Differential Manchester Encoding and Modulation
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Questions and Answers

What is the primary factor that affects signal interpretation in digital signaling?

  • Signal to noise ratio (correct)
  • Encoding scheme
  • Data rate
  • Bandwidth

    • What is the function of clocking in digital signaling?

  • To increase the data rate
  • To reduce the signal to noise ratio
  • To detect errors in the signal
  • To synchronize the transmitter and receiver (correct)

    • Which encoding scheme uses two different voltages for 0 and 1 bits?

  • Bipolar encoding
  • Unipolar encoding
  • Polar encoding
  • Nonreturn to Zero-Level (NRZ-L) (correct)

    • What is the primary advantage of using a higher signal to noise ratio?

    <p>Improved noise immunity</p> Signup and view all the answers

    What is the unit of measurement for modulation rate?

    <p>baud</p> Signup and view all the answers

    What is the primary goal of error detection in digital signaling?

    <p>To detect errors in the signal</p> Signup and view all the answers

    What is the term for the rate of data transmission in bits per second?

    <p>Data rate</p> Signup and view all the answers

    What type of encoding scheme is used by IEEE 802.5?

    <p>Differential Manchester Encoding</p> Signup and view all the answers

    What is the primary goal of modulation rate scrambling?

    <p>To replace sequences that produce constant voltage</p> Signup and view all the answers

    What is the primary disadvantage of using a high data rate?

    <p>Increased error rate</p> Signup and view all the answers

    What is a key feature of the B8ZS encoding scheme?

    <p>8-zeros substitution</p> Signup and view all the answers

    What is the term for the time taken for the transmitter to emit one bit?

    <p>Duration of a bit</p> Signup and view all the answers

    What type of keying is used for up to 1200bps on voice grade lines?

    <p>Frequency Shift Keying</p> Signup and view all the answers

    What is the primary advantage of using a high signal to noise ratio?

    <p>Improved noise immunity</p> Signup and view all the answers

    What is the primary advantage of Frequency Shift Keying over Amplitude Shift Keying?

    <p>Less susceptible to error</p> Signup and view all the answers

    What is the term for the rate at which the signal level changes?

    <p>Modulation rate</p> Signup and view all the answers

    What type of signal is used in public telephone systems?

    <p>Analog signal</p> Signup and view all the answers

    What is the frequency range of analog signals in public telephone systems?

    <p>300Hz to 3400Hz</p> Signup and view all the answers

    What is the primary goal of encoding techniques in modulation?

    <p>To provide error detection capability</p> Signup and view all the answers

    What type of PSK is used when the phase of the carrier signal is shifted relative to a previous transmission?

    <p>Differential PSK</p> Signup and view all the answers

    What is the primary advantage of Multiple FSK over Binary FSK?

    <p>More bandwidth efficient</p> Signup and view all the answers

    What is a characteristic of Nonreturn to Zero Inverted encoding?

    <p>Transition denotes binary 1</p> Signup and view all the answers

    What is the advantage of using Bipolar-AMI encoding over Nonreturn to Zero encoding?

    <p>No loss of sync with long strings of ones</p> Signup and view all the answers

    What is the purpose of the transition in Manchester encoding?

    <p>To serve as a clock and data</p> Signup and view all the answers

    What is the problem with long runs of zeros in Multilevel Binary encoding?

    <p>Loss of sync</p> Signup and view all the answers

    What is the advantage of Multilevel Binary encoding over Nonreturn to Zero encoding?

    <p>Lower bandwidth</p> Signup and view all the answers

    What is the purpose of scrambling data in Multilevel Binary encoding?

    <p>To avoid synchronization problems</p> Signup and view all the answers

    What is the difference between Pseudoternary and Bipolar-AMI encoding?

    <p>Pseudoternary has no advantage or disadvantage over Bipolar-AMI</p> Signup and view all the answers

    What is the purpose of inserting additional bits in Multilevel Binary encoding?

    <p>To avoid synchronization problems</p> Signup and view all the answers

    What is the benefit of using Multilevel Binary encoding?

    <p>Each signal element represents more than one bit</p> Signup and view all the answers

    What is the disadvantage of using Nonreturn to Zero encoding?

    <p>Long runs of zeros can cause synchronization problems</p> Signup and view all the answers

    Study Notes

    Signal Encoding Techniques

    • Signal encoding techniques convert digital data into analog signals or digital signals for transmission.

    Non-Return to Zero (NRZ)

    • NRZ encoding uses two different voltage levels to represent 0 and 1 bits.
    • The voltage remains constant during the bit interval.
    • No transition occurs during the bit interval.

    Non-Return to Zero Inverted (NRZI)

    • NRZI encoding uses a constant voltage pulse for the duration of a bit.
    • Data is encoded as the presence or absence of a signal transition at the beginning of the bit time.
    • A transition (low to high or high to low) denotes a binary 1, and no transition denotes a binary 0.

    Multilevel Binary Encoding

    • Bipolar-AMI encoding uses more than two voltage levels to represent 0 and 1 bits.
    • Zero is represented by no line signal, and 1 is represented by positive or negative pulses.
    • One pulses alternate in polarity.
    • There is no loss of sync if a long string of ones occurs.
    • Long runs of zeros are still a problem.
    • There is no net dc component.
    • The bandwidth is lower.
    • Error detection is easy.

    Multilevel Binary Issues

    • Synchronization is a problem with long runs of 0's or 1's.
    • Additional bits can be inserted to solve this problem (e.g., ISDN).
    • Data can be scrambled to solve this problem.
    • Each signal element only represents one bit.
    • The receiver distinguishes between three levels: +A, -A, and 0.
    • A 3-level system can represent log2(3) = 1.58 bits.
    • It requires approximately 3dB more signal power for the same probability of bit error.

    Manchester Encoding

    • Manchester encoding has a transition in the middle of each bit period.
    • The transition serves as a clock and data.
    • Low to high represents a binary 1, and high to low represents a binary 0.
    • This encoding is used by IEEE 802.3.

    Differential Manchester Encoding

    • Midbit transition is used for clocking only.
    • A transition at the start of the bit period represents a binary 0, and no transition represents a binary 1.
    • This is a differential encoding scheme used by IEEE 802.5.

    Modulation Rate and Scrambling

    • Scrambling is used to replace sequences that would produce a constant voltage.
    • Filling sequences must produce enough transitions to sync, be recognized by the receiver, and be replaced with the original sequence.
    • The design goals of scrambling include:
      • No dc component
      • No long sequences of zero level line signal
      • No reduction in data rate
      • Error detection capability

    B8ZS and HDB3

    • B8ZS (Bipolar with 8-zeros substitution) and HDB3 (High-Density Bipolar-3 zeros) are scrambling techniques used to solve the problem of long runs of zeros.

    Digital Data, Analog Signal

    • Digital data is transmitted over analog signals in public telephone systems.
    • The frequency range is 300Hz to 3400Hz.
    • Modems (modulator-demodulators) are used to encode and decode data.
    • Modulation techniques include Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK).

    Modulation Techniques

    • Amplitude Shift Keying (ASK) encodes 0/1 by different carrier amplitudes.
    • Frequency Shift Keying (FSK) encodes 0/1 by different frequencies.
    • Phase Shift Keying (PSK) encodes 0/1 by shifting the phase of the carrier signal.

    Digital Data, Digital Signal

    • Digital signals are discrete, discontinuous voltage pulses.
    • Each pulse is a signal element.
    • Binary data is encoded into signal elements.

    Terms and Concepts

    • Unipolar: All signal elements have the same sign.
    • Polar: One logic state is represented by positive voltage, and the other is represented by negative voltage.
    • Data rate: The rate of data transmission in bits per second.
    • Duration or length of a bit: The time taken for the transmitter to emit a bit.
    • Modulation rate: The rate at which the signal level changes, measured in baud.
    • Mark and space: Binary 1 and binary 0, respectively.

    Interpreting Signals

    • The receiver needs to know the timing of bits, signal levels, and encoding scheme.
    • Factors affecting signal interpretation include signal-to-noise ratio, data rate, bandwidth, and encoding scheme.

    Comparison of Encoding Schemes

    • Signal spectrum, clocking, error detection, signal interference, and noise immunity are key factors to consider when comparing encoding schemes.
    • Cost and complexity are also important considerations.

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    05-SignalEncodingTechniques.pptx

    Description

    This quiz covers the concepts of Differential Manchester Encoding and Modulation, including clocking transitions, scrambling, and design goals. It's essential for understanding data transmission and encoding schemes. Test your knowledge of these fundamental concepts in computer networks.

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