05-SignalEncodingTechniques-modified

05-SignalEncodingTechniques-modified - William Stallings...

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William Stallings Data and Computer Communications 8 th Edition Chapter 5 Signal Encoding Techniques
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Encoding Techniques Digital data, digital signal Analog data, digital signal Digital data, analog signal Analog data, analog signal
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Digital Data, Digital Signal Digital signal Discrete, discontinuous voltage pulses Each pulse is a signal element Binary data encoded into signal elements improve performance by using more complex  encoding schemes by altering the spectrum and  providing synchronization capability
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Terms (1) Unipolar All signal elements have same sign Polar One logic state represented by positive voltage the  other by negative voltage Data rate Rate of data transmission in bits per second Duration or length of a bit Time taken for transmitter to emit the bit
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Terms (2) Modulation rate Rate at which the signal level changes Measured in baud = signal elements per second Mark and Space Binary 1 and Binary 0 respectively
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Interpreting Signals Need to know Timing of bits - when they start and end Signal levels Factors affecting successful interpreting of  signals Signal to noise ratio Data rate Bandwidth
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Comparison of Encoding Schemes (1) Signal Spectrum Concentrate power in the middle of the bandwidth Clocking Synchronizing transmitter and receiver External clock – more expensive Sync mechanism based on signal
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Comparison of Encoding Schemes (2) Error detection Can be built in to signal encoding Signal interference and noise immunity Some codes are better than others Cost and complexity costs Some codes require signal rate greater than data rate
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Encoding Schemes Nonreturn to Zero-Level (NRZ-L) Nonreturn to Zero Inverted (NRZI) Bipolar -AMI Pseudoternary Manchester Differential Manchester B8ZS HDB3
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Nonreturn to Zero-Level (NRZ-L) Two different voltages for 0 and 1 bits Voltage constant during bit interval no transition I.e. no return to zero voltage e.g. Absence of voltage for zero, constant  positive voltage for one More often, negative voltage for one value and  positive for the other This is NRZ-L
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Nonreturn to Zero Inverted Nonreturn to zero inverted on ones Constant voltage pulse for duration of bit Data encoded as presence or absence of signal  transition at beginning of bit time Transition (low to high or high to low) denotes a  binary 1 No transition denotes binary 0 An example of differential encoding
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This note was uploaded on 02/10/2012 for the course CSC 411 taught by Professor Simmons during the Spring '08 term at S. Alabama.

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05-SignalEncodingTechniques-modified - William Stallings...

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