Voltages for 0 and 1 bits voltage constant during bit

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Unformatted text preview: zero voltage such as absence of voltage for zero, constant such positive voltage for one positive more often, negative voltage for one value more and positive for the other and Nonreturn to Zero Inverted Nonreturn nonreturn to zero inverted on ones constant voltage pulse for duration of bit data encoded as presence or absence of signal data transition at beginning of bit time transition transition (low to high or high to low) denotes binary 1 no transition denotes binary 0 example of differential encoding since have data represented by changes rather than levels more reliable detection of transition rather than level easy to lose sense of polarity NRZ NRZ NRZ Pros & Cons NRZ Pros easy to engineer make good use of bandwidth Cons dc component lack of synchronization capability used for magnetic recording not often used for signal transmission Differential Encoding Differential Data represented by changes rather than Data levels levels More reliable detection of transition rather More than level than In complex transmission layouts it is easy In to lose sense of polarity to Multilevel Binary Multilevel Pseudoternary one represented by absence of line signal zero represented by alternating positive zero and negative and no advantage or disadvantage over no bipolar-AMI bipolar-AMI each used in some applications Multilevel Binary Multilevel Bipolar-AMI Use more than two levels Bipolar-AMI zero represented by no line signal one represented by positive or negative pulse one pulses alternate in polarity no loss of sync if a long string of ones long runs of zeros still a problem no net dc component lower bandwidth easy error detection Bipolar-AMI and Pseudoternary Pseudoternary Trade Off for Multilevel Binary Trade Not as efficient as NRZ Each signal element only represents one bit In a 3 level system could represent log23 = 1.58 bits 1.58 Receiver must distinguish between three Receiver levels (+A, -A, 0) (+A, Requires approx. 3dB more signal power for Requires same probability of bit error same Manchester Encoding Manchester has transition in middle of each bit period transition serves as clock and data low to high represents one high to low represents zero used by IEEE 802. Differential Manchester Encoding Encoding midbit transition is clocking only transition at start of bit period representing 0 no transition at start of bit period re...
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