What are the benefits of modulation in communication systems?

Question

Why are there so many modulation schemes?

Answer 1

Modulation was initially introduced and is still dominant as a method of transporting the information signal over the air. The reason is that electromagnetic waves propagate across the air if their frequency is very high (say much higher than the frequency of human speech). Therefore, to send the speech signal over the air you need to transpose the speech signal into the high frequency that will pass through the air without substantial losses. That is precisely what the modulation does. Speech signal modulates the high frequency signal (called carrier) that travels through the air. The example might be to modulate the high frequency W carrier Asin(Wt) with low frequency w speech signal asin(wt). In the case of amplitude modulation you choose A=asin(wt). Then the modulated carrier signal becomes asin(wt)sin(Wt) = (a/2)(cos((W-w)t) - cos((W+w)t)). This so called double side band modulated carrier contains the speech information contained in values of a and w, however is the high frequency signal with frequencies (W-w) and (W+w) which allows it to travel large distances over the air. While order of magnitude of w = 1 KHz (speech range), the order of magnitude of W = 1 MHz and above (depending how far through the air you go).
There are other applications of modulation like collision detection, etc. However, generally, the modulation is a method used to transfer the information through the media.

Answer 2

modulation is simply the method of converting the signal to something that can be used by the communication media i.e. cable, air etc.

There are so many because they each have their own pros's and con's and develop along with technology developments

Answer 3

modulate v. (-ting) 1 a regulate or adjust. b moderate. 2 adjust or vary the tone or pitch of (the speaking voice). 3 alter the amplitude or frequency of (a wave) by using a wave of a lower frequency to convey a signal. 4 Mus. (cause to) change from one key to another.  modulation n. [Latin: related to *module]

module n. 1 standardized part or independent unit in construction, esp. of furniture, a building, or an electronic system. 2 independent self-contained unit of a spacecraft. 3 unit or period of training or education.  modular adj. [Latin: related to *modulus]

modulus n. (pl. moduli) Math. constant factor or ratio. [Latin, = measure: related to *mode]

I just deal with radio communication.

AM - Amplitude Modulation :

When amplitude increases, wavelength decreases and energy increases and vice versa. Thus, the reception of AM stations are generally stronger and easily available.

FM - Frequency Modulation :

When frequency increases also, energy increases and wavelength decreases. Thus, the reception of FM stations are generally weaker and rarely available.

TV signals :

Video is AM and audio is FM. Visual signals require energy range of visible region. Therefore, video signals require the concentration of the transmitter over amplitude, which requires electrons at higher energy. But audio signals require the concentration of the transmitter over frequency, which requires electrons at lower energy.

Both the cases may vary in their names but both deal with nothing but wavelength.

When wavelength increases, energy decreases and vice versa. This can easily be understood with SW transmission. It may be numbered as a long array as 1, 2, 3, ... according to various ranges of wavelength available.

Have you ever wondered that we can only see sunlight and we cannot hear it? Because the photons lie outside our audible range!