ADC_09_SIG_ENC TEC
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ANALOG & DIGITAL COMMUNICATION By Engr. Hyder Bux Mangrio Institute of Information & Communication Technologies Mehran University of Engineering and Technology, Jamshoro. 09TL-BATCH Lecture#: 30-36 Line Encoding Techniques 03/16/22 [email protected] 1
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Transcript of ADC_09_SIG_ENC TEC
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ANALOG & DIGITAL COMMUNICATION
By Engr. Hyder Bux Mangrio Institute of Information & Communication Technologies Mehran University of Engineering and Technology, Jamshoro. 09TL-BATCH Lecture#: 30-36 Line Encoding Techniques*[email protected]*
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Whenever a serial binary bit stream is transmitted, it must be encoded into a sequence representing 1s and 0s.High speed data communications and telecommunications system uses different encoding techniques as signalling standards.Used in communication links ranging from LANs and Modem to telephone trunks to satellite links *[email protected]*
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When choosing an encoding techniques, some important factors must be consideredChannel Bandwidth: The transmission medium must have a bandwidth wide enough to pass the spectral content of the encoded signal.Self Clocking: Serially transmitted data require a mechanism for synchronization to the individual bit times of the received data.
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If the separate clock is not provided with the signal, then encoding techniques must have self clocking mechanism. So that series of 1s and 0s does not conflict with recovery of the data. Bit Error Rate: The probability of bit errors can be minimized in noisy environments by selecting appropriate encoding techniques*[email protected]*
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Data Transparency:In some transmission protocols, the format of the data controls the operation of the receiver. Raw data must incorporate special encoding techniques into the code so that data are not mistaken for control characters *[email protected]*
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Digital signalDiscrete, discontinuous voltage pulsesEach pulse is a signal elementBinary data encoded into signal elements
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Number of signal level: This refers to number of values allowed insignalBit rate versus Baud rateThe bit rate represents the number of bits sent Per second, whereas baud rate defines the Number of signal elements per second in the signal
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In uni-polar encoding, only two voltage levels are used.It uses only one polarity of voltage levelBit rate same as data rateUnfortunately DC component is presentLoss of synchronization
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Polar encoding technique uses two voltagesOne positive level other one negativeFour different encoding techniques
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Bi-polar, uses the three voltage levels
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Two different voltages (+ and OR + and none) for 0 and 1 bitsVoltage constant during bit intervalno transition I.e. no return to zero voltagee.g. Absence of voltage for zero, constant positive voltage for oneMore often, negative voltage for one value and positive for the other*[email protected]*
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NRZ-I is variation of NRZ encoding.Considered as a differential encoding techniques because of its level is a function of the transition at the beginning of the signal element.If signal is logic 0, there is no change to opposite logic level, either at beginning or throughout cell. If signal is logic 1, then transition occurs at beginning of the cell and logic level change to the opposite value throughout cell.*[email protected]*
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ProsEasy to generate signalMake good use of bandwidthConsdc componentLack of synchronization capabilityUsed for magnetic recordingNot often used for signal transmission*[email protected]*
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RZ encoding can be classified into two categories: Unipolar RZ and Bipolar RZ.In Unipolar RZ encoding, a binary 1 is represented with a high level for half the bit time and returns to zero for the other half.In Bipolar RZ encoding, two non-zero voltages are used; a logic 1 and 0 alternate in polarities, each taking half the bit time before running to zero.Bipolar RZ is a self clocking code*[email protected]*
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Three levels Bit rate is double than that of data rate No dc component Good synchronization Main limitation is the increase in bandwidth
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Self clocking codes are encoding techniques used to ensure that each bit time associated with the binary serial bit stream contains at least one level transition (1 to 0, or 0 to 1).Sufficient spectral energy is generated at clock frequency so that the receiver can recover the data, even when long periods of 1s or 0s occurs.Self clocking codes include Bipolar RZ, Manchester and differential Manchester, Miller.*[email protected]*
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Telephones trunks circuits uses a self clocking RZ encoding called bipolar with 8 zeros substitution(B8ZS)B8ZS is also known as AMI*[email protected]*
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In Manchester encoding, a logic 1 is represented with low-to-high transition in the center(or beginning) of the cell and Logic 0 is represented with a high-to-low transition in the center(or beginning) of the cell Ethernet LAN systems employ Manchester encoding *[email protected]*
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In differential Manchester, a transition from low-to-high or high-to-low occurs at center of each cell, which provides for self clocking mechanism.A logic 1 or 0 are determined by the logic level of the previous cell.If the previous cell is a logic 1, there is no change at the beginning of the current cell.If the previous cell is a logic 0, then a transition occurs at the beginning of the current cell.Token ring LAN systems *[email protected]*
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Self clocking techniques in which a transition occurs at the center of each cell for logic 1s onlyNo transition is used for a logic 0 unless it is followed by another 0, in which case transition is placed at the end of the cell for the first 0Miller encoding used in digital magnetic recording. *[email protected]*
