Radio - the world thus broadcasts next to each other

When it comes to radio, many people may think that this is a very old concept. In fact, radio occupies a very important position in our lives. At present, radio has already become the most widespread mass medium. According to the Ministry of Industry and Information Technology, 95% of the world's population can receive radio signals. In our lives, radios are everywhere. The use of mobile phones, Wi-Fi connections, and intangible radios bring a lot of convenience to people's daily lives. However, due to the complexity of radio technology, the public still does not know much about radio knowledge. Let us walk into the world of radio together today.

The birth of radio

The theoretical basis of radio comes from the British physicist Maxwell's theory of electromagnetic fields. German physicist Hertz first discovered the existence of electromagnetic waves through experiments in 1887. All objects in the world emit electromagnetic waves. For example, light is the electromagnetic waves emitted by the sun. The infrared rays released by the human body and small animals are also electromagnetic waves. Although this electromagnetic wave cannot be observed by the human eye, snakes have this ability and rely on their keen and unique perception ability to capture prey at night. These electromagnetic waves propagating in free space are the radios mentioned in physics. This radio exists not only in the air but also in the vacuum, and the technology that people transmit signals through radio waves is radio technology.

Italian inventor Marconi is known as the "father of radio communication" because he was inspired by the Hertz experiment and began to experiment with radio transmission, and in 1894 he achieved a transmission distance of several meters. The truly iconic event occurred on December 12, 1901, on this day, after many experiments and long explorations, Marconi completed the first transatlantic radio communication, and telegrams from Britain were also received in the United States. This news greatly shocked people at the time. In the history of human beings, it has always been a long-cherished wish and an intractable problem to transmit news quickly. Many efforts have been made to pursue more exchanges. Since Marconi's invention, human communication has entered a new era. It no longer needs to rely on animal power transmission and letter delivery. Since then, radio can allow messages to be transmitted to the world at any time.

Soon, the wireless telegraph invented by Marconi was widely used around the world. In real life, the earliest application of radio technology was navigation, when people used Morse telegraphy to transmit information between ships and land. The coasts and fortresses of many countries have established Marconi-style radio stations. But it still has many shortcomings. First, the oscillating line and antenna of Marconi's transmitter are combined, which makes the transmitter very low power; second, the wireless communication used by Marconi cannot be tuned, which makes it transmit The radio waves of the radios were prone to interference with each other; even more vexing was the lack of reliable telegraph receivers in the Marconi wireless telegraph system.

In response to the drawbacks of Marconi's telegraph facility, German physicist Karl Ferdinand Braun made improvements. Starting in 1902, he invented new tuning technology based on the tuning powder detector of British engineer Joseph Lodge, which allowed wireless telegraphy to be sent and received directionally in different frequency bands, reducing interference. This technology is also the basis of radio . He also invented the magnetic coupling antenna, which independently designed the oscillator circuit and the antenna and coupled them together. This new design greatly enhanced the transmission power of wireless telegraphy. In 1909, the Nobel Prize Committee awarded the Nobel Prize in Physics to Marconi and Braun for their contribution to the cause of human radio engineering.

The beginning of radio technology

In the early days of radio technology, Morse code, which we often see in old movies, was a big "killer", and every radio operator had to master it proficiently. This is because the earliest wireless telegraphy can transmit very limited information, so people try to replace the message with a signal code that is on and off, and the famous Morse code came into being. In Morse code, there are two kinds of signals, namely the short "" and the delayed "—". People can express different meanings through different signal combinations, such as "·——" for the letter a, "—" ··" represents the letter d. In this way, with the blessing of Morse code, simple symbols can also convey a piece of text with content and interest. Although currently with the development of technology, Morse code has disappeared from daily life. However, many radio amateurs and military broadcasters still use it because of its ability to work under very harsh communication conditions and its high information density.

The emergence of radio also directly led to the birth of broadcasting, which to a large extent enriched people's lives. In 1920, the world's first official broadcast began in the United States, and later radio broadcasting in many other countries also flourished.

How radio technology works

Why radio technology can transmit information, there is such a typical metaphor to describe this process: when you throw a stone like a calm lake, the water waves will travel far away. If these water waves can record information, then as the ripples dissipate, the information can also travel far away. Radio waves can propagate in free space (such as air and vacuum), so as long as humans load information on radio waves of specific frequencies, they can achieve the purpose of transmitting information. Specifically, the technology works by generating radio waves when the strength of the current in the conductor changes. The radio wave is generated by changing the strength of the current in the conductor, and then information can be loaded on the radio wave through modulation. When the radio wave propagated through space reaches the receiving end, the electromagnetic field change caused by the radio wave will generate a current in the conductor. At this time, the information is extracted from the current change through demodulation to realize the information transmission.

The development of radio technology

Although initially, radio waves could only transmit some simple "beep" sounds, with the continuous development of technology, people's research on radio has gradually deepened, and radio is widely used in communication, navigation, radar, heating, power, and remote control. , astronomy and other fields. Among them, the application of radio in the field of communication is the most well-known, and the application of radio, telephone, television, emergency service (positioning), data transmission, etc. in people's lives has been very common. With the continuous development of computer technology and information technology, various wireless networks based on wireless transmission technology have increasingly become an important part of people's lives.

The development history of radio is, to a large extent, the history of people's research and use of various frequency bands. People's development and application of radio has gone through two stages: software radio and cognitive radio. Software-defined radio is a radio broadcast communication technology that was formally proposed by scientists in the early 1990s. A major feature of it is that it is based on a software-defined wireless communication protocol rather than hardwired. Frequency bands, air interface protocols and functions can be upgraded through software downloads and updates without a complete hardware replacement.

After decades of promotion and in-depth research around the world, the concept of software radio has not only been generally recognized, but also widely used. 3G, 4G, multi-band and multi-mode radios, and joint tactical radio systems are all designed and developed based on the concept of software radio. Even GPS that completes a single function needs to be designed in software to meet the development needs of navigation technology.

Cognitive radio refers to a wireless communication technology that includes an intelligent transceiver. It was proposed by scientists in the early 21st century to improve the utilization of idle spectrum. Smart transceivers in cognitive radios can detect which bands are not occupied and which are being used, and when certain bands are detected to be free, the CR system can temporarily use that band to communicate. Cognitive radio can sense the surrounding electromagnetic environment, communicate intelligently with the communication network through the radio knowledge description language (RKRL), and adjust the transmission parameters (communication frequency, transmit power, modulation method, coding system, etc.) in real time, so that the radio parameters of the communication system can be adjusted. It not only adapts to the rules, but also matches the environment, so as to achieve high reliability of the communication system and high efficiency of spectrum utilization whenever and wherever possible.

Compared with software radio and cognitive radio, the former focuses on the use of software to realize the signal processing of the radio system; while the latter emphasizes that the wireless system can perceive changes in the propagation environment, and adjust the system operating parameters accordingly to achieve the best results. adaptation. In this sense, cognitive radio is a higher-level concept that includes not only signal processing, but also high-level activities for reasoning and planning according to corresponding tasks, policies, rules, and goals.

Implementation of Radio Communication

Over the past 100 years, communication technology has developed rapidly. The application of telegraph, telephone, radio, television and other communication technologies has greatly accelerated the pace of modern life, making the ancient people's dream of "smooth ears" and "clairvoyance" a reality.

To carry out radio communication, it is necessary to send and receive radio waves. Antennas are necessary equipment to transmit and receive radio waves, and we can often see various antennas. To conduct radio communication, first of all, radio waves are emitted. There is an important component in the radio wave transmitter called the oscillator, which can generate a high-frequency alternating current. When the high-frequency alternating current flows through the antenna, a high-frequency electromagnetic field is generated in space. Since this electromagnetic field is undergoing periodic changes, new electromagnetic fields are generated around it... So, electromagnetic waves are emitted.

Radio broadcasting conveys sound, and television broadcasting conveys not only sound but also images. The high-frequency alternating current generated by the oscillator is used to carry information such as sound and images, and is called a carrier wave. The information to be transmitted is added to the carrier and transmitted, and the information can be transmitted to a distant place. Adding information to the carrier wave changes the carrier wave with the signal. This technique is called modulation. There are two ways to modulate, a common one is to make the amplitude of the high-frequency carrier change with the signal, which is called amplitude modulation (AM). Radio broadcasts in the medium and short wave bands use amplitude modulation. In the microwave band, the image signal of TV broadcasting also uses the amplitude modulation method. Another modulation method is to change the frequency of the high-frequency carrier with the signal. This modulation method is called frequency modulation (FM).

The amplitude of FM remains unchanged, the anti-interference ability is relatively strong, and the distortion in the transmission process is relatively small. However, the structure of the FM receiver is more complicated than that of the AM machine, and the service radius is relatively small. Many of the radio stations we are familiar with are FM radio stations that broadcast high-quality music and language programming.

There are many radio stations and TV stations in the world, and they are emitting electromagnetic waves all the time. Therefore, there are many electromagnetic waves around us. When receiving radio broadcasts, you must first select the one you need from the numerous electromagnetic waves. When we turn the knob of the radio to select a station, we are actually selecting the electromagnetic waves we need, which is technically called tuning. After tuning, the receiver gets a high-frequency current with information marks. This high-frequency signal current is not the desired signal itself. To get the required sound and image information, they must be "taken" out of the high-frequency signal current. This process is called demodulation. The signal obtained by demodulation is also amplified. If the sound information is transmitted, the speaker can be made to emit sound; if the image information is transmitted, the picture tube can be made to display the image.

application of radio technology

Today, our lives are inseparable from radio, and the application forms of radio are becoming more and more diverse, including not only wireless data networks, but also various types of mobile communications and radio broadcasting.

The earliest application of radio was in the field of communications, where people could use radio to transmit information over long distances for the first time. Once, in the vast sea, it was difficult to transmit information between ships. When radio technology came out, it was quickly applied to the field of navigation. Warships would use it to issue and receive instructions and report the situation; civilian ships would also use it to ask for help. , or pass other information. Mobile phones are the most commonly used wireless communication devices at present. As long as they are in the area covered by the signal, people can talk freely. In addition, wireless local area network, Bluetooth and other technologies all use radio technology to transmit data in short distances.

Radio navigation can guide people to their destination smoothly. In this technology, satellites can use radio waves to determine the vehicle's navigation parameters (such as bearing and speed), and calculate the deviation from the predetermined route, so as to make timely corrections and maintain the correct route. If this process is continued, the radio can continuously locate and eventually realize radio navigation. Radio navigation is not limited by time and weather, and has high precision, fast speed and easy operation. Modern wireless communication technology is more developed, and space communication technology is becoming more and more mature. In daily life, mobile communication has become indispensable. Mobile communication has gone through the 1G (analog), 2G (digital), and 3G (high-speed) eras, and has now entered the 5G era. Since the 3G era, mobile communication has really brought people into the era of multimedia mobile communication. Web pages, music, pictures, videos, etc. can all achieve a good customer experience on smart phones.

Wireless local area network has a wide range of applications in medical care, enterprise network coverage, warehouse management, catering retail, video surveillance, etc. In daily life, the logo of WiFi hotspot network can be seen everywhere. In fact, WiFi is a trademark of WLANA (Wireless Local Area Network Alliance). WiFi is one of the WLAN technical standards. The coverage radius of WiFi can reach about 300 feet (about 90m), and WLAN (plus antenna) can reach 5km.

In the era of rapid development of information technology, the Internet of Things is in the limelight. This network of connected things connects all objects through the network. Obviously, this scenario is unthinkable if connected via a wired network. The Internet of Things is widely used in intelligent transportation, environmental protection, government work, public safety, safe home, intelligent fire protection, industrial monitoring, environmental monitoring, elderly care, personal health, flower cultivation, water system monitoring, food traceability, enemy reconnaissance and intelligence collection. And many other fields, the application prospect is very broad.

radio technology today

In real life, the presence of radio technology is also very high, and the transmission of sound requires radio, such as wireless telegraphy, AM broadcasting, FM broadcasting, voice radio used in navigation and aviation, etc. Telephony, television, emergency services, data transmission, Bluetooth, navigation, radar, heating, power, astronomy, etc. are also inseparable from radio technology.

Some people sum up radio like this, saying that it is a "overpass" for people to communicate freely. With the rapid development of radio communication technology, mobile phones not only meet the needs of people to communicate freely anytime and anywhere, but also become a personal intelligent mobile terminal integrating communication, photography, entertainment, financial management, shopping and other functions. As early as 2013, data showed that the number of mobile phone users in my country exceeded 1.1 billion, ranking first in the world. The pager that once swept the country, the walkie-talkie used for dispatching and commanding, the Bluetooth used for short-range wireless communication, the Wi-Fi used for wireless local area networks and satellite phones, etc. are also inseparable from radio. Public mobile communication has experienced five generations of evolution. From simply meeting people's need to make phone calls while on the move to mobile communications (5G)

high-speed download capabilities, in which radio plays an important role. Radio is also a "colorful rainbow" that enriches people's cultural life. Radio and television rely on radio waves to present the news that happens all over the world every day to us thousands of miles away. After decades of development, my country's radio and television network has become the world's largest radio network. Statistics in 2013 have shown that more than half of the households in the country watch TV through wireless TV networks, there are more than 15,000 TV broadcast transmitters, and more than 30,000 TV transmitters. It can be said that our convenient life today is based on the application of radio technology.

Pay attention to radio safety

For a long time, the safety issue of radio has also aroused people's thinking. Take cognitive radio as an example, it faces five major security threats. First, information theft. Since the information transmission medium of radio communication is an open space, it greatly reduces the difficulty of illegally intercepting communication signals. Moreover, since the interception of the signal is a passive behavior, it is more difficult to find the problem through the method of signal detection. Second, malicious interference. The radio receiving antenna is in an open space. While receiving useful signals, it will also be interfered by various useless information existing in the space. For example, some malicious attackers can arbitrarily insert into the transmission channel of the receiver, which reduces the input signal-to-noise ratio of the receiver and affects the effectiveness of communication. In addition, some malicious attackers can make the receiver obtain wrong information by imitating the useful signal. Third, recognize the interference of users to authorized users. Due to environmental factors such as hidden terminal effects, the perception of the main user by the cognitive user is inaccurate and untimely, and the authorized user may be disturbed. cause inequity among users. Fourth, imitate an authorized user attack. In the case of a shortage of spectrum resources, the limited spectrum will be occupied for oneself, and in some malicious attacks, the availability of spectrum resources will be destroyed. Fifth, denial of service attacks. In cognitive radio networks, the common control channel is the physical basis for transmitting spectrum sensing information between nodes. The attacker saturates the control channel by sending a large amount of useless control information, making the control channel unavailable to other cognitive users. At the same time, cognitive radio also faces some other security threats. For example, attackers can exploit the security holes of various protocols at the application layer to reduce the service quality of cognitive radios through malicious programs such as viruses and Trojans.

Faced with these security threats, spread spectrum communication technology is an effective way to solve the problems of information theft and interference. Spread spectrum communication mainly includes direct spread, frequency hopping, etc. The main idea is to enhance the concealment and anti-interference ability of the signal by expanding the bandwidth of the communication signal. In addition, a more stringent authentication mechanism can also be used to prevent the leakage of information and data. Appropriate cryptographic algorithms can prevent the communication signal from providing the information of interest to the eavesdropper even if it is intercepted. Better identification of authorized user signals is a fundamental way to defend against impersonation of authorized user attacks. To this end, multi-dimensional discrimination can be performed simultaneously using physical characteristics other than the signal itself.

In order to raise people's awareness of the importance of radio, publicize the important role that radio plays as a communication carrier in promoting education development, information dissemination and major information release in natural disasters. On November 3, 2011, UNESCO decided to designate February 13 every year as "World Radio Day". While enjoying the convenience brought by radio technology, we must also pay attention to its safety. Various radio services "go their own way" on different frequencies. Through scientific planning and management of these "roads", the radio management agency ensures the safety and order of radio waves and escorts the normal operation of various radio services. Of course, creating a harmonious, green and safe electromagnetic environment also requires the joint efforts of the whole society.