Frequency-Hopping Spread Spectrum (FHSS) is one of the most typical Spread work methods in communication technology.It expands the bandwidth of information many times by using encoding and modulation method, and adopts spread code sequence to carry out frequency shift keying (FSK) modulation, so that the frequency of carrier is constantly changing.The information transmitted is controlled by selection with the combination of these spread-spectrum codes, and constantly changes in transmission.On the receiving end, due to the local generator which is exactly the same as the sending end, the spread code will be decompressed, and then the original information can be recovered properly through demodulation.

Advantages:

1. Confidentiality.The pseudo-randomness of frequency hopping pattern and the key amount of frequency hopping pattern make the frequency hopping system secret.Even if the analog voice of the frequency hopping communication, as long as the enemy does not know the use of frequency hopping patterns will have a certain confidentiality.When the key of frequency hopping pattern is large enough, it can resist interception.

2. Anti-interference.As the carrier frequency is hopping, it has the ability to resist the interference of single frequency and partial bandwidth.When the number of hopping frequency is large enough and the hopping band is wide enough, its anti-interference ability is strong.

3. Anti-multipath fading.By using the fast hopping of carrier frequency, the system has the function of frequency diversity, so that the system can resist multipath fading.The condition is that the frequency interval of the jump is greater than the relevant bandwidth.

4. The orthogonality of frequency hopping pattern can be utilized to form a frequency hopping code division multiple access system, share spectrum resources, and have the ability to withstand overload.

5. Frequency hopping system is instantaneous narrowband system, which can communicate with existing narrowband system.That is, when the frequency hopping system is at a fixed carrier frequency, the communication can be established with the existing fixed-frequency narrowband system.In addition, frequency hopping system is suitable for both analog and digital sources.

6. Frequency hopping system has no obvious near-far effect.This is because when the high-power signal produces near and far effects only at one frequency, the carrier frequency hopping to another frequency is no longer affected by it.This makes frequency hopping system easy to be applied and developed in mobile communication.