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Airborne UAV Helps New Agriculture Development

  2019-06-04

introduce:In the past year or two, the hottest topic in the scientific and technological circles is 5G. What does 5G G mean? Generation is short for Generation in English. It means "generation" in Chinese and "5G" is "5th generation".

In the past year or two, the hottest topic in the scientific and technological circles is 5G. What does 5G G mean? Generation is short for Generation in English. It means "generation" in Chinese and "5G" is "5th generation". Similarly, previous 1G, 2G, 2.5G, 3G, and 4G also indicate the generation.
Mobile communication has a long history from 1G to 5G. The world's first generation of wireless communication system was born in the 1980s, and today it is no more than 30 years. It is a standard post-1980s era.
Before that, there had been cable telephones in the world. But cable phone limited the place of the call, the phone can not move freely, if not sitting next to the phone, you have to walk a long way to call or answer the phone, the lack of that sense of timeliness, very uncomfortable.
I was impressed by the line-up during my college years. only a few telephones are kept in small compartments and there is a queue to make a call. If you're in front of a chat with your girlfriend, you may grind your teeth with hate. The style of painting is as follows: the phone calls are full of love words, all kinds of numbness, everyone can hear; the people waiting behind are all kinds of expressions, envy and contempt.
In the 1990s, Hong Kong movies often saw big bosses or gangster bosses with big bricks, special dragging, Trypan, special style. That's the first generation of wireless telephones. Of course, you can call it the first generation of mobile phones. At that time, "bricks" were valuable. For example, today's top-notch iPhone was also expensive. The average person could not use it. In the 1990s, owning a brick was a dream of many people.
By the way, this brick has a nickname, Big Brother. We are no strangers to its inventor, Motorola.
Cable telephone was born in Bell Laboratory of the United States. The first generation of wireless communication system, as a complementary role of cable telephone, was also born in the United States.
There are two reasons for this: on the one hand, the center of world communication technology was in the United States at that time, other countries did not enter this field at all; on the other hand, technology has inheritance, wireless communication system and wired communication system still have common or similar technology in many aspects, except for the so-called "last mile" of wireless access and wired access. Apart from the differences, other aspects are very close.
At that time, the United States had Lucent and Motorola, and Canada had a Nortel network. Together, the three North American manufacturers of telecommunications equipment established North America's dominance in the world's telecommunications rivers and lakes.
The first generation wireless communication system, like the wired communication system at that time, was based on analog signals.
Analog signals have many shortcomings, such as easy interference, low voice quality, insufficient coverage, and the "crosstalk" problem that many people have encountered when making landline calls, that is, you hear not the voice of the person you are talking to, but the voice on other people's telephone lines.
This has brought new challenges and opportunities to the telecommunications industry. As a result, the second generation communication system appeared, which is the first mobile phone wireless system that we are familiar with and used by many people, the so-called 2G.
The first mobile phones of our generation, whether Nokia, Ericsson or Siemens, are mostly based on GSM. GSM is the abbreviation of Global System for Mobile Communications, a digital mobile communication standard formulated by ETSI.
The focus is on ETSI, the European Telecommunication Organization.
At that time, European communication technology took advantage of this opportunity to rise. At the same time, new players appeared, Ericsson, Nokia, Siemens, not only launched their own mobile terminals, but also launched their own wireless communication system, becoming a new communication equipment supplier. Their emergence broke the situation of North America's dominant rivers and lakes.
GSM has a popular name "cellular mobile phone". The name honeycomb is interesting. It divides all the areas that need to be covered into many small pieces, each of which is approximately hexagonal, and all the small pieces are next to each other like honeycombs.
Seeing this, I have to admire the wisdom and imagination of these scientists.
GSM is based on TDMA, which is abbreviated as Time Division Multiple Access, or Time Division Multiple Access. Simply put, time segments are divided into many smaller segments, each of which is only available to a user at intervals.
For example, in a certain time segment, such as 1 second, divide this second into 8 milliseconds, then it can be divided into 125 small segments: 1-8 milliseconds to A user, 9-16 milliseconds to B user, 17-24 milliseconds to C user... In this way, within each 8 millisecond fragment, the user who owns the fragment ownership is exclusive, and other users can not use it.
The question is, if this is the case, it is equivalent to the user often entering the waiting state. Doesn't it feel that there is a pause? In fact, because of the limited recognition ability of human ears, as long as the time slice is small enough, the ears can not feel the delay.
Although the design of TDMA is exquisite, it is not flawless. The problem is that there are only a limited number of users that a base station can support, such as 992 users at 900MHz.
Unlike Europeans, Americans have taken another route, called CDMA, Code Division.

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