T305: Digital Communications

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T305: Digital Communications Block III – Message coding Arab Open University-Lebanon Tutorial 11

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Topic 1: Introduction (cont.) Elements of the starting terminal. Bedouin Open University-Lebanon Tutorial 11

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Introduction: fundamental point is to talk about Block 3: Message Coding The different themes secured: Topic 1: Introduction Revision: data transmission, flagging rate Topic 2: Pulse Code Modulation And Delta Modulation Topic 3: Facsimile Arab Open University-Lebanon Tutorial 11

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Topic 1: Introduction There are three principle sorts of coding: message, channel, and line coding. Components of a broadcast communications connect Arab Open University-Lebanon Tutorial 11

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Topic 1: Introduction (cont.) For a message source creating a simple yield, the initial step must be transformation to computerized shape . This is finished by testing and digitizing. The following stage is pressure . This includes crushing out excess in order to decrease the quantity of bits which must be transmitted. Channel coding may include the expansion of repetitive bits to consider mistake control. Bedouin Open University-Lebanon Tutorial 11

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Topic 1: Introduction (cont.) Finally, line coding and balance adjust the message for transmission over the specific medium that is utilized, for example change to radio floods of suitable recurrence for radio connections … .. There are a wide range of types of message coding. Beat code regulation (PCM), utilized as a part of phone frameworks Arab Open University-Lebanon Tutorial 11

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Topic 1: Introduction (cont.) Next comes delta tweak , which is firmly identified with PCM. Fax, (case of the utilization of pressure procedures) This is trailed by the advanced coding of pictures and, specifically, computerized communicate TV, which incorporates the coding of sound, utilizing the strategies that are being embraced for the computerized communicate radio frameworks. At long last, the message coding utilized for the European advanced portable communication framework, GSM. Bedouin Open University-Lebanon Tutorial 11

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Analog data transfer capacity Bandwidth Analog transmission capacity A simple flag has a recurrence range that covers a scope of frequencies. data transmission = f 1 – f 2. Romanticized recurrence range of a simple flag with cut-off frequencies f 1 and f 2 Arab Open University-Lebanon Tutorial 11

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Analog data transfer capacity A flag has a specific data transmission The directing channel through which the flag passes has additionally a transmission capacity The channel goes about as a channel f low < f sig < f max Filtering before transmission Arab Open University-Lebanon Tutorial 11

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Digital data transmission Digital transmission capacity : Is the greatest flagging rate over a correspondence channel flagging rate (baud): the quantity of images transmitted per unit time over an advanced transmission connect. One baud is one image for every second. Hypothetically: flagging rate S (baud) over a channel of transmission capacity B ( Hz) is : S = 2 × B practically speaking: B<=S <2x B Arab Open University-Lebanon Tutorial 11

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Digital data transfer capacity The most extreme piece rate of a computerized correspondence framework is regularly alluded to the 'data transfer capacity'. For a twofold framework: the flagging rate (baud)= the bit rate (bits every second). C (bit/s)=n*S (baud) n is the quantity of bits per unit time Also C (bit/s)=S *log 2 m= 2*B*log 2 m where m is the quantity of states in coded signals Arab Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation The base examining rate, which as indicated by the inspecting hypothesis is double the data transfer capacity, is known as the Nyquist rate . PCM was intended for discourse phone frameworks. The data transfer capacity of discourse signs starting from great quality amplifiers can surpass 20 kHz, and this would be suitable for hello fi frameworks, for communication, a recurrence band covering 300 Hz to 3.4 kHz is sufficient, and this is the transmission capacity utilized as a part of phone frameworks. Bedouin Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) It is not practicable to outline a channel that would let through all the required recurrence segments up to 3.4 kHz and that would totally cut off everything over this. In any case, it is conceivable to plan channels that leave parts behind to 3.4 kHz and that constrict higher recurrence segments increasingly as their recurrence increments over this esteem, in a manner that segments above 4 kHz have an insignificant impact. These are the channels that are utilized, yet this requires a base examining rate of 2 × 4000 = 8000 specimens for every second, which has been received as the standard rate. Bedouin Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) Encoding and deciphering the flag is then PCM encoded , which includes quantization – changing over every simple specimen into a n-bit computerized paired code word utilizing a simple to-advanced converter. Once quantized, the specimens are restricted to a limited, discrete arrangement of 2 n diverse conceivable qualities. The quantity of bits every second that must be transmitted for PCM signs is relative to n . Middle Easterner Open University-Lebanon Tutorial 11

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Quantization utilizing 16 discrete levels; (b) mistakes presented by the quantization procedure. Theme 2: Pulse Code Modulation And Delta Modulation (cont.) Encoding and unraveling (cont.) The quantization procedure is shown in Figure (a) for a framework utilizing 4-bit code words and subsequently 16 distinctive quantization levels. Each of these levels is designated a 4-bit code, albeit more mind boggling codes are utilized as a part of practice. Middle Easterner Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) Encoding and disentangling (cont.) If neighboring levels are isolated by q volts, then the greatest mistake presented by the quantization procedure is q/2, and the normal is zero. This is shown to some extent (b) of the figure, which is acquired by subtracting the quantized flag from the first message flag. Middle Easterner Open University-Lebanon Tutorial 11

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The mistakes spoke to by the distinction between the first and quantized signs set a basic impediment to the execution of PCM frameworks, in light of the fact that even a flag remade to match precisely with the transmitted computerized codes will experience the ill effects of these blunders. The impact is typically known as quantization commotion . Middle Easterner Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) Encoding and disentangling (cont.) The adequacy of a run of the mill discourse flag can differ massively both starting with one speaker then onto the next and over the ordinary talking scope of a solitary person. Truth be told, the scope of variety from the 'whisper of a peaceful speaker to the crying tones of an effective speaker can be as extraordinary as 50 to 60 dB. This is known as the dynamic scope of the flag. A dynamic scope of 60 dB implies that the proportion between the sufficiency of the loudest flag, V l, and the mildest, V s, is given by the expression: that is, V l/V s , = 1000. On the off chance that we accept that V s is of the request of one quantization interim, then to cover the entire scope of positive and negative signs with equivalent separating we require no less than 2000 unmistakable levels. Middle Easterner Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) Non-uniform encoding of a sinusoid. Littler quantization interims are utilized for little estimations of the flag than for huge qualities. Middle Easterner Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) Encoding and translating (cont.) Voice communication utilizes 8-bit non-uniform coding to cover a range which would require 12 bits for every specimen with uniform quantization. Such encoding – and the consequent unraveling of the got flag – is done electronically utilizing a gadget known as a codec ( co der/dec oder). Middle Easterner Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation (cont.) Encoding and deciphering (cont.) Analog discourse covers a band from around 300 Hz to 3.4 kHz, that is 3.1 kHz, around one-tenth of the base transmission capacity required for PCM discourse (32 kHz, a large portion of the flagging rate). Be that as it may, the upsides of advanced flags over simple – relative resistance to clamor and impressively expanded preparing adaptability – are the principle reasons why computerized coding has been received for most phone systems. Bedouin Open University-Lebanon Tutorial 11

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The tremendous number of phone links that have been laid between exchanging focuses and the homes or workplaces were intended for simple communication and are unseemly for PCM, for the most part on the grounds that the higher frequencies introduce in PCM signals have a tendency to emanate and couple into neighboring wire combines in the links, prompting to a type of obstruction known as crosstalk . Middle Easterner Open University-Lebanon Tutorial 11

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Encoding plans Analog information, Digital flag Analog information, Analog flag advanced simple voice Telephone CODEC Digital information, Digital flag Digital information , Analog flag simple computerized advanced Modem Digital transmitter Arab Open University-Lebanon Tutorial 11

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Topic 2: Pulse Code Modulation And Delta Modulation Codecs A codec can appear as a solitary incorporated circuit which does examining, quantization and coding of a transmitted flag, and in addition disentangling and recuperation of a got flag. Middle Easterner Open University-Lebanon Tutorial 11

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PCM Sampling signal in light of nyquist hypothesis Original flag PAM beat (before quantization) 3.9 4.2 3.4 3.2 2.8 1.2 4 PCM beat with quantized blunder 3 1 011 100 011 001 100 PCM yield 011100011011001100 Arab Open University-Lebanon Tutorial 11

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Nonlinear Encoding PCM refined technique

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