Digital Band-Pass Modulation

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Questions and Answers

Digital band-pass modulation relies on the variation of which characteristics of a sinusoidal carrier?

  • Frequency only
  • Phase only
  • Amplitude only
  • Amplitude, phase, or frequency (correct)

Which advantage does digital modulation have over analog modulation in terms of signal requirements?

  • Operates with higher signal-to-noise ratio
  • Operates with lower signal-to-noise ratio (correct)
  • Requires less bandwidth
  • Is immune to signal degradation

In Amplitude Shift Keying (ASK), how is digital data represented?

  • Variations in both frequency and phase
  • Variations in the amplitude of the carrier wave (correct)
  • Variations in the phase of the carrier wave
  • Variations in the frequency of the carrier wave

What distinguishes coherent ASK detection from non-coherent ASK detection?

<p>Coherent detection requires the carrier signal to be in the same phase at the transmitter and receiver. (C)</p> Signup and view all the answers

In Frequency Shift Keying (FSK), how are binary states represented?

<p>Two discrete frequencies (B)</p> Signup and view all the answers

What is the primary method of modulation in Phase Shift Keying (PSK)?

<p>Changing the phase of a constant frequency reference signal (C)</p> Signup and view all the answers

Which communication types commonly use Phase Shift Keying (PSK)?

<p>Wireless LANs and Bluetooth (D)</p> Signup and view all the answers

In Amplitude Phase Keying (APK), what characteristics of the signal are used to carry information?

<p>Both amplitude and phase (D)</p> Signup and view all the answers

What is a significant advantage of APK compared to M-ary PSK?

<p>Requires less power (B)</p> Signup and view all the answers

What is the primary purpose of Quadrature Amplitude Modulation (QAM)?

<p>Double the effective bandwidth (D)</p> Signup and view all the answers

Modern digital communication systems widely use digital band-pass modulation in which applications?

<p>Satellite links and microwave radio relay (D)</p> Signup and view all the answers

What does the 'optimality criterion' refer to in the context of noncoherent demodulation, especially in asynchronous CDMA channels?

<p>Near-far resistance (A)</p> Signup and view all the answers

Using the diagram of a coherent ASK demodulator, what is the purpose of the 'Sample & Hold Circuit'?

<p>To provide a steady voltage level for comparison. (C)</p> Signup and view all the answers

In non-coherent ASK detection, a square-law device is used. What is the primary function of this device?

<p>To produce a signal whose amplitude is proportional to the square of the input signal's amplitude. (A)</p> Signup and view all the answers

In digital modulation, what is the role of 'channel coding'?

<p>To introduce structured redundancy to improve the reliability of data transmission. (C)</p> Signup and view all the answers

Which of the following is an example of a 'waveform' used in channel coding?

<p>M-ary signaling (C)</p> Signup and view all the answers

What is the purpose of 'equalization' in the context of bandpass modulation?

<p>To mitigate the effects of multi-path fading and inter-symbol interference. (D)</p> Signup and view all the answers

What is the key difference between 'lossless' and 'lossy' compression techniques in bandpass modulation?

<p>Lossless compression fully preserves the original data, while lossy compression sacrifices some data to achieve higher compression rates. (C)</p> Signup and view all the answers

In Amplitude Shift Keying (ASK), if a higher amplitude of the carrier wave represents a binary '1' and no amplitude (carrier off) represents a binary '0', this is an example of:

<p>On-off keying (OOK). (A)</p> Signup and view all the answers

In synchronization for bandpass modulation, what does 'Frame Synchronization' primarily ensure?

<p>Correct start and end points of data frames. (C)</p> Signup and view all the answers

Which statement best describes 'Trellis-Code modulation' in the context of channel coding?

<p>A modulation scheme in which the signal is varied in a predetermined sequence to improve error performance. (B)</p> Signup and view all the answers

What is the main purpose of 'spreading' techniques like Direct Sequence (DS) in digital communication systems?

<p>To improve signal security and resistance to interference. (B)</p> Signup and view all the answers

In the context of digital bandpass modulation, which of the following is an advantage of coherent detection methods?

<p>Lower bit error rate. (C)</p> Signup and view all the answers

Which of these methods falls under 'Multiplexing/Multiple Access' techniques?

<p>Frequency Division (FDM/FDMA) (D)</p> Signup and view all the answers

Flashcards

Digital Band-Pass Modulation

Digital band-pass modulation is based on the variation of amplitude, phase, or frequency of the sinusoidal carrier, or some combination of these parameters.

Usage of Digital Band-Pass Modulation

Digital band-pass modulation is widely used in modern digital communication systems such as satellite links and wideband microwave radio relay systems.

Importance of Digital Band-Pass Modulation

An advantage of digital modulation is that it can operate with much lower signal-to-noise ratio than can analog modulation.

Amplitude Shift Keying (ASK)

Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave.

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ASK Demodulation Methods

ASK demodulation can be done in two ways: Coherent detection (Synchronous demodulation), and Noncoherent Detection (Asynchronous demodulation).

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Coherent ASK Detection

In coherent ASK detection, the carrier signal at the receiver stage is in the same phase with the carrier signal at the transmitter stage.

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Frequency Shift Keying (FSK)

Frequency-shift keying (FSK) is a method of transmitting digital signals using discrete signals by varying the frequency.

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Phase Shift Keying (PSK)

Phase-shift keying (PSK) is a digital modulation process which conveys data by changing the phase of a constant frequency reference signal (the carrier wave).

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Quadrature Phase Shift Keying (QPSK)

Quadrature Phase Shift Keying (QPSK) is a phase shift keying technique where the sine wave carrier takes four phase reversals such as 0°, 90°, 180°, and 270°.

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Quadrature Amplitude Modulation (QAM)

Quadrature Amplitude Modulation (QAM) is a method of combining two amplitude modulation (AM) signals into a single channel.

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Amplitude Phase Keying (APK)

Amplitude-phase keying (APK) is an alternative where both amplitude and phase are used in the modulation.

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Coherent Detection

With coherent detection, the receiver exploits knowledge of the carriers phase to detect the signal.

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Non-Coherent Detection

With non-coherent detection, the receiver does not utilize phase reference information.

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Study Notes

  • Digital band-pass modulation is explained

Learning Objectives of Digital Band-Pass Modulation

  • Gain an understanding of digital band-pass modulation
  • Learn about the types and applications of digital band-pass modulation
  • Appreciate the importance of this modulation in communication

Learning Outcomes of Digital Band-Pass Modulation

  • Comprehend the concepts of digital band-pass modulation
  • Learn the types of digital band-pass modulation and their uses
  • Understand the significance of this type of modulation in communication

Digital Band-Pass Modulation

  • Relies on changes in amplitude, phase, or frequency of the sinusoidal carrier, or a combination of these
  • One type is amplitude-shift keying

Uses of Digital Band-Pass Modulation

  • Widely implemented in modern digital communication systems
  • Utilized in satellite links and wideband microwave radio relay systems

Importance of Digital Band-Pass Modulation

  • Has the ability to operate with much lower signal-to-noise ratio compared to analog modulation
  • Maintains a consistent output level that is independent of the optical level
  • Prevents signal degradation as it passes along the system

Types of Digital Band-Pass Modulation

  • Amplitude shift keying (ASK)
  • Frequency shift keying (FSK)
  • Phase shift keying (PSK)
  • Amplitude phase keying (APK)

Amplitude Shift Keying (ASK)

  • Represents digital data by varying the amplitude of a carrier wave
  • ASK demodulation can be done in two ways:
    • Coherent detection (synchronous demodulation)
    • Non-coherent detection (asynchronous demodulation)

Coherent ASK Detection

  • The carrier signal used at the receiver stage is in the same phase with the carrier signal used at the transmitting stage
  • The carrier signal at the transmitter and receiver stages have the same values
  • It is referred to as Synchronous ASK detection or coherent ASK detection

Non-Coherent ASK Detection

  • The carrier signal used at the transmitter side and receiver side are not in the same phase with each other
  • This is also known as Asynchronous ASK detection
  • Demodulation is done using a square law device
  • A low pass filter forwards the output signal to reconstruct the original binary signal

Frequency Shift Keying (FSK)

  • Method of transmitting digital signals using discrete signals
  • Uses two binary states: logic 0 (low) and 1 (high) in a binary

Phase Shift Keying (PSK)

  • Digital modulation process that conveys data by changing the phase of a constant frequency reference signal (the carrier wave)
  • Modulation is done by varying the sine and cosine inputs at a precise time
  • Widely used for wireless LANs, RFID, and Bluetooth communication

Amplitude Phase Keying (APK)

  • In M-ary PSK, only the phase of the signal carries information
  • Uses both amplitude and phase
  • Less power is required for APK than for MPSK, but the system is more complicated

Quadrature Phase Shift Keying (QPSK)

  • The sine wave carrier takes four phase reversals: 0°, 90°, 180°, and 270°

Quadrature Amplitude Modulation (QAM)

  • Combines two amplitude modulation (AM) signals into a single channel
  • Helps double its effective bandwidth

Types of Bandpass Modulation

  • Formatting: includes character coding, sampling, quantization, and pulse code modulation (PCM)
  • Source coding: includes predictive coding, block coding, variable length coding, and synthesis/analysis coding
  • Baseband Signaling: includes PCM waveforms (line codes), non-return-to-zero (NRZ), return-to-zero (RTZ), and phase encoded
  • Equalization: includes maximum likelihood sequence estimation (MLSE), equalization with filters, and transversal or decision feedback

Bandpass Signaling

  • Coherent: Phase shift keying (PSK), Frequency shift keying (FSK), Amplitude shift keying (ASK), Continuous Phase Modulation (CPM), Hybrids
  • Noncoherent: Differential phase shift keying (DPSK), Frequency shift keying (FSK), Amplitude shift keying (ASK), Continuous Phase Modulation (CPM), Hybrids

Channel Coding

  • Waveform: M-ary signaling, Antipodal, Orthogonal, Trellis-Code modulation
  • Structured Sequences: Block, Convolutional, Turbo

Syncronization

  • Frequency synchronization
  • Phase synchronization
  • Symbol synchronization
  • Frame synchronization
  • Network synchronization

Multiplexing/Multiple Access

  • Frequency division (FDM/FDMA)
  • Time Division (TDM/TDMA)
  • Code Division (CDM/CDMA)
  • Space Division ( SDMA)
  • Polarization Division (PDMA)

Spreading

  • Direct Sequence (DS)
  • Frequency Hopping (FH)
  • Time hopping (TH)
  • Hybrids

Encryption

  • Block
  • Data stream

Coherent Detection

  • Exploits knowledge of the carrier’s phase to detect the signal
  • Requires expensive and complex carrier recovery circuit
  • Has a better bit error rate

Non-Coherent Detection

  • The receiver does not utilize phase reference information
  • Does not require an expensive and complex carrier recovery circuit
  • Has a poorer bit error rate
  • Differential systems have important advantages and are widely used.

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