How Interference Diversity of Hopping in GSM
In GSM system, the interference strength and distribution on each frequency carrier in cell are different, the carrier variation of the bursts of the same communication low the interference on signal, the radio wave interference on communication is equalized.
If no hopping is used, the mobile station will always work on fixed frequency carrier, each burst during the entire communication may receive fixed strong interference. In others words, hopping technology disperses the interference on different carriers with burst, this is called “interference equalization” or “interference diversity”.
As shown in the above figure, bursts B1, B2… are spread on frequencies f1, f2, f3… Co-channel interference exists in the cellular network because of frequency reuse, hopping makes the signal interference discontinuous to improve radio wave environment.
The interference varies from burst to burst, which improves the communication quality. Otherwise, the entire communication will suffer from strong interference. That is to say the interference is dispersed on different carriers with burst. Of course, the frequency conflict from hopping can result in strong instant interference, which can be solved by defining different MAIO.
In frequency hopping, the more frequency carriers in use, the less likely the frequency conflict can occur, and the higher the hopping gain. But frequency availability will be lowered when there are more hopping frequency carriers.