What are the wireless transmission methods?

Question 1: Besides the infrared, Bluetooth and nRF you mentioned, there are probably three wireless transmission modes: WLAN (wireless local area network), zigbee, CDMA, GSM and D-SCDMA, namely mobile phone, SDH spread spectrum microwave, MMDS, wireless TV (analog digital), DVB-T, DMB TH digital mobile TV, DAB and DMB. I can't remember anything else at once.

In addition, I will tell you the general principle of wireless transmission:

The principle of radio technology is that the change of current intensity in conductor will produce radio waves. Using this phenomenon, information can be loaded on radio waves by modulation. When radio waves propagate through space and reach the receiving end, the electromagnetic field changes caused by radio waves will generate current in the conductor. Through demodulation, information is extracted from the current change to achieve the purpose of information transmission.

Wireless transmission uses electromagnetic waves. It is divided into a transmitting part and a receiving part. The transmitting part consists of an oscillator that generates high-frequency signals, a modulator that adds audio signals to electromagnetic waves, and a high-frequency power amplifier, and is finally transmitted into space through an antenna. The receiving part consists of a receiving antenna, a high-frequency amplifier, a frequency converter, an intermediate-frequency amplifier, a detector and an audio power amplifier, and finally the sound is restored by a loudspeaker.

Now wireless transmission has gone beyond the scope of broadcast communication. Such as radio navigation, radio positioning, wireless Internet access and many other fields.

I have been monitoring wireless video transmission for 10 years, and I hope my advice will be helpful.

I'm from Shenzhen Haidian Technology Co., Ltd.,

If you think the answer is good, give me extra points! !

Question 2: The transmission mode of wireless transmission SmartAir technology is the only single antenna mode gigabit wireless high-speed transmission technology in the communication industry. The transmission rate of 1Gbps is realized by using multi-band OFDM air interface technology, low-delay scheduling technology of TDMA, and advanced wireless communication technologies such as low-density parity check code LDPC, adaptive modulation and coding AMC and hybrid automatic repeat request (HARQ).

Question 3: What devices or modes are there for wireless transmission? Bluetooth, wifi, infrared, those are all for civilian use.

Question 4: What are the methods of wireless file transfer between mobile phone and computer? 1, computers and mobile phones provide 1 QQ numbers for transmission respectively;

2. The computer and the mobile phone download the cloud disk at the same time, register the account, and transfer the file to the cloud disk, and the other party can download it at any time;

3. Log in to WeChat on the mobile phone, log in to the WeChat web version on the computer, and use the "file transfer assistant" to transfer;

4. If the computer has Bluetooth (the desktop can buy a wireless network card with Bluetooth), it can transmit with Bluetooth.

Question 5: The mode and principle of wireless transmission;

Wireless transmission can be divided into analog microwave transmission and digital microwave transmission.

First, the principle of simulating microwave transmission:

Analog microwave transmission is to directly modulate the video signal on the microwave channel (microwave transmitter, HD-630) and transmit it through the antenna (HD- 1300LXB). The monitoring center receives the microwave signal through the antenna, and then demodulates the original video signal through the microwave receiver (Microsat 600AM). If it is necessary to control the pan/tilt lens, add a corresponding command control transmitter (HD-2050) in the monitoring center, and configure a corresponding command receiver (HD-2060) in the monitoring front end. This monitoring method has the advantages of very clear image, no delay, no compression loss, low cost, simple construction, installation and debugging, etc., and is suitable for occasions with few monitoring points and few relays. Its weaknesses are: poor anti-interference ability, easy to be affected by weather and surrounding environment, and limited transmission distance, which has been gradually replaced by digital microwave, COFDM, 3G and CDMA.

Second, the principle of digital microwave transmission:

Digital microwave transmission is to encode and compress the video (HD-600 1D), then modulate it through the digital microwave (HD-9500) channel, and then transmit it through the antenna. On the contrary, the antenna receives the signal, performs microwave despreading, decompresses the video, and finally recovers the analog video signal. You can also install the corresponding decoding software through the computer after microwave despreading, and the computer will decompress the video, which is also supported by the computer. The storage server and the disk array are matched for storage; The resolution of this monitoring mode is 720 * 576,352 * 288 or higher, and the video has a delay of about 0.2-0.8 seconds by decoding the storage mode. The price of digital video surveillance varies greatly according to the actual situation, but there are also some incomparable advantages of analog microwave, such as more monitoring points, more complex environment, more situations requiring relay, more centralized monitoring points, better anti-interference ability than analog, and so on. It is suitable for use when there are many monitoring points and relays. Objectively speaking, the initial investment is higher.

Question 6: What are the transmission modes of digital TV?

Terrestrial wireless transmission digital TV (terrestrial digital TV)

Satellite transmission digital TV (satellite digital TV)

Cable transmission digital TV (cable digital TV)

signal transmission

According to the signal transmission mode of digital TV, it can be divided into three types: terrestrial wireless transmission, satellite transmission and wired transmission.

Product category

According to the product types of digital TV, it can be divided into digital TV monitors, digital TV set-top boxes and integrated digital TV receivers.

screen size

According to the display format of digital TV, it can be divided into 4: 3 and 16: 9.

number of scanning lines

According to the number of scanning lines, digital TV can be divided into HDTV scanning lines and SDTV scanning lines.

Clarity/clarity

It can be divided into low definition digital TV, standard definition digital TV and high definition digital TV. The image format of VCD belongs to the level of low definition digital TV, and the image format of DVD belongs to the level of standard definition digital TV.

Radio and television are gradually developing to high definition, and there are more high definition program formats such as 4k.

Question 7: What are the main modes of radio wave propagation? There is only one way for radio waves to spread: in space. Radio wave is an electromagnetic wave with very low frequency (below 3000MHz), which is easily absorbed or reflected by metals to produce shielding. Metals can convert electromagnetic fields with fixed frequency into electric current. Electromagnetic waves with a fixed frequency can be converted into metallic heat (bound electrons absorb electromagnetic waves of a certain energy level to produce transitions and photoelectric effects). Free electrons in metals will also react with the interference of electromagnetic waves, but I have never heard of the possibility that free electrons in metals can propagate electromagnetic waves, because electrons have mass and mutual electromagnetic force. The most troublesome thing is that when a certain range of electromagnetic waves irradiate metal at the same time, electrons will be interfered by these electromagnetic waves and cannot transmit current signals correctly. Because metals are transmitted by analog signals of current and voltage, the analog signals have the principle of time linearity. When the composite electromagnetic wave irradiates the metal, the electronic signal will be disordered and cannot be transmitted correctly. Therefore, free electrons cannot transmit composite electromagnetic waves. Please note that the principle of time linearity is the basis of analog circuit signals.

There is a saying that electrons, like photons, have wave-particle duality. When composite electromagnetic waves are converted from photons to free electrons, electrons will also propagate like electromagnetic waves, such as cathode rays and beta rays. Electrons are like photons. Please note that photons don't interfere with each other at all, so there is such a thing as a laser. Electrons don't have this ability. Electrons have strong electromagnetic repulsion and mass, so they repel each other and cannot form a laser beam. Electrons tend to be evenly distributed in metals. When high-frequency composite oscillating electromagnetic waves are generated, the distribution between electrons will be affected and disorder will occur, and this disorder will be illuminated as electrons, and electrons will not be able to transmit signals correctly, because the particles of electrons are much stronger than photons. If you have done electrical experiments, you know that when metals are stored with a DC power supply voltage of 654.38+ million volts, they will absorb some electrons and emit unknown screams. At this time, the electrons in the metal are in a state of high electromagnetic repulsion, and the electrons are obviously granular. It has been proved that the transmission of electrons in media is particle-like.

At present, it is only known that only transparent media can transmit electromagnetic waves and composite electromagnetic waves. The transparent medium only absorbs a small amount of photon energy of electromagnetic waves, and electromagnetic waves can propagate directly in the transparent medium without converting free electrons. At present, it only uses optical fiber.

According to different frequencies, electromagnetic waves are easily shielded in the infrared region, and even a few meters thick cement wall can shield low-frequency electromagnetic waves with considerable intensity. However, in the ultraviolet region, the penetration ability of electromagnetic waves is greatly increased; X-ray can penetrate muscles, but it will be partially reflected by bones, so it is used by medicine to look at bones; For cosmic gamma rays, most substances are transparent to this kind of gamma rays, and I think most people will understand this wisdom.

Question 8: What are the remote wireless data transmission methods? With what equipment? At present, there are many ways to realize wireless internet access, and these ways have different characteristics. Users can choose according to their actual needs and conditions. At present, two major mobile operators, including China Mobile and China Unicom, have launched corresponding wireless Internet access services. With a small network card, no matter where you are, you can still contact the world through the network.

Mobile computer

This way of surfing the Internet is to use the built-in modem of the mobile phone to connect the mobile phone with the notebook computer through data transmission lines and infrared rays.

It is understood that users only need to buy a mobile phone supporting wireless Internet access (with USB or infrared data association) and connect the matching data cable to the computer to use it. This method is suitable for both notebook computers and desktop computers, and there is no need to repeatedly plug and unplug the mobile phone card when making a phone call. In addition to using mobile phones and data lines, you can also use infrared access to the Internet.

Wireless network card computer

In this way, it is necessary to purchase an additional card-type device (PC card) and plug it directly into the PCMCIA slot or USB interface of a notebook or desktop computer to realize wireless Internet access.

There are several types of wireless network cards at present. One is the integration of machine and card. The number of the network card has been solidified on the PC card, and it can be used directly by inserting it into the PCMCIA slot of the notebook computer. The second is the separation of recording cards. The "mobile phone card" which records the number of the network card can be separated from the card body, and when inserted into the PCMCIA slot, the two can be plugged into the network together; The third type is USB wireless cat (MODEM), that is, it is plugged into the USB interface of desktop or notebook computer through USB connection, and the mobile phone card can also be plugged into the wireless cat.

Wireless local area network WLAN

WLAN is another convenient way to surf the Internet. At present, China Telecom, China Mobile, China Netcom and other operators have laid wireless local area networks in airport hotel, conference centers, exhibition halls and other places frequented by business travelers. Users only need to use computers or PDA with built-in WLAN cards to surf the Internet in places covered by WLAN (commonly known as "hotspots").

It is understood that several ways of wireless Internet access can not only access the Internet normally, but also send and receive short messages.

1. Internet access: As long as there are places covered by mobile operators or LAN signals, you can browse the web, transmit and download data, and send emails through wireless Internet access.

2. Use the wireless network card to surf the Internet: When using the SIM card of China Mobile or UTK card of China Unicom to surf the Internet, it has the function of sending and receiving short messages. For example, you can use your laptop or PDA to send short messages to friends and relatives.

However, in addition to the above short message function, SIM card or UTK card used for wireless Internet access has not yet opened other functions such as voice call, downloading SP (e.g. website) short messages and multimedia short messages. In other words, if you plug the wireless network card directly into the GPRS or CDMA mobile phone, you can only send short messages or use the mobile phone as a modem to connect the laptop to the Internet, but it is inconvenient to use because the mobile phone needs to be charged.

On the other hand, wireless Internet access can also be used for domestic roaming, and roaming in China does not require roaming fees, which means that the fees used in other places are the same as those used locally. However, international roaming is currently impossible.

Question 9: What are the ways for mobile phones and computers to transmit files wirelessly, such as logging in to qq and using a server to transmit files?

There is also wireless routing, which is directly transmitted by software. For example, the es file browser can turn a mobile phone into an ftp server.

This computer has Bluetooth function. Transmit by bluetooth.