Shulou(Shulou.com)06/01 Report--

This is a story about communication. If you are holding your mobile phone, please don't take this article too seriously as a boring academic article. This can only be regarded as a new understanding of life for a child from a communication background. You don't need a high reading threshold. I just hope that you can have a new understanding of the world through this short story.

Before I came into contact with communication theory, many questions puzzled me for a time. I don't understand why some heart-to-heart communication ends up misunderstood, and I don't understand why there are strange rules or laws that make people want to pull out their hair. I don't know why some seemingly reasonable plans end up full of loopholes. Until one day a few years ago, when I was taking notes against the blackboard, a word that I was no longer familiar with suddenly flashed in my head and answered a lot of old questions-the word is called signal-to-noise ratio.

Signal-to-noise ratio (Signal-to-noise ratio), referred to as SNR, these three words often appear in a variety of articles, literature, product specifications, but it is not a simple communication professional term, but a ubiquitous measurement. It can measure the state of a person's life and work, the efficiency of emotional communication between lovers and friends, and the running state of a community or a system.

Leaving aside the formulas and rules, let's take a look at Mini Game on a variety show. The rules of the game are very simple. Several people stand in line, and the last one draws a picture according to the words, and then the previous person looks at the picture and draws a new one. The process goes on and on. In the end, the front person guessed the first word according to the last picture, and the whole process could not talk. So what kind of jokes will come out of such a game?

The first person to get the problem is: Tiger. Although the painter was not good, he basically drew the shape of a wild animal.

However, the thinking of the next three people was so inspired that they drew the following three pictures:

When the last one saw the fourth picture, he was at a loss and could only guess an answer he didn't believe-the rabbit.

This game actually contains most of the content of a communication process. The tiger is the information, the picture is the coding, and the picture recognition is decoding. In the end, the wrong message is conveyed because the coding is mixed with artificial noise.

The two important concepts of information and noise appear in our lives all the time. Every word we say, every action and expression is information, and what interferes with the real information is noise. Signal-to-noise ratio is the ratio of signal energy to noise energy we need. (it should be the ratio of power), and this game actually verifies a cascade formula of noise figure: in a communication system, the closer to the previous stage, the greater the impact on the final transmission quality, which we will discuss later.

In fact, all communication technologies have only one purpose-to improve the signal-to-noise ratio. For communicators, the greatest enemy is noise. The first task for communications engineers is to find a space and make sure that it is affected as little as possible by noise. This space can be an actual physical space, or a frequency space, or a probability space, or other mathematical space. But first, let's take a look at how noise affects signal transmission.

In a noise-free space, I can theoretically transmit all the information in the universe in an instant. For example, I have a movie, movie size 3Gb, we change these 3 billion binary bytes into decimal, and then the number preceded by the decimal point into a decimal, such as 0.12345. Then I send you a DC signal with a strength of 0.12345. Fu, then you receive the signal and convert the length of time to binary, then you get all the information about the movie. But in practice, there may be a random noise, which makes the electrical signal strength increase randomly by 0.001-0.002 volts. This makes the number of the third place after the decimal point completely random and unavailable, ensuring that the correct number is only the first two digits, not to mention a movie, not even to send a Chinese character.

I remember when talking about the uniformity of cattle in middle school, the teacher always gave an example: if a car glides on a plank with no resistance, its speed will never change. In addition to communication, noise is resistance. If there is a world without noise, we no longer need to complain about the bad signal of our mobile phones, the Internet speed at home is too slow, and space scientists can control any spacecraft without difficulty. However, the reality is cruel, and noise is everywhere, so we have to increase the energy of the signal as much as possible to ensure higher communication quality. To put it simply, improve the signal-to-noise ratio of communication. For example, in the example just now, if we increase the signal strength tenfold to 1.2345. V, then we have one more digit to use for transmission.

The helplessness of noise comes from its randomness, if it is a definite additional interference, then we just need to measure and subtract from the original signal, but the noise is not deterministic, and randomness is reflected in both space and time, so we can only use a variance of probability distribution to measure noise power. Fortunately, in practice, this randomness is not uniform, for example, stronger in this space, weaker in other spaces, stronger in this frequency, weaker in other frequencies. There is a saying in those things in the Ming Dynasty: you can deceive some people for a lifetime, or you can deceive everyone for a period of time, but you can't deceive everyone all the time. Because random can not be uniform, let us have the opportunity to challenge the noise. There must be a space that will have weaker interference with the communication conditions we need, and that's what we're looking for.

Now let's take a look at the space mentioned earlier. Which spaces can be used to reduce the interference of noise as much as possible? Let's start with the most common physical space, by laying optical fiber or cable, we can allow electrical signals to be transmitted in a protected environment, but the cost is too high to achieve mobile transmission.

Then there is the frequency space. Communications tend to choose channels with lower interference in the selection of frequency channels. The following figure shows the frequency map of the absorption of electromagnetic waves by the atmosphere.

It can be seen that in the left low frequency region, the interference of the atmosphere to the electromagnetic wave is much lower than that of the high frequency, so we reserve more of the frequency space on the left for long-distance wireless communication. In the middle of the 60GHz, there is an obvious peak, so we leave it to the indoor short-distance communication, which is the frequency band used by the Wifi communication 802.11ad protocol.

Then there is the probability space. if we know enough about the random distribution of noise, then we can make the time accumulation of noise close to zero through multiple transmissions over a long time. Or select those numerical regions with lower noise probability distribution for transmission. To some extent, code division multiplexing technology is also one of them.

As for other more mathematical spaces, it is difficult to generalize in general language, in a word, communication engineers are always looking for a purer space with a higher signal-to-noise ratio for signal transmission. The final communication technology means is the result of the compromise of many factors, such as funds, communication environment, project requirements and so on.

Now let's expand our thinking a little bit to see what we have in real life is closely related to the signal-to-noise ratio in addition to the direction of communication.

Looking back at the original game, the message was blurred, distorted and even misinterpreted over and over again. The noise figure cascade formula tells us that in the process of information transmission step by step, the signal-to-noise ratio of each stage will be reduced, and the signal-to-noise ratio of each stage is related to the previous stages. For the management of an enterprise, it is actually a process of information transmission step by step. If you are a manager of an enterprise, you will often find that the management is inadequate, the tasks and indicators you have issued can not be carried out accurately and punctually, and the coordination between departments in the process of implementation is always unsatisfactory. The core reason for this is that there will be certain understanding errors every time your downward message is transmitted, and the larger the size of the enterprise and the more levels of departments, the more misinterpreted your management intentions will be. Therefore, the larger the enterprise, the more tedious and strict his management regulations will be, because the rules and regulations are an effective means to correct the deviation of information transmission.

In communication, there is an error correction method called check, which simply uses additional information to verify the accuracy of the original information. For example, the simplest parity method: send an extra number that indicates whether there are odd zeros or even zeros in the original message. The more additional information is sent, the more accurate the check of the original information is, but it also makes the data that needs to be sent longer and the data transmission efficiency less. The proportion of check information to all information is called redundancy. Of course, in other areas, redundancy can also indicate the ability of the system to continue to complete the task in the event of a partial error.

Therefore, it is not that more verification will achieve better execution ability, and too much redundancy will add additional costs to the system, such as the clock-in system, which apportions the administrative costs to all employees.

Even if this is the case for a small business, for the country, the formulation of laws is more complicated. It must ensure that a million readers can get the same interpretation in the face of the law, so the legal provisions we see are often obscure, precisely because it must ensure the accuracy of information transmission and self-consistency as much as possible.

In interpersonal communication, the birth of many misunderstandings, suspicions and even disputes stems from the inaccuracy of information expression. Human language is a very inefficient and fault-tolerant mode of transmission, with a transmission speed of about 1-10 bits per second. It may take a few minutes to describe a picture that flashes in front of me for a second. It's a pity that even if a person keeps expressing his inner feelings from the beginning of learning to speak, to his death, he can only say the information of 25Gb at most, which is not even as big as a flash drive. Human loneliness may have been written into the genes in the first place.

But doesn't it mean that the more accurate an information is, the better? Is it true that the higher the SNR, the better?

Sometimes not, sometimes in the communication between people, a vague information can often get better results than accurate information. For example, vague diplomatic language gives people the first impression of nonsense, but it contains a big philosophy.

For example, a classic joke: "my country is committed not to be the first to use nuclear weapons" can also be humorously interpreted as our commitment to use conventional weapons before using nuclear weapons.

Or a person's advice, directly pointing out that the other person's problems may hurt the other person's self-esteem, and counterproductive. On the contrary, vague and unintentional talk can instruct a person to reflect on himself.

The reason is that under certain circumstances, the act of "not taking a stand" can also convey a lot of information, and we hope to protect ourselves by minimizing the information conveyed to each other through a vague statement. Imagine when someone asks you, "did you lie?" If you choose to be silent, how will the other person understand it?

I have talked a lot about this article, and this article is a combination of some detailed ideas that I have sorted out over the years. Sometimes I feel glad that if I had not been exposed to communication theory, I might not have looked at the world I live in with such eyes. People will eventually want an explanation, which may not be correct, but at least it needs to be self-consistent.

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