What are the components of a wireless communication system and what are their functions?

Wireless communication system: also known as radio communication system, it consists of sending equipment, receiving equipment and transmission medium (wireless channel). It uses wireless electromagnetic waves to realize information and data transmission. The functions of each part are as follows:

1, sending device

(1) converter (sensor): converts the sent information into an electrical signal. For example, a microphone converts sound into an electrical signal.

(2) Transmitter: Convert the electrical signal output by the transducer into high-frequency electric oscillation with sufficient intensity.

(3) Antenna: converts high-frequency electric oscillation into electromagnetic wave and radiates it to the transmission medium.

2. Transmission medium-electromagnetic wave

In free space, there is the following relationship between wavelength and frequency:? In the formula, C = Fλ:C is the speed of light, and f and λ are the frequency and wavelength of radio waves respectively, so radio waves can also be regarded as electromagnetic waves with relatively low frequency. Divide the frequency or wavelength into sections, which are called frequency bands or bands respectively. ?

Different frequency bands have different methods of generating, amplifying and receiving signals, and different propagation capabilities and modes, so their analysis methods and application scope are also different. Radio wave is just an electromagnetic wave with a long wavelength, occupying a wide frequency range. ?

After the electromagnetic wave is radiated from the transmitter antenna, not only will the energy of the electric wave spread out, but the receiver can only receive a small part of it, and in the process of propagation, the energy of the electric wave will be absorbed or reflected by the ionosphere on the ground, buildings or high altitude; Or refraction or scattering in the atmosphere, leading to intensity attenuation.

According to the phenomenon of radio waves in the process of propagation, the main propagators of radio waves are diffraction (ground waves), reflection and refraction (sky waves) and direct (space waves). The key factor that determines the propagation mode is the frequency of the radio signal.

Radio waves propagating along the interface between the earth and the air are called surface waves, or simply ground waves. Diffraction propagation. The transmission path mainly depends on the electrical characteristics of the ground. In the process of ground wave propagation, because the energy is gradually absorbed by the earth, it quickly weakens (the shorter the wavelength, the faster the attenuation), so the propagation distance is not far. But the ground wave is not affected by climate and has high reliability.

Ultra-long wave, long wave and medium wave radio signals are all propagated through ground waves. Short-wave short-distance communication also uses ground wave propagation.

Sky wave: an electric wave that propagates through refraction and reflection of the ionosphere in the sky, also called sky wave. The ionosphere only reflects short-wave electromagnetic waves, so sky wave propagation is mainly used for short-wave long-distance communication.

Two outstanding characteristics: first, the propagation distance is long, and at the same time, the middle static zone is produced; Second, the spread is unstable, which changes with the change of day and night and season. Therefore, short-wave communication should be changed by the parties concerned to ensure the quality.

Space wave, also known as direct wave, is a radio wave that propagates directly from the transmitting point to the receiving point. The propagation distance of direct waves is generally limited to the line-of-sight range. In the process of propagation, its intensity decays slowly, and ultrashort wave and microwave communication are propagated through direct waves.

In ground direct wave communication, the field strength of the receiving point consists of two paths: one path leads directly to the receiving antenna, and the other path reaches the receiving antenna after being reflected by the ground. If the antenna height and direction are improperly erected, it will easily cause mutual interference (such as TV ghost).

The main factors limiting the communication distance of direct waves are the radian of the surface and obstacles such as mountains and buildings, so it is required that ultrashort wave and microwave antennas be elevated as much as possible.

3. Receiving equipment

Receiving is the reverse process of transmission.

(1) Receiving antenna: the propagation space of electromagnetic wave to it → high frequency electric oscillation.

(2) Receiver: high-frequency electric oscillating electric signal.

(3) transducer: information transmitted by electric signals.

Extended data

According to the different characteristics of key components in the wireless communication system, the wireless communication system mainly has the following types:

1, classified by operating frequency band or transmission mode.

There are medium wave communication, short wave communication, ultrashort wave communication, microwave communication and satellite communication. The so-called operating frequency mainly refers to the transmitting and receiving radio frequency (RF) frequency. Radio frequency is actually a broad term for "high frequency", which refers to the frequency suitable for radio transmission and propagation. One development direction of wireless communication is to open up higher frequency bands.

2, according to the communication way to classify.

There are mainly (full) duplex, half-duplex and simplex modes. The so-called simplex communication refers to the way of only sending or receiving; Half-duplex communication is a communication mode that can send and receive, but can't send and receive at the same time. Duplex communication is a communication mode that can send and receive at the same time. The example in the first picture is half-duplex mode. Change the antenna switch to duplexer to duplex mode.

3, according to the different modulation methods.

There are AM, FM, PM and mixed modulation.

4. Classify according to the types of messages transmitted.

There are analog communication and digital communication, which can also be divided into voice communication, image communication, data communication and multimedia communication.

Different types of communication systems have very different system composition and equipment complexity. But the basic circuits that make up the equipment are the same as their principles, and they follow the same rules. This book will study these basic circuits around analog communication and understand their laws. These circuits and laws can be applied to other types of communication systems.

Baidu encyclopedia-wireless communication