Frequency Hopping Communication Technology and its Application and Development

Introduction frequency-hopping communication is a branch of Spread-Spectrum communication. It has a strong anti-interference capability and is suitable for the military field. When the first frequency hopping radio station was launched in late 1970s, it predicted that its development momentum was unstoppable. By 1980s, the military around the world was equipped with frequency hopping radio stations. This decade is the fastest growing decade for Frequency Hopping radio stations. The widely used frequency hopping radio station was once hailed as the main feature of the development of radio communication in 1980s. In 1990s, frequency-hopping communication became increasingly sophisticated in the military frequency-hopping communication field. At the same time, the application of frequency-hopping communication was extended to the civil field. Industry insiders pointed out that frequency-hopping communication is an effective means to combat radio interference, and it is called the "killer" of radio communication ". Frequency-hopping communication is so amazing that it has been favored by many countries around the world, especially several major military Powers, in just 30 years since its launch.

2. Basic concepts of Frequency Hopping Communication:

2.1 It is defined that we are listening to a radio station. When the radio station plays the same program in both the medium-wave and short-wave bands, we have the following experience: If the medium-wave band signal is not good, then listen to the short wave band. When the short wave band signal is poor, listen back to the middle wave band. This method of improving the listening effect by changing the band is the common meaning of the frequency hopping. However, such frequency hopping only occurs at the receiver end and is implemented by manual intervention. We assume that when the frequency band sent by a broadcast station can also be "followed" by Radio users, this communication method is frequency hopping. Therefore, the frequency-hopping communication can be described as follows: the communication mode in which the communication sending and receiving Sides change the frequency synchronously is called frequency-hopping communication.

Compared with fixed-frequency communication, the 2.2 synchronization condition (Communication condition) always changes the carrier frequency of Frequency Hopping Communication. At work, the sender changes the frequency at a very fast rate (hop rate). The receiver must change the frequency with the sender in sync so that both parties can maintain communication. That is to say, during frequency-hopping communication, the receiving and receiving sides must adopt the same frequency-hopping pattern. Figure 1 shows the dissteps and synchronization between the two sides of the Frequency Hopping Communication. Figure A only has the same frequency hopping sequence. Figure B shows that the frequency hopping sequence and frequency hopping sequence are the same. Figure C shows the synchronization between the two sides of the Frequency Hopping Communication. The frequency hopping frequency, frequency sequence, and start and end time of the Frequency Hopping Communication are the same. It can be seen that, to successfully implement frequency-hopping communication between frequency-hopping radio stations, the receiving and receiving sides must satisfy three conditions at the same time: the frequency-hopping is the same; the frequency-hopping sequence is the same; the frequency hopping clock is the same (a certain error is allowed ). Three conditions are indispensable; otherwise, frequency-hopping communication cannot be implemented.

2.3 system composition Figure 2 is a diagram of the Frequency Hopping Communication System. Compared with traditional fixed-frequency communication, the difference lies in the dotted line in the figure. When sending a message, the carrier frequency output by the frequency synthesizer is continuously changed due to the control of the Frequency Hopping command generator (or pseudo-random code generator). Therefore, the signal frequency sent from the antenna is constantly changing. When the receiver receives the frequency hopping signal, in order to ensure that the mixer always outputs a fixed frequency difference (intermediate frequency), the Local Vibration Frequency must be synchronized with the external carrier frequency. In other words, the receiver's Local Vibration must also be a frequency hopping. It is hard to understand that the sending and receiving sides must maintain a consistent start time and end time; otherwise, normal communication cannot be achieved. Obviously, the key component of the Frequency Hopping Communication System is the frequency hopping, and the frequency hopping synchronization is the core technology of the Frequency Hopping System.

3. Main Features of frequency-hopping communication:

3.1 strong anti-interference frequency hopping communication the anti-interference mechanism is the guerrilla strategy of "One shot for another place". The enemy cannot understand the frequency hopping rule, so it has a strong anti-interference capability. On the one hand, our frequency hopping command is a pseudo-random code, and its cycle can be up to ten years or longer. On the other hand, the frequency of hop changes can reach thousands. Therefore, it is useless for an enemy to cast long-time interference at a certain frequency or several frequencies. In addition, the frequency of frequency hopping is constantly changed due to pseudo-random code control. The bandwidth occupied by the channel is very narrow during the residence time of each frequency. As the frequency hopping rate is very fast, the frequency hopping system is also a broadband system, which expands the spectrum. In fact, the hop bandwidth is the product of the number of frequencies and the channel bandwidth occupied by each frequency. According to the Spread Spectrum Communication Theory, the benefits of the extended spectrum can be exchanged for better signal-to-noise ratio. That is to say, if the frequency band is extended, information can be transmitted with the same information rate and any small error probability at a lower signal-to-noise ratio, reliable communication can be maintained even when the signal is completely lost by noise. It can be seen that strong anti-interference is the most prominent advantage of Frequency Hopping Communication.

3.2 high spectrum utilization people have long recognized that spectrum resources are very valuable. Therefore, improving the spectrum utilization is also one of the basic requirements of modern communication. Frequency Hopping Communication can use different frequency hopping patterns or clocks to achieve the purpose of sharing spectrum resources while working in a certain bandwidth, thus greatly improving the spectrum utilization.

3.3 Code Division Multiple Access (CDMA) multi-access communication means that many user groups form a communication network, and any two users in the network can communicate with each other. The Application of Frequency Hopping Communication can easily form such a multi-access communication network. Each user in the network is assigned a different address code, which is like a phone number. Each user can only receive signals sent by other users according to their address code to identify useful signals. signals sent to other users will not be demodulated.

3.4 compatibility for Frequency Hopping Communication, compatibility means that a Frequency Hopping Communication System can establish communication with a non-frequency narrowband Communication System at a fixed frequency. Obviously, the advantage of compatibility is that advanced frequency hopping radio stations can communicate with conventional fixed frequency radio stations. This is easy to implement in the Development of Frequency Hopping radio stations-you only need to add a frequency hopping module to conventional radio stations to become frequency hopping radio stations. Obviously, the frequency hopping module is a key component of the entire frequency hopping radio station.