Block Diagram Of A Communication System Computer Science Essay

auction hitch plat Of A Communication System Computer Science bear witnessThe doorway to the present wireless communication clays was opened by Guglielmo Marconi when he manoeuvreted the three-dot Morse formula for alphabet S by the uptake of electromagnetic waves over a 3-KM link in 1895. This laid the induction of sophisticated communication governing bodys ranging from broadcasting, satellite transmission and wireless razetually progressing to nowadays cell ph wizards. It wouldnt be wrong to say that wireless communication has thusly r organic evolutionized our present societyA sudden accession has been observed in the expansion of radio systems during the last devil decades. We extradite seen great evolution in Wireless communication systems from 1G narrowband analog systems in the 1980s to the 2G narrowband digital systems in the 1990s. Now the exist 3G wideband mul condemnationdia systems argon existence deployed. In the meantime, research and progress in the future-geneproportionn wideband multimedia radio systems is vigorously being pursued worldwide.To connect energetic drug exploiters to the public switched engagement the United States introduced branch radioteleph bingle service by the end of the 1940s. melio compute roving Telephone Service was launched by Bell Systems in sixties imputable to which lots of improvements worry direct dialing and increase in bandwidth took place. IMTS form the bases of the first analog cellular systems. The term cellular was apply due to the feature that coverage aras were split cells, they had a low business office transmitter and receiver.BLOCK DIAGRAM OF A communication SYSTEM soma 1. stuff diagram of a general communication system. linear vs. digital COMMUNICATION SYSTEMS explanation of digitalA method of storing, processing and transmitting education through the use of transpargonnt electronic or optical impulsions that represent the binary digits 0 and 1.Advantages of dig itallow-pricedreliableEasy to pull wiresFlexibleCompatible with former(a) digital systemsThe tuition in digital form underside save be familial without any debasement through a noisy stemmaIncorporated networksDis benefits of Digital sampling ErrorAs comp bed to analogue, cosmicr bandwidth is mandatory in digital communication theory for the transmission of the uniform information.Synchronization in the communications system is necessitate to recognize the digital signs, notwithstanding this is not the case with analogue systems.Definition of AnalogueAnalogue is a transmission standard that uses galvanizing im pulsations to emulate the audio waveform of sound. When you use a phone, the variations in your verbalize ar transformed by a microphone into interchangeable variations in an electrical contract and carried down the line to the exchange.Advantages of Analogueless bandwidth is requiredto a greater extent AccurateDisadvantages of AnalogueSignal loss and distortio n batch be seen due to the effectuate of random echo which is impossible to recover genesisS OF cellular SYSTEMSThe concept of cellular telephone set was introduced in AMPS, short for Advanced Mobile Phone Systems. AMPS divided the total bea into small regions called cells and this was from where the concept of cellular telephony started. cellular Systems had many advantages such as they increased quality, capacity, reliableness and availability of mobile telephone network. The generations of cellular systems argon lined below. early GENERATION CELLULAR SYSTEMSFirst generation cellular telephone systems were introduced in 1980s. They were based on Analog frequency flexion proficiency. Each contribute was assigned a sole frequence.First generation cellular systems offered solitary(prenominal) wireless voice services based on analog engine room. Digital call fors were only utilize for control information such as dialing a count etc. These systems were no able to cope wi th the increasing demands of users too they had real less capacity and provided poor voice quality. virtually first generations systems argonAdvanced Mobile Telephone System, AMPSNAMPS, AMPSTotal Access Cellular System (TACS)Nordic Mobile Telephone System (NMT-900)SECOND GENERATION CELLULAR SYSTEMSSecond genesis Cellular Systems provided larger capacity and provided oftenmultiplication better services to users comp ared to first generation systems. They were based upon Digital inflexion technique which led to great enhancement in networks capacity.Second Generation Systems used binary access techniques such as TDMA and FDMA.The biggest draw moxie of Second Generation Systems was that its polar systems were not compatible with all(prenominal) separate. thus roaming between different systems was not possible.Some of Second Generation Systems areNorth American Digital Cellular, NADCGlobal System for Mobile Communication, GSMpeaceable Digital Cellular, PDCCDMAONE, IS-95 CDMA In purchase localizeliness to overcome Second Generation compatibility riddle with increased info rates of modern meshing applications, 2.5 Generation standards were developed. The exceed thing about them was that they allowed already existing Second Generation systems to be upgraded so that they can be used for melloweder information rate transmission.2.5 Generation brought a new revolution in cellular telephony by staying services like game speed profits and location based mobile services.Some of 2.5 Generation Mobile Systems areGeneral Packet Radio Service, GPRSEnhanced Data Rate for GSM Evolution, keennessTHIRD GENERTAION CELLULAR SYSTEMSDesigned to provide high quality and high capacity in information communication, one-third Generation Systems require innovative spreading and transition techniques.Third Generation Systems are aimed to provide voice quality comparable to land line telephony and also to support high data rate.These systems are compatible with circuit switched as good as package switched data services. They are also compatible with the existing networks and use radio spectrum much to a greater extent efficiently than in the beginning.Some Third Generation Systems areWideband CDMA, WCDMAUniversal Mobile Telephone System, UMTSCDMA 2000beyond 3GThe highly developed version of the 3G mobile communication are the 4G mobile communication services. It is estimated that 4G mobile communication services will give increase in capacity, data transmission with high speed, broadband, HQ color painting images for users, graphic animation games in 3D, audio services in 5.1 transmit. For the system and architecture of 4G mobile communication many researches are done. Developments are make in the terminal protocol technology for high speed packet services, larger capacity, enabling downloading application programs by public software chopine technology, multimode radio access platform technology, and high quality media coding technolo gy over mobile networks.Why 4G?Services like wireless internet and teleconferencing can be carried by 4G.Global mobility and service portability.Wider bandwidths.increase here and now rates.Less expensive.Mobile networks can easily be scaled.CHAPTER 02Multiplexing is a process in which a single carrier is used to transmit several different communicates. These several signals are transmitted all together by combining them and forming one signal that will effectively motion through the carrier bandwidth. When one transmission is done and the signal r all(prenominal)es the finis point, the integrated signal re-assembles into its actual form and is whence real.Multiplexing is one of the or so used techniques today in almost every communication system. Because of the expert advance multiplexing, we have seen major increase in efficiency of a wide range of telephony services and online applications.Multiplexing has become an effective technique that assists in everything from vid eo conferences and web conferences up to bulk data transmissions and even making a simple Point-to-Point phone call.FDMAFDMA is the most usual technique used for multiple accessing. FDMA stands for oftenness division multiple access. It is clear from its notice that in this technique the oftenness is divided among the users as the available spectrum is shared out among them in the oftenness do important. The pass signals are transmitted onto carriers for different users development particular RF frequencies. Within FDMA structural design the Single alley Per Carrier (SPSC) is the simplest method where each channel is provided with a separate carrier. This escape finds its essence in the fact that the channels are assigned on the basis of demand. Within a cell all the channels are available to all users all the time, and the channels are assigned as soons as a content signal is trustworthy or a request is made.Guard bands are used to reduce the chances of interference from side by side(p) channels. These view as bands are present between the bands allocated for various channels.In the implementation of the first analog cellular systems, FDMA is the multiplexing technique that was used.TDMA succession division multiple access techniques allots different time intervals to different users for the transmission of signals and storage of the data is carried out in one frequency channel not like FDMA which uses one frequency per channel.Users are allowed to use the same frequency but the time slots are divided.In TDMA techniques the available spectrum is divided into small frequency bands as in FDMA, which are further sub-divided into various time slots. The user can access the frequency channel only for time slot allotted to him. User can use periodically the particular period of time.In TDMA systems, guard bands are required between whatsoever(prenominal) frequency channels and time slots.SDMASDMA stands for Space-Division Multiple Access. It is a M IMO (Multiple-Input, Multiple-Output, a multiple antenna schematic architecture) based wireless communication network architecture. It enables access to a communication channel by the process of identifying the user location and establishing a one-on-one mapping between the network bandwidth allotment and the acknowledged spacial location that is why its mostly suitable for mobile ad-hoc networks.For majority of the intumesce known mobile communication architectures such as CDMA, TDMA and FDMA, SDMA architecture can be configured and implementedCDMACDMA stands for statute division multiple access. CDMA systems are based on the spread spectrum technique. In which transmissions by all the users are carried out concurrently while operating at the same frequency and using the replete(p) spectrum bandwidth.For the identification and extraction of required transmission, each user is allotted with a unique code which cannot match with any other user. This issue of identification is du e to the fact that all the users transmit simultaneously. To fit this privacy, pretender-random noise codes or PN codes are used.These codes are actually the orthogonal codes and its advantage is that it reduces the chances of cross correlation among themselves. By using this PN code assigned to the special user, modulation of the pith signal from an individual user is done. Then we have the CDMA frequency channel through which all the modulated signals from different users are transmitted. At the receivers end, the want signal is then recovered by de-spreading the signal with a replica of the PN code for the specific user. The signals whose PN codes are not matched with the desired signal and are assigned to different users are not de-spread and as a result are regarded as noise by the receiver.CDMA differs from both TDMA and FDMA in a way that it allows users to transmit the signal at the same time and operate at the same nominal frequency so it requires less synchronization whereas in TDMA and FDMA frequency and time management is very critical so more dynamic synchronization is required. angiotensin-converting enzyme more advantage of CDMA is that fatten up systems spectrum is used by signals and consequently no guard bands are required to protect against adjacent channel interference.Intro to beam Spectrum CommunicationsFollowing are the major elements that can clearly describe the circulate Spectrum communicationsBy spread spectrum, bandwidth far in exorbitance is available than that is necessary to send the information. Due to this characteristic the transmission can be protected against interference and jamming at the same time providing multiple access capability.An independent code known as the postiche random code is used for signal spreading across the bandwidth. The distinct nature of this code separates spread spectrum communications from typical modulation techniques in which modulation always spreads the spectrum somewhat.For the re covery of the original signal the receiver is synchronized to the deterministic fraudulence random code. Users can transmit the signal at the same time and operate at the same nominal frequency by using independent code and synchronous reception.In order to protect the signal from interference a pseudo-random code is used. It appears to be random to anyone who does not have its pre-defined knowledge but in reality is deterministic, it is because of this fact that receiver is able to reconstruct the code needed for the recovery of the required data signal. This code used for synchronous detection is also called imposter noise sequence.Types of revolve Spectrum Communications feasting of bandwidth of the signal can be achieved by three waysFrequency hoppingThe signal is shuffled between different centre frequencies within the entire bandwidth available to the hopper pseudo-randomly, and the receiver used already knows where to look for the signal at a given time.Time hoppingThe si gnal is transmitted in short infracts pseudo-randomly, and the receiver knows when a burst is expected. carry sequenceVery high frequency is used to code the digital data. The code is pseudo-randomly feedd. The same code is generated at the receiver end, and in order to extract the original data this code is cipher to the have information float.CHAPTER 03SOURCE CODING AND DIGITAL MODULATION3.0 INTRODUCTIONDigital pitch contour is performed in order to represent digital data in a format that is compatible with our communication channel.Why Digital Modulation? Digital modulation schemes have greater capacity to convey large amounts of information than analog modulation schemes.3.1 DIGITAL DATA, DIGIITAL SIGNALDigital signal is binary data encoded into signal elements. Different encoding schemes for encoding digital data into digital signal are3.1.1 Non Return to nothing (NRZ)In NRZ there are two different voltage levels for 0 and 1. at that place is no transition in the middl e of the bit. The absence seizure of signal denotes 0 and a positive voltage level denotes 1. design 3.1, Non Return to Zero (NRZ)The major drawback of NRZ scheme is that it adds a dc component to the signal.3.1.2 Multilevel binary star (AMI)In this encoding scheme there are more than two levels. No signal represents 0 and 1 is delineate by some positive and negative voltage level. 1s pulses are opposite in polarity.Figure 3.2, Multilevel Binary (AMI)There is no dc component in this scheme and also there is no loss of synchronization for sequent 1s.3.1.3 Manchester CodingThere is transition in middle of each bit, which acts as a clock as well as data. The low to high transition represents 1 and high to low represents 0.Figure 3.3, Manchester Coding3.1.4 derivative ManchesterIn this scheme transition at the middle of the bit represents only clocking while transition at start represents 0 and no transition at start represents 1.Figure 3.4, Differential Manchester3.2 ANALOG DATA, DIG ITAL SIGNALAnalog data is first converted into digital data by using analog to digital converters. These converters use different techniques to complete their task, some of them are3.2.1 shudder Code ModulationIf a signal is renderd at regular intervals at a rate higher than in two ways the highest signal frequency, the samples contain all the information of the original signal. Each sample is assigned a digital value. Although its quality is comparable to that of analog transmission but still in this process some information is incapacitated and the original signal can never be recovered.Figure 3.5, Pulse Code ModulationDelta ModulationAnalog foreplay is approximated by a staircase cultivate. Function moves up or down at each sample interval by one level (d).Figure 3.6, Delta ModulationDelta modulation is easier than PCM in implementation, but it exhibits worse signal to noise ratio for the same data rate. But it is good for data compression.DIGITAL DATA, ANALOG SIGNALDiffere nt digital modulation techniques are premium free Keying (ASK)A modulation technique in which digital data is represented as variations in the amplitude of a carrier wave is called Amplitude-shift keying (ASK). One binary digit is represented by aim of carrier, at uniform amplitude and the other binary digit represented by absence of carrier.Figure 3.7, Amplitude Shift Keying (ASK)3.3.2 Frequency Shift Keying (FSK)In frequency shift keying different frequencies are used to represent incoming digital data. Say in case of Binary Frequency Shift Keying f1 is used to represent 0 while f2 is used to represent 1.Figure 3.8, Frequency Shift Keying (FSK)In MFSK more than two frequencies are used and hence bandwidth is more efficiently utilized.3.3.3 bod Shift Keying (PSK)A digital modulation technique in which data is transmitted by modulating and changing the phase of the reference signal is called Phase-shift keying (PSK). In case of PSK, a finite number of phases are used. A unique pattern of binary bits is assigned to each of these phases. Generally, each phase encodes an equal number of bits. The image is formed by each pattern of bits that is represented by the particular phase.Figure 3.9, Phase Shift Keying (PSK)Figure 3.10, Constellation Diagram of BPSKThe bandwidth of ASK and PSK are qualify asWhereas the bandwidth of FSK is given asWhere,R is the bit rateDF = f2 fc = fc f1CHAPTER 04 pathway CODING4.0 INTRODUCTIONWhy Channel Coding? In modern digital communication systems information is represented in bit sprouts, which are then modulated to analog waveforms in the first place being transmitted onto a channel. At receiver this analog information is demodulated into bit flowings, but because of the presence of interference and noise in the communication channel this bit drift may be corrupted. So to minimize occurrence of bits in hallucination and protect digital data from channel noise and interference channel coding is used.How Channel Coding is performed? Additional redundant bits are added to the message data stream to perform channel coding, these extra bits assist in error detection and field at the receivers end.Channel Coding at the cost of? Channel Coding is performed at the cost of bandwidth expansion and data rate reduction.4.1 TYPES OF CHANNEL CODING TECHNIQUESThere are two main types of channel coding techniques,Block CodesConvolutional Codes.Block Codes accepts k number of information bits and generate a block of n number of encoded bits, and thus are commonly known as (n.k) block codes. Some common examples of block codes are Hamming Codes and Reed Solomon Codes.Convolutional Coding is forward error correction technique that is up-to-the-minutely most widely used in modern communication systems, this particular technique is used for real-time error correction. opposed block codes which append redundant bits at the end of original message signal, Convolutional coding form a new codeword using original data stream. The encoded bits are not solely dependent on k current input bits but at the same time on spring input bits.4.2 CONVOLUTIONAL CODESIn this project Convolutional Coding is implemented. Convolutional Codes are further separate as 1. trellis Coded Modulation (TCM) 2.Turbo Codes.Trellis Coded Modulation (TCM) is non recursive, non systematic and does not require an interleaver.Turbo Codes on the other hand are recursive, systematic, parallel organize and they also require interleaver.In Wideband CDMA systems TCM is used for all channels while Turbo Codes may be used for DCH and FACH channels. Turbo Codes are sometimes sort out as separate branch of Channel Codes so from here frontwards word Convolutional Code will only be used for TCM.Types of infection ChannelsCoding SchemesCoding RateRACHConvolutional Coding1/2BCHPCHDCH, FACH1/2, 1/3Turbo Coding1/3 instrument panel 4.1, WCDMA Specifications4.3 CONVOLUTIONAL CODE REPRESENTATIONS4.3.1 Polynomial archetypeNo. of input in formation bits = kNo. of encoded bits = nNo. of stages (Constraint Length) = KCode Rate = k/nEncoded CodeWord = UThe sideline example shows how Convolutional Codes are represented.Let g1(x) and g2(x) be encoder polynomials, whereg1(x) = 1 + x + x2g2(x) = 1 + x2Let input message bit stream be 101, therefore input message bit stream polynomial will be,m(x) = 1 + x2The encoded codeword U will be crew of harvest-festival of g1(x) with m(x) and g2(x) with m(x),m(x) x g1(x) = 1 + 1.x + 0.x2 + 1.x3 + 1.x4m(x) x g2(x) = 1 + 0.x + 0.x2 + 0.x3 + 1.x4Therefore the codeword U, becomesU = (1,1) + (1,0).x + (0,0).x2 + (1,0).x3 + (1,1).x4U = 1 1 1 0 0 0 1 0 1 14.3.2 State revolution DiagramConvolutional Coding can be represented using State innovation Diagram. Following are State changeover Diagram and State Transition elude for code rate 1/2.Figure 4.1, State Transition Diagram for Code Rate Table 4.2, State Transition Table for Code Rate Again for the same input bit stream 10100, the code word U = 11 10 00 10 11. In the input message last two 00 bits are tail bits.4.3.2 Block Diagram RepresentationThe following diagram shows block diagram representation of Convolutional Coding withCode Rate = 1/2Constraint Length (No. of Stages) = 3Figure 4.2, Block Diagram Representation of Convolutional Code with Code Rate = The following example illustrates the process of Convolutional Coding using block diagram representation for input bit stream 101.So the final codeword becomes, U = 11 10 00 10 114.3.2 Trellis Diagram RepresentationFor input bit stream 101, the following diagram shows how Convolutional Coding is performed using Trellis DiagramFigure 4.3, Trellis Diagram RepresentationCHAPTER 05PULSE establishment TECHNIQUES3.0 INTRODUCTIONWhy Pulse Shaping? It is done in order to reduce Inter symbol Interference commonly known as ISI.How Pulse Shaping is performed? In order to achieve zip fastener-ISI the overall system reply moldiness be equal to Nyquist frequency resolu tion.5.1 RAISED cos FILTERInter Symbol Interference significantly degrades the data sensor ability to differentiate between a current symbol from cushy energy of adjacent symbol. This leads to the detection of error and increases BER. So in order to cater ISI, a real-time identification of Nyquist drivel is applied in modern communication systems. Raised cosine penetrate is one of the realization of Nyquist filter.where r = roll-off factor = 1 r 0and T = symbol period = 1/RRoll-off factor determines the filter bandwidth and represents a trade-off between the sharpness of the transition band of the filter and impulse rejoinder ringing magnitude of the filter.A Nyquist filter has following propertiesTime result eventually goes to zero in a time period barely equal to the symbol spacing.By sampling the symbol sequence at a given symbol time point, present symbol is not affected by the energy spreading from the adjacent symbols.The impulse response and the frequency response of the RC filter isFigure 5.1, Impulse Response of RC slabberFigure 5.2, Frequency Response of RC stressTime response of the RC filter goes to zero with a period that exactly equal to the symbol spacing. As the response equals zero at all symbol times draw off for the desired one none of the adjacent symbols interfere with each other.5.2 stand RAISED COSINE FILTERRC filter is divided into a sink raised cosine (RRC) filter pair, with one at the transmitter end, which performs the pulse shaping in order to constrain the modulated signal bandwidth, and the other at the receiver end, that performs matched detection for optimizing the SNR of a known signal in AWGN presence.The Root Raised romaine filter is so named because its transfer function exactly is the square root of the transfer function of the Raised Cosine filter.Where r = roll off factor and T is symbol period. The RRC filter bandwidth is equal to the root mean square (RMS) amplitude 2R.The impulse response and the frequ ency response of the RRC filter isFigure 5.3, Impulse Response of RRC FilterFigure 5.4, Frequency Response of RRC FilterBoth RC and RRC have similar pulse shapes, but the RRC pulse makes slightly faster transitions, therefore the spectrum of RRC pulse decays more rapidly as compared to the RC pulse. Another important difference between both pulses is that the RRC pulse does not have zero Inter Symbol Interference. Because of the fact that RRC filter is used at transmitter and receiver both, the product of these transfer functions is a raised cosine, which will result in zero ISI output.5.3 ROLL OFF FACTORThe roll-off factor, r, is a measure of the special bandwidth of the filter, i.e. the bandwidth meshed beyond the Nyquist bandwidth of 1/2T.Where f is excess bandwidth and Rs is symbol rate.CHAPTER 06SPREAD SPECTRUMSpread spectrum is a type of modulation where the data is spread across the entire frequency spectrum. This process of spreading the data across the entire spectrum he lps signal against noise and interference. These techniques are mostly employed in cell phones and also with wireless LANs.To qualify as a spread spectrum signal, two criterions must be metThe transmitted signal bandwidth must be in excess of the information bandwidth.Some function other than the data being transmitted is used to establish the bandwidth of the resultant transmission.Why Spread Spectrum ?Due to its max and peculiar properties spread spectrum is preferred over other modulation schemes. Some of these properties are characterized as advantages and disadvantages of a elemental spread spectrum system below.Advantages It reduces the effects of multipath interference and at times removes them entirely. Frequency band is shared simultaneously with other users. pseud random codes ensure protection of transmission and privacy. As the signal is spread over an entire spectrum it has a low power spectral density.Disadvantages Due to spreading operation it consumes more bandwid th. It is at times difficult to implement.Types of Spread Spectrum Techniques virtually commonly used techniques in a spread spectrum systems areDirect Sequence Spread SpectrumFrequency Hopping Spread SpectrumFrequency Hopping Spread SpectrumA frequency hopping spread spectrum hops from one narrow band to another all within a wider band. In general the frequency hopper transmitter sends data packets at one carrier frequency and then jumps to another carrier frequency before sending ore packets and continues the same routine throughout the period of transmission. The pattern that emerges seems to be random but is in fact periodic and easily trackable by pre configured transmitter and receiver. These systems can be vulnerable to noise at a particular hop but usually are able to send packets during the next hop.Direct Sequence Spread SpectrumMost widely used technique of spread spectrum is the Direct Sequence Spread Spectrum. A Direct Sequence Transmitter receives the incoming data str eam which is to be transmitted and then converts it into a symbol stream where the sizing of a symbol can be one or more bits. Using any of the modulation schemes for digital systems such as Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Keying (QPSK) this symbol stream is multiplied to a noise like sequence known as pseudo random sequence. It is also know as a chip sequence. As a result of this multiplication the bandwidth of the transmission is significantly increased.Figure 3. Direct Sequence Spread Spectrum SystemFigure 3. shows the operative of a basic Direct Sequence Spread Spectrum system. For clarity purposes, one channel is shown working in one direction only.TransmissionFor each channel a distinct and different Pseudo random code is generated.In order to spread the data the data stream is multiplied with the previously generated Pseudo random code.The signal obtained as a result of this multiplication is then modulated onto a carrier.This modulated carrie r waveform is then amplified before broadcasting.ReceptionThe carrier wave is amplified as soon as it is received by the receiver.The signal received is then multiplied with a locally generated carrier which gives the spreaded signal.Again a Pseudo random code is generated on the basis of the signal expected.The process of correlation is carried out on the received signal and the generated code which gives the original message signal.Pseudo-Random NoiseThe spread spectrum systems are constructed very similar to other conventional systems. The difference being the gain of pseudo random generators both at the transmitter and the receiver which generate the Pseudo noise sequences required for the functionality of Direct Sequence spread spectrum. These pseudo random noise sequences are used for spreading the signal at the transmitter side and dispreading at the receiv