Digital Band-Pass Modulation

• 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.