The essence of this technology is to disperse the spectrum of transmitted signals to a wider bandwidth than its original bandwidth, and it is often used in the field of wireless communication.

What are the advantages of this technology? First, it is immune to background noise, interference, and self-multipath interference; second, it has a good ability to resist man-made deliberate interference signals, which is also one of the important reasons why the spread spectrum was first applied to the military communication system to resist man-made interference; the relatively good secrecy makes it less likely that the communication process will be intercepted. This is because after the spectrum is spread, the power value per unit frequency is reduced, and the interceptor is not easy to obtain the information of the enemy's communication through the spectrum analyzer; even if the radio wave is received, because the interceptor does not know the connotation of the spectrum code, so it cannot reply to the coded information, so the spectrum distribution communication also has a simple confidential communication capability; and the ability to reduce electromagnetic interference is also very powerful; in addition, through the spectrum distribution technology, the code distribution multiplexing communication can be achieved, so that multiple users can use better communication quality at the same time independently.

Of course, the most basic spread spectrum technology will not play a role in future applications, but on the basis of this technology, 1G technology, 2G technology, and 3G technology will be developed.

What does this kind of G mean? In fact, it is a kind of data capacity, for example, when we speak, how many words can you hear in a minute, and the number of these words converted into signals is measured by G, and 1G technology can already make voice calls through wireless communication, in fact, the United States now has the prototype of this technology, which is an analog wireless telephone, and people are talking while walking with this kind of phone, and this technology is close to maturity!

"Ahh

Ren Weitian was dumbfounded, he had studied communication, and he understood many of the words mentioned by Liu Lang, but he was confused when it was combined, not that he didn't understand it at all, but that he felt that the technology in the other party's mouth was simply something that could only be possessed in science fiction.

"Lao Ren, don't you think it's amazing, it's a little incredible, but I think there are already 1G mobile phones on Hong Kong Island now, you should be able to get in touch with them in Shenzhen, maybe you can see the mobile wireless communication phone I mentioned this year!"

Liu Lang is not talking nonsense, 1G mobile phones are commonly known as "big brother" in China, why is it called "big brother"? There is a legend that this is how the boss of the underworld is called in the area of Guangdong Province on Hong Kong Island.

The underworld generally calls the small boss "Big Brother", and the leader is called "Big Brother", and only these big brothers can afford this kind of mobile phone.

On Hong Kong Island in the 80s, it was common to see a group of "horse boys" hugging a murderer with a dragon and phoenix on his body, and this person held a mobile phone and shouted: "Find me another 200 people, I will kill him .........!"

It is precisely because of the use of these bosses that the Hong Kong Island media simply use "big brother" to refer to mobile phones.

Whether this source is true or not, the message carried by the word "big brother" is clear, it was a symbol of status, status and wealth in those days, and for the people who not so long ago thought that "upstairs and downstairs, electric lights and telephones" were communism, it brought shock, not only because of its expensiveness, but also because of the magic of the high technology it displayed.

"Big Brother" was first invented by the American enterprise giant Motorola, and he remembers that in 88 years, Guangdong Province took the lead in building a 900MHz analog mobile phone in order to achieve mobile communication integration with Hong Kong and Macao, and Motorola also set up an office in Beijing to promote mobile phones. This heavyweight mobile phone is thick and bulky, shaped like a black brick, and weighs more than a pound.

It has no other functions except for making calls, and the call quality is not clear and stable enough, so it often has to be shouted. One of its large batteries can only last 30 minutes of calls when charged. Despite this, Big Brother is still very in-demand and money is hard to find. At that time, the public price of Big Brother was about 20,000 yuan, but it usually cost 25,000 yuan to buy it, and the black market price was as high as 50,000 yuan. This is not only prohibitive for the general public, but also small and medium-sized enterprises can not afford it.

"Big Brother" this kind of analog signal mobile phone in this era is a proper high-tech products and luxury jewelry, is Guangdong Province and Hong Kong Island telecommunications companies to introduce to the country, is expected to appear in the middle of this year on the market, Ren Weitian does not know this matter is not surprising.

But Liu Lang's reminder still made Ren Weitian's heart move, and he felt that this matter was worth paying attention to.

"Lao Ren, soon you will see the wireless telephone I said in Guangdong Province, this is the general trend of the development of the communications industry, in the future will "dominate" the entire human race, which involves a lot of professional knowledge, I can talk to you, first of all, wireless spectrum technology.

All radio services are inseparable from radio frequencies, and I believe you also understand that.

It's like a vehicle has to drive on the road, radio frequency is a kind of electromagnetic wave that exists in nature, it is a substance, it is an invisible and intangible natural resource that can be obtained equally by all countries, yes, it is a resource, and it is a very valuable resource, you must not underestimate it.

Why it's valuable is because it has six properties:

First, it is limited, due to the propagation characteristics of radio waves on higher frequencies, the radio service can not use the radio frequency of the higher frequency band indefinitely, at present human beings can not develop and utilize the frequency above 3,000 GHz, although the use of radio spectrum can be multiplexed in four ways: time, space, frequency and coding, but in terms of a certain frequency band and frequency, the use of frequencies in a certain area, a certain time and a certain condition is limited.

Second, it has exclusivity, and radio spectrum resources have the same attribute as other resources, that is, exclusivity, in a certain time, region and frequency domain, once used, other equipment can no longer be used.

Third, it has multiplexability, although the radio spectrum is exclusive, but 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-exhausting. Radio spectrum resources are different from minerals, forests and other resources, it can be used by human beings, but will not be consumed, not using it is a waste, improper use is a waste, and even due to improper use of interference and cause harm.

Fifth, it has inherent propagation properties. Radio waves propagate according to certain laws, are not limited by administrative territory, and have no borders.

Sixth, it is contaminating, and if radio frequencies are used incorrectly, they will not work properly due to interference from other radio stations, natural noise and man-made noise, or interfere with other radio stations so that they cannot work properly and cannot transmit information accurately, effectively and quickly. ”

"Ah.........h

Ren Weitian was dumbfounded, what exactly 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 it.

"These are just basic concepts, and I'm going to focus on the CDMA technology, old man, you have to listen up.