Digital Transmission Systems Quiz
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Questions and Answers

What is required for digital transmission systems to connect various points within the system?

  • Wireless signals
  • Standard electrical outlets
  • Optical fiber cable or coaxial cable (correct)
  • Satellite connections

    • Which of the following is a disadvantage of digital transmission?

  • Better processing of digital pulses
  • Incompatibility with existing analog systems (correct)
  • Noise immunity
  • Simpler measurement and evaluation

    • What type of encoding converts an analog signal to a digital signal?

  • Analog/Analog encoding
  • Digital/Analog encoding
  • Analog/Digital encoding (correct)
  • Digital/Digital encoding

    • Which method is NOT used in digital encoding?

    <p>Frequency Modulation (FM)</p> Signup and view all the answers

    What is one reason digital pulses are preferred over analog signals in certain applications?

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

    What must occur before analog signals can be transmitted in a digital transmission system?

    <p>They must be converted to digital codes.</p> Signup and view all the answers

    Which of the following differences signifies that digital transmission requires more bandwidth compared to analog systems?

    <p>Digital signals use more complex encoding methods.</p> Signup and view all the answers

    What is the primary reason digital signals are processed better than analog signals?

    <p>They are easier to regenerate.</p> Signup and view all the answers

    What is the first step in transmitting a signal digitally?

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

    Which pulse modulation method varies the position of a pulse within a time slot?

    <p>Pulse Position Modulation (PPM)</p> Signup and view all the answers

    Which of the following is considered the most prevalent form of pulse modulation?

    <p>Pulse Code Modulation (PCM)</p> Signup and view all the answers

    What does Pulse Amplitude Modulation (PAM) primarily vary?

    <p>The amplitude of the pulse</p> Signup and view all the answers

    Which pulse modulation techniques are primarily used in military applications?

    <p>Pulse Width Modulation and Pulse Position Modulation</p> Signup and view all the answers

    What characterizes Pulse Code Modulation (PCM) in terms of transmission?

    <p>Each code has the same number of bits.</p> Signup and view all the answers

    What is another name for Pulse Width Modulation (PWM)?

    <p>Pulse Duration Modulation</p> Signup and view all the answers

    How does Pulse Position Modulation (PPM) differ from Pulse Width Modulation (PWM)?

    <p>PPM varies the position of the pulse while PWM varies the width of the pulse.</p> Signup and view all the answers

    What does the dynamic range formula in dB indicate?

    <p>The logarithmic scale of voltage magnitudes.</p> Signup and view all the answers

    How is the number of bits required for a PCM code determined?

    <p>By the formula $2n - 1 ≥ DR$.</p> Signup and view all the answers

    What is quantization error a result of?

    <p>Rounding off the continuous amplitude waveform.</p> Signup and view all the answers

    What happens if the sample magnitude exceeds the highest quantization interval?

    <p>Overload or peak limiting occurs.</p> Signup and view all the answers

    What is the relationship between the smallest magnitude that can be decoded and the resolution?

    <p>Better resolution is achieved with smaller minimum step sizes.</p> Signup and view all the answers

    In the dynamic range formula, what does $V_{max}$ represent?

    <p>The maximum voltage magnitude that can be decoded by the DAC</p> Signup and view all the answers

    What is the dynamic range (DR) mostly associated with?

    <p>The capability to represent amplitude differences</p> Signup and view all the answers

    Which of the following statements about bits in PCM codes is true?

    <p>Each additional bit doubles the number of quantization levels.</p> Signup and view all the answers

    What does pulse code modulation primarily do?

    <p>Digitally encodes analog signals.</p> Signup and view all the answers

    What component in the PCM transmitter is responsible for converting PAM signals to serial binary data?

    <p>Parallel-to-Serial Converter</p> Signup and view all the answers

    Which frequency range does the bandpass filter in a PCM transmitter limit the signal to?

    <p>300 Hz to 3000 Hz</p> Signup and view all the answers

    What is the role of the digital-to-analog converter (DAC) in the PCM receiver?

    <p>Converts parallel PCM codes back to analog signals.</p> Signup and view all the answers

    What is the initial step in converting an analog signal to a digital format in PCM?

    <p>Sampling the signal.</p> Signup and view all the answers

    Which of the following best describes the term 'sampling' in the context of PCM?

    <p>Measuring amplitude at discrete time intervals.</p> Signup and view all the answers

    Which component serves as a low pass filter and is used in the PCM receiver?

    <p>Hold Circuit</p> Signup and view all the answers

    What term describes the integrated circuit that performs the encoding and decoding functions in PCM?

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

    What does Pulse Code Modulation (PCM) primarily do with the quantized signals?

    <p>Encode the quantized signals into a digital word</p> Signup and view all the answers

    If a system uses 256 quantization levels, how many bits are needed per sample?

    <p>8 bits</p> Signup and view all the answers

    According to the Nyquist theorem, what is the minimum sampling rate needed to digitize a 4000 Hz voice signal?

    <p>8000 samples per second</p> Signup and view all the answers

    What is one of the primary advantages of increasing the number of quantization levels?

    <p>Higher resolution of the signal</p> Signup and view all the answers

    Which of the following best describes delta modulation?

    <p>Tracks voltage changes with a single bit</p> Signup and view all the answers

    What is a potential problem associated with delta modulation?

    <p>Slope overload</p> Signup and view all the answers

    In PCM, how is the average quantization noise power related to the signal power?

    <p>It should be less than the signal power.</p> Signup and view all the answers

    What is the impact of taking more snapshots during the same time period in PCM?

    <p>It enhances signal reproduction accuracy</p> Signup and view all the answers

    What does granular noise refer to in signal processing?

    <p>Variations in the reconstructed signal not present in the original signal</p> Signup and view all the answers

    What is characteristic of adaptive delta modulation?

    <p>It adapts the step size depending on the signal amplitude</p> Signup and view all the answers

    Which of the following is a method of channel coding?

    <p>Linear Block Codes</p> Signup and view all the answers

    Which line coding format does NOT involve a change in voltage for every bit?

    <p>NRZ-L</p> Signup and view all the answers

    What is the purpose of source coding?

    <p>To eliminate redundancy in data</p> Signup and view all the answers

    Which code was invented by Samuel Morse?

    <p>Morse Code</p> Signup and view all the answers

    What does Information Rate refer to?

    <p>The amount of information per bit, also known as entropy</p> Signup and view all the answers

    Which technique is NOT commonly used for converting data into signals?

    <p>Huffman Coding</p> Signup and view all the answers

    Study Notes

    Digital Transmission

    • Digital transmission involves the transmission of digital signals between two or more points.
    • Signals can be binary or other discrete-level digital pulses within a communication system.
    • The source of the information can be digital or analog signals converted into digital pulses before transmission.
    • Received analog signals are converted back to their original form.
    • Information needs to be converted to either a digital or analog signal for transmission.

    Conversion Methods

    • Digital/Digital Encoding
    • Analog/Digital Encoding
    • Digital/Analog Encoding
    • Analog/Analog Encoding
    • Includes methods like Unipolar, Polar, Bipolar, PCM, DM, ASK, FSK, PSK, AM, FM, PM, and QAM

    Advantages of Digital Transmission

    • Better noise immunity compared to analog transmission.
    • Digital pulses are better suited for processing and multiplexing.
    • Signal regeneration is used rather than signal amplification.
    • Simpler to measure and evaluate.

    Disadvantages of Digital Transmission

    • Requires more bandwidth.
    • Requires precise time synchronization between transmitter and receiver.
    • Incompatible with existing analog systems

    Analog to Digital Conversion

    • Analog signals vary continuously with time.
    • Before transmission, analog signals are converted into digital pulses.
    • These digital pulses are then converted back to their original analog form at the receiver.
    • Sampling involves finding the amplitude of the signal at discrete time intervals.

    Pulse Modulation

    • Pulse modulation consists of sampling analog signals and converting them to discrete pulses.
    • Common methods include PWM, PPM, PAM, and PCM.
    • PWM (Pulse Width Modulation): The width of a constant amplitude pulse is proportional to the amplitude of the analog signal.
    • PPM (Pulse Position Modulation): The position of a constant-width pulse within a prescribed time slot is varied according to the amplitude of the sample.
    • PAM (Pulse Amplitude Modulation): The amplitude of a constant-width, constant-position pulse is varied according to the amplitude of the sample.
    • PCM (Pulse Code Modulation): The analog signal is sampled and converted into a serial bit binary code for transmission.

    Pulse Code Modulation (PCM)

    • PCM is the only digitally encoded modulation technique commonly used for digital transmission.
    • It's not a modulation type, but a form of digitally coding analog signals.
    • In PCM, the available voltage range is divided into levels. Each level has a corresponding binary number.
    • Each sample is represented by the binary number closest to its amplitude and transmitted serially.

    PCM System

    • Describes the functions in analog-to-digital and digital-to-analog conversion chains.
    • Includes components like bandpass filter, sampling, hold circuit, analog to digital conversion (ADC), and digital-to-analog conversion (DAC).

    Sampling

    • Analog signals vary continuously with time requiring sampling to send them digitally.
    • Sampling means measuring the amplitude of a signal at equal intervals.
    • Different sampling techniques include ideal, natural, and flat-top sampling.
    • Important for voice signals in PCM systems

    Sampling Theorem

    • Nyquist sampling theorem establishes minimum sampling rate (fs) for PCM systems.
    • Each cycle of an analog input signal must be sampled at least twice.
    • Minimum sampling rate is twice the highest audio input frequency (fs ≥ 2fa).
    • Too low sampling rate results in distortion (aliasing or foldover).

    Quantization

    • Converts an infinite number of possibilities into a finite number of conditions.
    • In PCM, quantization assigns PCM codes to absolute magnitudes.
    • Resolution is the voltage of minimum step size that can decoded by digital-to-analog converter.

    Quantization Error

    • Results from rounding off during quantization.
    • Dynamic Range (DR) is the ratio of minimum and maximum voltage that a signal can be decoded by DAC

    Encoding

    • PCM encodes quantized samples as digital words (PCM code words).
    • Each quantized sample is converted into an l-bit codeword, where L is the number of quantization levels.
    • L = log2L

    Delta Modulation

    • Tracks analog waveforms using a binary 1 (voltage rise) and 0 (voltage drop).
    • Two problems: slope overload and granular noise.
    • Adaptive delta modulation dynamically adjusts the step size depending on the input signal's amplitude characteristics.

    Source Coding

    • Eliminates redundancies in data using techniques like Huffman and Shannon-Fano coding.

    Channel Coding

    • Controlled introduction of redundancy reduces channel errors and increases coding gain.
    • Uses methods like Forward Error Correcting (FEC) codes (Linear Block Codes and Convolutional Codes) and Automatic Repeat reQuest (ARQ) methods.

    Line Coding Formats (Converting Data into Signals)

    • Different techniques convert data into signals including NRZ-L, NRZ-I, Manchester, Differential Manchester, and Bipolar AMI.

    Binary Transmission Conventions

    • Data transmission can be parallel or serial.
      • Parallel: Multiple bits sent simultaneously, less practical for long distances.
      • Serial: Bits sent sequentially, more suitable for long distances.
    • Serial transmission can be:
      • Asynchronous: Bits sent without strict timing alignment, using start and stop bits.
      • Synchronous: Precise timing synchronization required, no gaps or start/stop bits, continuous stream sent at fixed rate.
      • Isochronous: Data must arrive at a fixed rate, similar to synchronous but with more specialized application and requirements.

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    Digital Transmission PDF

    Description

    Test your knowledge on digital transmission systems with this quiz. Explore the advantages and disadvantages of digital encoding, types of encoding methods, and the reasons digital signals are often preferred over analog. Evaluate your understanding of key concepts in digital communications.

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