Overview of Analog System Pitfalls in Digital Systems Processing

I believe many people have heard of digital circuits, but do you know some of its shortcomings? In the 21st century, the Internet is developing rapidly. It is a competition for spectrum efficiency, and it is also a competition between different systems at the same level. Since the development standards of 2G mainly differ in the air interface, these systems need to be optimized to solve the shortcomings of the analog system. Taking the GSM standard as an example, the system will explain how the 2G digital system solves the problems of the analog system, and compare the advantages and disadvantages between the two.

First of all, we need to know what are the shortcomings of the analog system? The main shortcomings of the analog system include many and inconsistent standards, security issues, roaming issues, low spectrum efficiency and less spectrum, and insufficient service quality.

On the issue of standards, European communications authorities should first realize the importance of standardization and make steady progress through earlier standardization organizations and collaborations. From the beginning of determining the development of the second-generation system, to organizing various companies to set up permanent technical groups to discuss and formulate technical specifications, to convincing European countries such as Britain, France, Germany, and Italy to agree and support the GSM standard.

After winning the support of the motherland and operators, equipment manufacturers' investment in standards and investment in system equipment development will be better and safer. After passing a technical agreement, those working on standards continued to conduct research, while the main force of equipment vendors immediately invested in the development of system equipment. After commercialization in an advanced office, they immediately promoted the standard globally. In order to promote it, GSM The French name (Groupe Spécial Mobile committee) was changed to the English name (Global Standard for Mobile Communications). The abbreviation remains unchanged, but the meaning changes, which is conducive to the promotion of the standard around the world.

There are two security issues with the analog system. First, the system is easily eavesdropped because the air interface transmits analog signals, which are continuous and unencrypted. Therefore, as long as you have specific tools, you can scan continuously in the same way as tuning a radio. The frequency determines that a certain channel is the channel of the call being monitored, and can be monitored silently.

After digitization, the air interface sends digital signals. If you want to monitor, the monitoring tools must be much more complicated, because different layers of protocols need to be decoded layer by layer to get the corresponding voice-encoded data packets. This is from a technical complexity perspective. . Another mechanism is that the coding of GSM itself is more complicated than the frequency system itself. For example, GSM has frequency hopping technology, which means that a user's voice is sent at different frequencies at different times (the technology itself is to improve frequency efficiency), objectively This increases the difficulty of tracking wireless air interface signals.

And more importantly, the GSM air interface is encrypted. The mobile phone uses an encryption algorithm to encrypt the signal before sending it, and then decrypts it after the network receives it. This encryption algorithm is still very good. It was not until 2008 that hackers cracked the algorithm, but due to Due to computing power, it is impossible to put it into practice to decipher a user's voice. . Foreign GSM air interfaces are generally encrypted, but China's air interfaces are not encrypted. The reason is unknown.

Analog systems cannot implement roaming in early or standard protocols, that is, mobile phones in one city cannot be used in another city. Later, manual roaming was implemented in some cities through transformation. A temporary number was obtained through manual registration, and the mobile phone could be used in the roaming area. Later, automatic roaming was introduced, and the mobile phone could be used across regions without changing numbers.

Because the GSM system uses high-quality modems, channel coding, interleaving, frequency hopping and other technical means to improve spectrum efficiency, and adopts a closer frequency reuse method, the GSM system has great advantages over the original analog system. improve. In addition, the use of smaller cells, hierarchical networks, etc. can also better improve the capacity of the system. The overall capacity of GSM is 3-5 times that of the original analog system. Because this involves more technology and details, I will just briefly mention it here. As long as you know that the spectrum efficiency of GSM is much higher, the capacity will be much larger.

Through digital coding technology, many error correction measures are added during the coding process, so that partial signal loss can be restored, and it also ensures that as long as the signal quality is above a certain threshold, the voice quality can reach a certain level. The analog system transmits analog signals, and any signal loss will affect the voice quality.

Therefore, from the perspective of system design, GSM has basically solved the shortcomings in the analog system, and can be deployed quickly to develop a large number of mobile users. Of course, the improvement of spectrum efficiency and capacity is a necessary condition for mobile systems. Therefore, in the subsequent evolution from 2G to 3G and 4G, new standards and new technologies have further improved spectrum efficiency. The above is the method for digital systems to deal with the defects of analog systems. The editor's ability is limited and I hope more people can participate in the discussion.