Resume of "Understanding Modulation - ICT #7"

 MODULATION

    Before the electromagnetic waves are transmitted, they should be modulated to a high-frequency signal. SIgnal with higher frequency known as carrier signal.

Gambar 1

    Signal has amplitude, frequency, and phase. Carrier signals are varied depends on the message signals. For example, the frequency of the carrier signal is varied according to the amplitude of the message signal known as frequency modulation so the produced modulated signal is also a high frequency. 

Amplitude modulation, the amplitude of carrier signals is varied based on the value of the message signal.

Amplitude and frequency modulation are all analog types which can degrade the quality of signals. 

In today's world, all operations are carried out in digital form. How digital modulation techniques work?

a. AMPLITUDE SHIFT KEYING

    Based on the digital pulse, the amplitude of the carrier signal is adjusted as high amplitude means one and low amplitude means zero.

b. FREQUENCY SHIFT KEYING

     The frequency of carrier signals is adjusted, in this case, high frequency relates to one and low frequency relates to zero.

c. PHASE SHIFT KEYING

    The phase of the carrier signals is changed by 180 degress. When the digital pulse moves from one to zero or zero to one. 

Using the digital modulation technique wouldnt achieve a high data transfer. Inthis case, there is a technique that could send up to six bits of intformation as a single electromagnetic wave called quardature amplitude modulation.

QAM

QAM could modulate two different signals as a single signal and then transmit it. At the end, the combined signals could be separated by saving bandwidth.

Steps on how QAM works :

i) A signal is amplitude modulated using a carrier wave

ii) The second signal is amplitude modulated with a carrier wave of the same frequency and amplitude

iii) After giving the carrier a signal, a 90 degree phase shift

iv) Two modulated signals are combined and produce a single signal called multiplexed signal

Gambar 2

v) The multiplexed signal could be separated at the receiver or destiation. 

DIGITAL QAM

    Different combination of bits are joined together to create a multiplexed signal. This single signals is then used to transmit. Different amplitude and phase of the electromagnetic signals relates to various four bits of data.

The modulation technique can beb used for cellular communication, FM Radio, Wi-Fi, Optical Fibers, etc.

Source :

https://www.youtube.com/watch?v=Iyzpt3bKTTI