One of the important indicators of wireless signal-to-noise ratio

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This is a story about communication, holding the phone you please do not take this article too seriously as a dull academic article, this can only be regarded as a child of communication born a new understanding of life, do not need too high reading threshold, only hope that the screen you can through this little story to the world have a new understanding.

Before contacting the communication theory, I was puzzled by a lot of questions. I do not understand why some taoxin Potter lung communication finally produced a misunderstanding, and do not understand why there are some strange people want to get their hair out of the rules or laws, but also do not understand why some of the surface reasonable plan finally ended up flawed. Until a few years ago, when I was writing a note on the blackboard, a word that was so familiar to me suddenly flashed in my head, and answered a lot of questions once--the word is called the Snr.

signal-to-noise ratio ( Signal-to-noise ratio), referred to as SNR, these three words often appear in various articles, literature, product brochures, but it is not a simple communication professional terminology, but a ubiquitous measure of Libra. It can measure a person's life state, the work state, can measure the affection between the lover, the Friend exchange efficiency, also can measure a community or a system's running state.

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Without talking about formulas and rules, let's look at a little game in the art section. The rules of the game are simple, a few people lined up, the last one to draw a picture according to the words obtained, and then the previous person to look at the picture and then draw a new picture, the process has been passing forward. In the end, the first person guesses the initial word according to the last picture, and the whole process cannot talk. So what kind of jokes will the game end up with?

The first person to get the question is: Tiger. Although painters is not good, but he also basically painted a beast of the shape

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However, after the three human brain cavities opened, the following three images were drawn:

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The last person to see the fourth painting a blank face, can only randomly guess the answer that they do not believe--rabbit.

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This game actually contains a large part of the communication process, the tiger is information, the picture is coded, the figure is decoded . And the final message of the error message is because the code is mixed with artificial noise.

Information and noise are two important concepts that are not engraved in our lives today. Every word we say, each action and expression is a message, and the noise that interferes with the real message is. The Snr is the ratio of the signal energy to the noise energy we need. (should actually be the ratio of power) and this game actually validates a cascade formula for a noise figure: the closer to the front stage in a communication system, the greater the impact on the final transmission quality , which we'll talk about later.

All communication technologies, in fact, have only one purpose-to improve the signal-to-noise ratio. For the communicator, the biggest enemy is noise. The first task for communication engineers is to find a space and ensure that the space is as small as possible by noise. This space can be an actual physical space, or it can be a frequency space, or a probability space, or other mathematical space. But first, let's look at how the noise affects the signal transmission.

in a space without noise, theoretically I could transmit all the information in the universe instantaneously. For example, I have a movie, movie size 3Gb, we put this billions of binary bytes into decimal, and then put this number in front of the decimal point into a decimal, such as 0.12345 ..., and then I send you a DC signal , strength is 0.12345 ... Volts, then you receive a signal and then convert the length of time into binary, then you get all the information about the movie. In practice, however, there may be a random noise that increases the intensity of the electrical signal by 0.001-0.002 volts. This makes the third digit after the decimal point completely random and unusable, to ensure that the correct number is only the first two digits, not to mention a movie, even a Chinese character can not be sent.

Remember when you talked about cows in high school, the teacher would always give examples: if a small car on a plank without resistance, then its speed will never change. Communication, noise is resistance. If there is a world without noise, we will no longer have to complain about the bad signal of the cell phone, the speed of the home is too slow, space scientists can control any spacecraft without difficulty. However, the reality is brutal, noise is everywhere, we have to maximize the signal to send the energy to ensure a higher quality of communication. Simply to improve the signal-to-noise ratio of the communication. For example, if we increase the signal strength by ten times, it becomes 1.2345 ... Volts, then we have one more digit that can be used for transmission.

Noise is a helpless place from its randomness, if it is a definite additional interference, then we just have to measure and subtract in the original signal is good, but the noise is not deterministic, and the randomness is also reflected in the spatial and temporal, so in the measurement of noise power We can only use a probability distribution of the variance. Fortunately in practice, this randomness is not uniform, for example, in this space a bit stronger, other space is weaker, at this frequency stronger, at other frequencies weaker. There is a sentence in the Ming Dynasty: You can cheat some people for a lifetime, you can cheat everyone for a period of time, but you can't cheat everyone all the time. Because the random is not uniform, let us have the opportunity to challenge the noise. There must be a space. It has a 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 in the previous article. What kind of space can be used to minimize noise interference ? first of all, the most common physical space, through the laying of optical fiber or cable, we can let electrical signals in a protected environment transmission, but the cost is too high and can not do the mobile transmission.

Then the frequency space, communication in the choice of frequency channel more inclined to choose the lower interference channel, is the atmosphere of the electromagnetic wave absorption degree of frequency diagram:

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Then there is the probability space, if we know enough about the random distribution of noise, then we can make the noise accumulate in time by more than zero through the long time multiple transmission. or select a range of values with lower noise probability distributions for transmission. In a way, the Code division multiplexing technology is one of them.

As for the other more mathematical space is difficult to generalize in general language, in a word, communication engineers are always looking for a more pure, signal-to-noise ratio can be higher space for the transmission of signals. Finally, the communication technology means is the result of the compromise of funds, communication environment, project requirement and so on.

Now let's expand our thinking to see what we have in real life that is closely related to the SNR in addition to the direction of communication.

Looking back at the original game, information is constantly blurred, distorted, and even misinterpreted in the passing of the message. The Noise series Cascade formula tells us that the signal-to-noise ratio decreases each time, and the signal-to-noise ratio is related to the previous level in the process of transmitting information. For the management of an enterprise, it is actually a process of the information passing through gradually. Suppose you are a manager of a business, you will often find that the management of the inadequacy of the tasks and indicators you issued in the end often can not be accurately executed on time, and in the process of implementation of the coordination between the Department is always unsatisfactory. The most important reason here is that the message you send down will be a certain understanding error every time, and the larger the size of the enterprise, the more the level of the Department, your management intent will be more wrong interpretation. So the bigger the enterprise, the more cumbersome and strict the regulations are, because the rules and regulations are the effective means to rectify the deviation of information transmission.

In communication, there is an error correction method called calibration, which is simply to use additional information to verify the accuracy of the original information. For example, the simplest parity method: send an extra number that indicates whether the original information has an odd number of zeros or even a few zeros. The more information sent, the more accurate the verification of the original information, but also makes the data that needs to be sent longer and less efficient. The ratio of the checksum information to the total information is called redundancy, and of course in other areas, redundancy can also indicate the ability of the system to continue to complete the task in the partial error.

Therefore, not more checks will achieve better execution, too much redundancy will add additional cost to the system, such as the clock-in system, the administrative costs are distributed to all employees.

Even for a small business, the law is more complicated for the country. It must ensure that a millions number of readers can be interpreted the same way in the face of the law, so the legal provisions we see are often obscure, precisely because it is necessary to ensure the accuracy of information transmission and the self-consistency of each other as much as possible.

in interpersonal communication, a lot of misunderstanding, suspicion and even the emergence of disputes is due to the inaccuracy of information expression. Human language is a low-efficiency and low-tolerance mode of transmission, propagating at a rate of 1-10 bits per second . A second picture flashed in front of the eye, which may take a few minutes to describe a probable. Want to let people have some regrets, even if a person from the beginning of learning to talk about the moment to keep the feelings of the heart, to his death, can only speak up to 25Gb of information, which is not even as large as a USB drive. Man's loneliness may have been written into the gene in the beginning.

But isn't it that the more accurate a message is, the better? is the signal-to-noise ratio as high as possible?

Sometimes, sometimes, in communication between people, a vague message tends to get better results than accurate information. For example, vague diplomatic rhetoric, the first feeling of giving people is nonsense, but it contains a large philosophy.

A classic joke, for example: "My country's commitment not to use nuclear weapons first" can also be humorously understood as our commitment to use conventional weapons before using them.

Or a person's advice, straightforward point out that the other side of the problem may hurt each other's self-esteem, and play an counterproductive role. But the vague careless talk can make a person to reflect oneself.

The reason is because in some cases, the "Do not Express" the act itself can also convey a great amount of information, and we hope that through a vague stance to minimize the message to the other side to protect themselves. Imagine when someone questioned you: "Are you lying?" "If you choose to be silent, how will the other person understand?"

Many said a lot, this article is my years of consolidation of some fine points of view of the integration, sometimes think will feel lucky, if not contact with the communication theory, I may not use such eyes to examine their own life of the world. It is not necessarily true that a person will eventually want an explanation, but at least it needs to be self-consistent.

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One of the important indicators of wireless signal-to-noise ratio