Signal Encoding Techniques Chapter 7
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Questions and Answers

What effect does an increase in signal-to-noise ratio (SNR) have on the bit error rate?

  • It has no effect on the bit error rate
  • It decreases the bit error rate (correct)
  • It increases the bit error rate
  • It causes the bit error rate to fluctuate

Which encoding technique transmits digital information by varying the amplitude of a carrier signal?

  • Binary signaling
  • Frequency-shift keying (FSK)
  • Phase-shift keying (PSK)
  • Amplitude-shift keying (ASK) (correct)

Which of the following factors affects the complexity and cost of signal encoding?

  • The data rate achieved with a given signal rate (correct)
  • The temperature at which the signal is transmitted
  • The type of media used for transmission
  • The length of the signal transmitted

In which situation does an increase in bandwidth positively impact data transmission?

<p>It allows an increase in data rate (A)</p> Signup and view all the answers

Which of the following statements about phase-shift keying (PSK) is true?

<p>It involves encoding data bits as phases in the signal wave (D)</p> Signup and view all the answers

What is the primary function of signal encoding?

<p>To convert analog/digital data to analog/digital signals (C)</p> Signup and view all the answers

Why is digital data easier to manage than analog data in signal encoding?

<p>Equipment for digital data is less complex and costly (D)</p> Signup and view all the answers

What advantage does using analog data with an analog signal provide?

<p>It allows for easier and cheaper transmission (B)</p> Signup and view all the answers

Which statement describes digital data transmitted as an analog signal?

<p>It allows the use of modern digital equipment (B)</p> Signup and view all the answers

Which criterion is NOT related to the success of a receiver interpreting an incoming signal?

<p>The complexity of the receiver's design (B)</p> Signup and view all the answers

In which scenario is the use of a digital signal preferred?

<p>When digital data processing is advantageous (A)</p> Signup and view all the answers

Which type of signal is NOT typically used for voice transmission?

<p>Analog data as a digital signal (C)</p> Signup and view all the answers

What is a significant disadvantage of transmitting digital data as analog?

<p>It depends heavily on digital-to-analog conversion (A)</p> Signup and view all the answers

What does Amplitude-Shift Keying (ASK) use to represent the binary digits?

<p>Presence and absence of the carrier signal (A)</p> Signup and view all the answers

In Binary Frequency-Shift Keying (BFSK), how are the two binary digits represented?

<p>By two distinct frequencies near the carrier frequency (C)</p> Signup and view all the answers

What is a disadvantage of Multiple Frequency-Shift Keying (MFSK)?

<p>More susceptible to error (D)</p> Signup and view all the answers

What does the formula $f_i = f_c + (2i - 1 - M)f_d$ in MFSK represent?

<p>The frequency of the modulated signal element (C)</p> Signup and view all the answers

What characterizes Differential Phase-Shift Keying (DPSK)?

<p>Requires prior bits for phase reference (D)</p> Signup and view all the answers

What is the significance of the variable Ts in MFSK?

<p>It represents the time each output signal element is held (A)</p> Signup and view all the answers

Which modulation technique is most susceptible to sudden gain changes?

<p>Amplitude-Shift Keying (ASK) (A)</p> Signup and view all the answers

Which type of FSK modulation can be used at higher frequencies on LANs that utilize coaxial cable?

<p>Binary Frequency-Shift Keying (BFSK) (D)</p> Signup and view all the answers

What does the variable $L$ represent in the context of MFSK?

<p>The number of bits per signal element (A)</p> Signup and view all the answers

Which modulation technique uses two phases to represent binary digits?

<p>Phase-Shift Keying (PSK) (B)</p> Signup and view all the answers

Flashcards

Signal Encoding

The process of converting data (digital or analog) into an analog or digital signal suitable for transmission.

Encoding Scheme

A specific method of mapping data bits to signal elements, determining how data is represented in the signal.

Digital Data, Digital Signal

Using digital signals to transmit digital data. Often preferred due to its cost-effectiveness and ease of implementation.

Analog Data, Digital Signal

Using digital signals to transmit analog data. Enables the use of modern digital transmission and switching equipment.

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Digital Data, Analog Signal

Using analog signals to transmit digital data. Necessary for media like optical fibers and unguided media.

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Analog Data, Analog Signal

Using analog signals to transmit analog data. Straightforward and cost-effective for transmitting electrical signals.

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Signal Interpretation Success

The receiver's ability to accurately interpret the incoming signal depends on factors like signal strength, noise interference, and the chosen encoding technique.

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Choosing Encoding Techniques

The choice of an encoding technique depends on the type of data, the transmission medium, and the desired quality and reliability of data transfer.

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Signal-to-noise ratio (SNR)

The ratio of the power of a signal to the power of noise in a transmission medium. It determines how well the signal can be distinguished from noise and is crucial for reliable data transmission.

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Data rate

The rate at which data is transferred through a communication channel, typically measured in bits per second (bps).

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Bandwidth

The range of frequencies a communication channel can carry without significant distortion. It's the capacity of a channel.

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Higher data rate, higher bit error rate

As the data rate increases, the likelihood of errors in the transmitted data also increases. This is because faster transmission leaves less time for signal processing and error correction.

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Higher SNR, lower bit error rate

A higher SNR improves the ability of the receiver to distinguish the signal from noise, resulting in fewer errors. A stronger signal is easier to understand.

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Amplitude-Shift Keying (ASK)

A digital modulation technique where each binary digit is represented by the presence or absence of a carrier signal at a constant amplitude.

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ASK Disadvantages

ASK is susceptible to sudden gain changes and is an inefficient modulation technique, but it's suitable for transmitting digital data through optical fibers.

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Binary Frequency-Shift Keying (BFSK)

A digital modulation technique where each binary digit is represented by a unique frequency near the carrier frequency.

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BFSK Advantages

BFSK is less prone to errors than ASK, making it ideal for high-frequency radio transmission and coaxial cable-based LANs.

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Multiple Frequency-Shift Keying (MFSK)

A modulation technique extending BFSK, utilizing more than two frequencies to encode information. This method improves bandwidth efficiency at the cost of increased error susceptibility.

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MFSK Signal Element Duration

In MFSK, each signal element is held for a time period determined by the number of bits per element and the bit period, allowing for efficient encoding of multiple bits.

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MFSK Bandwidth Requirement

The total bandwidth required for MFSK transmission is proportional to the number of frequencies used and the frequency separation.

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Phase-Shift Keying (PSK)

A digital modulation technique that represents binary digits using different phases of a carrier signal.

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Two-Level PSK (BPSK)

A simple form of PSK where only two phases are used: one for binary '0' and the other for binary '1'.

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Differential PSK (DPSK)

A PSK variant where the phase shift is determined relative to the previous bit, ensuring reliable signal interpretation even in the presence of phase noise.

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Study Notes

Chapter 7 Signal Encoding Techniques

  • Signal encoding converts analog/digital data to analog/digital signals.
  • Encoding schemes map data bits to signal elements.
  • Slides are available in PowerPoint format for faculty use. (Slides can be modified if needed to suit student needs)
  • Authors request that the source textbook and copyright are acknowledged if slides are used in a class setting or online.

Reasons for Choosing Encoding Techniques

  • Digital data, digital signal: Equipment is less complex and inexpensive compared to digital-to-analog modulation equipment.
  • Analog data, digital signal: Modern digital transmission and switching equipment can be used.
  • Digital data, analog signal: Some transmission media only support analog signals (e.g., optical fiber, unguided media).
  • Analog data, analog signal: Easy and inexpensive transmission over voice-grade lines due to converting analog data in electrical form

Signal Encoding Criteria

  • Factors that determine interpreting incoming signals: signal-to-noise ratio (SNR), data rate, bandwidth.
  • Increased data rate results in increased bit error rate.
  • Higher SNR results in decreased bit error rate.
  • Increased bandwidth allows for increased data rate.

Factors used to Compare Encoding Schemes

  • Signal spectrum: Less bandwidth is required with less high-frequency components, and AC coupling is possible with no DC component. Transfer function of the channel is worse near band edges.
  • Clocking: Determines the beginning and end of each bit position.

AC Coupling vs DC Coupling

  • DC Coupling: Shows the original signal with both AC and DC components.
  • AC Coupling: Removes the DC component from the output signal.

Factors Used to Compare Encoding Schemes

  • Signal interference and noise immunity: Performance in the presence of noise.
  • Cost and complexity: The higher the signal rate for a given data rate, the greater the cost.

Basic Encoding Techniques

  • Amplitude-shift keying (ASK): Digital modulation technique that varies the amplitude of a carrier signal. High amplitude represents '1' and low amplitude represents '0'.
  • Frequency-shift keying (FSK): Frequency modulation scheme. Digital information is encoded on a carrier signal by shifting between several discrete frequencies.
  • Phase-shift keying (PSK): Modulation technique where data bits are expressed as phases in the signal wave.

Modulation of Analog Signals for Binary Data

  • Different modulation techniques for representing digital data in binary form. Diagrams illustrate ASK (Amplitude-shift keying), BFSK (Binary Frequency-Shift Keying) and BPSK (Binary Phase-Shift Keying).

Amplitude-Shift Keying (ASK)

  • One binary digit is represented by the presence of a carrier at a constant amplitude.
  • The absence of a carrier represents the other binary digit.
  • Carrier signal: Acos(2πft).
  • Susceptible to sudden gain changes.
  • Inefficient modulation technique.
  • Used for optical fiber.

Binary Frequency-Shift Keying (BFSK)

  • Two binary digits are represented by two different frequencies near the carrier frequency.
  • Less susceptible to errors than ASK.
  • Used for high-frequency (3–30 MHz) radio transmission.
  • Can be used at higher frequencies on LANs with coaxial cables.

Multiple Frequency-Shift Keying (MFSK)

  • More than two frequencies are used.
  • More bandwidth-efficient but more susceptible to errors.
  • The signal element duration is t = L * Tₛ.
  • Formula for f_i: f_i = f_c + (2i – 1 – M)f_d where i runs from 1 to M.
  • Bandwidth Calculation: W_d = 2Mf_d = M/Tₛ.

Phase-Shift Keying (PSK)

  • Two-level PSK (BPSK): Uses two phases to represent binary digits.
  • Differential PSK (DPSK): Phase shift is referenced to the previous bit; binary 0 signal bursts have the same phase as the previous signal burst, and binary 1 signal bursts have opposite phase.

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Chapter 7 Signal Encoding Techniques PDF

Description

This quiz delves into Chapter 7, focusing on various signal encoding techniques used to convert data into analog or digital signals. Explore the rationale behind choosing specific encoding methods and understand the criteria for effective signal encoding. Perfect for students looking to solidify their knowledge in this key area of signal processing.

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