Working principles of wireless networks (I): technologies behind magic

Working principles of wireless networks (I): technologies behind magic

This is the first part of a series of articles about decryption of wireless networks. In this article, analyst Craig Mathias describes in detail the behind-the-scenes technology that forms a modern wireless network.

Even if I have been working in the wireless field for more than 20 years, I am still amazed at this technology. Imagine that we store the information in one location, and then it will appear in another expected location. There is no physical connection between the two points. The magic of wireless networks continues from the first crystal wireless device in my primary school to the GB-level system currently in use.

Of course, there is no magic behind wireless technology-it is still a complex project built on a very basic physical principle. Therefore, in the three articles in this series, I will introduce in detail how wireless networks work. I will try my best to keep it simple so that some non-technical professionals can understand the mysteries of this process.

We start with the most basic concepts. One physical concept we all know is "electromagnetic spectrum ". This is the carrier of electromagnetic waves. It is produced by a relatively simple electronic device "oscillator. The oscillator emits a sine wave (remember this is the content of the high school ry class ?), Then we can adjust the oscillator to generate an electromagnetic wave with a specific frequency and amplitude. Frequency refers to the vibration speed of the electromagnetic wave, while amplitude refers to the intensity of the electromagnetic wave. Both indicators are subject to relevant laws and regulations-for example, in the United States, the Federal Communications Commission is responsible for determining who can use which frequency band of the electromagnetic spectrum (also known as the frequency band ), define their usage and use environment. You may also think that the legal issues involved here may be much more complex than all underlying physical and engineering designs.

Once a sine wave exists, the next task is to encode the information to be transmitted and add it to the electromagnetic wave. This process is called "modulation", and it is realized by changing the physical characteristics of electromagnetic waves. We modify the amplitude (such as AM radio), frequency (such as FM radio), or electromagnetic wave phase, which refers to the position where the frequency spans the 360-degree period at any specified time. We can also modify these variables in combination. For example, orthogonal amplitude modulation is a combination of amplitude and phase modulation, which is often used in satellite communications, modern Wi-Fi systems and some cellular systems, such as LTE. The better the modulation technology, the more data I can load on electromagnetic waves. This will produce some form of data compression, so we can achieve higher performance through the so-called "spectrum efficiency. The last step to send this modulated signal is to enlarge the signal (increase the power) and then send it to the air through the antenna. Later in this series of articles, we will introduce the antenna, the most important part of radio.

The working principle of the wireless network depends on other factors.

Radio is not just about sine wave and electromagnetic spectrum. After the signal is sent, the core problem is the so-called "wireless channel", which is known to transmit electromagnetic waves from one point to another. This is the most complex step. First, the power of the wireless wave quickly degrades along the distance ("flat attenuation")-which means that even high-power signals quickly weaken. Therefore, if the signal can reach and has enough power to be detected, the receiver at the other end must be sensitive enough to detect the signal. If the signal is too weak, it will become like noise. The goal is to improve the signal-to-noise ratio.

Next, the wireless wave may also be solid ("shadow attenuation"), ECHO and reflection of the main signal ("multi-path attenuation" or "Leili attenuation ") or intentionally interfering ("blocking", rarely occurring in non-military environments) or unintentional interfering and blocking. Wi-Fi and other systems running in the shared unauthorized band must use various technologies to avoid interference with other parallel (and legal) signals running in the same unauthorized band. Moreover, these systems must avoid interference with more important signals specified by the management department. The most common method to avoid interference here is to use various forms of spread spectrum radio, which will distribute the signal to a large number of different frequency bands, so as to improve the reliability at the expense of spectrum efficiency.

The best technology has not yet appeared

However, if the signal successfully reaches the expected receiver (according to statistics, wireless networks can do this in most applications ), then these amplified signals are demodulated and converted back to the original format. Currently, most wireless communication uses the numerical method, which means that we only send 1 and 0, so we may improve the reliability and performance in various forms, this process is also relatively simple. So far, we have at least explained why modern wireless systems can achieve high performance at a low price. For example, the current 802.11ac Wireless LAN product supports 1.3 Gbps Throughput, this seems to be very large, but there may be higher-speed products in the future. All of this is thanks to our ability to design and develop reliable and low-cost digital wireless systems based on some simple physical principles.