Chapter 783 The era of wireless communication has arrived
The essence of CDAM technology is a communication technology that breaks up the spectrum of the transmitted signal to a wider bandwidth than its original bandwidth. It is often used in the field of wireless communications.
What are the benefits of this technology? First, it is immune to background noise, interference and self-multipath interference; second, it has good resistance to man-made deliberate interference signals. This is also the earliest application of spread spectrum in military communication systems.
One of the important reasons for resisting human interference is that with better confidentiality, the possibility of interception of the communication process is lower. This is because after the spectrum is spread, the power value per unit frequency is reduced, making it difficult for interceptors
Obtain enemy communication information through a spectrum analyzer; even if the radio wave is received, since the interceptor does not know the connotation of the spread spectrum code, he cannot reply to the encoded information, so spread spectrum communication also has simple secure communication capabilities
; In addition, the ability to reduce electromagnetic interference is also very powerful; in addition, through spread spectrum technology, decoding multiplexing communication can be achieved, allowing multiple users to independently use better communication quality at the same time.
Of course, the most rudimentary spread spectrum technology will have no effect on future applications, but based on this technology, 1G technology, 2G technology, and 3G technology will be developed.
What does G mean? In fact, it is a kind of data capacity. For example, when we speak, how many words can you hear in one minute? The number of these words converted into signals is measured by G. 1G technology can already use wireless communication to
You can make voice calls. In fact, the United States already has the prototype of this technology. It is an analog wireless phone. People can hold this phone and talk while walking. This technology is almost mature!"
"ah!"
Ren Weitian was dumbfounded. He had studied communications and understood many of the words mentioned by Liu Lang, but when combined, he was confused. It wasn't that he couldn't understand at all, but he felt that the technology mentioned by the other party was straight out of science fiction novels.
Only then will you have it.
"Old Ren, do you think it's amazing? It's a bit unbelievable, but I think 1G mobile phones have already appeared on Hong Kong Island. If you are in Shenzhen, you should be able to get it. Maybe you can see what I mentioned this year.
Mobile wireless communication phone!”
Liu Lang is not talking nonsense. 1G mobile phones are commonly called "Big Brother" in China. Why is it called "Big Brother"? There is a legend that this is how the underworld boss is called in the Guangdong Province of Hong Kong Island.
In the underworld, the underworld boss is usually called Big Brother, while the leader is naturally called Big Brother. Only these big brothers can afford such mobile phones.
In Hong Kong in the 1980s, you could often see a group of "horse boys" shouting and hugging a fierce man with dragons and phoenixes painted on his body. This man held a mobile phone and shouted loudly: "Find me two hundred more people."
Come on, I'm going to kill him...!"
It is precisely because of the use of these bosses that the Hong Kong media simply refers to mobile phones as "Big Brother".
Regardless of whether this source is true or not, the message carried by the three words "Big Brother" is clear. In that era, it was a symbol of identity, status and wealth. Not long ago, it was believed that "upstairs, downstairs, lights and telephones"
Even for communist Chinese people, the shock it brings is inevitable, not only because of its expensiveness, but also because of the magic of high technology it displays.
"Big Brother" was first invented by the American giant Motorola. He remembered that in 1988, Guangdong Province took the lead in building a 900MHz analog mobile phone in order to integrate mobile communications with Hong Kong and Macao. Motorola also set up an office in Beijing.
, promoting mobile phones. This heavyweight mobile phone is thick and bulky, shaped like a black brick, and weighs more than one kilogram.
It has no other function except making calls, and the call quality is not clear and stable enough, and it often shouts. Its large battery can only last for 30 minutes of calls after being charged. Even so, mobile phones are still in very short supply, and it is hard to find one if you have money.
At that time, the public price of a mobile phone was around 20,000 yuan, but it usually cost 25,000 yuan to buy it. The black market price was once as high as 50,000 yuan. This not only made it prohibitive for ordinary people, but even small and medium-sized enterprises could not afford it.
many.
Analog signal mobile phones such as "Big Brother" are high-tech products and luxury accessories in this era. They were introduced to the country through cooperation between telecommunications companies in Guangdong Province and Hong Kong Island. They are expected to appear on the market in the middle of this year.
, it’s not surprising that Ren Weitian didn’t know about this.
But Liu Lang's reminder still moved Ren Weitian's heart, and he felt that this matter deserved attention.
"Old Ren, soon you will see the wireless phones I am talking about in Guangdong Province. This is the general trend of the development of the communications industry. It will "dominate" the entire human race in the future. This involves a lot of professional knowledge.
, I can talk to you about, first of all, wireless spectrum technology.
All radio services are inseparable from radio frequencies, I believe you also understand, Mr. Ren.
This is just like vehicles that must drive on the road. Radio frequency is an electromagnetic wave that exists in nature. It is a substance and an invisible and intangible natural resource that is equally available to all countries. Yes, it is a resource.
, and it is a very precious resource, you must not underestimate it.
Why is it so valuable? Because it has six characteristics:
First, it is limited. Due to the propagation characteristics of radio waves at higher frequencies, radio services cannot use higher frequency bands indefinitely. At present, humans cannot develop and utilize frequencies above 3,000 GHz. Although
The use of radio spectrum can reuse frequencies according to four methods: time, space, frequency and coding. However, in terms of a certain frequency band and frequency, the frequency of use is limited in a certain area, at a certain time and under certain conditions.
Second, it is exclusive. Radio spectrum resources share a common attribute with other resources, namely exclusivity. Within a certain time, region and frequency domain, once used, other equipment cannot be used again.
Third, it is reusable. Although the radio spectrum is exclusive, under certain time, region, frequency domain and coding conditions, radio frequencies can be reused and utilized, that is, different radio services and equipment can be frequency reused.
and shared.
Fourth, it is non-exhaustible. Radio spectrum resources are different from minerals, forests and other resources. They can be used by humans, but they will not be consumed. Not using it is a waste, and improper use is even more of a waste.
, and even cause harm due to interference caused by improper use.
Fifth, it has inherent propagation characteristics. Radio waves propagate according to certain rules, are not restricted by administrative regions, and are borderless.
Sixth, it is easy to pollute. If the radio frequency is used improperly, it will be interfered by other radio stations, natural noise and man-made noise and cannot work normally, or it may interfere with other radio stations, making them unable to work properly and making it impossible to operate normally.
Deliver information accurately, efficiently and promptly.”
"ah………!"
Ren Weitian was dumbfounded. What did Liu Lang study? How did he know so much about radio? He was a college student specializing in radio, but he didn't know much about this knowledge.
"These are just basic concepts. I want to focus on the technology of CDMA. Lao Ren, you have to listen carefully.