What Is a Spread Spectrum?

Spread Spectrum (SS) is a communication technology that spreads the spectrum of a transmission signal to a wider bandwidth than its original bandwidth. It is often used in the field of wireless communications.

Spread Spectrum (SS)

The so-called spread-spectrum communication can be simply expressed as follows: "Spread-spectrum communication technology is an information transmission method. The bandwidth of the signal occupied by the signal is much larger than the minimum bandwidth necessary for the transmitted information. Completed, it is realized by coding and modulation methods, which has nothing to do with the transmitted information data; at the receiving end, the same code is used for related synchronous reception, despreading and recovery of the transmitted information data. "

First, the spectrum of the signal is widened. We know that transmitting any information requires a certain bandwidth, which is called information bandwidth. For example, the information bandwidth of human voice is 300Hz --- 3400Hz, and the bandwidth of TV image information is several MHz. In order to make full use of the frequency resources, generally use signals with substantially equivalent bandwidth as much as possible to transmit information. In radio communications, the bandwidth of a radio frequency signal is comparable to the bandwidth of the transmitted information. For example, the AM signal is used to transmit voice information, and its bandwidth is twice the voice information bandwidth; the TV broadcast radio frequency signal bandwidth is only more than double its video signal bandwidth. These are all narrow-band communications. For general FM signals, or pulse-coded modulation signals, the ratio of their bandwidth to information bandwidth is only a few to a dozen. The ratio of spread spectrum communication signal bandwidth to information bandwidth is as high as 100 --- 1000, which belongs to broadband communication. Why use such a wide-band signal to transmit information? Does nt it waste precious frequency resources?

Second, the spectrum of the signal is widened by using a spreading code sequence modulation method. We know that a signal that is finite in time has an infinite spectrum. For example, a very narrow pulse signal has a wide spectrum. The frequency bandwidth of a signal is approximately inversely proportional to its duration. A 1 microsecond pulse has a bandwidth of about 1 MHz. Therefore, if the transmitted information is modulated with a narrow pulse sequence, a wide-band signal can be generated. The direct sequence spread spectrum system introduced below adopts this method to obtain the spread spectrum signal. This very narrow pulse code sequence, whose code rate is very high, is called a spreading code sequence. What needs to be explained here is that the spreading code sequence used is irrelevant to the transmitted information data, that is, it is the same as a general sinusoidal carrier signal and does not affect the transparency of information transmission at all. The spreading code sequence only serves to spread the signal spectrum.

3. De-spreading with correlation demodulation at the receiving end Just as in general narrowband communication, the modulated signal must be demodulated at the receiving end to recover the transmitted information. In the spread spectrum communication, the receiving end uses the same spreading code sequence as the transmitting end to perform demodulation with the received spread spectrum signal to recover the transmitted information. In other words, this correlation demodulation plays a role of despreading. That is, the expanded signal is restored to the original transmitted information. This process of expanding narrowband information into a wideband signal at the sending end and despreading it into narrowband information at the receiving end will bring a series of benefits. Understanding the mechanism of the spread spectrum and despreading process is the key to understanding the nature of spread spectrum communications. ^[2]

Direct-sequence spread spectrum (DSSS), or Direct Spread Spectrum (DS) for short, is a

Frequency-hopping spread spectrum ( FHSS ) is a type of spread-spectrum technology;

During World War II, the public image was a vase

• It is immune to background noise, interference, and auto multipath interference.

• It has a good resistance to artificial jamming signals, which is one of the important reasons for spread spectrum to be used in military communication systems to combat human interference.

• Better confidentiality, the possibility of interception of the communication process is lower. This is because after spreading, the power value of the unit frequency is reduced, and it is difficult for the interceptor to obtain the information of the enemy communication through the spectrum analyzer. Recover encoded information. Therefore, spread-spectrum communication also has a simple confidential communication capability.

• Reduce Electromagnetic Interference (EMI)

• If the clock generator of the electronic device is spread spectrum, that is, jitter is intentionally added to the clock signal, the energy that specifically causes electromagnetic interference can be dispersed by the specific frequency Further reducing its interference level is essentially the same as the spread spectrum of communication technology.

• The "Spread Spectrum" option is often seen in the BIOS settings of personal computers. The main purpose of this option here is to reduce electromagnetic interference. Depending on the system configuration, the amount of electromagnetic radiation may be effectively reduced. However, the side effect is that the signal clarity is reduced, which has a greater impact on the system stability after overclocking.

• By spread spectrum technology, code division multiple access (CDMA) communication can be achieved, allowing multiple users to independently and simultaneously use a larger bandwidth. ^[1]