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) (C)</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 (D)</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. (A)</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. (B)</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. (B)</p> Signup and view all the answers

What is the first step in transmitting a signal digitally?

<p>Sampling the signal (D)</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) (A)</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) (C)</p> Signup and view all the answers

What does Pulse Amplitude Modulation (PAM) primarily vary?

<p>The amplitude of the pulse (B)</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 (D)</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. (C)</p> Signup and view all the answers

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

<p>Pulse Duration Modulation (C)</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. (C)</p> Signup and view all the answers

What does the dynamic range formula in dB indicate?

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

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

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

What is quantization error a result of?

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

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

<p>Overload or peak limiting occurs. (B)</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. (C)</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 (D)</p> Signup and view all the answers

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

<p>The capability to represent amplitude differences (A)</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. (B)</p> Signup and view all the answers

What does pulse code modulation primarily do?

<p>Digitally encodes analog signals. (A)</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 (C)</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 (D)</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. (B)</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. (A)</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. (C)</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 (A)</p> Signup and view all the answers

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

<p>Codec (A)</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 (B)</p> Signup and view all the answers

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

<p>8 bits (D)</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 (D)</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 (B)</p> Signup and view all the answers

Which of the following best describes delta modulation?

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

What is a potential problem associated with delta modulation?

<p>Slope overload (A)</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. (C)</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 (C)</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 (B)</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 (C)</p> Signup and view all the answers

Which of the following is a method of channel coding?

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

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

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

What is the purpose of source coding?

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

Which code was invented by Samuel Morse?

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

What does Information Rate refer to?

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

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

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

Flashcards

Digital Transmission

The process of sending digital signals between two or more points.

Digital Signals

The transfer of information using binary or other forms of discrete digital pulses.

Analog-to-Digital Conversion

Converting analog signals to digital pulses for transmission.

Noise Immunity

The ability to resist noise and interference, resulting in clearer signals.

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Multiplexing

Digital signals simplify processing and merging multiple signals together.

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Signal Regeneration

Digital signals are regenerated, maintaining their quality over long distances.

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Bandwidth Requirement

Digital signals require wider frequency ranges for transmission.

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Time Synchronization

Precise timing synchronization between the sender and receiver is crucial for accurate digital transmission.

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Digital Signal Transmission: Why Sample?

Sampling an analog signal at discrete time intervals to obtain a finite series of numbers that can be transmitted.

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Analog-to-Digital Conversion (ADC)

The process of converting analog signals into digital signals suitable for transmission.

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Pulse Width Modulation (PWM)

A pulse modulation technique where the width of a constant amplitude pulse varies proportionally to the analog signal's amplitude at each sample.

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Pulse Position Modulation (PPM)

A pulse modulation technique where the position of a constant-width pulse within a specific time slot changes based on the sampled analog signal's amplitude.

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Pulse Amplitude Modulation (PAM)

A pulse modulation technique where the amplitude of a fixed width and position pulse is varied according to the amplitude of the sampled analog signal.

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Pulse Code Modulation (PCM)

A pulse modulation technique where the analog signal is sampled and then converted into a binary code for transmission. Each code has the same number of bits and transmission time.

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PCM: The Dominant Technique

PCM is the most commonly used digital modulation technique for transmitting digital signals.

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PAM: An Intermediate Step

PAM is a stepping stone for other modulation techniques like PSK, QAM, and PCM.

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Sampling and Holding

A process of converting analog signals to multilevel Pulse Amplitude Modulation (PAM) signals. This involves sampling the analog signal at regular intervals and assigning each sample a specific voltage level.

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Analog-to-Digital Converter (ADC)

A type of analog-to-digital converter that transforms the PAM samples from the sample and hold circuit into parallel binary codes.

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Parallel to Serial Conversion

A process of converting parallel binary codes into a serial data stream, where bits are transmitted one after another.

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Codec

A device that combines the encoding and decoding functions of PCM, converting analog signals to digital and vice versa.

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Serial to Parallel Conversion

A process of converting serial data into parallel binary codes, reversing the process of parallel to serial conversion.

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Digital-to-Analog Converter (DAC)

A type of digital-to-analog converter that transforms parallel binary codes back into multilevel PAM signals.

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Hold Circuit

A low-pass filter that smooths out the PAM signals, converting them back to their original analog form.

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Dynamic Range (dB)

The difference, in decibels, between the largest and smallest possible signal magnitudes a device can process without distortion.

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Dynamic Range (DR)

The ratio of the largest possible magnitude to the smallest magnitude that can be decoded by the DAC.

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Resolution

The size of the minimum step a device can detect.

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Quantization

The process of converting continuous analog signals into discrete digital values by rounding them off to the nearest quantized level.

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Quantization Error

The difference between the original analog sample and its quantized digital representation.

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Overload

When the input signal exceeds the maximum value the device can handle.

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Number of Bits required for PCM

The number of bits needed to represent a specific dynamic range.

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PCM Bits Formula

A formula to calculate the minimum number of bits required for a PCM code to represent a given dynamic range.

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Sampling

The process of converting an analog signal into a digital signal by taking discrete samples of the analog signal at regular intervals.

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Signal-to-Quantization Noise Ratio (SQNR)

The ratio of signal power to quantization noise power, often expressed in decibels (dB).

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Delta Modulation

A simple form of PCM that uses only one bit to represent the changes in the original signal.

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Slope Overload

A condition in delta modulation where the signal changes too rapidly for the single-bit modulation to accurately track the slope, resulting in distortion.

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Sampling Rate

The number of samples taken per second, also known as the sampling rate.

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Granular Noise

A type of noise that occurs in delta modulation systems when the analog input signal has a relatively constant amplitude. The reconstructed signal exhibits variations that were not present in the original signal, creating a granular effect.

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Adaptive Delta Modulation

A delta modulation system that adjusts the step size of its digital-to-analog converter (DAC) based on the characteristics of the analog input signal. This adapts to varying amplitudes and improves signal fidelity.

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Source Coding

Techniques used to remove redundancy in data. Huffman coding and Shannon-Fano coding are examples. They efficiently represent data with fewer bits.

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Channel Coding

Techniques designed to minimize the impact of channel errors during transmission. These methods introduce redundancy for error detection and correction.

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Forward Error Correcting Codes

A type of channel coding that uses codes with specific mathematical properties to detect and correct errors. Linear block codes and convolutional codes are examples.

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ARQ Methods

A type of error-control method where the receiver requests retransmission if errors are detected. It's used in conjunction with error-detecting codes to ensure data accuracy.

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Line Coding Formats

Methods for converting digital data into signals suitable for transmission over various mediums. They define the format of the signal using different coding schemes.

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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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