What Is Modulation?

Modulation has the following significance in biochemistry and molecular biology: (1) Reversible changes in cell differentiation and functional status. (2) Regulation of cells by biologically active substances. (3) Functional changes of cells (mainly immunologically active cells) under the action of biologically active substances (such as cytokines). (4) Regulation of the transcription frequency of specific genes. (5) Regulation of the reduction of messenger ribonucleic acid (mRNA) translation rate by codons. (6) Control of effector to regulatory enzyme. In communication technology, it refers to the process of intentionally or unintentionally changing the quantity representing one oscillation or wave with the change of one signal or another oscillation or wave.

[tiáo zhì] right!

Modulation in

Title : Modulation

Pinyin :

Basic explanation

To transmit information (as in

Modulation (modulation) is to process the information of the signal source and add it to the carrier to make it suitable for

There are many types of modulation,

Modulation is very important in electronics. The remarkable development trends are: due to the continuous increase of digital services, the capacity of digital communication systems needs to be continuously expanded, which requires the development of ultra-high-speed digital modulation technology;

Modulation has a very important role in communication systems. By modulation, not only can

In communication, we often use the following modulation methods:

(A) analog modulation: use a continuously changing signal to modulate a high-frequency sine wave

The main are: 1. Amplitude modulation (AM AM, double-sideband modulation DSBSC, single-sideband AMSSBSC, residual sideband modulation VSB, and independent sideband ISB)

2. Angle modulation (FM, FM, PM). Because the rate of change of phase is frequency, phase-modulated waves and frequency-modulated waves are closely related;

(2) Digital modulation: Use digital signals to modulate sine or cosine high-frequency oscillations

The main ones are: 1. ASK with Amplitude Keying;

2. Frequency keying FSK;

3. Phase keyed PSK;

(3) Pulse modulation: using pulse sequence as carrier

The main ones are: 1. Pulse Amplitude Modulation (PAM: Pulse Amplitude Modulation);

2. Pulse width modulation (PDM: Pulse Duration Modulation);

3. Pulse position modulation (PPM: Pulse Position Modulation);

4. Pulse code modulation (PCM: Pulse Code Modulation);

With the increase of communication traffic, spectrum resources are becoming increasingly tight. In order to increase the capacity of the system, the channel interval has been reduced from the original 100kHz to 25kHz, and will be further reduced to 12.5kHz, or even smaller. It is easy to adopt digital error control technology and digital encryption, which is easy to integrate and can enter the ISDN network, so the communication systems are transitioning from analog to digital.

Therefore, digital modulation technology must be used in the system. However, general digital modulation technologies such as ASK, PSK, and FSK cannot meet the requirements of mobile communications due to low transmission efficiency. Therefore, special research is required to have strong anti-interference and good error performance The digital modulation technology with high spectrum utilization can increase the bit rate of the transmission data in the unit spectrum as much as possible to meet the requirements of mobile communication narrowband data transmission. Such as

Minimum frequency shift keying (MSK-Minimum Shift Keying);

Gaussian Filtered Minimum Frequency Shift Keying (GMSK-Gaussian Filtered Minimum Shift Keying);

Four-phase phase shift keying (QPSK-Quadrature Reference Phase Shift Keying);

OQPSK-Offset Quadrature Reference Phase Shift Keying;

Four-phase relative phase shift keying (DQPSK-Differential Quadrature Reference Phase Shift Keying);

/ 4 quadrature phase shift keying ( / 4-DQPSK-Differential Quadrature Reference Phase Shift Keying);

It has been widely used in digital cellular mobile communication systems.