Frequency hopping anti-interception method in orthogonal frequency division multiplexing (OFDM) system

Abstract

The invention provides a frequency hopping anti-interception method in an orthogonal frequency division multiplexing (OFDM) system, which can improve signal to interference plus noise power ratio, and lowers the effect caused by broadband interference. The method comprises a small amplitude frequency hopping method for narrow-band interference and a random frequency hopping method for broadband interference. The space of each frequency point is equal to the bandwidth of a subcarrier, and the frequency points are not so excessive; and a plurality of subcarriers are selected to transmit data, a pseudorandom sequence is used for shifting of the subcarrier at each OFDM mark space, so that little signal bandwidth is increased, but the effects of rapid frequency hopping and anti-interception can be achieved simultanesouly. Under the interference of broadband, the scheme of random frequency hopping is adopted, at each OFDM mark space, a relatively small amount of subcarriers are randomly selected to transmit data, so that the signal to interference plus noise power ratio is improved, and the effect caused by broadband interference is lowered.

Description

technical field [0001] The invention relates to a frequency hopping anti-interception method in an OFDM system, belonging to the technical field of wireless communication. Background technique [0002] Frequency hopping is a commonly used spread spectrum method in wireless communication. Its working principle is that the carrier frequency of the transmission signal of the transmitting and receiving parties changes discretely according to a predetermined rule. In terms of the implementation of communication technology, frequency hopping technology is a communication method that uses code sequences to perform multi-frequency frequency shift keying. From the perspective of signal spectrum, frequency hopping signals generally occupy a wide frequency band. [0003] Commonly used frequency hopping code sequences are pseudo-random sequences designed based on m-sequences and RS codes. These pseudo-random code sequences are realized through a shift register plus a feedback structur...

AI Technical Summary

Problems solved by technology

Fixed-frequency interference will only interfere with some frequency points. As long as the other party does not know the law of carrier frequency hopping, it will be difficult to intercept the communication content

However, the disadvantages of conventional frequency hopping communication are: 1) large occupied bandwidth; 2) limited frequency hopping speed; 3) no ability to suppress high-power broadband interference

Such a large bandwidth will bring great difficulties to RF link design and AD / DA conversion.

[0006] 2) The output frequency of the oscillator needs to be changed when the conventional frequency hopping system switches the operating frequency point, and the phase-locked loop needs to re-enter the stable tracking state, which takes a long time, so the current fastest frequency hopping speed is only tens of thousands of times per second

[0007] 3) In the face of high-power broadband interference, if the interference spectrum covers all frequency points of the frequency hopping system, the conventional frequency hopping system will lose the anti-interference ability and the communication performance will deteriorate sharply

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