes obsessed with the pearl because it holds so much promise for him and his family. It blinds him to the simple beauty of his life. Juana begs him to throw it back into the sea, but he refuses. He says that it has become his soul and he cannot part with it. Comment: A good answer. Take this answer as one of the good example on how to tackle this question. Azuren The theme of greed emerges the moment the people in La Paz get to know about Kino's pearl and we begin to see changes in the characters.All of them have their selfish schemes when they know about the pearl. Even the priest, a person who is highly regarded in the community has plans on how to use the money from the sale of the pe arl. Since Kino is the only one who stands in the way of the others by possessing the pearl, he becomes every man's enemy. Therefore, many attempts are made to get rid of him. The greed of the people makes them willing to do anything to get the pearl, for example poison the child, burn Kino's house, destroy his canoe and even try to kill Kino and his family. Even Kino himself is affected by the pearl.Although he plans to use it to better himself and his family situation, he becomes obsessed with it and turns violent, even againts Juana. Kino's anger turn to rage when he discovers that Juana is about to throw away the pearl. He beats her up and kicks her. Kino whom we first see as a loving and protective family man, is now more concerned about the pearl. All of these show how money can change people and the theme of greed is one of the themes found in this novel. Comment: Your answer needs to be written in paragraphs to make it more organized. Be careful of your grammar.

Rowe vs Wade

Roe vs. Wade: â€Å"The Court today is correct in holding that the right asserted by Jane Roe is embraced within the personal liberty protected by the Due Process Clause of the Fourteenth Amendment. It is evident that the Texas abortion statute infringes that right directly. Indeed, it is difficult to imagine a more complete abridgment of a constitutional freedom than that worked by the inflexible criminal statute now in force in Texas. The question then becomes whether the state interests advanced to justify this abridgment can survive the ‘particularly careful scrutiny' that the Fourteenth Amendment here requires.The asserted state interests are protection of the health and safety of the pregnant woman, and protection of the potential future human life within her. But such legislation is not before us, and I think the Court today has thoroughly demonstrated that these state interests cannot constitutionally support the broad abridgment of personal liberty worked by the exist ing Texas law. Accordingly, I join the Court's opinion holding that that law is invalid under the Due Process Clause of the Fourteenth Amendment† (Craig and O'Brien 17).On January 22nd, 1973 Justice Harry Blackmun gave the decision of the Supreme Court in regards to the Roe vs. Wade case. A single pregnant woman, â€Å"Jane Roe,† had filed a class action lawsuit challenging the constitutionality of the Texas criminal laws regarding abortion, which stated having or attempting an abortion except on medical advice for the reason of saving the mother's life. Norma McCorvey, the plaintiff's legal name, was young and recently divorced at the time, searching for a way to resolve her unplanned pregnancy. â€Å"No legitimate doctor in Texas would touch me,† stated McCorvey. There I was – pregnant, unmarried, unemployed, alone and stuck† (Craig and O'Brien 5). The plaintiff's argument was that prohibiting abortion at any time before the actual birth of the chi ld violated a woman's constitutional right to privacy. The Supreme Court eventually agreed with Mrs. McCorvey, finding it justifiable that abortion under the fourteenth amendment was legal. A person's right to privacy had to now extend to the extent of choosing to have an abortion. Although the Court did not discuss the issue of when life actually begins, abortion became legal under this landmark Supreme Court decision.The debate over whether abortion should be legal had taken place in America for several decades, and the final decision rendered by Roe vs. Wade resonated through all of America, influencing society even to this date. Until inside the last half of the nineteenth century, when it was criminalized on a state by state basis across America, abortion was legal before approximately the fourth month of pregnancy. In early colonial medical guides there were recipes for instigating abortions with plants and herbs that could be grown in one's garden or easily procured in the wo ods.By the middle of the eighteenth century, commercial items were widely available that served the same purpose. Unfortunately, these drugs happened to be often fatal. The first statutes regulating acquiring an abortion, passed in the 1820s and 1830s, were actually laws for poison control: selling of commercial abortion agents was outlawed, but abortion itself was not. Despite these newly appointed laws, the business of abortion was booming by the 1840's, this included the sale of illegal drugs, which were advertised very widely in the popular press.However, this trend would change. Following the 1840's, abortion was under attack, and a string of anti-abortion laws would be put in place until the twentieth century. The pushing force behind this criminalization of abortion was doctors and the American Medical Association. The AMA was founded in 1847, and the elimination of abortion was one of its top priorities. To the growing movement, â€Å"abortion was both an immoral act and a medically dangerous one, given the incompetence of many of the practitioners then† (Joffe 28). However, the opposition went beyond these factors.To many people during the later years of the nineteenth century, abortion represented a threat to the traditional role of a woman in society and the authority of males. Abortion was a symbol of unrestrained female sexuality, expressing self-centered and self-indulgent qualities. The AMA's Committee on Criminal Abortion portrayed this view blatantly in 1871. â€Å"She yields to the pleasures – but shrinks from the pains and responsibilities of maternity; and, destitute of all delicacy and refinement, resigns herself, body and soul, into the hands of unscrupulous and wicked men† (Joffe 9). As the twentieth century arrived, over forty states had completely outlawed abortion unless the mother's life was in direct danger, and many others had put strict regulations in place. However in spite of these emerging laws, people stil l acquired abortions illegally for decades until the Roe vs. Wade decision. Frederick Taussig performed a study in 1936 which showed an estimated half million illegal abortions. In 1953, ninety percent of all premarital pregnancies ended in illegal abortions, and twenty percent of married couples had abortions performed.Illegal abortions climbed in numbers to over a million a year until Roe vs. Wade. Although the law dictated the morality of having an abortion, it was still a considerable part of society. The Roe vs. Wade decision was first argued in December 1971, after being before the Supreme Court for over a year. Although this decision would be later analyzed and debated over, little attention was brought up in regard to the case at the time. Chief Justice Burger opened the Court's oral arguments, and each was given only thirty minutes to present their case and answer questions.Sarah Weddington, who was the main lawyer defending Norma McCorvey argued that abortion needed to be legalized farther than the case in which a woman's life is in danger. The physiological and psychological factors could also warrant an abortion. However, seeing as how the Supreme Court has no jurisdiction over public policies, Weddington decided to argue that current abortion laws were in violation of the fourteenth amendment. The fourteenth amendment guarantees the right to liberty without due process of law, and the decision made this right extend to a woman's right to choose to be pregnant.During her closing argument, Weddington stated if â€Å"liberty is meaningful†¦ that liberty to these women would mean liberty from being forced to continue the unwanted pregnancy† (Craig and O'Brien 17). Jay Floyd, the assistant attorney general of Texas, then presented his case arguing against the legalization of abortion. Weddington had argued that many women had no other choice but to have an abortion because of their social and economic status. However, Floyd contended that d espite external factors, every person has free autonomy. Now I think she makes her choice prior to the time she becomes pregnant. That is the time of her choice. It's like, more or less, the first three or four years of our life we don't remember anything. But once a child is born, a woman no longer has a choice, and I think pregnancy then determines that choice† (Craig and O'Brien 17). Thus, Floyd argued, the fourteenth amendment had not been violated since pregnancy was a result of free will, and liberty was not denied. If pregnancy was a conscious choice on the woman's part, then abortion was not warranted.Another crucial chapter of the Roe vs. Wade trial was the debate of when a fetus is given constitutional rights. In response to Texas' harsh abortion restrictions, Floyd explained that Texas â€Å"recognized the humanness of the embryo, or the fetus† and had†a compelling interest because of the protection of fetal life† (Craig and O'Brien 17). However, there were many flaws with this statement in the court. First, the topic at hand was not the constitutional rights of embryos, but whether abortion was in violation of a person's right to liberty.Second, there had been no state law or court decision which had equated abortion with murder. Thus, Floyd's argument amounted to nothing more than personal opinion, with no relativity to the case. The Court needed to ensure the constitutional rights of the woman before protecting the â€Å"rights† of the unborn fetus. The fourteenth amendment as it is stated applies only â€Å"to all persons born or naturalized in the United States,† and if the Court granted the fourteenth amendment to unborn children, it would be an extreme case of judicial activism (Craig and O'Brien 20).After two years of listening to both sides, the Supreme Court finally came to a decision. The right to privacy and liberty was broad enough to include a woman's choice for abortion. The fourteenth amendment granted personal liberty, which includes a woman's body and unborn fetus. Although the Court determined the legality of abortion, they left the responsibility of how to implement it to the states themselves. Like Brown vs. The Board of Education of Topeka, a general decision on constitutionality needed to be left to local governments to be implemented. Where certain ‘fundamental rights' are involved, the Court has held that regulation limiting these rights may be justified only by a ‘compelling state interest,' and that legislative enactments must be narrowly drawn to express only the legitimate state interests at stake† (Craig and O'Brien 27). Although the court did not provide any precise methods of how to implement, it did set vague guidelines regarding the developmental stage of the fetus.A mother had the choice to abort the pregnancy in the first trimester, but limitations were put in place on abortion where it is allowed in the second and third trimesters if the right to liberty and privacy of the mother was still preserved. The immediate reactions to the Roe vs. Wade decision were heated and extreme, as abortion is still an extremely controversial topic. The president of Planned Parenthood hailed the decision as â€Å"a wise and courageous stroke for the right of privacy, and for the protection of a woman's physical and emotional health† (Craig and O'Brien 32).However, there were just as many people in agreement with the decision as its opposition. Cardinal Terence Cooke came after the Justices, claiming that â€Å"whatever their legal rationale, seven men have made a tragic utilitarian judgment regarding who shall live and who shall die† (Craig and O'Brien 32). Roe vs. Wade launched the abortion issue to the national level, making it a source of political and social arguments in the years to follow. On the tenth anniversary of the decision, The Washington Post discussed its effects on society. â€Å"[Roe vs.Wade] has dr astically changed the Court's image, fostered wholesale attack on ‘judicial activism' and mobilized thousands of supporters and opponents of legalized abortion in a debate that has reshaped the political terrain in many states and, at times, has virtually halted the work of Congress. Few court decisions have had a more immediate impact on such a personal aspect of American life† (Craig and O'Brien 35). The Roe vs. Wade decision has affected all parts of society, from the role of the Supreme Court to the level of humanness of an unborn fetus.Many scholars regard this case as the â€Å"Dred Scott† of the twentieth century. The decision ignited a national debate on judicial activism, and the part the Supreme Court plays on public policy. No other case similar to Roe vs. Wade has had such an extreme impact on public law. Furthermore, the case has drawn an imaginary line, diving the whole country into the pro-life or pro-choice category. Almost immediately following th e decision, a great deal of pro-life and pro-choice groups were created, and abortion has remained a prominent political, social, and moral issue.No other subject has resonated importance in American politics. Finally, the Roe vs. Wade outcome is considered a symbol of the changing society during the 1970's. In the past, abortion was highly restricted and frowned upon, mimicking the conservative society. However, as the 1970's marked a rise in liberalism and the need for individual freedoms, the Roe vs. Wade decision to make abortion legal mirrored this willingness to embrace a person's autonomy. Roe vs. Wade marked an unforgettable change in government, politics, and society.Works Cited Craig, Barbara Hinkson and David M. O'Brien. Abortion and American Politics. Chatham, New Jersey: Chatham House Publishers, 1993. Hickok, Eugene W. Justice vs. Law: Courts and Politics in American Society. New York: Free Press/Macmillan, 1993. Joffe, Carole. Doctors of Conscience: The Struggle to Pr ovide Abortion Before and After Roe v. Wade. Boston: Beacon Press, 1995. Olasky, Marvin. Abortion Rites: A Social History of Abortion in America. Washington DC: Regnery Publishing, 1992. Rubin, Eva R. Abortion, Politics, and the Courts: Roe v. Wade and its Aftermath. New York: Greenwood Press, 1987.

Should Congress Pass Comprehensive Immigration Reform

Should Congress Pass Comprehensive Immigration Reform? Every year close to a million people seek to come to the United States, some do so through legal routes, and others get here without alerting any officials. I believe that immigration is a good thing. Native Americans should be the only ones allowed to say anything negative about immigration. The rest of us might as well be illegal immigrants when compared to them. We wrote the laws once we got here so now we are as good as legal residents, but this is a whole different story. Congress should pass comprehensive immigration reform. First the arguments against immigration will be observed. One opponent of immigration reform claims, â€Å"With the immigration scam well underway in Washington [DC], the only real takeaway for the outside observer is that the Beltway ... Establishment truly thinks we are idiots†(Schlichter). 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