Modulation : Why do we require modulation in wireless communication?
Wireless communication relies heavily on modulation techniques. Coaxial cable, twisted pair, and other types of wired communication are commonly used. Wired communication, on the other hand, is best for short-distance communication. An antenna is required for wireless communication to transfer signals. Now, if we want to send a baseband signal, we'll need a very large antenna with a range of many kilometers. Baseband signals are ones that typically contain a low or medium frequency message signal. It's also known as a message signal without modulation. Modulation is a technique for increasing the frequency of a message signal by the carrier frequency to a significantly higher frequency.
So, now I'll explain why modulation is necessary. The main two goals of modulation techniques are to reduce antenna height and to multiplex data (Multiplexing).
Reducing the height of antenna:
For short-range baseband communication, wired communication is sufficient. However, for long-distance communication, wireless is the best option. We know that the transmitter antenna emits a specific radiation pattern. The signal then travels through the earth's atmosphere until it reaches the receiver. We should be aware that antenna height is important for reliable transmission. The wavelength of the working frequency determines the antenna height. The antenna height should be
Ht = λ/4 and λ = c/f
Where, Ht = height of antenna
λ = wavelength of operating frequency
c = speed of light
f = operating frequency
We can also derive the following equations from the above equation:
As Ht = λ/4,
Therefore, Ht =c/4f; or Ht α 1/f
So, we can say that antenna’s height is inversely proportional to the operating frequency. If frequency is more, height of antenna should be smaller and vice-versa for reliable communication.
Example:
Let assume, operating frequency of a communication band is 20 KHz. Then the height of antenna, Ht, should be
Ht = c/4f = (3*10^8) / (4*20*10^3) = 3.75 kilometers
We can observe that the antenna height for reliable 20 KHz band communication should be 3.75 kilometers. As a result, we choose modulation, in which the lower frequency is shifted to the higher frequency. It is a method of enhancing transmission frequency while lowering antenna height.
Multiplexing:
Multiplexing is another significant advantage of modulation techniques. The parallel data streams are multiplexed into a serial data stream. Simply put, modulation techniques allow us to deliver many simultaneous data streams from the transmitter to the receiver across a single channel. To your knowledge, we use the modulation technology to enable multiplexing in wired connection as well.
#Multiplexing
Communication channel
