I. What is spread spectrum communication technology?
Spread spectrum communication technology is an information transmission method in which the bandwidth occupied by the signal is much larger than the minimum bandwidth required for the transmitted information. The bandwidth expansion is accomplished by an independent code sequence, which is achieved by encoding and modulation methods and is independent of the transmitted information data. At the receiving end, the same code is used for correlation synchronization reception, despreading and recovery of the transmitted information data.
Spread spectrum communication technology uses spreading code for spread spectrum modulation at the transmitting end and correlation demodulation for signal reception at the receiving end. Since spread spectrum communication requires spreading code for modulation and transmission, and signal reception requires correlation despreading between the same spreading codes, this provides a foundation for frequency reuse and multiple access communication. By fully utilizing the correlation characteristics between different spreading codes and assigning different spreading codes to different users, signals from different users can be distinguished and unaffected by interference from other users, thus achieving frequency reuse.
There are three main types of commonly used spread spectrum techniques: direct-sequence spread spectrum, frequency-hopping spread spectrum, time-hopping spread spectrum, and linear modulation. However, in practical applications, a combination of these techniques is often used.
II. What is Frequency Hopping Spread Spectrum?
Frequency Hopping Spread Spectrum (FHSS) is a technique that repeatedly switches the carrier frequency during radio transmission to reduce interference and avoid interception.
In frequency-hopping spread spectrum (FPS), a wide section of the bandwidth spectrum is divided into many possible broadcast frequencies for signal transmission. FPS digital radio transmission methods involve radio signals propagating in narrower spectral ranges, hopping to other narrow ranges in a pseudo-random order, all within a defined overall range, to achieve better noise immunity than DSSS, a larger range than DSSS, and inherent signal security.
FHSS stands for Frequency Hopping Spread Spectrum, where the RF carrier frequency varies according to a pseudo-random sequence (PRS or PN sequence). Both the transmitter and receiver are aware of this PN sequence, thus facilitating demodulation/decoding of information. The RF frequency does not change within a single chip's duration. Based on this fact, there are two types of FHSS: Fast Hopping FHSS and Slow Hopping FHSS. In Fast Hopping FHSS, the hopping rate is faster than the message (information) bit rate. In Slow Hopping FHSS, frequency hopping is performed at a rate slower than the information bit rate.
Frequency hopping spread spectrum characteristics:
(1) Anti-interference. Communication is carried out using discrete frequency points. Even if a certain frequency point is interfered with, other frequency points can still maintain normal communication.
(2) Strong compatibility. It has a large number of frequency points and can communicate with other devices on any frequency point.
(3) Easy to implement multiple access communication.
