Amplitude Modulation Techniques

Learning Objectives

• Objective is to understand amplitude, angle, and pulse modulation
• Need to understand how to compute exact values and apply modulation in real scenarios

Learning Outcomes

• Intended to understand amplitude, angle, and pulse modulation
• Intended to know basic calculations
• Intended to understand how to use and apply modulation

What is Amplitude Modulation?

• A modulation technique in electronic communication
• Commonly used to transmit messages through radio waves
• Involves varying the amplitude of the wave proportionally to the message signal, like an audio signal
• Provides an efficient way to shift an acoustic or speech signal to a desirable frequency
• It is one of the earliest modulation methods used in radio
• Invented in the 20th century by Landell de Moura and Reginald Fessenden, who experimented with radiotelephony in the 1900s
• Definition: a type of modulation where the carrier wave's amplitude varies proportionally to the modulating data or signal

Types of Amplitude Modulation

• Double sideband-suppressed carrier modulation (DSB-SC)
• Single Sideband Modulation (SSB)
• Vestigial Sideband Modulation (VSB)

Double-Sideband Suppressed (DSB-SC)

• Carrier transmission in which frequencies have symmetrical spacing
• The space is above and below the carrier frequency
• The carrier level is reduced to the lowest practical level or completely suppressed

Single-Sideband Modulation (SSB or SSB-SC)

• Used to transmit information, such as an audio signal, by radio waves
• Refines amplitude modulation via transmitter power and bandwidth efficiently
• Amplitude modulation produces twice the maximum frequency of the original baseband signal
• Single-sideband modulation avoids the bandwidth increase and power waste, but increases device complexity and difficult tuning at the receiver

Vestigial Sideband Modulation (VSB)

• A process where the "vestige" part of a signal is modulated alongside one sideband
• It is a form of AM that encodes data in a signal by altering the carrier frequency

Amplitude Modulation Designations by ITU (1982)

• A3E: double-sideband a full-carrier
• R3E: single-sideband reduced-carrier
• H3E: single-sideband full-carrier
• J3E: single-sideband suppressed-carrier
• B8E: independent-sideband emission
• C3F: vestigial-sideband
• Lincompex: linked compressor and expander

Communication Systems and Modulation

• Used to transmit and receive messages (information) from one place to another in the form of electronic signals
• Categories include:
  • Analog signal transmission
  • Digital signal transmission
• m(t) represents the modulating signal (input signal) or baseband signal
• Am = Amplitude of the modulating signal
• (ωmt + Ɵ) = Phase of the signal where phase contains both frequency (ωmt) and angle (Ɵ) term

What is Modulation?

• A process in a communication system, requiring fundamental elements
• Elements: a high-frequency carrier wave and the information to be transmitted (modulating signal or input signal)
• Done using a device from one place to another within the communication system

Amplitude/Phase

• Varying the amplitude of the carrier wave in accordance with the modulating signal makes it amplitude modulation
• It can be frequency modulation and phase modulation
• Modulation is the phenomenon of "Superimposition of modulating signal (input signal) into the carrier wave”

Mathematical Expression for Amplitude Modulation

• m(t) = Am cos ωmt is modulating signal
• c(t) = Ac cos ωct is carrier signal
• The AM’s modulated wave, generated when the carrier amplitude changes

Angle Modulation

• It is a class of carrier modulation used in telecommunications transmission systems
• It is made up of frequency and phase modulation
• Modulation based on altering the frequency or phase of a carrier signal to encode the message signal
• Information can be encoded:
  • Time varying phase
  • Time varying frequency
• Angle modulation is closely related to an SDR (Software Defined Radio)
• Comparison of NBFM (Narrowband Frequency Modulation) with WBFM (Wideband Frequency Modulation), FM generation, demodulation
• The angle modulated wave is expressed as s(t)=100cos[2πfct+t∫−∞m(τ)dτ]

Types of Angle Modulation

• Phase Modulation (PM)
• Frequency Modulation (FM)

Phase Modulation

• A modulation pattern for conditioning communication signals for transmission
• Encodes a message signal as variations in the instantaneous phase of a carrier wave
• It is one of the two primary forms of angle modulation, along with frequency modulation
• M.I = ∆Θ, where ∆Θ represents the peak phase difference

Frequency Modulation

• Involves encoding information in a carrier wave by varying the instantaneous frequency of the wave
• Used in telecommunications, radio broadcasting, signal processing, and computing
• Formula to calculate frequency modulation bandwidth is 2(∆f + fi)

Angle Modulation Comparison Table FM and PM

• FM
  • Frequency deviation is proportional to modulating voltage
  • Associated with each change in f, there is some phase change
  • m, is proportional to the modulating voltage as well as the modulating frequency fm
  • It is possible to receive FM on a PM receiver
  • Noise immunity is better than AM and PM
  • Signal to noise ratio is better than that of PM
  • FM is widely used
  • Frequency deviation is proportional to the modulating voltage only
• PM
  • Phase division is proportional to the modulating voltage
  • Associated with the changes in phase, there is some change in f
  • m is proportional only to the modulating voltage
  • It is possible to receive PM on an FM receiver
  • Noise immunity is better than AM and worse than FM
  • The frequency division is proportional to both modulating voltage and Frequency
  • PM is used in some mobile systems

Applications of Angle Modulation:

• Radio Broadcasting
• Two-Way Mobile Radio
• Microwave Communication
• TV Sound Transmission
• Cellular Radio
• Satellite Communication

Pulse Modulation

• A technique where signals are transmitted via pulses
• Divided into Analog Pulse Modulation and Digital Pulse Modulation
• Analog: pulse amplitude, pulse width, pulse position
• Digital: pulse code, delta

Pulse-Amplitude Modulation

• Is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses
• Is an analog pulse modulation scheme

Types of Pulse Amplitude Modulation

• Single polarity PAM: ensures all pulses are positive using a DC bias
• Double polarity PAM: pulses are both positive and negative

Sampling techniques for transmitting a signal using PAM include

• Flat Top PAM: the amplitude of each pulse is directly proportional to modulating signal amplitude
• Natural PAM: the amplitude of each pulse is directly proportional to modulating signal amplitude

Natural PAM Specifics

• After the pulse occurs, follows the amplitude of the pulse for the rest of the half-cycle
• In pulse modulation, the unmodulated carrier signal is a periodic train of signals

Advantages of Pulse Amplitude Modulation

• Both modulation and demodulation are simple
• Easy to construct transmitter and receiver circuits

Disadvantages of Pulse Amplitude Modulation

• Large bandwidth is required for transmission
• More noise
• Amplitude varies, so power required to keep the amplitude stable will be more

Applications of Pulse Amplitude Modulation

• Mainly used in Ethernet Communication
• Microcontrollers use for generating control signals
• Used in photo-biology
• Acts as an electronic driver for LED circuits

Pulse Time Modulation

• Pulses have the same amplitude
• Timing characteristics are made proportional to the amplitude of the sample signal
• Time modulation is the frequency, position or width.
• Pulse Width Modulation, or pulse duration modulation
• The width of the pulse is varied in proportion to the amplitude of the signal, reducing the power loss

Benefits from Constant Amplitude of Signal

• Amplitude Limiters ensure these levels
• Amplitude clipping avoids noise production

Adivantages of PTM

• Low power consumption
• Efficiency if 90 percent
• Less noise interference
• High power handling capacity

Disadvantages of PTM

• The circiut is complex
• Voltage spikes are seen
• The sytem is expensive

Applications of PTM

• Used in encoding purposes
• Used in controlling brightness
• Helps to prevents brighteness
• Used in audio and video amplifiers

Pulse Position Modulation (PPM)

• Amplitude and pulse width are kept consistent
• The position of each pulse is varied with reference to a particular pulse
• An analog modulation scheme where the position of the pulse with respect to a reference pulse varies

Advantages of PPM

• Constant Amplitude Noise Interference is less
• Can separate the signal from a noisy signal
• The most Power Efficiency
• Needs Less Power when Compared to Pulse Amplitude Modulation

Disadvantages of PPM

• The System is Highly Complex
• The System Requires More Bandwidth

Application PPM

• Used in Air Traffic Control Systems and Tele Communication Systems
• Remote-controlled planes use pulse-code modulations
• Used to compress data and storage

Pulse Code Modulation

• Signals are sampled and in pulse form
• Also uses a sampling technique
• Numbers represent the length of the sample at a particular
• Encoding, decoding and quantization of the circuit
• Delta Modulation is where the rate is very high-Here, the quantization