Digital Modulation
In short, digital modulation is the process of encoding a digital information signal into the amplitude, phase, or frequency of the transmitted signal. The encoding process affects the bandwidth of the transmitted signal and its strength against channel weakness. There are many types of digital embedding techniques, and they are used as needed.
It has important applications, especially in modern communications between computers and the Internet, but its types are as follows:
1.AMPLITUDE SHIFT KEYING ASK:
The amplitude-shift embedding method is one of the simplest numerical modification methods, where the binary digital information 0 and 1 is represented with two different amplitudes. The state of 0 is represented by an amplitude of zero, and the state of 1 is represented by an amplitude of a. This type of modulation has some disadvantages due to its sensitivity to transmission errors such as interference, noise and signal dispersion by multipath, so it is not possible to guarantee the correctness of the signal in the case of wireless transmission in the presence of such errors. The amplitude of the output depends on the input data, whether it should be a zero level or a positive and negative difference. Depending on the carrier frequency.
2. Frequency Shift Keying FSK:
FSK is one of the widely used digital modulation methods. In this method the binary digital information 0 and 1 is represented by a signal of constant amplitude and the frequency is changed for each case. The state of 1 is represented by the frequency f1 and the state of zero by the frequency f2. This type of modulation is considered less sensitive to transmission errors such as interference, noise and scattering of the multipath signal.
3. Phase Shift Keying PSK:
In this type of modulation, a change in the phase angle of the signal occurs by (180°) at every change of digital information in binary form from 0 to 1 or vice versa, provided that the amplitude and frequency value is fixed, and this type of modulation is less sensitive than transmission errors from interference, noise and dispersion The signal, due to the multiplicity of paths compared to the previous two types, but the transmitting and receiving circuits in it are more complex,
If the carrier is modified using one bit of the input signal, the phase is adjusted by 180° and the speed is 1200 bits/sec. If the carrier is modified using 2 bits of the input signal, the phase is adjusted by 90° and the speed is 2400 bits/sec. If the carrier is modified using 3 bits of the input signal, the phase is adjusted by 60° and the speed is 4800 bits/sec. If the carrier is modified using 4 bits of the input signal, the phase is adjusted by 45° and the speed is 9600 bits/sec. If the carrier is modified using 6 bits of the input signal, the phase is adjusted by 45° and the speed is 28800 bits/sec. If the carrier is modified using 8 bits of the input signal, the phase is adjusted by 30° and the speed is 56600 bits/sec.
4. Gaussian Phase Shift Keying GPSK:
One of the modulation methods used in modern wireless communication systems is the minimum displacement modulation method (MSK), which is a developed method of frequency shift modulation (FSK) while reducing the sudden change of frequency and shape. In this method, digital information is separated into even and odd bits, and the time period for each digital information is doubled.
It uses two frequency values, and one of the two frequencies is chosen according to the following:
✔️ If both the even and odd information are in state 0 the high frequency f2 is used and the wave is reversed (change in phase angle by 180°)
✔️ If the even information is in state 1 and the odd information is in state 0 then use the low frequency f2 and with the wave inverted (change in phase angle by 180°)
✔️ If the even information is in case 0 and the odd information is in case 1, the low frequency f2 is used without changing the phase angle
✔️ If both the even and odd information are in case 1, the high frequency is used without changing the phase angle
By adding a Gaussian low-displacement filter to the minimum displacement rate we get what is called the Gaussian minimum displacement rate (GMSK). It is the rate used in the European wireless communication systems GSM and DECT.
❇️ What is the difference between digital modulation and analog modulation?
✔️ In long-distance communication, the signal can be regenerated by repeaters so that the effect of interference does not accumulate
✔️ Ease of manufacturing digital embedding devices due to the possibility of using integrated digital circuits and thus increasing reliability
✔️ Signal storage due to the ease of storing the numbers it represents
✔️ Reduce the effect of interference by using the appropriate symbols for this purpose.
Please check:
Introduction to Signals Modulation Part 1
Modulating process role in communication systems Part 2
The types of Modulation: Analog Modulation
Thank you.
