Physical Layer Signal Encoding Techniques

Physical Layer Signal Encoding Techniques - CSCI 232 -...

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CSCI 232 - Computer Networks Physcal Layer Signal Encoding Techniques George Blankenship 1 Physical Layer Signal Encoding Techniques George Blankenship 1 CSCI 232 Computer Networking: Physical Layer Signal Encoding Techniques George Blankenship Physical Layer Signal Encoding Techniques George Blankenship 2 Lecture Outline • Digital data, digital signal – Digital signals – Self-clocked signals – Error detection • Digital data, analog signal – Modulation • Analog data, digital signal – Digitization of analog data –PCM • Analog data, analog signal Physical Layer Signal Encoding Techniques George Blankenship 3 Digital Data, Digital Signal • Digital signal – Discrete, discontinuous voltage pulses – Each pulse is a signal element – Binary data encoded into signal elements
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CSCI 232 - Computer Networks Physcal Layer Signal Encoding Techniques George Blankenship 2 Physical Layer Signal Encoding Techniques George Blankenship 4 Encoding Schemes • Nonreturn to Zero – Nonreturn to Zero-Level (NRZ-L) – Nonreturn to Zero Inverted (NRZI) • Multilevel – Bipolar -AMI – Pseudoternary – Manchester – Differential Manchester Physical Layer Signal Encoding Techniques George Blankenship 5 Nonreturn to Zero • Voltage constant during bit interval – no transition (no return to zero voltage) • NRZ-Level – Two different voltages for 0 and 1 bits – Unipolar • Absence of voltage for zero • constant positive voltage for one – Bipolar • Negative voltage for one value • Positive for the other •NR Z I – 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 Physical Layer Signal Encoding Techniques George Blankenship 6 NRZ •P r o s – Easy to engineer – Make good use of bandwidth Cons – Lack of synchronization capability
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CSCI 232 - Computer Networks Physcal Layer Signal Encoding Techniques George Blankenship 3 Physical Layer Signal Encoding Techniques George Blankenship 7 Multilevel Binary • Use more than two levels – No net dc component – Lower bandwidth – No loss of sync with a long string of ones/zeros – Zeros/ones still a problem – Easy error detection
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This note was uploaded on 09/03/2010 for the course CS 232 taught by Professor Susan during the Summer '09 term at GWU.

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Physical Layer Signal Encoding Techniques - CSCI 232 -...

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