Wireless communication technology – an overview

Wireless communication technology essentially uses wireless transmission media to achieve interconnection and interoperability between terminals. This wireless medium can be electromagnetic waves or light waves. In fact, according to the theory of quantum mechanics, light waves are also a kind of electromagnetic waves. The difference between them is The wavelengths are different. Today qihe smt pick and place machine sharing A brief summary of wireless communication technology.

With the transmission medium, the next step is encoding, that is, how to modulate the electromagnetic wave signal to represent the information we want to transmit. According to the characteristics of electromagnetic waves, information can be expressed by modulating the amplitude, frequency, phase, etc. of electromagnetic waves, which is our common amplitude modulation, frequency modulation, and phase modulation.

With encoding, the next step is communication. If there are only two communication terminals, then things are simple. For example, through amplitude modulation coding, an amplitude of 1 represents 1, and an amplitude of 0 represents 0. What if there are many communication terminals? Will the communications between them interfere with each other? I am very sure of that. what to do? This leads to coding methods for identifying the identity of communication terminals. Common ones include the following:

FDMA, translated into Chinese, is frequency division multiple access technology, which modulates radio waves into many frequencies that do not interfere with each other, and each frequency represents a communication line. To put it more professionally, the total bandwidth is divided into multiple orthogonal channels, and each user occupies one channel. For example, the frequency band allocated for wireless cellular phone communications is divided into 30 channels, each of which is capable of transmitting voice calls, digital services and digital data.

TDMA, translated into Chinese, is time division multiple access technology, which divides time into multiple cycles, and each cycle is divided into multiple time slots, in a cycle. Each time slot corresponds to the transmission information of a user, and different sources are distinguished according to the time slot. address of the user signal, thus completing the multiple access connection.

CDMA, translated into Chinese, is code division multiple access technology. The technical principle is based on spread spectrum technology, that is, the information data that needs to be transmitted with a certain signal bandwidth is modulated with a high-speed pseudo-random code with a bandwidth much larger than the signal bandwidth, so that the original data signal The bandwidth is expanded, then modulated by the carrier and sent out. The receiving end uses exactly the same pseudo-random code to perform correlation processing with the received bandwidth signal, and replaces the broadband signal with a narrowband signal of the original information data, that is, despreading, to achieve information communication.

Wireless LAN technology. The three technologies of FDMA, TDMA, and CDMA can provide a dedicated connection for each communication channel. It can be understood that the medium is not shared, so it can ensure that long-distance communication is not interfered with, so it is mostly used for long-distance communication. Also using electromagnetic waves, the technology used in wireless LAN is CSMA/CA technology. Its working principle is:

(1) First detect whether the channel is in use. If the channel is detected to be busy, wait for a random period of time before sending data.
(2) If the receiving end receives the frame correctly, it will send a confirmation frame ACK to the sending end after a period of time.
(3) The sending end receives the ACK frame and confirms that the data is transmitted correctly. After a period of time, there will be an idle period.

It can be seen that the CSMA/CA technology used in wireless LAN shares the transmission medium. Two communication terminals compete for the transmission medium. If there are too many terminals, the transmission channel will be crowded, so it is not suitable for large-scale remote communication. Communication is only suitable for small-scale local communication. Because of this, we call the wireless communication network using CSMA/CA technology a wireless LAN.

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