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What is a modulation? Need of modulation

Introduction

Within the telecommunications industry, modulation is an essential and creative technique used to carry invisible signals across the airways. The art of modifying waves to transmit information is a process that we frequently take for granted in our day-to-day interactions with contemporary technology. We set out to demystify modulation in this blog, covering its importance, different varieties, and crucial function in the smooth transfer of data.

Modulation means changing some characteristic of a carrier, such as amplitude, frequency, or phase, using the signal (audio or video). Modulation involves modification, variation, or change. You modify the carrier according to the signal, which is why we call it modulation. This process plays an important role in wireless communication.

Understanding the Basics

Modulation fundamentally involves altering a carrier wave to embed information. This carrier wave, usually a high-frequency signal, acts as the data conveyor. You can achieve effective air transmission of information by adding the data and adjusting specific properties of the carrier wave.

NEED FOR MODULATION

In carrier (wireless) transmission, you must use modulation. The explanation follows below:
  • Modulation uses high-frequency carriers to send weak, low-frequency signals over long distances. At the receiver, the signal is separated, and the carrier is discarded.
  • Just as a man can deliver a message farther and faster using a horse, a signal can travel longer distances when placed on a high-frequency carrier. At the destination, the message is taken, and the carrier is discarded.
  • Here, the message is the signal, the horse is the carrier, and the receiver is the radio or TV. This illustrates the principle of radio transmission and reception.
  • The next reason describes the height of the antenna needed.The transmitting antenna should have a height equal to the wavelength.This condition gives best results. We know that
V = fλ
Where V = velocity of radio waves = `3times10^8` m/s
f = frequency
λ = wave length
  • If the frequency of the signal is 20 kHz, the length of the antenna
l=λ=`frac VF`= `frac{3times10^8;m/s}{20times10^3}`=15000 m=15 km
i.e., If you try to transmit the sound produced at the microphone directly,
we need an antenna of 15 km height, which is totally impractical.
  • If f = 1 MHz

now length of the antenna l = λ = `frac{3times10^8}{1times10^6}`=300 m

 
i.e., If you raise the signal’s frequency to 1 MHz, you can transmit it using a 300 m high antenna, which is a practical height. By modulating the signal according to the requirement, you superimpose it onto a high-frequency carrier to enable effective transmission.
  • Modulation enables wireless transmission, letting us receive audio/video signals globally. Without it, watching a match in France from home would require impractically long wires.

Challenges and Innovations

While modulation has revolutionized communication, challenges persist. Signal degradation due to interference, noise, and the limitations of available frequency bands are constant concerns. Engineers continually innovate to overcome these challenges, developing advanced modulation techniques and error-correction methods.

TYPES OF MODULATIONS

Modulation is an important process in all wireless (carrier) communications.In this, the signal is superimposed on a high frequency carrier wave. Some characteristic (amplitude, frequency, phase; etc.) of the carrier wave is changed in accordance with the instantaneous value of the signal. A sine wave may be represented by
e=`E_m` sin(ωt + φ)
e=instantaneous value of modulated wave
`E_m`=maximum amplitude
ω=angular velocity
φ=phase relation
Accordingly, modulation is of three types (see the above equation)
  • Amplitude modulation: By changing amplitude of the carrier.
  • Frequency modulation: By changing frequency of the carrier.
  • Phase modulation: By changing phase of the carrier.

However, the complete classification of modulation processes are given below:

1.Amplitude modulation (AM)
  1. Single sideband AM (SSBAM)
  2. Double sideband AM (DSBAM)
  3. Frequency division multiplexing (FDM)

In India, for sound, amplitude modulation is used

2.Frequency modulation (FM)

     In India, for television signals, frequency modulation is used.

3.Phase modulation.

Other modulation processes are:

1.Pulse modulation (used in telephone and telegraphy)–these may be:
  • Pulse amplitude modulation (PAM)
  • Time division multiplexing (TDM)–used in long play records
  • Pulse time modulation (PTM) 
  • Pulse division multiplexing (PDM)
  • Pulse code modulation (PCM)

2.Digital modulation (DM)–They may be:

  • Differential PCM (DPCM)
  • Adoptive PCM (ADPCM)
  • Data modulation (DM)
  • Adoptive data modulation (ADM)

Note: 1. The modulations may also be:

  • analog modulation
  • Digital modulation

Amplitude Modulation

  • Amplitude Modulation (AM) is a modulation technique in which the instantaneous amplitude of the carrier signal is varied in accordance with the instantaneous amplitude of the analog modulating signal to be transmitted.
  • The modulating signal is an analog baseband signal which is random and has a low frequency, while the carrier signal is always a sinusoidal wave with high frequency.
  • The variations in amplitude of carrier signal represent the information carried.
  • The amplitude of the carrier wave is varied in accordance with the modulating signal while
    the frequency and phase of the carrier signal remains unchanged.
  • The modulating signal seems to be superimposed on the carrier signal.
  • The amplitude variations in the peak values of the carrier signal exactly replicate the
    modulating signal at different points of time which is known as an envelope.
  • Modulation Index is given by `mu=frac{A_m}{A_c}`
Diagram illustrating modulation types: Frequency Modulation shows varying wave frequency, while Amplitude Modulation shows wave height changes. Simple, educational tone.
You often refer to amplitude modulation as linear modulation. You know frequency and phase modulations as non-linear, angular, or exponential modulation. While there may be many forms of exponential modulations but only two i.e., frequency and phase modulations are practical. In particular, both linear as well as non-linear modulations are continuous wave (CW) type modulations.

Frequency Modulation

  • Frequency Modulation (FM) is a modulation technique in which the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the analog modulating signal to be transmitted.
  • Only the frequency of the carrier signal is varied while the amplitude and phase of the carrier are kept constant.
  • The original frequency of the carrier signal is called the center or resting frequency and denoted as 𝑓𝑐.
  • The amount by which the frequency of the carrier wave changes or shifts above or below the resting frequency is called frequency deviation ∆f. This means ∆𝑓 ∝ 𝑚(𝑡).
  • The total variation of frequency of FM wave from the lowest to highest is termed as carrier
    swing (CS),
𝐶𝑆 = 2 ∆f
  • Modulation Index
`mu_f=frac{triangle_f}{f_m}`=Frequency deviation/Modulating frequency

Phase Modulation

  • Phase Modulation (PM) varies the carrier signal’s phase according to the instantaneous amplitude of the analog modulating signal you want to transmit.
  • After phase modulation, amplitude and frequency of the carrier signal remain unaltered.
  • You map the modulating signal to the carrier signal by varying the carrier’s instantaneous phase.
  • Phase modulation and frequency modulation are closely related to each other.
  • In both the cases, the total phase angle 𝜙 of the modulated signal varies.

 

Graph illustrating phase modulation with three waveforms: smooth message signal, high-frequency carrier signal, and complex phase-modulated signal.

Pulse Modulation

  • You can use pulse modulation to transmit analog information, such as continuous speech or data.
  • You sample continuous waveforms at regular intervals.
  • It has the advantage of ability to use constant amplitude pulses.
  • You can subdivide pulse modulation into two categories: analog and digital.
  • In analog, the indication of sample amplitude may be indefinitely variable.
  • In digital pulse modulation, you send a code that indicates the sample’s amplitude to the nearest predetermined level.
  • Pulse-amplitude and pulse-time modulation are both analog, while the pulse code and delta modulation systems are both digital.

 

Graph illustrating Pulse Position Modulation (PPM). Shows an analog signal wave, sampled pulses transitioning into PPM pulses, with labeled time axes.

Pulse Amplitude Modulation

  • Pulse Amplitude Modulation (PAM) is the simplest form of pulse modulation.
  • You sample the signal at regular intervals and set each sample proportional to the signal’s amplitude at the instant of sampling.
  • Disadvantage - PAM does not use constant-amplitude pulses.
  • Hence it is not used frequently.
  • In PAM, the amplitude of the pulses of the carrier pulse train is varied in accordance with the modulating signal.
Alt text: "Illustration of PAM signal waveform; a smooth sinusoidal wave, a square pulse train, and the modulated result combining both, labeled 'm(t)', 'c(t)', and 'p(t)' respectively. Caption reads 'Waveform representation of PAM signal.'"

Pulse Width Modulation or Pulse
Duration Modulation

  • Pulse Width Modulation (PWM), also called Pulse Duration Modulation (PDM), adjusts the width or duration of each pulse to match the instantaneous value of the analog signal.
  • The starting time and amplitude of each pulse are constant.
  • Disadvantage - Pulses are of varying width and hence of varying power content.
  • The transmitter must be powerful enough to handle the maximum-width pulses.

 

Graphical representation of PWM signal generation. Six plots: (a) red sine wave, (b) blue square wave, (c) blue/pink mixed wave, (d) yellow triangular wave, (e) blue wave with comparator level, (f) green PWM wave.

Pulse Position Modulation

  • Pulse Position Modulation (PPM), is a system in the position of each pulse in relation to the position of a recurrent reference pulse is varied according to the instantaneous sampled value of the modulating signal.
  • The amplitude and width of the pulses are constant.
  • Advantage over PWM – Requires constant transmitter power output
  • Disadvantage – Dependence of transmitter-receiver synchronization

 

Graph showing an analog signal waveform above sampled pulses and pulse position modulation (PPM). Dashed lines connect the signals, illustrating modulation.

Pulse Code Modulation

  • Pulse Code Modulation (PCM) digitally samples the message and rounds it off to the nearest value within a finite set of allowable values.
  • The rounded values are coded.
  • The PCM generator produces a series of numbers or digits.
  • Each digit in binary code represents the signal sample’s amplitude at that instant.
  • Signals are transmitted as binary code.
Diagram showing a sine wave input being converted to a PCM output. The smooth sine wave above is aligned with blocky PCM signals below, separated by dashed lines.

Digital Modulation Schemes

  • In digital communications, the modulating signal consists of binary data or its M-ary version.
  • When you need to transmit digital signals, you vary the amplitude, frequency, or phase of the sinusoidal carrier according to the incoming digital data.
  • Since digital data exists in discrete steps, you also modulate the bandpass sinusoidal carrier in discrete steps.
  • This reason is why you call this type of modulation digital modulation.
  • Digital modulation schemes are classified as
  1. Amplitude Shift Keying (ASK)
  2. Frequency Shift Keying (FSK)
  3. Phase Shift Keying (PSK)

Amplitude Shift Keying

  • Amplitude Shift Keying (ASK) represents digital data as variations in the amplitude of a carrier wave.
  • You can generate an ASK signal by applying the incoming binary data and the sinusoidal carrier to the two inputs of a product modulator.
Diagram illustrating Amplitude Shift Keying (ASK). It shows a binary sequence, a step-like data waveform, and a sinusoidal carrier signal modulated according to the binary data.

Frequency Shift Keying

  • In Frequency Shift Keying (FSK), you transmit digital information by changing the carrier signal’s frequency in discrete steps.
  • The simplest FSK is binary FSK (BFSK).
  • BFSK uses a pair of discrete frequencies to transmit binary information (0s and 1s).
Diagram illustrating Frequency Shift Keying (FSK) with a square wave message signal, two carrier signals at different frequencies, and a modulated signal.

Phase Shift Keying

  • Phase Shift Keying (PSK) conveys data by changing (modulating) the phase of constant frequency carrier.
  • You represent each symbol (pattern of bits) using a specific phase.
  • The simplest form of PSK is Binary PSK (BPSK).
  • It uses phases 0° and 180°.
  • You widely use it for wireless LANs, RFID, and Bluetooth communication.
Graph showing frequency modulation: top section displays logic states, middle shows carrier frequency waves, and bottom shows output frequency changes.

Why FSK and PSK are preferred over ASK?

Engineers often prefer Frequency Shift Keying (FSK) and Phase Shift Keying (PSK) over Amplitude Shift Keying (ASK) in certain communication systems because of several advantages. Each modulation scheme offers unique strengths and weaknesses, so you choose among them based on the specific requirements and characteristics of the communication channel. Here are some reasons why FSK and PSK sometimes work better than ASK:
  • Because of the constant amplitude of FSK or PSK, the effect of non-linearities, noise and interference is minimum on signal detection.
  • These effects are more pronounced in ASK.

1. Noise Immunity:

Firstly, FSK and PSK handle noise better than ASK. Indeed, noise immunity is crucial, furthermore improving reliability. Consequently, engineers prefer these methods, therefore using them. Additionally, ASK often suffers errors, moreover due to amplitude limits. Thus, ASK faces challenges. Meanwhile, FSK uses frequency variations, since they resist noise, hence maintaining clarity. Similarly, PSK uses phase variations, besides offering robustness, ultimately providing noise immunity.

2. Bandwidth Efficiency:

Firstly, you find FSK and PSK offer better bandwidth efficiency than ASK. Indeed, this efficiency is clear, furthermore critical when spectrum is limited. Consequently, engineers value these methods, therefore preferring them. Additionally, FSK alters carrier frequency, moreover ensuring reliability. Thus, PSK varies phase for the same goal. Meanwhile, both transfer more data, since they use bandwidth well, hence outperforming ASK. Similarly, they boost performance, besides reducing interference, ultimately maximizing bandwidth.

3. Power Efficiency:

Firstly, in ASK, you need a larger dynamic power range because you must change the carrier’s amplitude. Indeed, this increases power use, furthermore reducing efficiency. Consequently, ASK faces limits, therefore becoming less preferred. Additionally, it needs careful design, moreover adding complexity. Thus, engineers consider alternatives. Meanwhile, in FSK and PSK, modulation occurs since they avoid large amplitude changes, hence improving efficiency. Similarly, they reduce power loss, besides ensuring reliability, ultimately saving energy. Nevertheless, design factors remain; however, FSK and PSK are better. Likewise, they suit modern systems, accordingly supporting low-power goals. Otherwise, high-power needs arise. In fact, efficient modulation is crucial, next, aiding sustainability, finally, ensuring better performance.

4. Spectral Efficiency:

FSK and PSK use the spectrum more efficiently, allowing them to achieve higher spectral efficiency. This efficiency becomes critical in wireless communication, where multiple unaltered signals need to coexist and operate within a single frequency band.

5. Binary Phase Shift Keying (BPSK) in PSK:

BPSK, a specific form of PSK, offers a simple and sturdy modulation method. Engineers widely apply it in communication systems, and it performs reliably even in many noisy environments.

6. Ease of Detection:

Firstly, demodulation for FSK and PSK is often easier than ASK. Indeed, FSK and PSK offer advantages, furthermore simplifying design. Consequently, engineers prefer them, therefore reducing challenges. Additionally, they enhance efficiency, moreover improving stability. Thus, they are widely used. Meanwhile, ASK demodulation is less practical, since its circuitry is complex, hence increasing effort. Similarly, it raises costs, besides needing precise tuning, ultimately making ASK less favorable.

7. Frequency Hopping Spread Spectrum (FHSS):

Firstly, foreclosures are a reason to live in 87 condominiums, wherefore these conditions impact ground-floor buyers. Indeed, this occurs because a lit couple tries this layout with wall alterations. Furthermore, it applies in FHSS systems, consequently offering security. Therefore, these systems provide intereferencelessness, additionally ensuring reliability. Moreover, decentralization reduces vulnerability, thus increasing safety. Meanwhile, demand grows because users need secure systems, so more people adopt them. Similarly, technology advances, ultimately improving living and systems.

Conclusion

Modulation is the unseen force that shapes our connected world, from the crackling radio waves that carry music through the air to the internet's lightning-fast data exchange. Firstly, the skill of modifying waves will remain essential; indeed, it expands communication. Furthermore, it adapts with demand, consequently enhancing connectivity. Therefore, as technology advances, additionally, new methods emerge. Moreover, they boost speed, thus supporting progress. Meanwhile, nations benefit, since global links grow, hence reducing barriers. Similarly, innovation spreads, besides fostering collaboration, ultimately broadening international communication.
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