Physical Layer Signal Encoding Techniques - Slides

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

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SCI 232 CSCI 232 Computer Networking: Physical Layer Signal Encoding Techniques eorge Blankenship George Blankenship Physical Layer Signal Encoding Techniques George Blankenship 1
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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 2
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Digital Data, Digital Signal • Digital signal – Discrete, discontinuous voltage pulses ach pulse is a signal element Each pulse is a signal element – Binary data encoded into signal elements Physical Layer Signal Encoding Techniques George Blankenship 3
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Encoding Schemes • Nonreturn to Zero – Nonreturn to Zero-Level (NRZ-L) – Nonreturn to Zero Inverted (NRZI) • Multilevel ipolar - MI Bipolar AMI – Pseudoternary anchester – Manchester – Differential Manchester Physical Layer Signal Encoding Techniques George Blankenship 4
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Nonreturn to Zero oltage constant during bit interval • 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 ositive for the other Positive for the other •N R 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 5
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NRZ ros Pros – Easy to engineer – Make good use of bandwidth Cons – Lack of synchronization capability Used for magnetic recording Not often used for signal transmission Physical Layer Signal Encoding Techniques George Blankenship 6
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Multilevel Binary • Use more than two levels – No net dc component ower bandwidth – Lower bandwidth – No loss of sync with a long string of ones/zeros – Zeros/ones still a problem – Easy error detection • Bipolar-AMI ero represented by no line signal – Zero represented by no line signal – One represented by positive or negative pulse
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Physical Layer Signal Encoding Techniques - Slides - CSCI...

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