Introduction to Spread Spectrum Communication_The Principle of Anti-Jamming for Spread Spectrum Communication

Spread spectrum communication, abbreviated as spread spectrum communication, is an information transmission method in which the bandwidth occupied by the signal is much larger than the minimum bandwidth necessary for the transmitted information; the extension of the frequency band is through an independent code sequence (generally a pseudo-random code). To complete, using the coding and modulation methods, it is independent of the transmitted information data; at the receiving end, the same code is used for synchronous reception, despreading and restoring the transmitted information data.

Introduction to Spread Spectrum Communication_The Principle of Anti-Jamming for Spread Spectrum Communication

Spread spectrum communication system, bandwidth for spread spectrum processing

Principle of anti-interference of spread spectrum communication

Spread spectrum communication is an abbreviation for spread spectrum communication. It refers to a communication method in which the RF bandwidth used to transmit information is much larger than the bandwidth of the information itself.

The basic theoretical basis of spread spectrum technology is the Shannon formula in information theory, which can be expressed as:

C=Wlog21+S/N (1)

Where C is the channel capacity (bit/S), W is the channel bandwidth, S is the signal power, and N is the noise power.

Considering the typical case of S/N<<1 in the communication environment, the approximate expression (2) can be obtained by performing several mathematical transformations on the equation (1).

W=CN/S2 (2)

It can be seen from Equation 2 that for any given noise signal ratio, as long as the bandwidth for transmitting information is increased, it is theoretically possible to increase the information rate transmitted without error in the channel. For a given channel capacity, it can be achieved by increasing the channel bandwidth while reducing the signal-to-noise ratio correspondingly, or by reducing the channel bandwidth and correspondingly increasing the signal-to-noise ratio. If the channel capacity C is constant, the bandwidth W and the signal-to-noise ratio S/N are interchangeable, that is, by increasing the bandwidth, the information can be reliably transmitted at the same information rate with a lower signal-to-noise ratio. Even in the case where the signal is overwhelmed by noise, as long as the signal bandwidth is increased correspondingly, reliable communication is maintained, that is, the spread spectrum method can be used to transmit information in a broadband manner in exchange for the benefit of the signal-to-noise ratio. This is the basic idea and theoretical basis of spread spectrum communication.

SNR is the signal to noise ratio. It is the signal to noise power ratio, which is equal to Eb*R/(N0*B), R is the data bit rate, and B is the signal occupied bandwidth rather than the bandwidth of the RF/IF channel. In a spread spectrum system, the same value is usually taken as the chip rate of the spread spectrum signal.

The concept of Eb/N0 is the ratio of the energy per bit to the noise power spectral density. If only thermal noise is considered, the system capacity (data bit rate) and the bandwidth ratio it occupies tend to zero, then the theoretical limit of Eb/N0 is the Shannon limit -1.6 dB. It can be seen from the Shannon formula R=B*log2(1+SNR) that the data rate of transmission is certain, the power of the signal is certain, and the bandwidth occupied by the transmission signal is increased, which can reduce the SNR requirement of the system, that is, reduce the Eb/N0. Requirements. The spread spectrum system uses a method of increasing the bandwidth occupied by the signal to reduce the SNR requirement of the system.

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